Gear Ratios

[DonC]

Tony:
Spent a lot of time with gear ration calculators before I decided on my final setup. Try http://www.368s.com/tools_rpm.phtml for an easy to use calculator. Just plug in the numbers for transmission, rear end ratios, your planned tire size and it will give you the theoretical values for speed at rpm in all the gears.
Heed the advice about going with too low a rear end ratio. I'm running about 450 HP with 315/35/17 tires and a 3.07 rear on a TKO600 w/ 0.82 fifth and can spin the tires at will in 1st or 2nd and run 2300 rpm @ 70MPH on the freeway.
Very tractable in town and a real pleasure to drive. One of the more common mistakes people make is to compare the Cobra to other cars and what they're running for final drives. Your Cobra is going to be LIGHT and that makes a BIG difference in what will be useable in the end.
DonC

[Anthony]

http://www.clubcobra.com/forums/show...threadid=59664

[Excaliber]

I wouldn't assume you will be able to run in the 11's. MOST replicas are in the 12's, some low some high.

Sure a number of replicas run in the 10's, even 9's, but these are the exception not the rule.

12.2 or .3 is a really good ET. Most of us are NOT trying to set really low ET's. I'm not! My 60 ft time is over 2 seconds, pretty slow for drag racing! I'm not trying to hard, don't want to break stuff.

My 12.5 to 1 667 horse FE was SO radical it was a BIG hassle driving it on the street. I'm rebuilding it now with lower compression, milder cam and "softer" more street friendly carbs. Setting it up for "road race" use this time around. I expect my new ET will be mid 12's, I'll be very happy with that!

[niles]

I have a med. cammed Cleveland stoker with a TKO. I built it with a Dana 3.08, knowing that was a tall ratio, intending to go with with a 3.55 later. Now that I have the engine producing, I wouldnt think of changing it. Its perfect with the TKO; 1st is usable(47mph at 6k), 2nd pulls good from 20 to 78 mph. For spirited driving between 20 and 110 only one shift(shifts take a lot of time)
You can still smoke them at 1/2 WOT in first. 2nd only spins them above 5000 at WOT(sometimes). A friend has a 428 pro built motor with a 3.50 rear that can smoke them in 3 gears. I pull him easily on roll ons. He's spinning and smoking, I'm grapping one shift and GONE.

I have a TKO with a .68 5th. BIG mistake; need 75 before I can go to 5th. Stay with a tall rear ratio and get .82 OD at any cost!!!
It's the beat of all worlds. A four spped tol tear around with and an OD for quiet highway speeds.

Listen to the experienced; you dont need muscle car gears in a light cobra.

gn

[Naumoff]

Thanks Niles. All this info is very helpful. It seems with all the tranny choices I could go with the 3.07 and make all changes through the trans for almost any kind of driving. In talking to a contractor I was working with who races a 5.0 Mustang turbocharged five speed in street trim with slicks. He finally broke into the 10s and is running a 3.0 gear. He said he wouldn't touch his rear but that he was going to change the trans. I just need to get my mind set right for a very light car. Launching a light. When I was in High school it was the stop light where you usually won the race. If you left before the other guy and pulled away from him, he usually gave up. So with heavy cars and not many trannys to chose from the rear is where you went. I have been out of hot rodding for 20 years and I am glad there is aforum like this to educate me to what is going on in high performance cars today.