Rear Gear Ratio??

turnpike boy · #1 (**permalink**) 09-24-2007, 08:25 PM

I've got a Unique with Jag rear; 4.09 final drive, Tremec 3550, 0.68 5th. gear, 331" with cam specs 228*/236*, .605/.589 lift, AFR 185's, Victor Jr., Speed Demon 650 mechanical secondaries.

Very, very fine to drive. Anything under about 60 mph, like around town, use whichever gear makes you happy because the car pulls like a Clydesdale no matter which one used. 4th. gear, 3000 rpm is a hair over 60 mph - right up the cam's alley, so roll-ons with anybody are smile contests.

Wanna cruise? - no problem. Nobody runs the highways around here at under 75 mph anyway, which is 2500 rpm for me; again, right about where the cam really starts to work. 2700 rpm is about 82 mph, perfect for the left lane on Rt. 80 or the Penn Turnpike or.....you get the idea. Hi gear passing is a joy unlimited.

Anybody in here tells you the hi 5th. gear ratios are useless is wrong. It might be that the .82's work better with lower ratios, but around town that 4.10 will be the most effortless drive you ever had. And the pull 2/3/4 has to be felt to be believed. First is about worthless (mine is 3.27 first) but makes crawling traffic a no-sweat proposition - put it in gear, let out the clutch, and just idle along. No in/out with the clutch pedal.

No regrets whatsoever here.

Ron61 · #2 (**permalink**) 09-25-2007, 05:04 AM

I had 235/60/15s on my Cobra if I remember correctly and a 3:27 rear end ratio, with the .68 split in the transmission. I checked it with the highway patrol radar and the readings were right on. 70 MPH in 5th was 1900 RPM and 60 MPH I don't remember, but the engine was more of a racing engine and I didn't even use 5th on the freeway about 70% of the time as the traffic caused the engine to lug. But 2nd, 3rd, and 4th worked very well. However if I had another car I think I would go to 3:56 gears and a much milder engine.

Ron

enyawix · #3 (**permalink**) 09-26-2007, 08:16 PM

what was the stock 5.0 rear end gear?

JAM1775 · #4 (**permalink**) 10-01-2007, 11:05 AM

I'd move up to 377 rear gears as the cheapest, easiest way to go with a slightly added bit of acceleration. At 61mph, from your #'s, you would probaly add another 2K RPM to make it 2200 which your motor should like.
Now you can cruise highways. First gear would still be very manageable .
I have 373's with the 600's .287 first gear. That comes out almost exactly as though I had my old tremec 3550 with 3.27 first gear and converted 327 rear gears. You'd get similar results moving to 377's and your 2nd/3rd/4th gears would get more spark to boot.