Just4fun

I haven't changed the gears yet and I'm only getting 21 miles to the gallon on the highway, putting in 3:73 in next week any way. Just have to enjoy yourself.

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Daniel60

Maybe your car isn't broken in and a course if you drove drive at sea level your mileage could vary.

viking396

I could see your question if I was thinking of getting 3.73's (not enough difference crossing the traps between 3.55 and 3.73) but not 3.90's. The 3.90 is a good gear selection for mixed driving, I see highway driving quite a bit and the difference on the highway between 3.90 and 4.10 is more than people think in 5th gear.

cableguymicah

Well when I had my 3.73 I got 18---dont drive much, plus never highway--with my 4.10's I get 14

viking396

What is the motor turning at driving at 65?

CrazyAl

Guys, this is really easy to figure out.

When you change gears, it's all a matter of the difference between your current ratio and your new ratio, which is easily calculated by means of percentage. For example, if you have 3.55s and you switch to 4.10's, then the percentage change is (4.10- 3.55) / 3.55, or about 15.5%.

This means that your acceleration will go UP by 15.5%, and your engine RPM will also go up by the same 15.5% (That's where the extra torque comes from) Fuel mileage isn't exactly linear with respect to RPM, but it's close enough. You're mileage will go DOWN by the same figure: 15.5%, assuming your driving habits don't change.

So, if you're getting 26 MPG highway now, you will be getting approximatley 22.1 after the swap.

The impact on city driving probably won't be as bad, becasue you can shift into higher gears "earlier" than you previously did.

Oh, and the SCT-II tuner will correct your speedo for gear ratios as well.

cableguymicah

When I had 3.73 3rd gear at 65mph was about 3k rpm-- though usually switch gears around 3k drving normal--with the 4.10's its about 3500l rpm at 65 in third gear

mustangman02232

T-3650 (5 speed) have a 5th gear ratio of .68, so my $.02, 4.30s but 4.10s will be fine as well, 3.73s are a waste on the T-3650, even with a blower

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cableguymicah

i agree most people say 4.10s is to much for a s/c car....I disagree and feel I dont lose anyting or much of anything up top, nothing a little tunning wont fix

Sleeper05

i get 23mpg on the highway with 4.30s...

in the city its more like 13 tho