Just posted a thread about gear install but thought I would throw this in too. I'm going to be installing a aluminum flywheel along with clutch next weekend. I was thinking I would need to upgrade the gearing ratio too since it will spin quicker now.

I was thinking 4.10s because that is all that's recommended here but then again this site is generally tilted towards the drag racing mindset. My car is still going to be driven on the street (m6) but I want it to be set up for some road racing events this summer. Top speed I think I'll be hitting down the striaghts would be around 120 mph. Would 4.10s still be suitable for this?

I don't want to lose to much of the 1/4 mile capability though, since it would be nice to have it if I ever need it.

Basically, I knwo 4.10s are a good comprimise on the street and for the 1/4 mile, but are they friendly for road racing and how much would they hurt my ability to still have a good push at around 130mph?

 

Using the calculator on here, your top speed in 4th would be about 125 or so. I don't think you'd wanna go around the road course in 5th, so it seems you may want to stick with some 3.73s to have a good compromise between street and drag/autox racing. That should keep you within your powerband on the straightaways. I'd try to find some more accurate calculators for your particular setup to find out for sure. I think when I cross the line in the 1/4 with my 4.11 gears, I'm getting up around 5800 and my mph is only 105, even though that's just trap speed. Hope this helps.

 

more gear the better
i'd say 3.90s if you can get them, motive sells them
the higher gear will always accelerate faster at any rpm/speed until you hit your top speed.
autos have a smaller final drive gear ratio or something so its easier for autos to cruise at top speed
(what i've been told)

 

Thanks for the suggestion. I couldn't get the calc here to work (no excel) but I found a good one here: http://www.5speedtransmissions.com/gear_calculator.html and damn does 1st gear really last till 50mph? Never noticed.

I set it up for a 25.66 inch tire, which I belive the cars with 17s have. According to them though the top speed is just 111, which seems to be more in line with what your car is running and not like the cz28 calc came up with. In fact, typing in the 4.11 ratio gives it a 5653 rpm readout, which is probaly right on considering OEM tach lag.

Those 3.90s that were recommended come up nice on the chart, reading out a 117 top speed in 4th and a 159 in 5th, right in line with the limiter, But, how are they strength-wise? I have heard some people recommend 4.10 over 4.11 (or vice-wersa, not sure) because one is inherently stronger then the other. Plus, the people running an m6 don't generally approve of 3.73s because supposedly they don't offer a noticable differance. I wonder if these are any better.

 

Unless something has changed recently, 3.90s are not avail for the 7.5" 10 bolt. All i'm saying is don't get your heart set on them untill your SURE they are avail for your rear.

I'd recommend 3.73s.

-brent

 

Do you have a direct link? Like 94formulabz posted, I looked up and d/l motive's pdf on the ratios they carry and they jump from 3.73 to 4.10 on the 7.5"

 

Alright, I just spent quite awhile searching and from everything I read I guess I'll have to go with 3.73s (stronger, and less dragstrip minded, plus great when the car is upgraded and 4.10s become impossible to hook up), unless someone can come up with a place to find 3.90s. I already tried google it just turns up pages of unrelated stuff.

 

Yeah, I had the tire diameter for stock tires on there, sorry. The data you calculated is right on. I think you'll like the difference with the 3.73s both at the strip and for RR. Let us know how you like them. FWIW, the 4.11 are stronger because they have less teeth.