Here's why the AT engine has less power potential than the 6MT
02-05-2004, 02:29 AM
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Here's why the AT engine has less power potential than the 6MT
As we all know the 4 port Renesis engine as found in the auto transmission cars is the lower power version. I've seen many people inquire as to how power can be gained on these cars to bring them up to par with the 6 port engines and I am sad to say that the cars are stacked against you and you're almost out of chips. There are several reasons why this engine just isn't going to give you any more serious power. The good news is that you can change this with forced induction! You just can't get much more out of it unless you do.
There are some very technical topics that need to be dealt with that will fully expose the potential or lack thereof of this version of the Renesis. They are:
1: Port timing
A: Primary port size
B: Secondary port size
C: Exhaust port differences
2: Port area
3: Intake runner design
4: Air flow affects of runner area
5: Thoughts on forced induction
Since I as usual will be very long winded again I am seperating this into an outline fashion.
1: Port timing.
Total port timing has much to do with where the engine produces optimal power and how wide the power band is. The greater the total port timing, the higher and narrower the usable power band. Sounds kind of strange. The shorter the port timing, the lower and wider the usable powerband. On a rotary port size is directly related to port timing. Unlike a piston engine, we can not just install a larger set of valves for greater flow but still retain the same cam profile for the same timing. It just doesn't work that way.
A: Primary port size: The port sizes and therefore port timing of the primary ports is very different. The primary port open timing is the same between each engine at 3 degrees after top dead center. However the closing points are different. The 4 port closes at 60 degrees after bottom dead center whereas the 6 port engines port closes at 65 degrees after bottom dead center. Remember that a shorter opening time is better for a lower power band and is also limited in total power production.
B:Secondary port sizes: The secondaty ports as with the primaries are also timed very differently between both stlyes of engine. The Secondary ports as with the primaries open at the same interval of 12 degrees after top dead center. However once again the port closing intervals is different. The 4 port engine closes at 45 degrees after bottom dead center whereas the 6 port engine closes at 36 degrees after bottom dead center. It would appear that the secondary ports have the advantage on the 4 port engine. Maybe they do but the 6 port engine still have 2 more ports to go so the benefit ends at the top of the 4 port engine's powerband that stay open until 80 degrees after bottom dead center. Look at a dyno comparison of the 4 port vs the 6 port engine and see where the 6 port engine starts to make more power than the 4 port engine. Then look at where the 2 additional ports open up on the 6 port engine. Coincedence? I think not! Remember that the 4 port engine is tuned for greater average power down low than the 6 port engine and this timing scenario alone is a big contributor. The old 4 port engines has secondary ports that stayed open as late as 60 degrees. By default the older engines are more suited to better top end than the current engine bases on port timing.
C: Exhaust port differences: The exhaust ports aren't even timed the same between these 2 engines. They both close the same time at 3 degrees before top dead center. The opening point is a little different though. The 4 port engine opens at 40 degrees before bottom dead center and the 6 port engine opens at 50 degrees before bottom dead center. Again shallower timing and a later opening are better for low end power. Another strike against the 4 port in the power department. Remember that a port with less timing is also a port with less area and therefore flow which takes us to the next section.
2: Port area: By now you have seen that the total port area is less on the 4 port engine than it is on the 6 port engines. This also applies to the intake runners. The total port area on the 4 port Renesis is even much less than the old 4 port 13B engines. This smaller area helps to keep the incoming air velocity high. However we come to a point where too much velocity is harmful. We'll call this the Z factor. After air hits .6 mach or 60% or the speed of sound in the intake system, it begins to lose useful energy. I actually have a chart somewhere that shows this. Once the velocity exceeds this speed, no more or at least very little more power can be achieved. What will happen is that the air begins to heat up dramatically. Hotter air molecules are bigger air molecules. bigger molecules take up more area per volume and suddenly that pipe appears much smaller. Once you get to a certain rpm, you've hit an airflow brick wall. There is no point in trying to rev these engines higher to achieve more power. You had better be ready to increase total port area, total intake runner area, and decrease total intake runner length. The 4 port engine has a lower redline for many reasons but the fact that it can't inhale enough air due to velocity reasons for a higher redline should be reason enough to understand why it is where it is.
3: Intake runner design: As we all know an intake manifold can make or break an engine in the power department. The runners should be relatively straight with a minimum number of bends. A good manifold will have gentle bends where necessary and not conduct any excess heat. Luckily the Renesis intake manifold is the single best intake manifold that Mazda has ever designed. There are very many reasons why it shouldn't be changed. Upon first glance it appears that the only difference between the 4 port and 6 port Renesis manifolds is the fact that one adds 2 more runners. Oh how wrong could that statement be! Each manifold was designed specifically for that particular engine and it's powerband. Each manifold has a valve known a VDI which stands for Variable Dynamic Intake. The VDI valve opens at 7250 rpm on the 6 port engine and lower on the 4 port engine to bridge different runners together. This in essence lets the engine see a shorter runner than is what is actually there. We basically have 2 different runner lengths. Each set of runners is tuned to a certain rpm and by changing this the powerband is widened. So we not only have variable timing but also a variable length manifold as well. V-tech eat your heart out! The intake runner lengths between engines are as follows. I'll classify them into long and short to signify when the VDI valve is open and closed. Closed is long open is short.
4 port engine
primary runners long: 27.4"
primary runners short: 14.8"
secondary runners long: 29.1"
secondary runners short: 16.5"
6 port engine
primary runners long: 19.8"
primary runners short: 13.5"
secondary runners long: 20.4"
secondary runners short: 14.2"
auxillary runners: 17.3"
The auxillary runners on the 6 port engine are not tied into the VDI system on the manifold since they split off earlier in the manifold. Since they are only open for a short time they are tuned around this event. As you can see even the runner lengths are different between the 4 port and the 6 port engines. Longer runners promote better low end. Note that the primary and secondary runners for each rotor are siamesed together until after the VDI valve. The above lengths do not take into account for this but rather are measured to the point where the manifold splits between front and rear rotors. Since each runner can receive a tuning benefit from both primary and secondary ports due to the VDI valve also being siamesed, the VDI effect is over a broader range than it was on the later 2nd generation RX-7 where VDI first appeared.
Another good feature of this manifold over previous manifolds is the use of composites for the upper half. Composites unlike aluminum dissipate heat very well. Aluminum is a great radiator of heat and will just grab it and hold it. This heats up the intake air. This isn't a problem when the engine is revved up as the airflow through the runners serves to cool down the manifold but the problem is greatest when the car is idling. While a total composite manifold would be best in regards to heat, at least half of it is. My only concern is how much psi will it hold should forced induction be applied.
4: Air flow effects of runner area: As I have previously stated we have a phenomenom known as the Z factor to worry about. How to optimize this though can yield some fantastic results and in this respect Mazda has done some homework. When only 2 runners are receiving air, the velocity through them is higher than if 4 were receiving air. Duh! This will yield superior power right up to the point that the Z factor hits .6 mach or so. This is a good rpm to open up another set of runners. Guess what? The Renesis does this! At a higher rpm another set opens up and power stays high all the way through the powerband. Brilliant! Too bad they screwed up with the ecu tuning. The 4 port engine runs into a very bad problem. It runs out of runner area. Basically it has the runner area of a 6 port engine minus the auxillary ports. That is alot less airflow potential. It doesn't matter if we make a shorter intake manifold that tunes to a higher rpm, we are still flow limited.
5: Thoughts on forced induction: Please understand that this next paragraph is using the 6 port engine as a baseline for potential so don't get too discouraged. Typically in the past the 4 port engines were thought to be the better choice in the forced induction arena. However the 4 port engines of the past also had greater runner area that was nearly equal to the 6 port runner area, they outflowed the 6 port engines on the flowbench, and they were simpler. All of this has changed with the new 4 port Renesis. The secondary ports are no where near as big as the older engines. The timing is not near as great. The total runner area is much less. This all adds up to an engine with less airflow. How does a turbo spool up? Airflow! If we were to add a turbo to the 4 port Renesis, it would be one with a very small exhaust housing that is designed for small gains. A lack of airflow through the engine will make it very slow to spool. A high compression ratio helps to combat this but we can't perform miracles. It would actually spool up faster if all the ports were open simultaneously by diabling the secondary shutter valves. This applies to 4 and 6 port engines. The faster we can get more air into the engine the faster we can get it out and therefore spool up the turbo. Remember that since we are relying on positive manifold pressure we just want all the area we can get so as much air gets in as fast as possible. Based on the fact that there is so much less runner and port area than the previous 4 port and 6 port engines, the new 4 port Renesis is not a good candidate for forced induction as the 6 port engine is. You could still get some very nice power out of it though so don't think it would be bad to use forced induction. You are just ultimately (somewhere over 350 hp or so) going to lose potential as compared to the 6 port engine.
The 4 port Renesis as well as the 6 port were designed to maximize performance in their respective power ranges. Through careful port timng, sizing, and runner lengths, Mazda has just about maximized the performance capabilities of these engine. Their tuning is insufficient though but once this engine is tuned properly, gains will be few and far between. There is always room for a little more power but gone are the days of 35hp gains from and exhaust. The 4 port engine has so much going against it in terms of pure power production that it should not even be considered a viable market for performance products. Gains would be too small to justify the product prices. Remember that a gain lower in the powerband equals less total horsepower than a gain at an engine designed to run at a higher powerband. If you have a mod that can add 10hp at 9000 rpm, it will only add about 4 or 5 at 7000 rpm. Performance gains for the 4 port engines will be much less. Sorry 4 port guys, if you are performance nuts hellbent on getting the most power from an RX-8 that you can, you bought the wrong model. Don't be discouraged though. Forced induction can still give you the speed and power that could still make this car a force to be dealt with by most other cars on the road.
There are some very technical topics that need to be dealt with that will fully expose the potential or lack thereof of this version of the Renesis. They are:
1: Port timing
A: Primary port size
B: Secondary port size
C: Exhaust port differences
2: Port area
3: Intake runner design
4: Air flow affects of runner area
5: Thoughts on forced induction
Since I as usual will be very long winded again I am seperating this into an outline fashion.
1: Port timing.
Total port timing has much to do with where the engine produces optimal power and how wide the power band is. The greater the total port timing, the higher and narrower the usable power band. Sounds kind of strange. The shorter the port timing, the lower and wider the usable powerband. On a rotary port size is directly related to port timing. Unlike a piston engine, we can not just install a larger set of valves for greater flow but still retain the same cam profile for the same timing. It just doesn't work that way.
A: Primary port size: The port sizes and therefore port timing of the primary ports is very different. The primary port open timing is the same between each engine at 3 degrees after top dead center. However the closing points are different. The 4 port closes at 60 degrees after bottom dead center whereas the 6 port engines port closes at 65 degrees after bottom dead center. Remember that a shorter opening time is better for a lower power band and is also limited in total power production.
B:Secondary port sizes: The secondaty ports as with the primaries are also timed very differently between both stlyes of engine. The Secondary ports as with the primaries open at the same interval of 12 degrees after top dead center. However once again the port closing intervals is different. The 4 port engine closes at 45 degrees after bottom dead center whereas the 6 port engine closes at 36 degrees after bottom dead center. It would appear that the secondary ports have the advantage on the 4 port engine. Maybe they do but the 6 port engine still have 2 more ports to go so the benefit ends at the top of the 4 port engine's powerband that stay open until 80 degrees after bottom dead center. Look at a dyno comparison of the 4 port vs the 6 port engine and see where the 6 port engine starts to make more power than the 4 port engine. Then look at where the 2 additional ports open up on the 6 port engine. Coincedence? I think not! Remember that the 4 port engine is tuned for greater average power down low than the 6 port engine and this timing scenario alone is a big contributor. The old 4 port engines has secondary ports that stayed open as late as 60 degrees. By default the older engines are more suited to better top end than the current engine bases on port timing.
C: Exhaust port differences: The exhaust ports aren't even timed the same between these 2 engines. They both close the same time at 3 degrees before top dead center. The opening point is a little different though. The 4 port engine opens at 40 degrees before bottom dead center and the 6 port engine opens at 50 degrees before bottom dead center. Again shallower timing and a later opening are better for low end power. Another strike against the 4 port in the power department. Remember that a port with less timing is also a port with less area and therefore flow which takes us to the next section.
2: Port area: By now you have seen that the total port area is less on the 4 port engine than it is on the 6 port engines. This also applies to the intake runners. The total port area on the 4 port Renesis is even much less than the old 4 port 13B engines. This smaller area helps to keep the incoming air velocity high. However we come to a point where too much velocity is harmful. We'll call this the Z factor. After air hits .6 mach or 60% or the speed of sound in the intake system, it begins to lose useful energy. I actually have a chart somewhere that shows this. Once the velocity exceeds this speed, no more or at least very little more power can be achieved. What will happen is that the air begins to heat up dramatically. Hotter air molecules are bigger air molecules. bigger molecules take up more area per volume and suddenly that pipe appears much smaller. Once you get to a certain rpm, you've hit an airflow brick wall. There is no point in trying to rev these engines higher to achieve more power. You had better be ready to increase total port area, total intake runner area, and decrease total intake runner length. The 4 port engine has a lower redline for many reasons but the fact that it can't inhale enough air due to velocity reasons for a higher redline should be reason enough to understand why it is where it is.
3: Intake runner design: As we all know an intake manifold can make or break an engine in the power department. The runners should be relatively straight with a minimum number of bends. A good manifold will have gentle bends where necessary and not conduct any excess heat. Luckily the Renesis intake manifold is the single best intake manifold that Mazda has ever designed. There are very many reasons why it shouldn't be changed. Upon first glance it appears that the only difference between the 4 port and 6 port Renesis manifolds is the fact that one adds 2 more runners. Oh how wrong could that statement be! Each manifold was designed specifically for that particular engine and it's powerband. Each manifold has a valve known a VDI which stands for Variable Dynamic Intake. The VDI valve opens at 7250 rpm on the 6 port engine and lower on the 4 port engine to bridge different runners together. This in essence lets the engine see a shorter runner than is what is actually there. We basically have 2 different runner lengths. Each set of runners is tuned to a certain rpm and by changing this the powerband is widened. So we not only have variable timing but also a variable length manifold as well. V-tech eat your heart out! The intake runner lengths between engines are as follows. I'll classify them into long and short to signify when the VDI valve is open and closed. Closed is long open is short.
4 port engine
primary runners long: 27.4"
primary runners short: 14.8"
secondary runners long: 29.1"
secondary runners short: 16.5"
6 port engine
primary runners long: 19.8"
primary runners short: 13.5"
secondary runners long: 20.4"
secondary runners short: 14.2"
auxillary runners: 17.3"
The auxillary runners on the 6 port engine are not tied into the VDI system on the manifold since they split off earlier in the manifold. Since they are only open for a short time they are tuned around this event. As you can see even the runner lengths are different between the 4 port and the 6 port engines. Longer runners promote better low end. Note that the primary and secondary runners for each rotor are siamesed together until after the VDI valve. The above lengths do not take into account for this but rather are measured to the point where the manifold splits between front and rear rotors. Since each runner can receive a tuning benefit from both primary and secondary ports due to the VDI valve also being siamesed, the VDI effect is over a broader range than it was on the later 2nd generation RX-7 where VDI first appeared.
Another good feature of this manifold over previous manifolds is the use of composites for the upper half. Composites unlike aluminum dissipate heat very well. Aluminum is a great radiator of heat and will just grab it and hold it. This heats up the intake air. This isn't a problem when the engine is revved up as the airflow through the runners serves to cool down the manifold but the problem is greatest when the car is idling. While a total composite manifold would be best in regards to heat, at least half of it is. My only concern is how much psi will it hold should forced induction be applied.
4: Air flow effects of runner area: As I have previously stated we have a phenomenom known as the Z factor to worry about. How to optimize this though can yield some fantastic results and in this respect Mazda has done some homework. When only 2 runners are receiving air, the velocity through them is higher than if 4 were receiving air. Duh! This will yield superior power right up to the point that the Z factor hits .6 mach or so. This is a good rpm to open up another set of runners. Guess what? The Renesis does this! At a higher rpm another set opens up and power stays high all the way through the powerband. Brilliant! Too bad they screwed up with the ecu tuning. The 4 port engine runs into a very bad problem. It runs out of runner area. Basically it has the runner area of a 6 port engine minus the auxillary ports. That is alot less airflow potential. It doesn't matter if we make a shorter intake manifold that tunes to a higher rpm, we are still flow limited.
5: Thoughts on forced induction: Please understand that this next paragraph is using the 6 port engine as a baseline for potential so don't get too discouraged. Typically in the past the 4 port engines were thought to be the better choice in the forced induction arena. However the 4 port engines of the past also had greater runner area that was nearly equal to the 6 port runner area, they outflowed the 6 port engines on the flowbench, and they were simpler. All of this has changed with the new 4 port Renesis. The secondary ports are no where near as big as the older engines. The timing is not near as great. The total runner area is much less. This all adds up to an engine with less airflow. How does a turbo spool up? Airflow! If we were to add a turbo to the 4 port Renesis, it would be one with a very small exhaust housing that is designed for small gains. A lack of airflow through the engine will make it very slow to spool. A high compression ratio helps to combat this but we can't perform miracles. It would actually spool up faster if all the ports were open simultaneously by diabling the secondary shutter valves. This applies to 4 and 6 port engines. The faster we can get more air into the engine the faster we can get it out and therefore spool up the turbo. Remember that since we are relying on positive manifold pressure we just want all the area we can get so as much air gets in as fast as possible. Based on the fact that there is so much less runner and port area than the previous 4 port and 6 port engines, the new 4 port Renesis is not a good candidate for forced induction as the 6 port engine is. You could still get some very nice power out of it though so don't think it would be bad to use forced induction. You are just ultimately (somewhere over 350 hp or so) going to lose potential as compared to the 6 port engine.
The 4 port Renesis as well as the 6 port were designed to maximize performance in their respective power ranges. Through careful port timng, sizing, and runner lengths, Mazda has just about maximized the performance capabilities of these engine. Their tuning is insufficient though but once this engine is tuned properly, gains will be few and far between. There is always room for a little more power but gone are the days of 35hp gains from and exhaust. The 4 port engine has so much going against it in terms of pure power production that it should not even be considered a viable market for performance products. Gains would be too small to justify the product prices. Remember that a gain lower in the powerband equals less total horsepower than a gain at an engine designed to run at a higher powerband. If you have a mod that can add 10hp at 9000 rpm, it will only add about 4 or 5 at 7000 rpm. Performance gains for the 4 port engines will be much less. Sorry 4 port guys, if you are performance nuts hellbent on getting the most power from an RX-8 that you can, you bought the wrong model. Don't be discouraged though. Forced induction can still give you the speed and power that could still make this car a force to be dealt with by most other cars on the road.
Last edited by rotarygod; 05-05-2005 at 11:14 PM.
02-05-2004, 03:38 AM
#2
Forgive me for not reading that entire post(data overload lol) but, what about the power potential of the this 4 port if it had a semi PP? I know this would be a serious mod but, think of the power potential. You could use a flapper valve (like the renesis aready uses)in the newly designed 6 port LIM to reduce the overlap a motor PP has to control idle but, the power potential should be phenominal in upper rpm's. What do ya think?
02-05-2004, 01:48 PM
#5
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Mikeb
No need to despair you are just going to get yourself a manual rx8, if you want to work on your performance.
Great post rotary dog (god in reverse) as u are a HOT DUDE with devilish ROTARY information.
Its always a pleasure all beith a long one to read your posts.
cheers
michael
No need to despair you are just going to get yourself a manual rx8, if you want to work on your performance.
Great post rotary dog (god in reverse) as u are a HOT DUDE with devilish ROTARY information.
Its always a pleasure all beith a long one to read your posts.
cheers
michael
02-05-2004, 02:10 PM
#6
Administrator
one question. when did you get a crack at the 4port engine? i saw the pic in the other thread that i think started you on this path, but where did you find the info?
edit: off topic but did you see that thread in genereal auto about that new engine design from australia. the site mentioned that they were using wasted spark.
edit: off topic but did you see that thread in genereal auto about that new engine design from australia. the site mentioned that they were using wasted spark.
02-05-2004, 02:37 PM
#7
Administrator
Originally posted by mikeb
you just ruined my day
you just ruined my day
I REALLY DOUBT that you could gain that much on the AT.
The AT does not even HAVE the 3rd set of intake runners that the MT has.
The AT makes peak power around 7,000rpm as a result.
On top of that the auto tranny sucks up some of the power.
Lastly, there is a damned fine reason they capped the AT power.
From what I have heard that tranny will break if you fed it much more power.
REALLY. You do NOT want to do this!
If you want a faster RX-8 sell the AT and get an 6MT.
That is the right way.
Without ANY modifications you will get an extra 30hp right off the bat.
02-05-2004, 04:19 PM
#8
Registered
Thread Starter
Originally posted by zoom44
one question. when did you get a crack at the 4port engine? i saw the pic in the other thread that i think started you on this path, but where did you find the info?
one question. when did you get a crack at the 4port engine? i saw the pic in the other thread that i think started you on this path, but where did you find the info?
As far as the semi peripheral port goes, that goes well beyond the scope of bolt on performance. If someone is willing to go this far, they would probably be willing to adapt an entirely different engine to suit their needs also. I didn't get into porting at all but I'm sure there are some gains to be had from porting. The 4 port engines can't be ported out anywhere near what even the old 4 ports had stock. Even if the engines were ported, the auto would lose some of its powerband for the benefit of gaining more top end. A new torque converter would have to be figured into the package. If a semi peripheral port were used, I would use them instead of another set of ports not in addition to. Too much airflow is a decrease in velocity and only good for extreme rpms. We don't need any more. I would be more inclined to use only the side primary ports with a set of secondary peripheral ports and that is all. No outer side ports what so ever.
The 6 port engine would be the best porting candidate. The primary ports can't be opened any earlier or else the corner seals will fall into the intake runner. Their closing can only be adjusted. The secondary ports could be modified to open at the same interval as the primary ports but this is only 9 degrees earlier. The secondary ports on the 6 port engine can't be closed later since the closing side is the top and this is where the auxillary ports are. The auxillary ports could be closed a little later but with the rotating sleeve installed there isn't a whole lot of benefit to going any later. The sleeve will be the limiting factor in determining how high. Basically the most benefit will be from smoothing out the transition from runner to port opening. The exhausts are probably where the biggest benefit will be from as far as porting goes. They have thick steel inserts that really disrupt the airflow leaving the port. Their inner radius needs to be backcut for airflow reasons. These ports can probably be opened and closed a little later. There is only 6 degrees of dwell (non port overlap) on this engine so closing them later may actually get rid of this situation. They can't go very far though due to fears of a corner seal falling in. The past 6 port engines had small but noticable porting gains. I think the Renesis will have even less. I don't think streetable porting on this engine will yield an impressive gain. I bridge type of porting may hold some merit though.
02-05-2004, 05:04 PM
#9
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Originally posted by zoom44
short memory you have there mike! canzoomer said this in response to you in november:
I REALLY DOUBT that you could gain that much on the AT.
The AT does not even HAVE the 3rd set of intake runners that the MT has.
The AT makes peak power around 7,000rpm as a result.
On top of that the auto tranny sucks up some of the power.
Lastly, there is a damned fine reason they capped the AT power.
From what I have heard that tranny will break if you fed it much more power.
REALLY. You do NOT want to do this!
If you want a faster RX-8 sell the AT and get an 6MT.
That is the right way.
Without ANY modifications you will get an extra 30hp right off the bat.
short memory you have there mike! canzoomer said this in response to you in november:
I REALLY DOUBT that you could gain that much on the AT.
The AT does not even HAVE the 3rd set of intake runners that the MT has.
The AT makes peak power around 7,000rpm as a result.
On top of that the auto tranny sucks up some of the power.
Lastly, there is a damned fine reason they capped the AT power.
From what I have heard that tranny will break if you fed it much more power.
REALLY. You do NOT want to do this!
If you want a faster RX-8 sell the AT and get an 6MT.
That is the right way.
Without ANY modifications you will get an extra 30hp right off the bat.
I was in denial back then
02-05-2004, 06:35 PM
#10
Originally posted by rotarygod
As far as the semi peripheral port goes, that goes well beyond the scope of bolt on performance. If someone is willing to go this far, they would probably be willing to adapt an entirely different engine to suit their needs also. I didn't get into porting at all but I'm sure there are some gains to be had from porting. The 4 port engines can't be ported out anywhere near what even the old 4 ports had stock. Even if the engines were ported, the auto would lose some of its powerband for the benefit of gaining more top end. A new torque converter would have to be figured into the package. If a semi peripheral port were used, I would use them instead of another set of ports not in addition to. Too much airflow is a decrease in velocity and only good for extreme rpms. We don't need any more. I would be more inclined to use only the side primary ports with a set of secondary peripheral ports and that is all. No outer side ports what so ever.
As far as the semi peripheral port goes, that goes well beyond the scope of bolt on performance. If someone is willing to go this far, they would probably be willing to adapt an entirely different engine to suit their needs also. I didn't get into porting at all but I'm sure there are some gains to be had from porting. The 4 port engines can't be ported out anywhere near what even the old 4 ports had stock. Even if the engines were ported, the auto would lose some of its powerband for the benefit of gaining more top end. A new torque converter would have to be figured into the package. If a semi peripheral port were used, I would use them instead of another set of ports not in addition to. Too much airflow is a decrease in velocity and only good for extreme rpms. We don't need any more. I would be more inclined to use only the side primary ports with a set of secondary peripheral ports and that is all. No outer side ports what so ever.
Well that semi PP idea was really meant for potential an aftermarket engine upgrade for other rotary powered vehicles. I should have specified before. My bad! I already understand that it would take a ton of work just to make something like this work for the auto Rx8 but this type of engine in some kind of Mazda racing car would be awesome. Anyways I still feel that if provides a really good "foundation" to be a powerfull power plant "if" put in the right hands.
02-06-2004, 01:02 AM
#13
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Thread Starter
I never measured the lengths of that manifold. I even had one for a while. I only know the S4 n/a lengths. I do know though that when VDI is actuated on the S5 manifold that the effective length is shorter than the S4 and hence more top end power.
02-08-2004, 01:28 PM
#14
Stuck in a love triangle
So I guess thismeans that the auto Rx8 has the same mod capability as those toned V6 versions of the muscle cars had like the V6 Firebird V6 Camaro and V6 Mustang. All looks and no muscle. Youcouldnt do anything for those "little girl" engines exceptfor intake and exhaust to make them sound like they were fast. They came stock w/200 hp and I dont think anything could bedone to get that number over 207. Well there were always nitrous shots but Idont consider nos to be a "true" mod.
Last edited by JeRKy 8 Owner; 02-08-2004 at 01:34 PM.
02-08-2004, 04:14 PM
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Originally posted by JeRKy 8 Owner
So I guess thismeans that the auto Rx8 has the same mod capability as those toned V6 versions of the muscle cars had like the V6 Firebird V6 Camaro and V6 Mustang. All looks and no muscle. Youcouldnt do anything for those "little girl" engines exceptfor intake and exhaust to make them sound like they were fast. They came stock w/200 hp and I dont think anything could bedone to get that number over 207. Well there were always nitrous shots but Idont consider nos to be a "true" mod.
So I guess thismeans that the auto Rx8 has the same mod capability as those toned V6 versions of the muscle cars had like the V6 Firebird V6 Camaro and V6 Mustang. All looks and no muscle. Youcouldnt do anything for those "little girl" engines exceptfor intake and exhaust to make them sound like they were fast. They came stock w/200 hp and I dont think anything could bedone to get that number over 207. Well there were always nitrous shots but Idont consider nos to be a "true" mod.
that will get me over 207
04-18-2004, 09:36 PM
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Interesting thread ... and I'm sure rotarygod is accurate in his overall assessment. However, that being said, and I may be wrong, but I believe this new RENESIS NA 4-porter still "spanks" the previous NA factory 4-porters in the power department and does so with much greater EPA burdens to boot. The bulk of the potential has been reached, once you are at the end of the envelope, you're at the the end of the envelope. My uneducated assessment is I have a pretty sophisticated 4-porter that MAZDA has been willing to bring closer to that desireable edge, from the factory. All that means is there is not much room for those that like to tune (witness the intake and exhaust folks struggle), but those of us who are not "tuners" can be content in the knowledge that MAZDA has not cheated us the owners, but rather the tuners it would seem.
04-20-2004, 11:24 PM
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what do you think of the potential of = length "headers" to help with shortened exhaust runners, maybe not adding much hp but moving the usable power band down lower. And the possibility of doing a duel throttle body set up with two smaller tb's for each rotary on a shorter manifold which could produce a higher velocity lower volume air source to better match up the air flowing out and not bunch up the air. And adding a higher stall toque converter possibility with a different final drive gear to improve the 60 foot times. And smaller dimeter lighter weight rims and brake rotors to lower the moment of inertia need to turn the wheels also under-drive pulleys. I don't know, I wouldn't put a bullet in the head of the 4 port just yet, I think we need to let these creative after market geniuses play a bit first.
Last edited by aboutime; 04-21-2004 at 10:17 PM.
04-26-2004, 05:52 AM
#21
I don't buy Kool-Aid
I dont know. I ran with a MT/G35 last week would have had him if not for the light. But then I just got out of a 3G/sporty and into a RX-8/sporty... Yea the RX-8 in: MT or sporty has way more HP then the 3G, so with some mods and a TB or SC you will feel da pow-wa in a sporty 8.
Or so I think.
Or so I think.
04-26-2004, 10:17 AM
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well RG, it sounds to me like you just wanna spite me on this one :P
considering how small the ports are on this motor, it sounds like there's a TON of room to go up and down on this motor to grow and match the 4 port version of this motor, especially knowing that this motor doesn't have that tertiary port, so you can still keep closure timing sane when you turbo this motor.
holes can me made BIGGER (especially when they're small, as you say), but hard to take away
the tertiary port is the 6 port motor's biggest knock against it, turbo-wise.
and that 6* of dwell, gotta go.
considering how small the ports are on this motor, it sounds like there's a TON of room to go up and down on this motor to grow and match the 4 port version of this motor, especially knowing that this motor doesn't have that tertiary port, so you can still keep closure timing sane when you turbo this motor.
holes can me made BIGGER (especially when they're small, as you say), but hard to take away
the tertiary port is the 6 port motor's biggest knock against it, turbo-wise.and that 6* of dwell, gotta go.
04-26-2004, 03:25 PM
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I remember when i got my cougar and hooked it up. The only regret i ever had about that car was that i didnt get a manual.
I couldnt live with myself if i didnt get the 8 in a manual no matter the traffic or the learning curve.
I couldnt live with myself if i didnt get the 8 in a manual no matter the traffic or the learning curve.
04-26-2004, 07:01 PM
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Wakeech: if the casting thickness is not large enough, how can you make the ports and runners equal in size to the older engines? The key is the casting. If you do this, the intake manifold no longer works and now you need a custom built one. Oh yeah, :P back at ya!!!
There really isn't much point in trying to use shorter intake runners. The intake already changed its effective length to tune for higher rpm's. Depending on how short the new runners are, the intakw will make far less low to midrange power but gain a little on the top end or it will lose ultimate top and bottom end due to incorrect tuning. We are really limited by ultimate flow through those small ports which is why we don't want to raise the redline. A shrter manifold would be useless without a higher redline. The car would have far less average power and would be slower and more lethargic as a streetdriven car.
The exhaust header needs to be treated very different than just large or short runners. You need one length runner for the outer ports and another length runner for the center port. No one is doing this yet which is why I feel that every header on the market is nothing more than an expensive paperweight.
There really isn't much point in trying to use shorter intake runners. The intake already changed its effective length to tune for higher rpm's. Depending on how short the new runners are, the intakw will make far less low to midrange power but gain a little on the top end or it will lose ultimate top and bottom end due to incorrect tuning. We are really limited by ultimate flow through those small ports which is why we don't want to raise the redline. A shrter manifold would be useless without a higher redline. The car would have far less average power and would be slower and more lethargic as a streetdriven car.
The exhaust header needs to be treated very different than just large or short runners. You need one length runner for the outer ports and another length runner for the center port. No one is doing this yet which is why I feel that every header on the market is nothing more than an expensive paperweight.
Last edited by rotarygod; 04-26-2004 at 09:59 PM.