I did some research on my wifes GTO it's a 4 spd auto with overdrive and the gear ratio is 3.46 with a 6.0 motor and will snap your neck.Now the published top speed for it was around 175 mph.So I do not understand why a corvette with 2 over drive gears could not handle a set of 3.73's.Again my camaro with a moser 9" 4.30's could barry the speedo in 5th gear and I sill had a couple of thousand RPM'S to play with before I went 6th gear.MY Z28 rear wheeled 436 hp na I had more top end and could get there faster.In 4th gear my top speed at 7000 RPM was 120 mph so I don't under stand how you are coming up with your conclusions.My Corvette has.
1st gear is 4.03
2nd gear is 2.36
3rd gear is1.53
4th gear is1.15
5th gear is 0.85
6th gear is0.67
reverse is -3.06
these are the gear ratio's w/6speed auto's with the Z51 packege.I just copied it off what the dealer gave me.No mater what auto you got everybody has a 2.56 final.I would like to have better bottom end without losing most of my top end.So I have been told the rev limiter is set at 6500 rpm giving the gear ratio's in the tranny and 6th being 0.6 what would the top speed be with 3.73's.Thanks for your help.

 

Since about half way through the thread, I have been specifically talking about F-bodies and 'vette WITH THE 4-SPEED AUTO. Thosedon't have the "two overdrive gears", and as such, it is not too prudent to go very high in gear ratio: a 3.73 in them would result in a car that was not bvery pleasant to drive on the street, reving too high around town and on the highway.

Answering your question,the '06 - '07 production standardvette with the 6-speed auto and stock tires, assuming no tire expansion due to centrifugal force, the speeds at the red line in gear with a 2.56 (stock) rear axle cacluate out to: 50,79,133, and 175 in the first four gears, and if it would pull the red line in 5th and 6th, 237 and 320. With 3.15 these drop to 40, 64, 108 and 142, andit could pull 6500 in 5th and 6th, 192 and 260respectively (incidently the car would need an extra 75 RWHP over stock to pull the red line in 5th, doable with light mods).
With a 3.42 speeds are 34, 58, 99, 131 and 177 and 239, and with the 3.73 they are 34, 54, 91, 120, 162 and 218.

In chosing the rear end ratio, it is not just the gear ratio, it is the gapsbetween the gears that concerns me: overdrive gears always have huge gaps, so even when you change ratio, they are not good for the strip.

In a stock car,with a 3.73, top speed would drop overall (the car could pull redline in 5th (162, 13 mph below stock top speed) but probably not get much past 4500 in 6th (152) with stock power.

But I was talking heavily modded cars, and with a 3.73in a 140+ mph trap speed capable car, the 3.73 isn't too good: the gap from 4th to 5th is huge: you shift out of 4th at 6500 RPM at120 (in a really modded car, this would be just past the 8th mile), and the revs drop to just over 4750 in 5th, and you have to slog through that the rest of the 1/4 in that gear. A 3.42 would not be quite so bad, but still drops you into a dog of a gear at 131 (e.g., long before the end of the 1/4 in a modded car). But I think best would beto use a 3.15, rely on a modified torque converter to get you off the line fast, then you do not shift into that hug gap until 142.

Beyond that I reiterate thata change from 2.56 to 3.73 would also run into all sorts of computer issues unanticipated until they bit you.This is a 50% increase over stock change, so far out of range of the original programming that a lot more than the engine A/F, ingition advance maps, etc., are likely to be affected. I would anticiopate gobs of headach4es getting the car perfect.

 

Thank you for all your help.I know my vett is diffrent than my camaro.The Vett is great once you get it going but with the auto out of the hole it is a dog and I think it could be alot better without looseing street driving.It feels like out of the whole the torque is just not there.I have did no mods to my Vett yet.It was made at the end of june and I bought it the 1st of aug.so any thoughts will be welcome.The end goal in a few years is to save up for a twin turbo that mounts in the rear end of the car.The car has power I wish it had more on the bottom end.Again thanks for any help you all have been great.

 

Twin turbos that mount on the rear of the car? I'm curious about the kit. Do you have a link to any description?. I've looked at a couple of "rear-mount" turbo kits installed on C5s,but those mount on the rear of the engine compartment (unlike the Lingenfelter which mounts forward of the front wheels or the other kits that mount to the side).

 

Makes perfect sense to me, a "kick in the rear" to get cha goin'!

 

Is that like a boot in the ***? Man I oughta be fast ...I got lots of those from my dad when I was a kid.

 

Well, with that A$$ kickin' 454 you've got, I'd say it did ya some good, eh?

 

They did it to a 05 on one of performance shows on the weekend.I orderd some stuff from west coast corvettes and the guy that I talked to knew alot about that project and they had donated some of the parts.