ahrmike

The easiest way to explain this is that the s2000 is just not designed for MOHs. The reason why ou cars idle at1k instead of a easy slow 600rpm or so is due to the cams. From the ground up our cars are made for power. If our engines didn't switch cams so late in the rpm range they could have designed a cam that would bmore efficient at lower rpms, but since we have 9k rpms of rev, our cams are higly inefficient at the low end.

Ralleh

That's interesting about the cams and makes sense.

I just read through a bunch of threads about this and never saw where anyone actually said if it's possible, only honest questions and troll answers from various defectives.

Seems like the most realistic thing would be to install an AP2 transmission so it's more fun down low and cruises at lower RPMs in 6th, although they made 5th taller as well. Personally, I would want to pull only 1st and 6th out of an AP2 tranny and swap those into the AP1, leaving the rest the same. Anyone know if that's possible?

YELLOW JACKET

I've seen as high as 33 mpg with mine, running 70 to 80 mph highway. if your looking for good gas mileage, buy a hybrid! these cars do well for such a high reving engine. it could be worse, you could be getting 5 phone poles per gallon lol. cruise control helps with highways mileage.

moogleii

I'm not sure why you're getting so many defensive responses, but i'm pretty sure the answer is "yes."

If we had a taller 6, we'd get more mpg. Once you're cruising, you don't even need to be at peak torque, either. It would suck at the track though.

And yaeh, cutting your cruise speed would help greatly. I cruise at 80-85, and my mileage is about 20-21 (well, with mixed driving, I have no huge commutes).

Ralleh

Yeah, in every other one of these threads, weirdos come out of the woodwork and lambaste the OP. Not really sure why. I like to know how things work, instead of thinking of the drive train as a magical black box. I guess I'll just have to acquire an AP2 tranny off of a salvage s2k and swap 1st and 6th and see if it makes a difference. I know there are people on this forum who have f20cs with an AP2 tranny, so maybe they could post what RPMs they're at in 6th at 70mph for a comparison.

Ludedude

I had one of those...it worked OK but the smell was weird. Maintenance was inconvenient too.

Ralleh

Looks like 6th gear is only 2% taller due to the larger reduction gear, but if you swapped it into an AP1 tranny with it's smaller reduction gear you would end up with a bigger difference. I dunno what the math is on this though.

moogleii

You could just cruise slower instead of going through the hassle of swapping hardware. Unless that's not an option lol

Ralleh

The scenario I'm talking about is someone who cruises for hours at a time on the freeway at the speed limit. Usually dangerous to drive below the limit. Also, annoying.

ahrmike

Ok, so Ralleh coming back to my explanation on why our cars are inefficient.

1) Cams
2) Gearing
3) Aerodynamics
4) Temperature
5) Weight v. Power


Cams: Our max RPM (9K/8.5K) dictates our 2nd cam grind (Not totally, but a bunch). Since our crossover is at 6K, this determines the 1st cam agressiveness - it has to be making "power" at 6K, since the cam1 and cam2 have to match up in torque/hp as much as possible to be smooth. Since our first cam is making power til 6K and then more so that it matches up with the cam2, the agressiveness of cam1 is dictated. This means that its highly efficient in the higher side of the 1-6K, but bad on the lower end...its really lopey, which is why our car idles at 1K. IF you heard a V8 with cams idling, you know what I am talking about - its rough, it hesitates, it misfires down low, and it smells of unburnt gas @ idle. The v8 can idle at lower RPMS with a agressive cam just cuz it has more POWER pulses, which smooth out the power as well as since they have a heavier flywheel, which stores energy to "Push" the car over to continue turning if it misses a power pulse.

2) Gearing: Our gears are made to be short shift, all 6 gears are supposedly useable for track applications. This means that all gears have to be close enough so that at a shift, we get the most acceleration as we bang the next gear - this is why 1-2 shift, 2-3 shift at redline, we drop back to the lower end of Vtec where as higher shifts we dont drop as much since we want more "power to continue us on. The 1-2,2-3 lets the engine drop a bunch so we dont lose time shifting. Some cars have a 6th gear loaf gear like the Vette, if we had one we WOULD get better mpg but not significantly.

3) Aerodynamics. Our car is VERY unaerodynamic. the whole rake of the windshield which allows the car to be stronger on rollover is a liability for aero. Its practically vertical, which is terrible for the Cd (drag coeff.). As speeds go up, aerodynamic drag increases to the velocity squared, so higher speeds = car needs more power to plow through = use more gas...remember more power = need more gas


4). Temp. The engine running hotter will allow for higher efficiency (thermodynamics thing, dont ask...) BUT it makes less power and is more dangerous if a cooling component fails, so we're not running as hot as we could be...some pass cars MIGHT be running hotter, not too sure on this.

5) The highest efficiency of a motor is when youre making max power. SO the HIGHEST efficiency you can theoretically get is if youre making x amount of power at Y rpm. to be the most efficient, you have to gear the car so that its moving AS slow as possible so that aerodynamic drag is lowest (really really slow), while being NOT so geared that the mechanical drag (goes up if geared more) is lowest possible. Basically, if we did this performance would be pure crap.

I think that pretty much covers why our 2L cars arent as efficient as most...what we do have going for us is that our casr are really light. IF our cars were as heavy as most 2L sedans, our MPG would be even worse...

Main Idea:

Our car was NOT designed with MPG in mind at ALL.