Which is better for my Cobra: Tremec .62 or .82 OD?

Excaliber · #1 (**permalink**) 10-30-2009, 09:22 PM

Myself I would also carefully consider the FIRST gear ratio as well. Often with a five speed it is way to low. Resulting in serious wheel spin, while fun, it gets hold shifting really early or just using 2nd gear to take off.

My favorite "recipe" for gearing is:
The first four gears would be equivelant or close to the ratios you find in a top loader 4 speed. The icing on the cake would be a 5th gear at .8 Rear gear ratio can vary depending on what you like. 3.5 is a good call for my "recipe", in general. I might tend to go a bit higher IF the first gear ratio in my chosen trans is fairly low. I like to see about 40 mph in FIRST gear before shifting. That is just about optimum in my opinion.

RICK LAKE · #2 (**permalink**) 10-31-2009, 05:00 AM

TimSullivan Tim more important is what is the first gear ratio? The other thing is where your torque band starts. FORGET HP. You are not going to spend your time at 6,000 rpms all the time. Torque is what moves the car down the road. Ask for 550 ft of torque at 2,500 rpms. The idea is to be about 400-500 rpms into the torque band for cruising. You are building a stroker. Would recommend calling Keith Craft for a custom hydro roller in your motor. Unless you plan to race the car all the time a 6,500 rpm limit would be great and give long life to the drive train.
A 2.70's first gear and .82 overdrive would be a good combo. You don't want the motor to luggin 5th gear on the highway. 1,900 would be a min to have good power in 5th to accell to a higher speed and not have to downshift.
As for first gear I have run 3.25 and 3.00 with 3.31 gears, It's a waste of time starting out in 1st. 2nd gear is 2.45 and the car still pulls away with little effort. Have to remember you and the car weight is under 3,000 lbs. Good luck with the build. Rick L.

Ron61 · #3 (**permalink**) 10-31-2009, 06:31 AM

I had 3:27 gears in my Cobra and the .62 Tremec. I wish I had gotten the .82 as I hardly ever found a place that I could drive in 5th gear without lugging the engine. By the gear, tire, RPM ratio chart, in 5th gear my gears were about 2:10s. My coupe has 3:56 gears in it and the difference is quite remarkable.

Ron

patrickt · #4 (**permalink**) 10-31-2009, 06:39 AM

Tim, I have the .64, but, I have a 3.54 rear. With a 3.46 rear, I'd go with the .82.

Chilibit · #5 (**permalink**) 10-31-2009, 06:55 AM

Here is a handy tool.

http://www.secondstrike.com/Technical/GearingHelp.pdf

I elected to use the 0.82 and after 25k miles I have never regretted the choice.

mdross1 · #6 (**permalink**) 11-27-2009, 08:00 AM

I did the rear gear change 3.54 to 3.70,with the .62 od behind a 550hp 460 suggested by Mike Forte.It is the perfect combo for me.Like you have read it is all about getting it right.My first combination was Okay for a while 3.54 rear,with a TopLoader.