high rpm vs low rpm = mpg
05-14-2009, 07:46 AM
#27
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this is a easy method to test, fuel up, drive like crazy bitch prm 3-4 or 5 till tank emply, fuel up record the mpg, then drive like an old lady prm 1.2 to 2.5 then compare.... you get the picture
05-14-2009, 08:31 AM
#28
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I'm guessing 24 city and 16 highway....
05-14-2009, 09:01 AM
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shifting at 1.5k is almost impossible in our cars -- we just dont have the low-end torque required.
2~2.5k is doable, but its killing me :P
on the other hand, if you have a diesel you can shift at 1.5k all day long since you have plenty of torque from almost idle
but driving my rx8 hard like I do, and in the city only, leads to 11~12mpg
but hey, it's fun!
2~2.5k is doable, but its killing me :P
on the other hand, if you have a diesel you can shift at 1.5k all day long since you have plenty of torque from almost idle
but driving my rx8 hard like I do, and in the city only, leads to 11~12mpg
but hey, it's fun!
05-14-2009, 09:09 AM
#30
Uhh, I think everyone has begun to ignore the OP. OK I'll shoot. Basically, most engines are more efficient at high RPMs. They use more of the gas and energy from the engine and convert it to mechanical energy. So that is more efficient as you are putting more energy from the gas onto the road converting into acceleration. At higher speeds, the acceleration of the car is countering the deceleration caused by road/tire resistance and drag by air resistance.
This does not make the engine more fuel efficient on the road. This means that you get more power more efficiently. At lower RPMs, you are not getting as much power out of the car as you can but you are also not using as much fuel as you can consume. So there, that is why your car is more fuel efficient at lower RPMs because you are simply not using as much gas.
Basically, you are looking at two different types of efficiency.
This does not make the engine more fuel efficient on the road. This means that you get more power more efficiently. At lower RPMs, you are not getting as much power out of the car as you can but you are also not using as much fuel as you can consume. So there, that is why your car is more fuel efficient at lower RPMs because you are simply not using as much gas.
Basically, you are looking at two different types of efficiency.
05-14-2009, 09:56 AM
#31
We're not ignoring the OP as he opened this can of worms by throwing in "MPG." So it was impossible to discuss engine (power) efficiency at high or low rpm without factoring in fuel use impact.
As you well said R.F.P. the only way to get better MPG (fuel efficiency) is to use less gas, which is lower speed/rpm. No rocket science required.
As you well said R.F.P. the only way to get better MPG (fuel efficiency) is to use less gas, which is lower speed/rpm. No rocket science required.
05-14-2009, 10:37 PM
#32
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Thanks for the information and suggestions everyone. Rotarygod you do seem to rock the house. As refugeefrompistons points one effeciently of an engine, our rotarys, means one thing though that does not mean more mpg. It is good to know that in the case of our engines we (at least my take) need to do the following:
1. ride it as we want to (high or low rpms if desired)
2. blip her towards the red line zone now and then (at least to 6250)
3. dont' worry about having to run her above 4k for more mpg...won't happen but do run at/over 4k if it makes us happy.
and since...black sheep here, I have an auto 07 model gt I can be happy letting the automatic shift as it wants when it wants and if I want to play or have more power (of what an auto offers) then I just shift her into manual mode and play. On highways will just let her run at lower rpm ranges in auto without feeling I'm doing the wrong thing so long as I get the rpm ranges up there at some point each/most times I take her out for a ride.
btw...god only knows what my log acct password is and I do have a 'motor' login id but not a clue at the moment where I wrote down the password.
ride safe and enjoy your rides.
1. ride it as we want to (high or low rpms if desired)
2. blip her towards the red line zone now and then (at least to 6250)
3. dont' worry about having to run her above 4k for more mpg...won't happen but do run at/over 4k if it makes us happy.
and since...black sheep here, I have an auto 07 model gt I can be happy letting the automatic shift as it wants when it wants and if I want to play or have more power (of what an auto offers) then I just shift her into manual mode and play. On highways will just let her run at lower rpm ranges in auto without feeling I'm doing the wrong thing so long as I get the rpm ranges up there at some point each/most times I take her out for a ride.
btw...god only knows what my log acct password is and I do have a 'motor' login id but not a clue at the moment where I wrote down the password.
ride safe and enjoy your rides.
05-15-2009, 05:38 AM
#34
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its all relative to me....
yes it would be nice to have 'more power' but not at the price of giving up my auto/manual setup. plus, to me, having to play in a 7,500 to 9,500 rpm range in order to have 'more fun' is not only not required but also a bit beyond what a sports car should require.
disclaimer -
i would guess to high in sports cars run the way a rotary does...offer high in rpm ranges, just like high end motorcycles. that is all well and good and maybe as it should be. for me my rotary running up to around 6,500 to 7k is enough to make me happy.
really it seems an engines hp to rpm range should offer a 'flat' power band through much of the rpm range and offer it beginning at a low rpm range. I realize our rotary engines do not offer that and I can live with that. my ride makes me happy enough as is (more space then my mx5 nc offered, four seats, great visuals, nice inside package and the rotary sound, even when running below 7k.
enjoy your rides...late for work
yes it would be nice to have 'more power' but not at the price of giving up my auto/manual setup. plus, to me, having to play in a 7,500 to 9,500 rpm range in order to have 'more fun' is not only not required but also a bit beyond what a sports car should require.
disclaimer -
i would guess to high in sports cars run the way a rotary does...offer high in rpm ranges, just like high end motorcycles. that is all well and good and maybe as it should be. for me my rotary running up to around 6,500 to 7k is enough to make me happy.
really it seems an engines hp to rpm range should offer a 'flat' power band through much of the rpm range and offer it beginning at a low rpm range. I realize our rotary engines do not offer that and I can live with that. my ride makes me happy enough as is (more space then my mx5 nc offered, four seats, great visuals, nice inside package and the rotary sound, even when running below 7k.
enjoy your rides...late for work
05-15-2009, 05:55 AM
#35
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High RPM's is what real sports cars are all about to me.
Whether you drive it like that is always up to you.
That's one thing I like about the Honda 2000 but this is all another ball of wax maybe better served in a new thread.
I will agree that I think this car can be very fun below the redline [when it has a real manual transmission like a real sports car]....
Whether you drive it like that is always up to you.
That's one thing I like about the Honda 2000 but this is all another ball of wax maybe better served in a new thread.
I will agree that I think this car can be very fun below the redline [when it has a real manual transmission like a real sports car]....
05-15-2009, 12:26 PM
#36
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I dare anyone to follow through on "drive it like you stole it" and "rev crap out of it". Driving at the upper rpm limits, even in cold weather, is non-sustainable beyond the first minute or so. They keep telling me "oh, the engine is only running at 1/3 the rpm gauge". So if it idles 750 gauge, it's only 250 rpm? And the renesis is only running 3000 rpm at 9000 rpm gauge? It can't handle 3000 rpm (9000 rpm gauge) for the duration of the drive?
The track day drivers claim to stay at the rpm powerband limits the whole time on the track. I just don't believe it, not possible without melting the thing down. They have to be shifting to higher gears to allow the engine to cool itself down once in a while during the race.
The track day drivers claim to stay at the rpm powerband limits the whole time on the track. I just don't believe it, not possible without melting the thing down. They have to be shifting to higher gears to allow the engine to cool itself down once in a while during the race.
Last edited by User24; 05-15-2009 at 12:29 PM.
05-15-2009, 12:47 PM
#37
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I dare anyone to follow through on "drive it like you stole it" and "rev crap out of it". Driving at the upper rpm limits, even in cold weather, is non-sustainable beyond the first minute or so. They keep telling me "oh, the engine is only running at 1/3 the rpm gauge". So if it idles 750 gauge, it's only 250 rpm? And the renesis is only running 3000 rpm at 9000 rpm gauge? It can't handle 3000 rpm (9000 rpm gauge) for the duration of the drive?
The track day drivers claim to stay at the rpm powerband limits the whole time on the track. I just don't believe it, not possible without melting the thing down. They have to be shifting to higher gears to allow the engine to cool itself down once in a while during the race.
The track day drivers claim to stay at the rpm powerband limits the whole time on the track. I just don't believe it, not possible without melting the thing down. They have to be shifting to higher gears to allow the engine to cool itself down once in a while during the race.
05-15-2009, 02:23 PM
#38
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In terms of getting the best fuel economy, there is always an optimum engine speed for every vehicle speed/road incline/wind/ etc.
A lower rpm level means less internal explosions per given unit of time(less fuel injected due to lower frequency of injection), but also means less mechanical leverage requiring higher percentage of maximum throttle input to keep a constant speed/accelerate, whatever you are trying to do.
A higher rpm level means more internal explosions per given unit of time(more fuel injected due to higher frequency of injection), but also means more mechanical leverage requiring a lower percentage of maximum throttle input to keep a constant speed/accelerate, whatever you are trying to do.
So, as you can see, for every vehicle speed/road incline, etc, the optimum engine speed is going to require a perfect combo of rpm and throttle percentage level.
A lower rpm level means less internal explosions per given unit of time(less fuel injected due to lower frequency of injection), but also means less mechanical leverage requiring higher percentage of maximum throttle input to keep a constant speed/accelerate, whatever you are trying to do.
A higher rpm level means more internal explosions per given unit of time(more fuel injected due to higher frequency of injection), but also means more mechanical leverage requiring a lower percentage of maximum throttle input to keep a constant speed/accelerate, whatever you are trying to do.
So, as you can see, for every vehicle speed/road incline, etc, the optimum engine speed is going to require a perfect combo of rpm and throttle percentage level.
05-15-2009, 04:39 PM
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in a regular piston engine I would think lower rpm range would be better mpg. thought I read a post that said rotary engines are more efficient at higher rpm ranges. even if that were true I don't know that it would amount to much of a mpg difference. for instance, on the highway in top gear (manual or stick) running at 2k rpm or 4k won't matter i would think but wished it did.
in city driving, well outside of town on a four lane each way road 4k or higher is nice but it would be nice to think just running along for a period of time at 2k would help the mpg but don't think it does really.
in city driving, well outside of town on a four lane each way road 4k or higher is nice but it would be nice to think just running along for a period of time at 2k would help the mpg but don't think it does really.
I think most of the other posters have not understood the question, since you don't seem to be asking about acceleration but cruising. Yes, cruising at 50MPH in 6th gear at 3000RPM will get you more MPG then cruising at 50MPH in 2nd gear at 8000RPM. The high RPM band is there for acceleration and I doubt MAZDA designed the stock RX-8 for the durability of constantly cruising at high RPM.
I dare anyone to follow through on "drive it like you stole it" and "rev crap out of it". Driving at the upper rpm limits, even in cold weather, is non-sustainable beyond the first minute or so. They keep telling me "oh, the engine is only running at 1/3 the rpm gauge". So if it idles 750 gauge, it's only 250 rpm? And the renesis is only running 3000 rpm at 9000 rpm gauge? It can't handle 3000 rpm (9000 rpm gauge) for the duration of the drive?
The track day drivers claim to stay at the rpm powerband limits the whole time on the track. I just don't believe it, not possible without melting the thing down. They have to be shifting to higher gears to allow the engine to cool itself down once in a while during the race.
The track day drivers claim to stay at the rpm powerband limits the whole time on the track. I just don't believe it, not possible without melting the thing down. They have to be shifting to higher gears to allow the engine to cool itself down once in a while during the race.
05-15-2009, 06:49 PM
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I think most of the other posters have not understood the question, since you don't seem to be asking about acceleration but cruising. Yes, cruising at 50MPH in 6th gear at 3000RPM will get you more MPG then cruising at 50MPH in 2nd gear at 8000RPM. The high RPM band is there for acceleration and I doubt MAZDA designed the stock RX-8 for the durability of constantly cruising at high RPM.
I know/think most of the rx8 forum members love the high revs they can get out of their rides. I do take her up to 4, 5, 6, touch into 7 but mostly she begins to have enough power beginning at 3k then 4, 5, 6 is just 'more ice cream' and a cherry (well at least for a auto model).
Like another post on the site for the person considering trading their's in....he simply has not found something that give him what the rx8 does for steering/ride/control...etc. The rx8 is not perfect but is darn fun for a four seater.
Been an enjoyable read on this thread though thinking my question (and that not asked) has been completely covered. Again, I really appreciate all the good information provided. Now eveyone go take the 8 out for a nice friday evening ride
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