Modifications for lower RPMs
#21
Instead, it’s really a question of efficiency. At what RPMs does this engine most efficiently convert the energy in the fuel into horsepower? I don’t know this figure, but the Honda engineers definitely do. And the key is to use the gearing to keep the RPMs as close to this figure as is possible.
However, straying from this figure slightly--either by going above it or below it--is not going to make a huge difference in gas mileage. The OP is asking about mods to lower the RPMs to save fuel. I’m pretty confident that the costs involved in doing so would be higher than the savings you’d get from the slight increase in fuel efficiency wrought by bringing the RPMs closer to this ideal figure over the life of the car.
#22
I can see that you’re skeptical, but it really is basic physics. Yes, your mileage will drop if you lock it into 4th gear, but not by as much as you might think, and not simply because of the higher RPMs. Think of it this way: if the gearing were switched so that the RPMs went from 4000 to 2000 when traveling at 80mph your mileage would not double, as you might expect if it were simply a function of the RPMs.
Instead, it’s really a question of efficiency. At what RPMs does this engine most efficiently convert the energy in the fuel into horsepower? I don’t know this figure, but the Honda engineers definitely do. And the key is to use the gearing to keep the RPMs as close to this figure as is possible.
However, straying from this figure slightly--either by going above it or below it--is not going to make a huge difference in gas mileage. The OP is asking about mods to lower the RPMs to save fuel. I’m pretty confident that the costs involved in doing so would be higher than the savings you’d get from the slight increase in fuel efficiency wrought by bringing the RPMs closer to this ideal figure over the life of the car.
Instead, it’s really a question of efficiency. At what RPMs does this engine most efficiently convert the energy in the fuel into horsepower? I don’t know this figure, but the Honda engineers definitely do. And the key is to use the gearing to keep the RPMs as close to this figure as is possible.
However, straying from this figure slightly--either by going above it or below it--is not going to make a huge difference in gas mileage. The OP is asking about mods to lower the RPMs to save fuel. I’m pretty confident that the costs involved in doing so would be higher than the savings you’d get from the slight increase in fuel efficiency wrought by bringing the RPMs closer to this ideal figure over the life of the car.
~SB
#23
I can see that you’re skeptical, but it really is basic physics. Yes, your mileage will drop if you lock it into 4th gear, but not by as much as you might think, and not simply because of the higher RPMs. Think of it this way: if the gearing were switched so that the RPMs went from 4000 to 2000 when traveling at 80mph your mileage would not double, as you might expect if it were simply a function of the RPMs.
Instead, it’s really a question of efficiency. At what RPMs does this engine most efficiently convert the energy in the fuel into horsepower? I don’t know this figure, but the Honda engineers definitely do. And the key is to use the gearing to keep the RPMs as close to this figure as is possible.
However, straying from this figure slightly--either by going above it or below it--is not going to make a huge difference in gas mileage. The OP is asking about mods to lower the RPMs to save fuel. I’m pretty confident that the costs involved in doing so would be higher than the savings you’d get from the slight increase in fuel efficiency wrought by bringing the RPMs closer to this ideal figure over the life of the car.
Instead, it’s really a question of efficiency. At what RPMs does this engine most efficiently convert the energy in the fuel into horsepower? I don’t know this figure, but the Honda engineers definitely do. And the key is to use the gearing to keep the RPMs as close to this figure as is possible.
However, straying from this figure slightly--either by going above it or below it--is not going to make a huge difference in gas mileage. The OP is asking about mods to lower the RPMs to save fuel. I’m pretty confident that the costs involved in doing so would be higher than the savings you’d get from the slight increase in fuel efficiency wrought by bringing the RPMs closer to this ideal figure over the life of the car.
Actually it's slightly more complicated than that... But the easiest way to figure out where the car is most fuel efficient is simply monitoring spark advance, AFRs and IDC percentage with a scan tool as you cruise at different speeds.
And as specboy pointed out in an earlier post, the easiest way to bring down engine speed is just simply get a marginally taller wheel tire combination. 5-10mm more sidewall would bring you down 200-400rpm depending on tire temperature and pressure under extended cruising.
Dropping from 3500 down to ~3100rpm will make a big difference if VTEC disengages.
#24
I bought the 2010 5MT because I missed the fun of a manual transmission. My 98 Accord is fun because of the Power, but the trany is horrible. It is going out again at 100K. I wish the fit had a 6th gear, but now I just crank the music up. The fun is better than the noise. Paddle shifters just are not the same.
#26
Actually it's slightly more complicated than that... But the easiest way to figure out where the car is most fuel efficient is simply monitoring spark advance, AFRs and IDC percentage with a scan tool as you cruise at different speeds.
And as specboy pointed out in an earlier post, the easiest way to bring down engine speed is just simply get a marginally taller wheel tire combination. 5-10mm more sidewall would bring you down 200-400rpm depending on tire temperature and pressure under extended cruising.
Dropping from 3500 down to ~3100rpm will make a big difference if VTEC disengages.
And as specboy pointed out in an earlier post, the easiest way to bring down engine speed is just simply get a marginally taller wheel tire combination. 5-10mm more sidewall would bring you down 200-400rpm depending on tire temperature and pressure under extended cruising.
Dropping from 3500 down to ~3100rpm will make a big difference if VTEC disengages.
As far as noise is concerned, I find that by far the greatest source of noise on the highway is the tires. Wind noise and engine noise are a distant second. So I personally don't see this as a good reason for spending lots of money to get taller gearing either.
#27
Hello all,
I was wondering if anybody has done any modifications to get lower highway RPMs. My work commute is mostly highway, so the 3500-4000RPM cruise is clearly suboptimal.
Possibilities I've seen discussed are larger wheels, a taller final drive gear, or a complete set of new gears. Warranty voiding aside, has anyone tried anything like this? What were your results? Did MPG improve?
Josh
I was wondering if anybody has done any modifications to get lower highway RPMs. My work commute is mostly highway, so the 3500-4000RPM cruise is clearly suboptimal.
Possibilities I've seen discussed are larger wheels, a taller final drive gear, or a complete set of new gears. Warranty voiding aside, has anyone tried anything like this? What were your results? Did MPG improve?
Josh
Increasing tire size is the only realistic means of lowering rpm as all the others cost a lot more than trading your manual for automatic. Even then only a small increase in tire diameter will fit the tire in the fender well so you might lower rpm by 5%, not worth much either.
#28
Increasing tire size is the only realistic means of lowering rpm as all the others cost a lot more than trading your manual for automatic. Even then only a small increase in tire diameter will fit the tire in the fender well so you might lower rpm by 5%, not worth much either.
JDM 6sp tranny swap or moving to an auto is the only real way to drop RPMs. If it's noise... Dynamat might do some good.
~SB
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