Need a little help with rear gear selection!

[Fitter480]

Hi guys need some help. I found a tremec T56 out of a 2005 SSR, Took it out to D&D performance and had them go thought it for me. This is what they told me. The trans has a one piece cluster, carbon frictions, triple double syncros and a 32 spline output shaft. The gearing is as follows. 1st= 3.01, 2nd= 2.07, 3rd= 1.43, 4th=1.0, 5th= .84, 6th= .57.

Here's the question: Behind a LS7 in a '67 Camaro what rear gear? I was leaning toward a 4:10 in a 9" ford but now I'm not so sure.

[ProdigyCustoms]

1st gear will be to short with a 4.10. you won't make it under the traffic light before shipping. A 12.3 to 1 starting line ratio is too deep. A 3.73 or 3.55 will put upk in the 10.5 to 11.2 range and is more accepatable.

Also, if you were to try to autocross a 4.10 gear, 12:1 starting line ratio, you will find yourself between 1st and 2nd gear all the time. on the drag strip you will just roast the tires.

[chicane]

I don't think that I would use more than about a 3.50 gear with that transmission gear set. However... 6th gear is still going to be rather useless.

With the 4.1x ring and pinion, it will yield:

12.341 (Way too short)
8.487
5.863
4.1x
3.444
2.337 (Acceptable)

With the 3.50 ring and pinion it will yield:

10.535 (Acceptable)
7.245
5.005
4.1x
2.94
1.995 (Way too tall)

As you can see the 3.50 ring and pinion would put you in the high side of the preferred first gear final ratio... but 6th is useless... unless you are cruising at 100+ MPH... and even then, any OD beyond 0.75 is unbelievably inefficient anyway.

[Fitter480]

Ok, I understand what you guys are saying. But how do you come to the final drive ratio? and what would be considered acceptable 1st gear and overdrive final ratios? Thanks again, you advice is a great help. I'm trying to figure if what Frank is saying is workable. I would love to pull as steep a gear as possible even if first is a bit short. But I hear ya on the 4:10 That's no longer a option.

[sik68]

The steepest 1st gear ratio'd car I've ever been in is a stock Nissan 350Z.

350Z
3.794 ratio 1st gear
3.538 ratio final drive
= 13.42 multiplication

Putting around, 1st gear is over 1/2 way through the intersection...the owner thought it was tolerable but disliked it for every day driving.

I've also ridden in a 335i BMW

BMW 335i
3.08 ratio 1st gear
4.055 ratio final drive
= 12.49 multiplication

My friend took me for a joyride as he just tuned the car for an extra 80hp and 100tq, I actually felt that this car was geared very well for hard launches and acceleration. The short 1st was nice when it was time to wind it out.

Porsche 911 Carrera
3.82 ratio 1st gear
3.44 ratio final drive
= 13.14 multiplication

So looking at a 12.x:1, it is probably steep, but given that the some oem's run well into the 13 range, it's probably not too ridiculous. Maybe you can recall some manual cars you've driven to give an impression of what a certain ratio feels like.

[ProdigyCustoms]

I agree with Chicane, with that first gear I like the 3.55-3.55 gear the best. If you ever autocross it you will thank me. nothing worse then needing to shift JUST before the corner, or standing on the rev limiter for 50 feet.

You have a lot of power there, I would want to kill a little torque anyway. nothing worse then a car with to much power and gear to hook. You end up getting your ass handed to you my slower cars that hook and go! A little grunt and go in a street car is not a bad thing.