Blair

I have a 2010 Gt with 3.31 gears. I am not going to modify the engine more than a tune, pulleys and maybe headers. No forced induction. I am going to be replacing the gears and am trying to decide between 3.73 and 4.10 ratio. I do HPDEs and an ocasional autocross. At the tracks I run I almost never get up over 125 mph or so. If I do the 3.73s 4th gear tops out at 140mph. If I do 4.10s, 4th gear tops out at 127mph according to my calculations.

The 3.73s will give me more headroom to go faster. However, the 4.10s will get me up to my current high speed faster. Any insight is appreciated...

Thanks,
Blair

RodeoFlyer

There's really no way to give you a proper answer.

The rule of thumb is to run out of gear when you run out of track. There are too many variables, including your tire diameter, what track, how you drive at that track, etc. The difference between a guy that can drive well and a guy that can't after at the end of a straight is easily a few hundred rpm.

Once you have decided what your favorite track is, and are both comfortable and consostent on that track, you can start to figure out what gear to run.

Blair

Thanks for the reply. I am running 27.0" tires in the stock 2010 size of 255/40/19. I was leaning more to the 3.73s to keep from running too long near redline in fourth, but since I am not going FI, others have suggested that 4.10s are a better option to improve acceleration. I don't want to put a lot of money or mods into the engine to maintain reliability. Seems like the 4.10s would maximize my bang for the buck. After all the FR500C's used to run 4.10s, but they have 6 speed transmissions as well. I imagine though if I'm topping out with the 3.31s at 125 mph, I will probably hit that a lot sooner with the quicker acceleration of the 4.10s and end up hitting the rev limiter or needing to shift at the end of the straight. But then again, if the 4.10s give me a better dig when I accelerate out of a corner, it might be worth it to put up with a little more shifting and redlining. I find myself in the situation coming out of some corners in the 25-30mph range where i really should be downshifting to first because the car is a bit of a dog out of the corner in 2nd gear. I imagine in that same situation the 4.10 gearing would get better acceleration out of the corner in 2nd gear.

houstonnw

What is the drop in gear ratio from 4th to 5th? In terms of lap times, I think that avoiding the need to shift up to 5th would be my highest priority.

-Wayne

Sleeper_08

According to my Road & Track article 5th is 0.68:1.

Based on the data I have going from 4th to 5th slows you down but that was up the hill on the back straight at Mosport.

Blair

I guess that answers my question then... I'll go with the 3.73s. I should get more dig out of the corners in 2nd yet the 140mph redline in 4th should keep me out of shifting to 5th.

Thanks all

Argonaut

Take it from me, 4.10s are a poor choice for track work and even worse for AX. I put them in before I got interested in track/AX. I'd constantly run out of gear, especially in AX, bouncing off the rev limiter in 2nd but without enough time to shift to 3rd. I traded the 4.10s in for 3.73 and still feel its a bit too much gear but a good compromise between street and track. I run on a variety of tracks from Shenandoah which is very tight and slow to VIR which is BIG. On Shenandhoah the 3.73 are great but on VIR they stink, way to much gear.

My advice is go no bigger than 3.73 and even consider 3.55 depending on where you run (ex: if I lived closer to VIR I would have put in 3.55s)

Blair

The closest track to me is Sebring and I go there most often. Sometimes I go to Palm Beach and Homestead, but mostly Sebring. Sebring is a fast track with several long straights, but on my prior GT with 3.55s I always had plenty of gear left at the end of the straights so I figured I could use more. Probably best to play it safe and stick with the 3.73s. Now I just gotta keep my fingers crossed that they don't make noise after the install...

Vapour Trails

+1
4.10s are teh suck for autocross. I'm constantly hitting the limiter. My times could be faster. 3.55s are going back in. They suck for highway economy and engine noise too. Previous owner was a drag racer so now I have to pay more money to fix the gears.