Why 1.3?
12-06-2003, 10:40 PM
#26
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You make some valid points. You try typing for that long and not miss something!
I didn't really want to go too far into the shape aspect of the chamber vs a round chamber. I am well aware that efficiency is affected. The whole comparison to an equivalent piston engine piston size was merely for reference purposes only.
As far as the longevity issues goes. I'll go by the cars me and my friends have owned. Between me and my 2 best friends, we have cumulatively owned 19 different RX-7s within the past 10 years. Every generation. The ones that had the worst problems were also the cars that were taken care of the least. Only 2 of the cars had bad engines. One was a turbo and the other was a first gen car that had been raced many times. Both of those cars looked like a cowboy should have put a gun to them and ended their misery. The first gens seemingly run forever. 150000 miles on a first gen is purely pathetic. They will easily top 200000 with no issues what so ever provided that the owners take care of them. This is true for any car though. My friend Dave has a mid '80s 626 that currently has somewhere around 280000 miles on it. The car was originally turbocharged but it died. The car is just a nonturbo now. This same friend has also owned 2 first gens with 200000+ miles and a 2nd gen with that many. I have yet to see a turbo RX-7 get this though. Obviously both can go this long but you do make a good point. The biggest issue is the engine tolerance for stupid lazy owners like I was as a kid. I had many issues with my old 2nd gen back when I didn't know a thing about cars of maintenence. I learned everything by doing it so I messed up pretty bad sometimes. Lets just say that I had the ceramic from 2 seperate spark plugs break and run through the motor. I lost a small screw into the intake manifold and started the engine. I overheated it twice. I ran it low on oil and out once when an oil line broke. Yes I was driving the car at the time. I was also bad about oil changes. I pulled that engine at 140000 miles not because it was dead, but because I had a new ported engine that I had built and wanted to drop onto it. The old engine still ran great and when it was removed it was the fastest that that car had ever been without a turbo. The thing about the rotary is that it is rev happy. Many people that own them will rag them out pretty bad. You also have to realize that the rotary is not as tolerant to lack of oil changes and almost not at all to overheating. Admittedly many piston engines are more tolerant of poor maintenance habits but the truly low maintenance engine is a fairly new thing. We only just heard within the past decade about cars that only need spark plugs every 100000 miles. Ford will even admit that the Tempo engine was designed to run for only about 100000 miles. We had one and that car started to fall apart after about 80K or so. Until the Renesis emerged, the rotary engine was relatively the exact same design that it was 35 years ago. For its time it was at the forefront of durability. A rotary will actually just plain wear out after about 250000 miles. The seal tolerance just gets too high and it doesn't seal as well anymore. Yep there are piston engines that can top that I'll admit it. My basis for reliability simply comes from only having 3 moving parts. Statistically they are much less liely to have problems than say 60 moving parts. We can't break a valve or drop one, throw a rod, etc. I'd love to see someone throw a rotor sometime! A failure for a rotary is usually a water seal failure, bearing failure, or an apex seal breaking and the occasional oil injector failure. The piston equivalent is breaking a piston ring. It also may have the other problems as well as the problems I listed above. I personally have never had to replace a head gasket on my RX-7. The problems lie within the material selection for the engines. Sometimes I think that there are Mazda engineers with their heads up their asses just for the warmth.
Mazda really needs to listen to some of the creative rotary owners out there that make them truly durable. They need a center bearing, all of the engine housings need to either be made out of aluminum (preferred) or steel. The current mix and match system is why overheating is so bad. The aluminum and cast iron heat up and cool down at different rates and develop sealing problems between them. Aluminum is less tolerant but lighter so I vote for it since I take care of my cars (now, not as a kid!). Mazda needs to use a seperate oil reservoir for oil metering that uses 2 stroke oil. Just have a reservoir with a low level sensor on it and if it drops too low the car goes into fail safe mode (limp home mode). I am also waiting to see the results of using the much lower 5W20 oil in the RX-8 vs 10W30 or 20W50 in the older rotaries. They need full length dowel pins. Many people custom machine new larger dowel locations and then stregthen the engine by adding. The simple thing is to use just 2 dowel rods the full length of the engine. The holes go all the way through so why use 4 total pins with 2 end to end on each side? This makes no sense and is a reason why the engine can flex slightly when under severe stress. Mazda race engines used braces under and over the engine that prevented this from happening. Mazda knows what needs to be done but the financial department sometimes has a bigger say in the product design than the designers do. Mazdatrix has a neat picture of what happens when an engine gets so well built that the typical failures don't happen. On a turbo rotary it is possible to dent or break a rotor from detonation if the seals don't break. While still bad, that is impressive that an engine can be built tough enough from basically factory parts (rotor housings, rotors, bearings, etc.) that the weakest link is a rotor. The aftermarket has always made stronger engine parts for piston engines. The bastards!
As far as overlap and scavenging goes, from an economy standpoint overlap is irrelevant on a turbo car because of backpressure from a turbo, and if the exhaust is of a poor design on a non turbo it may not help there either. The 13B engines in the 2nd gen RX-7 have a box for an exhaust manifold. The engine does not scavenge this way. The 13B also has overlap. while a properly designed header system can promote scavenging and help the intake suck in more air, a poor system can actuall have the exact opposite effect and stop some of the air from entering due to greater exhaust pressure. When I installed a header and removed the cat on my n/a 2nd gen, I gained power everywhere not just up high. Gas mileage got better and low end was even improved dramatically. While the RX-8 exhaust isn't as bad as the RX-7 was the point is still valid. As long as there is a cat and muffler in the way to restict the exhaust, the benfits of scavenging will always be reduced. The center exhaust port messes everything up anyways. The lack of overlap and siamesed center port are also the reasons why no exhaust is giving impressive gains anywhere compared to the older motors. Overlap as you said is important for efficiency at higher rpms but only if the exhaust is open enough and designed to take use of this. Most street cars aren't. When an engine is at 100% efficiency, there is still 10% of exhaust that gets recirculated back into the intake. You would think that this would cause the air to keep progressively get hotter and hotter but this isn't so. When the air gets heated during combustion it only goes so high. The old gas that was recirculated have been diluted pretty heavily by the incoming air and consequently cooled down alot. When combustion happens again, this amount of gas doesn't combust while the other does and the whole thing heats back up. Basically it is the same as a slight dilution and temperature rise befor combustion. Even your good scavenging overlap engine will still have some exhaust recirculate. while some gas does get trapped and cariied back to the intake side in the Renesis, it also does in the other rotaries as well. The difference is that it is typically the NOx within the exhaust in the Renesis that goes around again where it gets expelled in the 13B. Others do go around again though including some but not as much of the NOx. These get reburned which results in a cleaner emission. The epa has a huge say in what gets built.
You did make some great points and I thank you for making them. Hell, I'm just glad that people actually read that huge post and this one for that matter!
I'll add everything in if I ever publish a technical book on the rotary engine. Hopefully by then I'll learn how to type without the grammar and speeling errors too!
I didn't really want to go too far into the shape aspect of the chamber vs a round chamber. I am well aware that efficiency is affected. The whole comparison to an equivalent piston engine piston size was merely for reference purposes only.
As far as the longevity issues goes. I'll go by the cars me and my friends have owned. Between me and my 2 best friends, we have cumulatively owned 19 different RX-7s within the past 10 years. Every generation. The ones that had the worst problems were also the cars that were taken care of the least. Only 2 of the cars had bad engines. One was a turbo and the other was a first gen car that had been raced many times. Both of those cars looked like a cowboy should have put a gun to them and ended their misery. The first gens seemingly run forever. 150000 miles on a first gen is purely pathetic. They will easily top 200000 with no issues what so ever provided that the owners take care of them. This is true for any car though. My friend Dave has a mid '80s 626 that currently has somewhere around 280000 miles on it. The car was originally turbocharged but it died. The car is just a nonturbo now. This same friend has also owned 2 first gens with 200000+ miles and a 2nd gen with that many. I have yet to see a turbo RX-7 get this though. Obviously both can go this long but you do make a good point. The biggest issue is the engine tolerance for stupid lazy owners like I was as a kid. I had many issues with my old 2nd gen back when I didn't know a thing about cars of maintenence. I learned everything by doing it so I messed up pretty bad sometimes. Lets just say that I had the ceramic from 2 seperate spark plugs break and run through the motor. I lost a small screw into the intake manifold and started the engine. I overheated it twice. I ran it low on oil and out once when an oil line broke. Yes I was driving the car at the time. I was also bad about oil changes. I pulled that engine at 140000 miles not because it was dead, but because I had a new ported engine that I had built and wanted to drop onto it. The old engine still ran great and when it was removed it was the fastest that that car had ever been without a turbo. The thing about the rotary is that it is rev happy. Many people that own them will rag them out pretty bad. You also have to realize that the rotary is not as tolerant to lack of oil changes and almost not at all to overheating. Admittedly many piston engines are more tolerant of poor maintenance habits but the truly low maintenance engine is a fairly new thing. We only just heard within the past decade about cars that only need spark plugs every 100000 miles. Ford will even admit that the Tempo engine was designed to run for only about 100000 miles. We had one and that car started to fall apart after about 80K or so. Until the Renesis emerged, the rotary engine was relatively the exact same design that it was 35 years ago. For its time it was at the forefront of durability. A rotary will actually just plain wear out after about 250000 miles. The seal tolerance just gets too high and it doesn't seal as well anymore. Yep there are piston engines that can top that I'll admit it. My basis for reliability simply comes from only having 3 moving parts. Statistically they are much less liely to have problems than say 60 moving parts. We can't break a valve or drop one, throw a rod, etc. I'd love to see someone throw a rotor sometime! A failure for a rotary is usually a water seal failure, bearing failure, or an apex seal breaking and the occasional oil injector failure. The piston equivalent is breaking a piston ring. It also may have the other problems as well as the problems I listed above. I personally have never had to replace a head gasket on my RX-7. The problems lie within the material selection for the engines. Sometimes I think that there are Mazda engineers with their heads up their asses just for the warmth.
Mazda really needs to listen to some of the creative rotary owners out there that make them truly durable. They need a center bearing, all of the engine housings need to either be made out of aluminum (preferred) or steel. The current mix and match system is why overheating is so bad. The aluminum and cast iron heat up and cool down at different rates and develop sealing problems between them. Aluminum is less tolerant but lighter so I vote for it since I take care of my cars (now, not as a kid!). Mazda needs to use a seperate oil reservoir for oil metering that uses 2 stroke oil. Just have a reservoir with a low level sensor on it and if it drops too low the car goes into fail safe mode (limp home mode). I am also waiting to see the results of using the much lower 5W20 oil in the RX-8 vs 10W30 or 20W50 in the older rotaries. They need full length dowel pins. Many people custom machine new larger dowel locations and then stregthen the engine by adding. The simple thing is to use just 2 dowel rods the full length of the engine. The holes go all the way through so why use 4 total pins with 2 end to end on each side? This makes no sense and is a reason why the engine can flex slightly when under severe stress. Mazda race engines used braces under and over the engine that prevented this from happening. Mazda knows what needs to be done but the financial department sometimes has a bigger say in the product design than the designers do. Mazdatrix has a neat picture of what happens when an engine gets so well built that the typical failures don't happen. On a turbo rotary it is possible to dent or break a rotor from detonation if the seals don't break. While still bad, that is impressive that an engine can be built tough enough from basically factory parts (rotor housings, rotors, bearings, etc.) that the weakest link is a rotor. The aftermarket has always made stronger engine parts for piston engines. The bastards!
As far as overlap and scavenging goes, from an economy standpoint overlap is irrelevant on a turbo car because of backpressure from a turbo, and if the exhaust is of a poor design on a non turbo it may not help there either. The 13B engines in the 2nd gen RX-7 have a box for an exhaust manifold. The engine does not scavenge this way. The 13B also has overlap. while a properly designed header system can promote scavenging and help the intake suck in more air, a poor system can actuall have the exact opposite effect and stop some of the air from entering due to greater exhaust pressure. When I installed a header and removed the cat on my n/a 2nd gen, I gained power everywhere not just up high. Gas mileage got better and low end was even improved dramatically. While the RX-8 exhaust isn't as bad as the RX-7 was the point is still valid. As long as there is a cat and muffler in the way to restict the exhaust, the benfits of scavenging will always be reduced. The center exhaust port messes everything up anyways. The lack of overlap and siamesed center port are also the reasons why no exhaust is giving impressive gains anywhere compared to the older motors. Overlap as you said is important for efficiency at higher rpms but only if the exhaust is open enough and designed to take use of this. Most street cars aren't. When an engine is at 100% efficiency, there is still 10% of exhaust that gets recirculated back into the intake. You would think that this would cause the air to keep progressively get hotter and hotter but this isn't so. When the air gets heated during combustion it only goes so high. The old gas that was recirculated have been diluted pretty heavily by the incoming air and consequently cooled down alot. When combustion happens again, this amount of gas doesn't combust while the other does and the whole thing heats back up. Basically it is the same as a slight dilution and temperature rise befor combustion. Even your good scavenging overlap engine will still have some exhaust recirculate. while some gas does get trapped and cariied back to the intake side in the Renesis, it also does in the other rotaries as well. The difference is that it is typically the NOx within the exhaust in the Renesis that goes around again where it gets expelled in the 13B. Others do go around again though including some but not as much of the NOx. These get reburned which results in a cleaner emission. The epa has a huge say in what gets built.
You did make some great points and I thank you for making them. Hell, I'm just glad that people actually read that huge post and this one for that matter!
I'll add everything in if I ever publish a technical book on the rotary engine. Hopefully by then I'll learn how to type without the grammar and speeling errors too!
Last edited by rotarygod; 12-06-2003 at 10:51 PM.
12-06-2003, 11:19 PM
#27
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ROTARY GOD
I finished reading your epic very interesting why dont you get it translated to japanese and send it to the head engineers at mazda japan , maybe they will listen to some of the rxowners views and do something constructive towars the improvemts that you guys have pointed out.
keep up the good work.
michael
I finished reading your epic very interesting why dont you get it translated to japanese and send it to the head engineers at mazda japan , maybe they will listen to some of the rxowners views and do something constructive towars the improvemts that you guys have pointed out.
keep up the good work.
michael
12-07-2003, 12:18 AM
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Hey, just so you know that people appreciate your efforts, I've read all your long posts, rotarygod (as well as liveforphysics' there). Thank you both for those well-thought out and clearly explained posts 
12-07-2003, 09:26 AM
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Rotary g and Mr Physics,
great posts-both of you.I,d like to go on record as being the first to suggest the separate oil tank (for metering) on this forum in a previous thread.Of course I could be completely wrong.
Another point of note is that the combustion shape in the wankel,
or area of flame propagation is the worst of any internal combustion engine ; long, thin and partially divided. For this reason fuel efficiency will never be at the level of it's recipricating cousins.
Mazda's engineers are pretty bright although you are correct in stating they;like anyone else are limited by budgets.Some of the recomendations made by RG may be more applicable to rotary race cars and some are presently being applied (center bearing etc.)The added dowels; long or short,are not sufficiently necessary in normally aspirated motors or low boost applications.
Back to the center bearing: It's advantages are beyond 10k rpms.
Mr Physics, you are really correct about the reliability advantages of rotaries being more apparent in racing than on the street. The last normally aspirated rotaries did not regularly see as much as 120k miles.
Whether in racing or production, Mazda will spend what time and money they see as necessary to achieve specific goals.
great posts-both of you.I,d like to go on record as being the first to suggest the separate oil tank (for metering) on this forum in a previous thread.Of course I could be completely wrong.
Another point of note is that the combustion shape in the wankel,
or area of flame propagation is the worst of any internal combustion engine ; long, thin and partially divided. For this reason fuel efficiency will never be at the level of it's recipricating cousins.
Mazda's engineers are pretty bright although you are correct in stating they;like anyone else are limited by budgets.Some of the recomendations made by RG may be more applicable to rotary race cars and some are presently being applied (center bearing etc.)The added dowels; long or short,are not sufficiently necessary in normally aspirated motors or low boost applications.
Back to the center bearing: It's advantages are beyond 10k rpms.
Mr Physics, you are really correct about the reliability advantages of rotaries being more apparent in racing than on the street. The last normally aspirated rotaries did not regularly see as much as 120k miles.
Whether in racing or production, Mazda will spend what time and money they see as necessary to achieve specific goals.
12-07-2003, 09:50 PM
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Rotorygod-
I can not deny your testamonials reguarding your experiences with durability. I can only say that i see many more lower milage wankels in the junkyard then i see japanesse piston engines. Anyone is welcome to draw what ever conclusions they like from that. I have no doubt that much of the wankel failiers are from neglect, I think most people forget an oil change now and then, or even dont notice they are low on coolant once or twice, if your engine is forgiving, it sure is nice. If the basis for there duribility is basied on the fewer moving parts, i ask what about a toyota 4ag head? or a honda b16a head? Both are performance heads that take huge abuse for 200k miles and still operate like the day they are created. I have only heard of these heads EVER failing when people incorectly install cams, or try to "improve" them. Both of these units easily have over 50 moving parts in them. My feelings on the statement that something is less likely to because of less moving parts only hold true in a theoretical world. From my experience, they thing with a weak point always fails first, whether it has 10moving parts or 10000. If you want to compare the durability of a 'built' wankel, i think its only fair to also compare it to a similarly 'built' piston engine. Once you have forged H beam rods, forged ceramic coated pistons, moly-rings, forged steel crank, and stainless valves; you have a package that is pretty much indestructable when operated at a sensible output level. Yes, you can break any engine if you run it at 110%, but if you build it to take xhp and operate it at .7x hp, you have nearly an invincable piston engine. Throughing rods, dropping valves, ect... just stops. Anyways, a disscussion on durability is never going to end up getting anywhere due to 1000 factors from maintenece to climate that effect it greatly.
Scavenging......... I think you may want to re-think most of that paragraph, espically the following lines.
"As far as overlap and scavenging goes, from an economy standpoint overlap is irrelevant on a turbo car because of backpressure from a turbo"
scavenging is not only relivant on a turbo car, but infact so crucial that turbos can increase scavenging. Some engines even use turbo scavenging where the turbo is only an exaust turbine just to help an engine scavenge. Turbos reduce port reversion as well when in a situation with a bit of overlap. I think you may want to research that a bit more before making statements like the above.
"As long as there is a cat and muffler in the way to restict the exhaust, the benfits of scavenging will always be reduced."
Scavenging has long compleated its task before a muffler. I think you are confused with these things that do increase back-pressure haveing a negitive effect on scavenging. It is based on timing the ports high velocity burts to create a low pressure area from the last cylinder fireing to draw to next pulse with less resistance. Cats and muffs much after the collector can increase back pressure, but have a very mild effect on scavenging. Yes, they reduce the speed the pulses get to escape with, but the fact remains, they still get velocity, and scavenging still is a hugely vital part of flushing the chamber to reduce the amount of exaust gases reburned. This is also much the job of anti reversion valve angles in a piston engine, another effect that a wankel does not get to employ. Scavenging also reduces pumping losses on an engine and increses exaust gas velocity by not having such a hard low pressure area that the pulse has to 'escape' from.
The cumbustion chamber design has effectively been skirted, this is ok, it wasnt about the CCs design, but i find it hard to have any discussion where efficiency is mentioned with out looking at the piece that decides 80%+ of the efficancy of an engine. I honestly can not think of a worse design for an area to burn fuel then a wankels CC. Its a knock promoting, heat absorbing, delayed burntime having, slow flame front propagaing, end gass trapping abortian of a shape to burn fuel in. I find it amazing that even with SO much less paracitc losses in mechanical drag on the engine, that they can still be so poor at the conversion of chemical potential energy into mechanical energy.
I have an idea for people interested in modding wankels for lower emisions and improved power and fuel economy. How about ceramic coating the face of the rotor so that you dont waste quite as much heat energy in warming that oil, and more will go to the wheels. This would also make the engine more durable as well as lower NO emmsions from having less fire contact with metal which is the cause of the gas.
-Luke
I can not deny your testamonials reguarding your experiences with durability. I can only say that i see many more lower milage wankels in the junkyard then i see japanesse piston engines. Anyone is welcome to draw what ever conclusions they like from that. I have no doubt that much of the wankel failiers are from neglect, I think most people forget an oil change now and then, or even dont notice they are low on coolant once or twice, if your engine is forgiving, it sure is nice. If the basis for there duribility is basied on the fewer moving parts, i ask what about a toyota 4ag head? or a honda b16a head? Both are performance heads that take huge abuse for 200k miles and still operate like the day they are created. I have only heard of these heads EVER failing when people incorectly install cams, or try to "improve" them. Both of these units easily have over 50 moving parts in them. My feelings on the statement that something is less likely to because of less moving parts only hold true in a theoretical world. From my experience, they thing with a weak point always fails first, whether it has 10moving parts or 10000. If you want to compare the durability of a 'built' wankel, i think its only fair to also compare it to a similarly 'built' piston engine. Once you have forged H beam rods, forged ceramic coated pistons, moly-rings, forged steel crank, and stainless valves; you have a package that is pretty much indestructable when operated at a sensible output level. Yes, you can break any engine if you run it at 110%, but if you build it to take xhp and operate it at .7x hp, you have nearly an invincable piston engine. Throughing rods, dropping valves, ect... just stops. Anyways, a disscussion on durability is never going to end up getting anywhere due to 1000 factors from maintenece to climate that effect it greatly.
Scavenging......... I think you may want to re-think most of that paragraph, espically the following lines.
"As far as overlap and scavenging goes, from an economy standpoint overlap is irrelevant on a turbo car because of backpressure from a turbo"
scavenging is not only relivant on a turbo car, but infact so crucial that turbos can increase scavenging. Some engines even use turbo scavenging where the turbo is only an exaust turbine just to help an engine scavenge. Turbos reduce port reversion as well when in a situation with a bit of overlap. I think you may want to research that a bit more before making statements like the above.
"As long as there is a cat and muffler in the way to restict the exhaust, the benfits of scavenging will always be reduced."
Scavenging has long compleated its task before a muffler. I think you are confused with these things that do increase back-pressure haveing a negitive effect on scavenging. It is based on timing the ports high velocity burts to create a low pressure area from the last cylinder fireing to draw to next pulse with less resistance. Cats and muffs much after the collector can increase back pressure, but have a very mild effect on scavenging. Yes, they reduce the speed the pulses get to escape with, but the fact remains, they still get velocity, and scavenging still is a hugely vital part of flushing the chamber to reduce the amount of exaust gases reburned. This is also much the job of anti reversion valve angles in a piston engine, another effect that a wankel does not get to employ. Scavenging also reduces pumping losses on an engine and increses exaust gas velocity by not having such a hard low pressure area that the pulse has to 'escape' from.
The cumbustion chamber design has effectively been skirted, this is ok, it wasnt about the CCs design, but i find it hard to have any discussion where efficiency is mentioned with out looking at the piece that decides 80%+ of the efficancy of an engine. I honestly can not think of a worse design for an area to burn fuel then a wankels CC. Its a knock promoting, heat absorbing, delayed burntime having, slow flame front propagaing, end gass trapping abortian of a shape to burn fuel in. I find it amazing that even with SO much less paracitc losses in mechanical drag on the engine, that they can still be so poor at the conversion of chemical potential energy into mechanical energy.
I have an idea for people interested in modding wankels for lower emisions and improved power and fuel economy. How about ceramic coating the face of the rotor so that you dont waste quite as much heat energy in warming that oil, and more will go to the wheels. This would also make the engine more durable as well as lower NO emmsions from having less fire contact with metal which is the cause of the gas.
-Luke
12-07-2003, 10:53 PM
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I dont mean to sound like i am a wankel hater, there are applications where i think they are perfect. If i had to make a tube chasis road race car, it would get a wankel, also for drag i think a turbo wankel is a awsome powerplant.
I dont want to come off as bashing, just want to get some intelectual conversation going on.
I dont want to come off as bashing, just want to get some intelectual conversation going on.
12-07-2003, 11:36 PM
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I do actually like to brag about wankel durability. In race applications they have been unparalled for longevity.How about in excess of 100 race hours without a pulldown.This is what my friend Rick Engman has gotten out of some of his engines (R26B).
His team owner Jim Downing ;some of you may have heard of him,ran Daytona 24, Sebring 12hour,24hours of le Mans and over 40 test hours on an engine without taking it apart. When he did the corner seal springs didn't exist anymore. The apex seal springs were shot but the ceramic seals;from which I take my name were practically unworn.So also were the surfaces they operated against: housings, apex seal grooves etc. At this point you begin to see new things fail as one of you pointed out. Cracks in the rotors, cracks in the spark plug region of the housings etc.
As iI've pointed out before (To much argument the reason for the relatively short engine life of the 89 to 91 NA engines is poor oil metering. Those driven at the lowest revs (automatic, lady driven;no offense) saw the least apex seal life.The pump employed then didn't put out enough in low throttle situations.
Result: cleaner HC emissions and in extreme situations 70k mile engine failure.
His team owner Jim Downing ;some of you may have heard of him,ran Daytona 24, Sebring 12hour,24hours of le Mans and over 40 test hours on an engine without taking it apart. When he did the corner seal springs didn't exist anymore. The apex seal springs were shot but the ceramic seals;from which I take my name were practically unworn.So also were the surfaces they operated against: housings, apex seal grooves etc. At this point you begin to see new things fail as one of you pointed out. Cracks in the rotors, cracks in the spark plug region of the housings etc.
As iI've pointed out before (To much argument the reason for the relatively short engine life of the 89 to 91 NA engines is poor oil metering. Those driven at the lowest revs (automatic, lady driven;no offense) saw the least apex seal life.The pump employed then didn't put out enough in low throttle situations.
Result: cleaner HC emissions and in extreme situations 70k mile engine failure.
12-08-2003, 03:43 AM
#34
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I don't take anything personally. I didn't say that a piston engine can't and many time doesn't outlive many rotaries. In fact I agreed with this comment by stating that the rotary as we know it today in terms of durability isn't really any better than it was 40 years ago. I just disagree with the comment that they typically don't live to 200000 miles. Any engine will if you take care of it. Yes a built engine is tougher be it piston or rotary, I also agree with that statement. Something that many rotary owners don't realize is that just because then THEY can't get the engine to run, doesn't mean that it is bad. Many many people get rid of their rotary cars because they think the engin ehas blown when many times it hasn't. Several of the cars we have bought and fixed up were from non rotary enthusiasts that owned them and figured that the engine was dead or dying. I've picked up a few of these for a few hundred dollars and had to spend next to nothing to get them running perfectly. Lots of people don't know how temperamental they can be and most mechanics don't know any more or hardly anything for that matter as to how to fix or even work on them. I'm sure a few of them in the junkyards are truly dead but I'm willing to bet that a huge majority of them can still run for a long time with the proper maintenance.
I don't need to rethink a single thing about scavenging. You can not honestly claim that a turbo that is a several psi restiction in the exhaust is going to promote scavenging. How? There is not a factory turbocharged car available that does this. A very custom setup can be made to work well though and if done properly can even have less exhaust backpressure than positive intake pressure. Most of the cars out there don't have this though.
The ability of an engine to scavenge effectively is most certainly affected by backpressure. If there is a restiction, yes it will still scavenge as designed but the effect isn't as great. Backpressure and scavenging need to work together to have a perfectly working system.
I don't need to rethink a single thing about scavenging. You can not honestly claim that a turbo that is a several psi restiction in the exhaust is going to promote scavenging. How? There is not a factory turbocharged car available that does this. A very custom setup can be made to work well though and if done properly can even have less exhaust backpressure than positive intake pressure. Most of the cars out there don't have this though.
The ability of an engine to scavenge effectively is most certainly affected by backpressure. If there is a restiction, yes it will still scavenge as designed but the effect isn't as great. Backpressure and scavenging need to work together to have a perfectly working system.
12-08-2003, 04:42 AM
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For the durability side, i totally agree with everything you wrote up there. I bet many junked cars would be saveable for piston and rotory, but i bet more for rotorys.
Look up turbo scavenged engines.
A turbine wheel acts like a one way valve, it is hit by exaust pulses that transfer a portion of there velocity into energy to spin the turbine wheel. When reversion tries to occur, and the low pressure area behind the exaust pulse tries to suck the pulse back, the turbine wheel is like a 1 way valve. Its of course much more complex then this, but i am trying to be brief. A pressure value recorded in a properly tuned turbo manifold is from a frequency of high pressure pulses. This is true with any exaust setup. Some are very much worse then others, but exaust is not a flow, its pulses. Its almost like trying to measure AC power with a DC guage. One is sustained pressure, one is high/low fluctuations. Both will make the guage move and record "backpressure". Exaust is honestly such an advanced thermo-compressable-fluid-dynimics topic it will boggle the mind. Espically as one learns the the best exaust systems taper smaller as they go, unlike the exaust you see on every car.
I am happy to see this can maintain intelectual disscussion.
Please check out turbo scavenging, its a facinating topic.
Look up turbo scavenged engines.
A turbine wheel acts like a one way valve, it is hit by exaust pulses that transfer a portion of there velocity into energy to spin the turbine wheel. When reversion tries to occur, and the low pressure area behind the exaust pulse tries to suck the pulse back, the turbine wheel is like a 1 way valve. Its of course much more complex then this, but i am trying to be brief. A pressure value recorded in a properly tuned turbo manifold is from a frequency of high pressure pulses. This is true with any exaust setup. Some are very much worse then others, but exaust is not a flow, its pulses. Its almost like trying to measure AC power with a DC guage. One is sustained pressure, one is high/low fluctuations. Both will make the guage move and record "backpressure". Exaust is honestly such an advanced thermo-compressable-fluid-dynimics topic it will boggle the mind. Espically as one learns the the best exaust systems taper smaller as they go, unlike the exaust you see on every car.
I am happy to see this can maintain intelectual disscussion.
Please check out turbo scavenging, its a facinating topic.
12-08-2003, 06:06 PM
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Actually I do have to concur somewhat in relation to scavenging in turbo engines. The problem is that there are so many terrible design exhaust manifolds out there that don't really direct the energy around very well. Big common chambers, unequal lengths, improper locations for a wastegate, too small of an exhaust wheel on the turbo, etc get used everyday and cause problems of their own. There are so many bad designes out there that have pressure waves, harmfully in terms of performance, interacting each chamber to another before they even get to the turbo. A simple log manifold is not going to do anything to help scavenge the engine. However a proper set of headers that collect at the proper angle and have the proper length feeding the turbo can help the engine spool up faster. In some ways a properly scavenging engine can help the turbo rather than the turbo helping to scavenge the engine.
Marcus Williams had a 3rd gen RX-7 drag car with a bridgeport. A bridgeport has high overlap and needs all the scavenging it can get. A set of good headers on a naturally aspirated engine is a must. A very bad setup can actually result in less power than a much smaller port with less overlap. Backpressure plays a big role in this as well. Since scavenging is using the gas velocity of one chamber to help suck the gasses from the other chamber and therefore more air into the engine, even a turbo should be able to do this. A small turbo or one with a heavy exhaust wheel will not do this. On Marcus' car, he wanted some mega power. He was using a big single turbo. He designed everything right. He had a very free flowing exhaust wheel and housing for as little pressure as he could get. He ran into a brick wall at about 20 psi of boost. The car wouldn't make any more power with added boost on top of this. He ran a pressure probe before the turbo exhaust housing to see how much pressure he had. At 20 psi of boost he had 23 psi of pressure in the exhaust. The exhaust pressure was holding back some of the incoming air and recirculating alot of exhaust back through the combustion process again. One rotor was definitely not helping to suck the gasses out of the other side of the engine through scavenging. He changed his turbo setup to use 2 smaller single turbos instead of one big one. The smaller wheels start to spin faster and the turbos also flow more air this way as we are no longer mixing all the exhaust energy from 2 housings into one unit. The result was far more power and much faster spoolup time. The exhaust pressure probes revealed that at 23 psi of boost he now only had 19 psi of exhaust backpressure. If this is the phenomenon that you are calling scavenging in a turbo engine then I can see how it could happen. Too many of the designs on the road right now do not just automatically promote it though.
I guess I can see the point if technically there is always scavenging going on but the effects of backpressure can cancel out the benefits if great enough. Is this what you are referring to?
You obviously do "live for physics"!!! I have a couple of very good books that are over the heads of most people but I'll bet that you could understand them easily. The first one is an older book and while a little technical is by no means difficult to understand.
It is called: Scientific Design of Exhaust and Intake System.
The other two are very technical and are probably an engineering textbook at some school somewhere. They are:
The Internal Combustion Engine in Theory and Practice Volumes 1 and 2. Volume 1: Thermodynamics, Fluid Flow, Performance. Volume 2: Combustion, Fuels, Materials, Design.
These are some interesting books. The first books is about 260 pages or so but the other 2 books are over 500 pages each. You'd probably thrive on these or maybe you already have them.
Do you have a book about turbos and scavenging? I'd love to pick it up and see what the technical wordings of all the effects are called. Maybe I really do know what is going on but just don't have the technical explanations for them down. Who knows? I already have a problem with putting what I am thinking into words sometimes anyways.
I'm always ready to have good technical chat back and forth. I don't take anything as hostile and I hope you don't either. If you do then it wasn't my intention.
Marcus Williams had a 3rd gen RX-7 drag car with a bridgeport. A bridgeport has high overlap and needs all the scavenging it can get. A set of good headers on a naturally aspirated engine is a must. A very bad setup can actually result in less power than a much smaller port with less overlap. Backpressure plays a big role in this as well. Since scavenging is using the gas velocity of one chamber to help suck the gasses from the other chamber and therefore more air into the engine, even a turbo should be able to do this. A small turbo or one with a heavy exhaust wheel will not do this. On Marcus' car, he wanted some mega power. He was using a big single turbo. He designed everything right. He had a very free flowing exhaust wheel and housing for as little pressure as he could get. He ran into a brick wall at about 20 psi of boost. The car wouldn't make any more power with added boost on top of this. He ran a pressure probe before the turbo exhaust housing to see how much pressure he had. At 20 psi of boost he had 23 psi of pressure in the exhaust. The exhaust pressure was holding back some of the incoming air and recirculating alot of exhaust back through the combustion process again. One rotor was definitely not helping to suck the gasses out of the other side of the engine through scavenging. He changed his turbo setup to use 2 smaller single turbos instead of one big one. The smaller wheels start to spin faster and the turbos also flow more air this way as we are no longer mixing all the exhaust energy from 2 housings into one unit. The result was far more power and much faster spoolup time. The exhaust pressure probes revealed that at 23 psi of boost he now only had 19 psi of exhaust backpressure. If this is the phenomenon that you are calling scavenging in a turbo engine then I can see how it could happen. Too many of the designs on the road right now do not just automatically promote it though.
I guess I can see the point if technically there is always scavenging going on but the effects of backpressure can cancel out the benefits if great enough. Is this what you are referring to?
You obviously do "live for physics"!!! I have a couple of very good books that are over the heads of most people but I'll bet that you could understand them easily. The first one is an older book and while a little technical is by no means difficult to understand.
It is called: Scientific Design of Exhaust and Intake System.
The other two are very technical and are probably an engineering textbook at some school somewhere. They are:
The Internal Combustion Engine in Theory and Practice Volumes 1 and 2. Volume 1: Thermodynamics, Fluid Flow, Performance. Volume 2: Combustion, Fuels, Materials, Design.
These are some interesting books. The first books is about 260 pages or so but the other 2 books are over 500 pages each. You'd probably thrive on these or maybe you already have them.
Do you have a book about turbos and scavenging? I'd love to pick it up and see what the technical wordings of all the effects are called. Maybe I really do know what is going on but just don't have the technical explanations for them down. Who knows? I already have a problem with putting what I am thinking into words sometimes anyways.
I'm always ready to have good technical chat back and forth. I don't take anything as hostile and I hope you don't either. If you do then it wasn't my intention.
12-08-2003, 07:40 PM
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Exellent post!!
I agreed with all of it.
Proper setup has always been, and will allways be crucial to makeing anything perform correctly. I was just assuming this would be considdered.
The books you mentioned, I have most of them within 10ft of me. I also have many more, i am sure you do to. Its been good to discuss with you. If you crave very very advanced engine disscussion topics, i recomend you check out
www theoldone .com and click BBS
Its got some seriously sharp minds on it, and nearly everyone does about 99% lurking and just makes a few posts. The quanity of posts is quite low, but the quailty is very high(generally) and most people do post a small book
Just a caution, they are open minded, but wankels are generally frowned apon due to the cumbustion chamber design. Also, if a post lacks content, it is generally deleated by the mods.
Its a great place to lurk the archives, i learn there everyday.
-Luke
PS, check out that xylene disscussion, it got f%$*ed into outerspace!!!! I have never seen a thread get loaded with soooo much BS!! I tried to straighten it out a bit, you should help too!
I agreed with all of it.
Proper setup has always been, and will allways be crucial to makeing anything perform correctly. I was just assuming this would be considdered.
The books you mentioned, I have most of them within 10ft of me. I also have many more, i am sure you do to. Its been good to discuss with you. If you crave very very advanced engine disscussion topics, i recomend you check out
www theoldone .com and click BBS
Its got some seriously sharp minds on it, and nearly everyone does about 99% lurking and just makes a few posts. The quanity of posts is quite low, but the quailty is very high(generally) and most people do post a small book
Just a caution, they are open minded, but wankels are generally frowned apon due to the cumbustion chamber design. Also, if a post lacks content, it is generally deleated by the mods.
Its a great place to lurk the archives, i learn there everyday.
-Luke
PS, check out that xylene disscussion, it got f%$*ed into outerspace!!!! I have never seen a thread get loaded with soooo much BS!! I tried to straighten it out a bit, you should help too!
01-06-2004, 02:17 PM
#38
Nice to see some posts that lack the b.s. factor. I would like to ask our two resident sages if they would like to switch the conversation to the torque/horsepower generated by rotary engines, how it compares to recip. piston engines, and what it all means in the "real world". I have some thoughts of my own, but I want to offer the topic up before I barge in the room. Thanks.
C.R.
C.R.
03-23-2004, 02:36 AM
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Originally posted by liveforphysics
..I am not saying that a wankel cant do 200+k miles, just that it seems a whole lot of piston engines do, and i have only seen a few wankels do it.,,
..I am not saying that a wankel cant do 200+k miles, just that it seems a whole lot of piston engines do, and i have only seen a few wankels do it.,,
04-23-2004, 09:56 PM
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SOme good info here, but also some ignores engineering and manufacturing basics.
1st: Why 13B? The main reason is Japan requires engines be certified by the government. Mazda first had the 10a, then 12a, and when they made the 13B in 1974 they wanted to note the tremendous changes so used the "B". Many people refered to the 74 and later 12A as a 12B, but officially it was stiill a 12a because of the government certification. The RX8 should be the 13C, but again can't because it is still a 1.3L engine so 13B. The 12a was used in the RX7 until 85.
2nd. The machine to make the rotor housing is VERY special. It is not like buying a cylinder boring bar. The shape is called a epitrochoidal curve (modified to allow for the diameter of the end of the apex seal). As such it has been cheapest and easies for Mazda to change the width for each engine. The 10a is 60 mm wide, 12a 70 mm, and 13B 80mm wide.
3rd. IS heat disapation. The rotary, we can all agree, makes a lot of power in a small package. As such it also makes a lot of heat. The primary way to capture and disapate this heat is by the cooloing water around the housings and the oil sprayed into the rotor. This heat is disapated by the surface area exposed to the water or oil. When you increase the width too much you do not get enough additional surface area to disapate this heat, so problems. Mazda found this in early work and did a lot of testing to determine the size they use. SO larger is not easy...
4. The rotary is bad on gas milage because it has too much surface area for the contained volume. A spherical combustion chamber, like a bubble, has the least surface area while a rotary is really a long thin retactangle. With present day materials the surface must be much cooler than the burning gases. As the flame approches the cold surface it actually stops burning because it is so cold and leaves some unburned fuel. Gas turbins use material that can run real hot, so don't have this problem and both cost a lot and are very efficient.
5. Theroritacal efficiency of a auto cycle (gasoline sparked) engine is primarily determined by the compression ratio. But high ratios also cause more heat and possible detonation - exploding instead of burning fuel. High octan fuel actually has less chemical energy than low octane fuel, but requires more heat to explode. The compression make more additional power than the lost power of the high octane fuel. But if the engine does not require it you will get more power and better fuel economy from the lowest octane fuel your engine can run on without detonation. With 10:1 the 8 does make more power, but will get better milage if you use regular and just live with the 5500 to 6500 loss of power when the ecu retards the timing because of detonation.
6. The ENGINEERING METHOD to determine displacement is the swept volumn in one rotation of the output shaft. PERIOD. But as above there have been many arguments, especially in racing, that the rotary is really a 4 or 6 stroke engine. Mazda uses the accepted engineering method.
There are many publications by Mazda from back in the 1970s (before the www). There was even some machinest that read about the rotary and made his own 7 or 9 lobe (don't remember) rotary engine that ran and was later shown in Popular Science.
1st: Why 13B? The main reason is Japan requires engines be certified by the government. Mazda first had the 10a, then 12a, and when they made the 13B in 1974 they wanted to note the tremendous changes so used the "B". Many people refered to the 74 and later 12A as a 12B, but officially it was stiill a 12a because of the government certification. The RX8 should be the 13C, but again can't because it is still a 1.3L engine so 13B. The 12a was used in the RX7 until 85.
2nd. The machine to make the rotor housing is VERY special. It is not like buying a cylinder boring bar. The shape is called a epitrochoidal curve (modified to allow for the diameter of the end of the apex seal). As such it has been cheapest and easies for Mazda to change the width for each engine. The 10a is 60 mm wide, 12a 70 mm, and 13B 80mm wide.
3rd. IS heat disapation. The rotary, we can all agree, makes a lot of power in a small package. As such it also makes a lot of heat. The primary way to capture and disapate this heat is by the cooloing water around the housings and the oil sprayed into the rotor. This heat is disapated by the surface area exposed to the water or oil. When you increase the width too much you do not get enough additional surface area to disapate this heat, so problems. Mazda found this in early work and did a lot of testing to determine the size they use. SO larger is not easy...
4. The rotary is bad on gas milage because it has too much surface area for the contained volume. A spherical combustion chamber, like a bubble, has the least surface area while a rotary is really a long thin retactangle. With present day materials the surface must be much cooler than the burning gases. As the flame approches the cold surface it actually stops burning because it is so cold and leaves some unburned fuel. Gas turbins use material that can run real hot, so don't have this problem and both cost a lot and are very efficient.
5. Theroritacal efficiency of a auto cycle (gasoline sparked) engine is primarily determined by the compression ratio. But high ratios also cause more heat and possible detonation - exploding instead of burning fuel. High octan fuel actually has less chemical energy than low octane fuel, but requires more heat to explode. The compression make more additional power than the lost power of the high octane fuel. But if the engine does not require it you will get more power and better fuel economy from the lowest octane fuel your engine can run on without detonation. With 10:1 the 8 does make more power, but will get better milage if you use regular and just live with the 5500 to 6500 loss of power when the ecu retards the timing because of detonation.
6. The ENGINEERING METHOD to determine displacement is the swept volumn in one rotation of the output shaft. PERIOD. But as above there have been many arguments, especially in racing, that the rotary is really a 4 or 6 stroke engine. Mazda uses the accepted engineering method.
There are many publications by Mazda from back in the 1970s (before the www). There was even some machinest that read about the rotary and made his own 7 or 9 lobe (don't remember) rotary engine that ran and was later shown in Popular Science.
Last edited by TRZ750; 04-23-2004 at 10:02 PM.
04-24-2004, 12:19 AM
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Finally in the above post TRZ750 answered the original question of WHY 1.3L - and nicely done too.
However since someone mentioned 'doing the math' I'd like to see the differential formulas for calculating the minimal and maximal areas between the curves described by the epitrochoid/rotor... From there it's trivial math but if someone is going to do the math - then let's post the formulas.
As TRZ750 said better than I - As opposed to 1.2L or 1.4L or whatever... The overall size of the housing is fairly set so they generally only vary displacement in design by widening or narrowing the rotor as he said. The rotor housing can only be widened so far before inefficiency tradeoffs in combustion and mass creep in and ~80mm seems to be the generally accepted optimal tradeoff point. From 80 mm we get 1.3L (or multiples thereof if you like)
Just my $0.02 worth - really just want to call attention to TRZ750's excellent and quite correct answer to the original question posed.
However since someone mentioned 'doing the math' I'd like to see the differential formulas for calculating the minimal and maximal areas between the curves described by the epitrochoid/rotor... From there it's trivial math but if someone is going to do the math - then let's post the formulas.
As TRZ750 said better than I - As opposed to 1.2L or 1.4L or whatever... The overall size of the housing is fairly set so they generally only vary displacement in design by widening or narrowing the rotor as he said. The rotor housing can only be widened so far before inefficiency tradeoffs in combustion and mass creep in and ~80mm seems to be the generally accepted optimal tradeoff point. From 80 mm we get 1.3L (or multiples thereof if you like)
Just my $0.02 worth - really just want to call attention to TRZ750's excellent and quite correct answer to the original question posed.
08-24-2004, 04:25 PM
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Why is the rotary the engine of choice to begin with, other than the historical context? Seems that the 220hp 3.0 V6 in the Mazda 6 would give it better low end and performance overall, especially with a little tweaking. The 6 runs to 60 in roughly the same time as the RX8 and hauls nearly 300 extra pounds. Why not give it a V6 and let the gas mileage and perfromance numbers go up?
08-24-2004, 04:34 PM
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Originally Posted by Painless
Why is the rotary the engine of choice to begin with, other than the historical context? ....
rx8cited
08-24-2004, 05:50 PM
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Originally Posted by rx8cited
Let's start with its physical size
Originally Posted by rx8cited
and smaller number of moving parts compared to a V6 of similar HP.
rx8cited
rx8cited
Either the niche Rx8 will choke on it's thirsty smoggy 'tradition' as little more than a flash in the pan from a company w/ a poor history of supporting it's niche cars or they'll wise up and shoehorn a V6 in it w/ a hood bulge and go mainstream w/ an otherwise nifty car before other makers effectively copy the form factor w/ more realistic powerplants.
Then again a new C5 w/ a $15K end of model discount is awfully tempting w/ C6s already rolling.
08-24-2004, 07:25 PM
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First off the engine's lower center of gravity in relation to a piston engine makes packaging a little different. It's not only how much something weighs that counts but also where you put the weight. The rotary engine is also somewhat of a tradition with Mazda sports cars and racing. Is it the best thing out there? Probably not.
My advice to you is that if you think the rotary is so inferior, you should spend more time with other forums talking to people who sympathize with you rather than wasting your time here. You won't get us to say it is a bad engine since it isn't. Go buy a Vette or some other piston powered car and be happy. The rest of us not content on following the crowd will remain happy here. Thanks for stopping by, now go away since you are trying to start a war here.
My advice to you is that if you think the rotary is so inferior, you should spend more time with other forums talking to people who sympathize with you rather than wasting your time here. You won't get us to say it is a bad engine since it isn't. Go buy a Vette or some other piston powered car and be happy. The rest of us not content on following the crowd will remain happy here. Thanks for stopping by, now go away since you are trying to start a war here.