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subtlez28
04-27-2010, 05:53 AM
I am building an 84 C4 Corvette as a street legal, but track (road course) focused car. It is getting an LS1 and T56. It will be pretty well gutted and my weight goal is 3000 lbs w me in it.

Details here: https://www.pro-touring.com/forum/showthread.php?t=61422

I'm upgrading from the Dana 36 to a Dana 44. I have purchased two:
1- 3.45
2- 3.08

I picked up the 3.45 first, but later snapped up the 3.08.

My thought is, in my 02 Z28 I run my local road course mostly in 3rd gear, needing 4th for two straights. In a couple spots I run out of 3rd gear nearly to a corner. Because of the time to shift up to 4th, then back down to 3rd for corner exit... the upshift is not helpful. The Z28 has 3.42, and I always thought a bit higher (numerically lower) gear would help me get more use out of 3rd. And hooking up in 1st gear on a street tire is nearly impossible.

So the Vette will have more power (LS6 heads/cam), more tire (315s all around), better suspension, and less weight. I'm thinking this will exaggerate my running out of 3rd gear problem...

Plus, I have been very intrigued by the standing mile and open road race events. I would like to make them in a year or two. And down the road (with more power) it would be cool to be able to hit the magic 200 mph mark.

So, using a gear calculator, assuming a 25.68" tire (315/35/17) I have come up with the following final drives and mph at 6000 rpm:
3.45-
1st 9.18 FD = 49.9 mph
2nd 6.14 FD = 74.6 mph
3rd 4.49 FD = 102.2 mph
4th 3.45 FD = 132.8 mph
5th 2.59 FD = 177.1 mph
(I wont bother w 6th)

3.08-
1st 8.19 FD = 55.9 mph
2nd 5.48 FD = 83.6 mph
3rd 4.00 FD = 114.5 mph
4th 3.08 FD = 148.8 mph
5th 2.31 FD = 198.4 mph

This is getting kind of long winded... My question is:

If I go with a 3.08, will I be giving up to much acceleration?

Will the manual trans make the higher (numerically lower) gear work well?

Or will the light weight, ability to actually use 1st gear, and being able to avoid overdrive up to ~150 mph at bigger tracks like Road America outweigh the the lost torque multiplication?

I basically want a well rounded gear that will let the car do well in multiple tracks and forms of racing.

Am I crazy to go w a 3.08? Is the 3.45 to 3.08 difference enough to really worry about?

Thanks in advance for your thoughts and shared experiences!

-Shaun-

subtlez28
04-27-2010, 06:09 AM
Just playing around w the calculator again...
If I bump up to 6500 RPM, the 3.08s give me 60 mph in 1st (should make for an impressive 0-60 time). Also 161 mph in 4th. I like that as I want to avoid using OD on the track.



Question for mods: Would this question be appropriate for Open (Pro-Touring) Discussion? I'm wondering if it would get more views there.

68Formula
04-27-2010, 06:23 AM
I think for what you have planned for the car, and the rest of the combination, you've answered your own question. Go with the 3.08. The only problem I see, is the 6th gear won't be of any use on the street (at least, not at legal posted limits).

subtlez28
04-27-2010, 02:32 PM
Thanks. I hear what you are saying. I kinda wish I had a TKO-600 5-speed, as I don't really need the double overdrive for this car.

However, the calculator puts RPMs at 1512 doing 75 mph... That might be usable.

funcars
04-27-2010, 05:20 PM
I would say that 1500 rpm will probably drone pretty bad driving on the street. In my 90 I never use 6th gear because it gave me a headache.