30 Mpg
06-28-2006, 10:56 PM
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30 Mpg
Over the last few years Dodge had a real hit with the Magnum suing a sequential shutdown on an old cammed-up 340 to deliver an honest 25 MPG at 65 - 70 MPH. Cadillac tried that many years ago but it didn't work. Last year the Corvette gang tried the same trick and it works very well - 28 MPG. Interesting.
So why does a V8 get better gas mileage on 4 cylinders then 8 when producing low amounts of power (it takes about 25-30 HP to sustain 70 MPH in a Magnum)?
Compression. At part throttle feeding 8 cylinders to produce 25 HP in a 340 HP motor is like running on 4.5:1 compression. Not very efficient. Pack more air in only 4 cylinders and the effective compression climbs to about 7:1. That accounts for an increase in efficiency of about 30%.
It turns out the more times a motor fires per revolution the better. Thats part of why you don't see it on 6 and 4 cylinder motors.
In the case of a rotory it gets even better at least to a point. On lobes that take a break from firing there is no backwash from the exhaust since the Renesis has no overlap between exhaust and intake. Backwash is what made the Cadillac Northstar attempt at sequential shutdown a failure. Letting the air flow through the chamber actually adds a little power since it absorbs some of the heat like a stirling cycle.
I wonder....
So why does a V8 get better gas mileage on 4 cylinders then 8 when producing low amounts of power (it takes about 25-30 HP to sustain 70 MPH in a Magnum)?
Compression. At part throttle feeding 8 cylinders to produce 25 HP in a 340 HP motor is like running on 4.5:1 compression. Not very efficient. Pack more air in only 4 cylinders and the effective compression climbs to about 7:1. That accounts for an increase in efficiency of about 30%.
It turns out the more times a motor fires per revolution the better. Thats part of why you don't see it on 6 and 4 cylinder motors.
In the case of a rotory it gets even better at least to a point. On lobes that take a break from firing there is no backwash from the exhaust since the Renesis has no overlap between exhaust and intake. Backwash is what made the Cadillac Northstar attempt at sequential shutdown a failure. Letting the air flow through the chamber actually adds a little power since it absorbs some of the heat like a stirling cycle.
I wonder....
06-28-2006, 11:09 PM
#2
Originally Posted by kartweb
Over the last few years Dodge had a real hit with the Magnum suing a sequential shutdown on an old cammed-up 340 to deliver an honest 25 MPG at 65 - 70 MPH. Cadillac tried that many years ago but it didn't work. Last year the Corvette gang tried the same trick and it works very well - 28 MPG. Interesting.
So why does a V8 get better gas mileage on 4 cylinders then 8 when producing low amounts of power (it takes about 25-30 HP to sustain 70 MPH in a Magnum)?
Compression. At part throttle feeding 8 cylinders to produce 25 HP in a 340 HP motor is like running on 4.5:1 compression. Not very efficient. Pack more air in only 4 cylinders and the effective compression climbs to about 7:1. That accounts for an increase in efficiency of about 30%.
It turns out the more times a motor fires per revolution the better. Thats part of why you don't see it on 6 and 4 cylinder motors.
In the case of a rotory it gets even better at least to a point. On lobes that take a break from firing there is no backwash from the exhaust since the Renesis has no overlap between exhaust and intake. Backwash is what made the Cadillac Northstar attempt at sequential shutdown a failure. Letting the air flow through the chamber actually adds a little power since it absorbs some of the heat like a stirling cycle.
I wonder....
So why does a V8 get better gas mileage on 4 cylinders then 8 when producing low amounts of power (it takes about 25-30 HP to sustain 70 MPH in a Magnum)?
Compression. At part throttle feeding 8 cylinders to produce 25 HP in a 340 HP motor is like running on 4.5:1 compression. Not very efficient. Pack more air in only 4 cylinders and the effective compression climbs to about 7:1. That accounts for an increase in efficiency of about 30%.
It turns out the more times a motor fires per revolution the better. Thats part of why you don't see it on 6 and 4 cylinder motors.
In the case of a rotory it gets even better at least to a point. On lobes that take a break from firing there is no backwash from the exhaust since the Renesis has no overlap between exhaust and intake. Backwash is what made the Cadillac Northstar attempt at sequential shutdown a failure. Letting the air flow through the chamber actually adds a little power since it absorbs some of the heat like a stirling cycle.
I wonder....
this is going to be intersting... compression does not change on a motor it is mechanical...
as to the vet, new shut downs. i think the compter shuts down individual cylinders in an order to keep them warm, but still not shoot the injector...
as to the old caddy system.... it was way before the northstar.. it accually disabled the valves from operating on 4 of the cylinders...
this is from memory so i might miss something..
search olddragger he did an experiment on a rx7 a while back. deactivating one rotor...
beers
06-29-2006, 12:10 AM
#3
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been discussed to the point where we figured a scheme wher it could work shutting individual chambers off in an order etc etc. we then were able( thanks to DAN at Rotary News) to out the question o fdisplacement on demand to the president of MNAO who said that MZ would not be going in that direction. i believe rotary god also tried it on one of his engines.
06-29-2006, 09:23 AM
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Originally Posted by zoom44
the president of MNAO who said that MZ would not be going in that direction. i believe rotary god also tried it on one of his engines.
06-29-2006, 10:06 AM
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Originally Posted by zoom44
been discussed to the point where we figured a scheme wher it could work shutting individual chambers off in an order etc etc. we then were able( thanks to DAN at Rotary News) to out the question o fdisplacement on demand to the president of MNAO who said that MZ would not be going in that direction. i believe rotary god also tried it on one of his engines.
06-29-2006, 07:20 PM
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[QUOTE=swoope]this is going to be intersting... compression does not change on a motor it is mechanical...
QUOTE]
Technically that is correct, but rather then go into the explanation of BMEP, I mentioned compression. Otto did the same thing when he devised the Otto efficiency cycle about 100 years ago. I would bet less then half the folks here really understand compression, and less then 1% understand BMEP.
Two reasons diesels are so efficient, the first being they have no air restriction like a throttle valve to maintain high pressure, the second because they have high compression ratios. Following the Otto Cycle Efficiency curve, the difference in efficiency from 12:1 to 18:1 is about the same as 10:1 to 12:1.
Yes both the Vette and the Magnum alternate shutdown cylinders for several reasons. One is to recover the heat. In the case of the Magnum it makes a huge difference. Ford and GM are reported to be adding this feature to some of their trucks in 2007.
Considering the nature of the rotory it would seem to be a prime candidate, and probably eliminate the need for an air pump. Let's just hope that at 25,000 cars a year they have enough on the engineering budget to give it a try.
QUOTE]
Technically that is correct, but rather then go into the explanation of BMEP, I mentioned compression. Otto did the same thing when he devised the Otto efficiency cycle about 100 years ago. I would bet less then half the folks here really understand compression, and less then 1% understand BMEP.
Two reasons diesels are so efficient, the first being they have no air restriction like a throttle valve to maintain high pressure, the second because they have high compression ratios. Following the Otto Cycle Efficiency curve, the difference in efficiency from 12:1 to 18:1 is about the same as 10:1 to 12:1.
Yes both the Vette and the Magnum alternate shutdown cylinders for several reasons. One is to recover the heat. In the case of the Magnum it makes a huge difference. Ford and GM are reported to be adding this feature to some of their trucks in 2007.
Considering the nature of the rotory it would seem to be a prime candidate, and probably eliminate the need for an air pump. Let's just hope that at 25,000 cars a year they have enough on the engineering budget to give it a try.
06-29-2006, 07:43 PM
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I modified a 13B a couple of years ago to shut down 1 rotor at will. I had to floor it to hold 50 mph. It also vibrated like crazy. Wasn't a verey successful experiment.
Gas mileage is based on fuel used per time. A big V8 spinning at 1800 rpm and a small engine spinning at 4000 rpm could potentially use the same amount of fuel. I'm not going to get into all the details here but lets just say part of the problem is the absolutely worthless 4.44 rear end in the car.
Gas mileage is based on fuel used per time. A big V8 spinning at 1800 rpm and a small engine spinning at 4000 rpm could potentially use the same amount of fuel. I'm not going to get into all the details here but lets just say part of the problem is the absolutely worthless 4.44 rear end in the car.
06-29-2006, 08:05 PM
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I was thinking this same thought... I have a friend with friends in the electronic tuning industry with the kind of knowledge I don't possess.
My thought was to "idle" every other face on both rotors, which should still preserve a measure of smoothness while cruising. I also want it tabbed to the cruise control so that the vehicle would run at normal "full power" until the cruise is engaged, then it would cut the fuel and spark to every other rotor face.
He is supposed to get back to me as to their thoughts if it could be done.
My thought was to "idle" every other face on both rotors, which should still preserve a measure of smoothness while cruising. I also want it tabbed to the cruise control so that the vehicle would run at normal "full power" until the cruise is engaged, then it would cut the fuel and spark to every other rotor face.
He is supposed to get back to me as to their thoughts if it could be done.
07-02-2006, 05:06 PM
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In addition to sequential shutdown I would bet there may be another trump card on the table that would power while dropping fuel comsumption.
Rotories put a lot of heat out the tailpipe - much more then any other production motor in relation to fuel consumed. Would it be possible to capture that heat to boil water and turn a turbine? Thats not so far fetched as it sounds, at least according to BMW.
Turbosteamer
Rotories put a lot of heat out the tailpipe - much more then any other production motor in relation to fuel consumed. Would it be possible to capture that heat to boil water and turn a turbine? Thats not so far fetched as it sounds, at least according to BMW.
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07-02-2006, 05:25 PM
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it's always possible to do it that way, there are other solutions too like putting a stirling engine in the exhaust. There is also a technology out there that allows you to turn a temperature differential into electric power without any moving parts, I forget what it's called but as of this moment it's pretty much just a concept because the materials we have available just don't allow it to be efficient. But besides the last option, adding another engine or steam turbine as well as the batteries is going to increase your weight to a point where the car won't be very sporty anymore.
Another interesting technology that CAT is developing is compound turbocharging for it's big diesels like in mining trucks, in this configuration, any excess boost from the turbocharger is blown off thru another turbine which generates electrical power, but as far as I know the big mining trucks have an electric drive train anyway to save weight and wear so this extra generated power isn't stored, but used instead.
Another interesting technology that CAT is developing is compound turbocharging for it's big diesels like in mining trucks, in this configuration, any excess boost from the turbocharger is blown off thru another turbine which generates electrical power, but as far as I know the big mining trucks have an electric drive train anyway to save weight and wear so this extra generated power isn't stored, but used instead.
07-02-2006, 05:43 PM
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Wouldn't it make more sense to just increase the gear ratios of 6th and maybe 5th gear? Make it so you can cruise in 6th gear at 80mph the way you kinda cruise now in 6th gear at 55mph. you might have to adjust 4th as well so the gaps aren't as big. But yeah my car doesn't like going below 80, it would be nice if it could do it in a more environmentally and wallet friendly way.
07-02-2006, 05:51 PM
#14
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Originally Posted by PhotoMunkey
My thought was to "idle" every other face on both rotors, which should still preserve a measure of smoothness while cruising. I also want it tabbed to the cruise control so that the vehicle would run at normal "full power" until the cruise is engaged, then it would cut the fuel and spark to every other rotor face.
He is supposed to get back to me as to their thoughts if it could be done.
He is supposed to get back to me as to their thoughts if it could be done.
thats exactly what we worked out 3years ago +
of course it can be done but then is it worth it?
oh here is alink- i had the wrong guy it was a VP
https://www.rx8club.com/showthread.p...mand#post64114
there are more around here somewhere
i knew so little then
07-02-2006, 06:32 PM
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Originally Posted by daisuke
Another interesting technology that CAT is developing is compound turbocharging for it's big diesels like in mining trucks, in this configuration, any excess boost from the turbocharger is blown off thru another turbine which generates electrical power, but as far as I know the big mining trucks have an electric drive train anyway to save weight and wear so this extra generated power isn't stored, but used instead.
A small steam turbine system would add weight, but probably not much more then an intercooled turbocharger. I think the Mazda folks have done a spectacular job wringing out the most of what the rotory has to offer and if thats true the next step will take "thinking out of the box". Literally.
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