My T-56 came out of a 1997 Z-28 (so, I have the 2.66 1st gear).

With that said, what kind and ratio of gears would you pick?

Right now, I'm leaning torwards a Moser 12 bolt with GM performance 4.10's.

But I'm still having a hard time trying to decide between 3.73's and 4.10's.

What brand and ratio would you guys pick?

 

I'd go with 3.73's. I currently have 4.10's in my V8 ride and, trapping at a hair over 100 mph in the 1/4, puts me well over 6000 rpms on 235 50 16 street tires. That's too high for my tastes. I'm downgrading the next time I get the chance. The 4.10's make for a hell of a punch on the street, but you go through gears too quick.

 

3:42 are the lowest numerical gear I would use.


What are you going to use the car for?

 

You sound like you have a killer set-up there can can benifit from 3.73's or 4.10's. Where do you ****y at. if you shift at 5,500 than 3.73's are your best bet. If you hit 6,xxx than 4.10's are the way to go. Two overdirves allows you to have some serious gears.

 

I have 4.10's, and I think they're great. yeah it can be a lil high when goin through the traps, but u'll take a lot of people off the line, and if you have the HP you should have no problem holding it. Many many people forget, that even though a T56 has TWO overdrives, that 6'th gear is nearly the same ratio as 5'th gear in a T5.

 

The 1993 T-56's had a .62 6th gear which is the same as the T5 5th gear. However, the 1994 thru present has a .50 6th gear which allows you to run a big gear and have great highway manners. Since the Later T-56 has that huge overdrive you have great gears to get down the track and street yet you can slip her into 6th and still enjoy a nice low rpm ride at high speeds.

 

yeah i would vote for 3.73 s too.

 

Well, I currently have the stock G92 posi 3.23 disc brake rear. I'm ditching it as soon as I get the chance for a Moser 12 bolt (still waiting on funds).

My T-56 is a '97 year model tranny, so it's the smaller geared 6-speed.

I shift at 5,500 - 5,600.

Even with the 3.23's, 1st gear is violent , but thats on street tires. I'll eventually be running arround town on some ET streets when I get the 12 bolt in.

So, you guys think 4.10's are too much? I'd like to cross the traps at the top of third gear without having to shift into 4th, if possible.

My car has plenty of power! So, if I go with 4.10's, maybe I'll get some 28 inch tires instead of 26's. Maybe some 28x10x16 et streets. Would 28in tires compensate enough with the 4.10's to still cross the traps under 5,800 at the top of third gear?

Or is 3.73's with 26 inch tires a better bet?

Also. how much difference will I notice going from 3.23's to 3.73's? And, is it that much more of a difference going from 3.73's to 4.10's?

Thanks!

 

4.10s

 

Well to kind of put this in perspective fo you I will use my 1995 Z as an example. It has the T-56, same gear ratios as you with a 3.42 rear end. I shift at 5500rpm and at the top of third I am about 75-85mph at 5500-5700 rpm. I have not yet had this car to the track but from what I have read T-56 and 3.42 geared LT1's usualy trap anywhere from 98 to 102mph. Fourth gear in my car tops out right around 105-110ish. This would put me solidy in fourth. If you shift at the same RPM as I do you could easily use a 4.10 gear and trap right at the redline of fourth. I really don't think you will go wrong with either gear. But since you shift on the low side I would go with the 3.73's. Now, if you reved to 6200rpm I would say get the 4.10's. That would keep you in fourth at rediline and out of fifth if you shifted at 5500. What speed do you trap at? I have a ton of formulas at my disposal I can figure out your exact rpm and speed for any gear set-up with any tire.

 

Haven't been to the track yet, but my quickest G-tech time has been 11.9 @ 116. So, with my current small gears, I'm figuring a best of low 12's at 108 - 110 at an actual track. I've street raced and won against a few mid - low 12 sec. track cars.

With gears and slicks, I'm only shooting for 11.90's at what ever mph I can pull.

 

Ok, for those of you who think 4.10's are the way to go, do you think that 3.73's will still be enough gear with 26 inch tires?

 

Yes. I think since you shift at 5,500 rpm you will love the 3.73's. When i get home later I will do some math for you and kinda make up a chart to show you your RPM's at 5500rpm with different tires and rear gears. I will assume 3rd and 4 gear trapps.

 

I have an excel spreadsheet that I made up to do calculations for different gear ratios and what the result (speed at what rpm) would be produced. I'll post it when I get out of this boring class and get home.

 

not sure if you can get it for a moser 12bolt or not (i don't see why you couldn't) but i bet 3.90 would put you right in the sweet spot

 

YEa, thats what I was thinking when I figured I would run 4.10's with 28 inch tall tires. That would probably get me close to 3.90.

But, now I'm not so sure if the 4.10's will be too much for the street. Yea I do have a six-speed, but I dont want to just sit there and spin in 1st and 2nd. Hell, it does that now with the 3.23's!

Keep em coming guys, ANY comments and recommendations are appreciated!

 

Ok man I think I solved your problems. Here are some calculations for you assuming the following.

Assumptions:
You use 26" tall tire (.98% diameter accounting for slight squat)
I went ahead and did these calculations for a 275/40/ZR17 tire which is your best 26" tall tire (25.66"). You shift at 5,500 rpm exactly

I used 3rd and 4th gears for the T-56, 1.3 and 1.0 respectively and used 3 different rear end combos for you. My calculated speeds are RPM limited and have nothing to do with distance, however if you know your trap you can match your gear to put you at redline when you cross the finish.

Ok herre we go

For a 3rd gear RPM limited run (5500)
3.42=92.7mph
3.73=85.03mph
4.10=77.36mph

For a 4th gear RPM limited run (5500)
3.42=120.56mph
3.73=110.54mph
4.10=100.57mph

My conclusions

Since you shift at 5500rpm and trap between 100 and 110 mph I would use a 3.73 gear with a 26" tall tire and you will trap in fourth right before redline. So pretty much a perfect set-up. I can do any combo you would like.

 

Ok, here it is. I added some instructions in there, but it's fairly easy to use. I may do a standalone VB executable if I get enough reponse.

http://mypage.iu.edu/~kyafoley/speed...-speedcalc.xls

If you have any ?'s email me...

 

Thanks! I wish I could get some 3.89 gears for the moser 12 bolt.

Looks like I may end up going with 3.73's and 26x10x16 ET streets for track and 315/35/17 Nitto Drags for the street.

I do not want to shift into fifth at all when making a pass.

I was hoping to stay at the top of third when crossing the traps, even if I have to spin it to 6,000!

 

Looks like you have your answer. 3.73's will allow you to trap at a high rpm but will still allow you to rev a little higher if you want to down the road.

 

I didn't think about slicks, I'll have to add that into it to allow sizing other than p-metric (or whatever it's called). Maybe when I get some time I'll write up a little program that will do all kinds of little auto math calculations and post it up here...

 

what do you want?

im a programmer... im at work right now, and im BORED.

 

btw, VBscript may be a better choice if its just a bunch of simple calculations...

alot of people dont like downloading random EXEs off the internet..... plus VB requires alot of overhead files for even the most basic (hehe) install.

 

Check out my stuff. Mine takes care of inches or mm. You just take out the conversion factor when you switch. Since I used a 275 with an aspect ratio of 40 I converted it to inches. The 315/35 is roughly the same size as that drag 26" drag tire he listed. Height wise that is.

 

I have a 9 bolt and got 3.91's. I don't have the car done yet so no results. When I kill the 9 bolt I'm going with a 9" rear. Better than a 12 bolt period. The parasitic loss between the 2 is minimal. The 9" is way easier to change gears in, parts are more readily available and cheaper. And it's just plain stronger! 12 bolts are nice, but 9" are what everyone serious uses....from drag racers to SCCA guys. Not to mention if you buddy up with someone who has one (and is running the same spline axles as you) and they have different centersections with different ratio's, you can swap the centersection in minimal time and really see what works!

 

When I had my 99SS w/nitrous and T-56 I put 4.10s in and loved them for everything. Went through the trap @11.99/124mph at 6000rpm shifts. Crossed at 6000 in 4th. On the highway, I could cruise at 80mph at 2200rpm. Gas mileage was about 28hwy, 21city. And boy, were they fun in town!!!

 

See, I wont be shifting that high. I'm hoping to cross the traps arround 5,500 rpms.

3.90 gears sound like they would be perfect!

How much more is the 9 inch setup with disc brakes for a thirdgen compared to the 3rdgen 12 bolt disc rear? Is it more difficult to install than the 12 bolt?