JohnAlley

I currently have a 2000 Corvette full race prep that I run in NASA ST2. It has 3.42 gears in a ZR1 Rockland gearbox ( 2.29 1st gear). I am wanting to make the car quicker off the corners so I think a gear change is in order. Most of my races are in the midwest so not a lot of long stretches of track. Has anyone got 3.7x gears in their racecar and if so how does that change the way you drive, shifting, etc. Any other suggestions or ideas are welcomed.

andy3101

http://xse.com/leres/ss/calculator.html

you can plug in your numbers and see the desired outcome with different gearing.

I have 3.73 with the 2.29 gearbox and usually only use 2nd thru 4th. long track like Road America I use 5th.

if you are comfortable with 3rd thru 6th shifting 4.10 gears could be option also. if you have data to see your speeds and shift points at the tracks you run that would help you decide.

Hi Volts Z06

While I agree that optimizing your gear ratio is important, I also believe that unless you are running a sequential gearbox, the time it takes to shift costs you a lot at the end of the race. I recall being taught in Comp School that the less you can shift- the faster you will go. This obviously is going to depend on the track but I think the rule of thumb is to try and optimize your car for 3rd and 4th gear which is what you are going to use most of the time.

LateBreak

Hi Volts is correct, it's generally ideal to minimize your number of gear changes on a given lap. Marking up a track map with your current shift points, along with braking/lift points with estimated RPM can help you determine what the gear change will do to your shifts per lap. This is obviously a bit track dependent though, so what helps on one track may hurt on another.

That said, some good friends had DRM put 3.73's in their C5 track car and they said it completely transformed the car for the better Not sure what they took out, it could have been 2.73's as the car was originally an auto that had been swapped to M6.

Lasco001

I first 4.1 with ZR1 gear
Now I have 3.9 with ZR1 gear
I find the pairing perfect, from the curves it is awesome

Cölestin

zigspeed10

A gear change by itself will not make your car accelerate faster, for drag racing it might help but only because they start from a stand still and they need that short gear to quickly get into the powerband.

At Mid Ohio you should be using second gear in the key hole, madness all the way to the bridge, the carousel, and maybe going into thunder valley.

For comparison, a 2.66 box and 3.42 rear will have about the same second and third gear as a 2.29 box with 3.73 rear. Right now I have the 2.66 and 3.42 rear and wish my second gear was a little longer. I'm actually building a 2.29 box right now to put in just to have the longer second gear.

The reason I'm playing with gear ratios is to move my shift spots on the track, I'm detuned in ST3 so I'm always at peak power.

If you have a peaky motor getting the gearing right will be more important than if you have a broad power curve.

Here is an example that always blows people's minds, all else being equal, 2nd gear at 6000 rpm making 300hp will accelerate the same as 3rd gear at 4500 rpm making 300hp.

troyguitar

At that point you might as well run a 2.73 and chug along in 4th gear forever, no? Zero shifts ever, always at peak power, always have left foot braking available.

NemesisC5

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yooper

subscribed also

zigspeed10

What I meant is that the rpm drop between shifts doesn't drop me out of peak power. I hit peak power around 4700 and holds it to the rev limiter.

LateBreak

I'm gonna go ahead and call BS on this

Gear ratio multiplies torque from the engine at the expense of top speed. Increased Torque = Increased Acceleration, its Physics 101

Also, in the (close, but not exact) words of Doug Rippie: "A road race is just a bunch of drag races connected by corners."

zigspeed10

This statement is true.

The link that people don't make is that the torque at higher rpm is less than the torque at a lower rpm. Your multiplication factor is better in second gear as opposed to third but you have less torque to multiply.

LateBreak

Agreed, all I was saying is that deeper gears in the diff will increase acceleration in all gears with no other changes. In simple terms, a 10% gear ratio change will yield a SOTP change equal to a motor with 10% more torque. If you can do this without adding any upshifts or downshifts to your lap, it's a win.

There are a lot of factors involved, but the basic ideal setup is to be using your whole powerband with as few shifts per lap as possible.

In the OP's case, if you're not within 10% of redline at the end of any straights, I'd say to go with the 3.73's and improve acceleration off the corner.

0Anthony @ LGMotorsports

Most of the later W.C. Vette's we ran either a 3.73 or 3.90 gear in the rear with that box. In rare occasions a 4.10 diff was used too.

We had 25.5" tall tire, 7400 RPM rev limit and figured a max speed of 170 mph at most tracks using 2nd through 5th gear.

troyguitar

7400 using 2nd-5th sounds like a blast. Probably need a beefed up valvetrain though I assume?

0Anthony @ LGMotorsports

Ti intake valves, stainless exhaust, dual springs...stock rockers.

troyguitar

That doesn't seem like a big deal. I was under the impression most people stayed away from running 7k+ because it tore stuff up. If I could run 7400 with minor changes I'd probably do well with 3.90 or 4.10's since my speeds are lower than a W.C. car, hmmm...