rear end gear help

worksalot · #1 (**permalink**) 02-04-2002, 07:08 PM

needing a bit of advice and hoping someone with a similair car has been through this.here is what i have
B&B cobra 2460lbs
3.08 rearend gears
t-5 trans
302 with trick flow twisted wedge heads,E-303 roller cam with fms roller lifter,rpm intake with 670 holley street avenger carb.
here is my question....does anyone else have a similair set up and tried the 3.55 gears?would this give me a better 1/8 or 1/4 time(although i have now idea what it currently is...would i be faster)or help out with stoplight fun???also any guestimates on horse power i have not had it dynoed
thanks for your help
john b

Clois Harlan · #2 (**permalink**) 02-05-2002, 09:11 AM

I have a B&B and mine also had 308 gears with a T-5 behind my 360 hp 302. Best move I ever made was to trade out my high gears for 3.73:1 gears. This made my car a lot more fun to drive. With my old gears I never seemed to get out of the hole quick or smooth. At the Run and Gun in Saint Louis my best time was a 12.92 with street tires. In Tulsa last year at the Ford Performance and Shelby meet I turned 12.78 w/ street slicks.

I highly recommend the change, I was out running many cars I probably could not have w/ my old gears (3.08:1). My cost for everything was about $475.00.

worksalot · #3 (**permalink**) 02-06-2002, 04:23 PM

thanks for the info,i know this is going to sound very uncobraishbut do you know what rpm you turn at around 65mph with the 3.73s,the reason i ask is because mine is a weekend cruiser through the country side and i guess i want the best of both worlds that is why i was leaning toward the 3.55.also was wondering if anyone on the forum had built a 302 with the 289rods and special piston to improve the rod to stroke ratio and what were the results..i am entertaining the thought of an engine project for the cobra,winter weather sure makes me figity.thanks
johnb

JAM1775 · #4 (**permalink**) 02-06-2002, 04:50 PM

I have a 460HP FFR with Tremec and 3.73 gears. I love the set up. The T5 has a slightly steeper first gear (3.34 vs.3.27)but you may overcome that steepness with your 302 and may be able to just lay into it and learn to pull 2nd quickly. Now 2nd/3rd/4th will be a blast with the 3.73's ! I run about the same OD as your T5 and I rev 2150@60, 2350@65 and around 2550@70mph with 15" wheels and 26" tires. If you upgrade power you may still stay with the 3.73 because you will fall in love with the 2nd gear snap. Just sell the T5 and invest the balance in a T5Z. The difference may be $400 for the gear change and $500 bal for the T5Z upgrade. The Z's long first gear will compute and feel just like 327's but 2nd/3rd/4th will be 3,73's all the way .

427sharpe · #5 (**permalink**) 02-08-2002, 05:03 PM

worksalot;
a general rule of thumb to help you---
if you change NOTHING but rear end gearing, the ratio differential can be applied to your rpm as well. For example, if you are running 3.08 gears and you are turning 2500 rpm @ 60 and you change to 3.73 gears, you will be turning ABOUT 3025. How to get there? 3.73/3.08=1.21 x 2500=3025. You can be more precise with a longer formula----if you want it email me and I will send it back to you or just post a request here. I dont want to post it unless you want it because it's rather long and tedious (but it is informative).

worksalot · #6 (**permalink**) 02-08-2002, 06:43 PM

427sharpe thanks for that bitof info,yesterday i sat down and figured my tire size,drive shaft rotation,engine rpm....so on and so forth to figure out my changed rpm,but never once did i think to simply divide the ratios.thanks for helping me out.truly i am still a bit upset that it didn't dawn on me to do that.
thanks again
john b

JAM1775 · #7 (**permalink**) 02-09-2002, 04:05 PM

worksalot...go to
www.prestage.com
Select Car Math.
There are formulas which include RPMs at MPH factoring
tire size, tranny and rear gear ratios.

justa6 · #8 (**permalink**) 02-10-2002, 05:27 PM

I had a 3.50 rear in my Buick V6 Powered Johnex. The Buick's torques and HP are probably a little higher in the RPM range
so I changed my 3.50 for a 4.11 which is fine as the Tremec has a very high 5th gear. It makes the car completely different. As someone else said it makes the car very "crisp". I was also at Run and Gun last year with the 3.50 gears it ran an 11.40 with a 60' time of around 1.75 we took it out with the new gears and it ran 10.8 with a best 60' time of 1.48 and it cruises BETTER as the cam I've got doesn't like being lugged in Overdrive so now it cruises at around 2500 RPM on 26 in Diameter 17" wheels.

Bottom line is you'll like deeper gears IF, as you have, an Overdrive trans. IMO, its the only way to "fly"...

Regards,