Help with rear gears for a 1st gen with t-56

[68firehawk]

I know there is other threads on this but none for my exact circumstance.

So i've decided on my rim and tire set up and im currently haveing my axle shortened and set up for the car. So that means i'm to the curtial point of choosing gears. I'm thinking 3.89's will get me to exactly where I want to go but I would like some more imput on the matter.

I have a full floating 31 spline 9"
Tires are 335/35 R 17
My LS1 will be well over 450 horse

I would like to be able to do 200+, cruze comfortably at 75 or 80 and scare myself in the first few gears. Is this possible? I would like to keep from having the gerbox altered, for now.

and does anyone know where I can find a gear ratio calculator?

Thanks

Jake

[zbugger]

3.73's would be a good choice for that, but for the 200+ you'll need something near a 3.55 or a little lower. And don't expect your car to pull 6th too easily untill you're over at least 150+. Good thing about a 9" rear is that you can swap gears easily. It's called testing and tuning.

[68firehawk]

Allen

Gear ratio wise, is there a way to estimate my top speed with 3.73's?

Jake

[gen3bu]

http://tciauto.com/tech_info/calculators.htm#6

[USAZR1]

6th gear is too tall to ever run 200mph. If you have enough motor to do it,it will have to be done in 5th. My 90 ZR-1 with 422rwhp LT5,ZF six speed,and 4.10 cogs would run 182mph at 7400 rpm on the Pony Express 100. Tires used were Michelin Pilot 335/35/17's. With stock 3.45 cogs,the car would run 195mph at around 6,500 rpm.
With either gearset,shifting into 6th would slow the car down.
You better have a good driveshaft to do this stuff,too.

[68firehawk]

Thats exactly what I was worried about. If 6th could even handle the pressure or not. I'm estimating over 450rwp and the tires. I happened to buy are michelin Piolts 335/35/17. Yes the driveshaft will be built to handle whatever I throw at it.

I don't really want to gear her so high that I can't scare the crap out of my self in the first few gears. I've probably set my sights to high for top speed, for now.

On your ZR-1 where you did 182 in 5th with 4.10's?

So i'm guessing if I went with 3.73's I could come close to 190 in 5th. I think I read somewhere if you change out sincros and raise the gearing a little you could use 6th. Is it even worth it? Is everyone just gearing them their run top speed in 5th? It's easy enough to change out rear gears so I may just gear it for 180 or so and modify the transmisson later.

Jake

[USAZR1]

Thats exactly what I was worried about. If 6th could even handle the pressure or not. I'm estimating over 450rwp and the tires. I happened to buy are michelin Piolts 335/35/17. Yes the driveshaft will be built to handle whatever I throw at it.

I don't really want to gear her so high that I can't scare the crap out of my self in the first few gears. I've probably set my sights to high for top speed, for now.

On your ZR-1 where you did 182 in 5th with 4.10's?

So i'm guessing if I went with 3.73's I could come close to 190 in 5th. I think I read somewhere if you change out sincros and raise the gearing a little you could use 6th. Is it even worth it? Is everyone just gearing them their run top speed in 5th? It's easy enough to change out rear gears so I may just gear it for 180 or so and modify the transmisson later.

Jake

I ran the 182 number at the Big Bend Twin 50 ORR. John Lingenfelter once told me that trying to run top speeds in 6th gear would fry the rear tailshaft bushings in the trans.
You could try a 3.89 gearset in your 9". What rpm is the HP peak at on your engine?

[69Lowbird]

68 Camaro with 3.73 gears and a LT1 T-56 cruised 70 in sixth at 2500 RPM

[68firehawk]

Peak HP will be somewhere around 7000rpm's. I'm worried that if I chose 3.89's my 6th gear cursing at 70 is going to be to high.

I'll try and do some calc's on the website you gave me next.

Jake

[Ralph LoGrasso]

Jake,

even with the 3.89s, the .62 6th ratio is going to keep revs low at 70mph.

The biggest problem for 200mph runs isn't going to be gears, it's going to be aero drag, and power. When you pick gears, don't pick a gear that is so tall that it drops you too far down in your powerband when you shift from 4th to 5th. You want something that will keep the revs up just enough. That is why top speed runs are done in 5th and not 6th, you fall too far out of your powerband in 6th. Do a search in this forum, there is a big thread on this very same topic started by me concerning what rear gears to use in a first gen with a T56, 335/30/18s (almost same diameter as 335/35/17s) for top spead gearing. All top speed runs will be done in 5th with the T56, unless you swap to closer ratio 5th/6th gears like the G-force .89/.79 5th/6th.

[Ralph LoGrasso]

Here's the thread, lots of good info:

https://www.pro-touring.com/forum/showthread.php?t=1335

[USAZR1]

68 Camaro with 3.73 gears and a LT1 T-56 cruised 70 in sixth at 2500 RPM

Not sure what but something doesn't compute here. I'm running a Viper T56 (.50 sixth) with 4.11 cogs in the Fab 9 and 26" tall 335/35/17's. At 70 mph,I'm running right at 2,000 rpm in 6th gear. 2,500 rpm would be close to 85-90mph. What ratio is the LT1 T56's sixth gear?

[CarlC]

I agree with Clint. The numbers don't add up if 6th is a 0.5.