Has anybody tried regearing the rear end to make it a little taller for better highway fuel economy? It seems like my 6mt is screaming at 80mph. Throttle response is great, but I wouldn't mind a little less if it gave me 3 or 4 more mpg (if that's a realistic number).

 

80mph on the 6mt is 3050rpm which isnt that bad, and keeps you in the powerband for quick passes and easy cruising without chnaging gears or atleast it is for me but im still interested in seeing the results if you do the "regearing"...

 

Realistically, you're looking at maybe a 1-2 mpg change.

The cost for doing it can buy you, litterally, 300+ gallons of gas. That's at least 6000 miles if you're doing 20 mpg.

So, assuming you get a 2 mpg savings, you'd have to drive over 100k miles to make it worth it.

 

Right now gas is around $2.15 in North Carolina...but lets say on average it will be around $3 the next year.

I drove 40k miles last year. If I got on average 22 mpg, I burned 1818.18 gallons. If I swapped and got an extra 2mpg = 24mpg I would burn 1666.67 gallons. A 151.51 gallon difference, which would be $454.53 if gas is $3 a gallon next year...so it could potentially pay for itself after a year or two (depending how much the swap was).

I'm assuming a lot here, and not sure how much it would cost to swap, but I'd like to see if anyone has done it. I do a lot of 65+mph driving.

Maybe we could get more than 2mpg? The shape of our cars is pretty slippery and they aren't that heavy.

 

Interesting thread, I am actually computing similar thing, not in rear, but in getting 08 vs. wait for 09. The 09 will be probably $3K more for first few months realisticly, vs the maybe 2MPG I'll save in gas literally will be under $400-$500 year, so the feul is not an issue, better to by an 08, EXCEPT, the day I take delivery now I am taking not only the its now a used car hit, but the year old car hit, vs. with an 09 it should keep some of that value a little longer. Seeingas I flip cars so fast not sure an 08 is a good deal unless they really sweeten the incentives...

 

2 MPG is a pretty agressive number for gas savings. Remember, with a taller FD, you need to give the car a little more throttle to maintain the same speed.

 

how about regearing so the car is faster? 5 and 6th are too close together. I don't like 4th gear going to 120ish, I want more power out of 3,4, and 5 and 6 can be the dog gear!

 

The twin turbo guys used to swap the taller automatic equipped 3.3 rear gear into the 6mt pumpkin to get more traction in the lower gears. In the 1/4 mile, you did not need to shift out of 4th before the line. If I remember correctly it only dropped the rpm's a couple hundred at the same highway speeds.

 

I don't have any numbers to prove it, but I think it would make a difference. At 80mph the car feels like it could use another gear. I'm trying to find the parts, anybody got any ideas?

 

I have a 3.3 fd in my 6mt Z, at 80 its at around 2700rpm I just swapped my 3.5 with an automatic Z since those guys like the shorter gears....I really haven't felt any loss of power i still spin through 1st and 2nd on my 295's I also didn't notice much of a gain in gas mileage, but I usually don't pay attention to that.

 

You know those Honda Civic Si guys? The ones that get 30 mpg easily on the freeway?

They do 4000 RPM at 80mph.

S2k guys do even higher at 80

 

Dude, Mike, gonna have to agree to disagree here. Until somebody else (or me) does it, we won't have an answer. S2000's don't exactly get great mileage for what they are. They also have a stratospheric red line.

While driving I've definitely been in 6th, forgot about it thinking I'm in 4th, bumped it out and reached for an imaginary 7th gear in the top right. Gearing just seems too short.

 

if you sit at too low an rpm while cruising on the freeway you will lug the motor to maintain speed and waste a good deal of gas. since we don't have that much torque, this isn't a great idea. you could regear it to about 1800rpm at 65, i suppose, but that wouldn't gain you much at all.

you will pick up more mileage by changing your driving style than by changing your FD, and altering your driving style is free.

 

every engine/drive train has a sweet spot where efficiency is at peak.
& RPM can be completely different car to car.

You can't just compare brand X at 3K RPM vs Brand Y at 4K RPM... there are just too many variables.

 

Klumzyee is running the 5AT FD in his 6MT. The 5AT FD is taller.

I speak from experience when I say that it's not worth doing.

S2k's typically get 30ish on the freeway cruising at 80.