tko-600... .082 or .064

[ERA713]

1/1 to 1/0.64 was just to big a leap for me.I was lucky to find a buyer at an auto swap meet for my 0.64 tremec 600 for $400 less than I had paid so it.was'nt that big of mistake.I would recommend the 0.82.

[Ron61]

I had the 3:27 gears and a .60 split and with my motor at over 500 horse, it was a bit to much as I was just tacking 1900 RPM at 70 MPH. With my cam and set up, that was lugging the motor and I would have been much better off with the .8 split in the transmission. I would get the .8 if I were getting another car.

Ron

[patrickt]

Most of us "peacefully cruise" at 65-75mph. If you do the math and your engine doesn't hiccup at the RPM that .64 and your rear+tire size equate to, then I think you'll be happy with the .64 trans. My first four gears take me up to 140mph. The only thing I use fifth gear for is peaceful hiway cruising, and it does that quite well. But,for instance, if your 15" wheel/3.54-rear FE coughs, sputters, and bucks at 2000RPM then .64 is not right for you (unless you swap out your cam and replace it with a trusty ol' solid flat tappet). But I'm telling you, having the ability to cruise on the hiway as quietly, and as smoothly, as if you were coasting with the engine off really enhances the overall enjoyment of owning a Cobra.

[Ron61]

Pacrickt,

You are right for most people, but my engine was built for racing and then when I got to old and sick, it just didn't work out well for cruising with that ratio and a .6 split. My cam came in at around 3600 RPM and with the .6 split it effectively raised my rear end ratio to 2.10 with the street tires I used. So at the 1900 RPM at 70 MPH I was lugging the engine and a .8 would have been better for that use. I would say that 80% of my cruising was done in 4th gear as the traffic and speed limits stopped me from getting the engine up to where it ran well.

Ron

[patrickt]

Originally Posted by Ron61

Pacrickt,

You are right for most people, but my engine was built for racing and then when I got to old and sick, it just didn't work out well for cruising with that ratio and a .6 split. My cam came in at around 3600 RPM and with the .6 split it effectively raised my rear end ratio to 2.10 with the street tires I used. So at the 1900 RPM at 70 MPH I was lugging the engine and a .8 would have been better for that use. I would say that 80% of my cruising was done in 4th gear as the traffic and speed limits stopped me from getting the engine up to where it ran well.

Ron

Perfect example of a need for a .82 and not a .64 gear. If you have a rear numerically lower than 3.5, or an engine that isn't at least awake below 2500rpm, I wouldn't go with the .64 trans. It can be a tricky call, and if in doubt, I'd go with the .82 gear.

[maxum_101]

ok this is a bit complicated... lets say i have a spf cobra with a 3.46 rear 17 inch tires and a roush 427r engine what would be a good 5th gear to have? i want to be able to drive hwy at a comfortable rpm and still be able to hammer it around town . anyone out there have this set up that can give their comments on this?

[Slick61]

Originally Posted by maxum_101

ok this is a bit complicated... lets say i have a spf cobra with a 3.46 rear 17 inch tires and a roush 427r engine what would be a good 5th gear to have? i want to be able to drive hwy at a comfortable rpm and still be able to hammer it around town . anyone out there have this set up that can give their comments on this?

I'm running a KCR 427W in my Backdraft with 3.73 rear & the 0.82 overdrive. At first I wished it had the 0.64, but with my cam, it would be completely useless at anything below 80 mph.

2600-3000 rpm on the freeway is PERFECT for my engine... the engine sounds fantastic, is running in the sweet spot for the cam, it's not too loud, and I still have good, tractable power on-tap for quick maneuvers. 3000 rpm puts me right around 75 mph, with 80 mph coming at ~ 3200 rpm. It's great. Above that, the wind buffeting is too uncomfortable for long-distance cruising. I know several people with the 0.64 overdrive who practically never get to use 5th, as the engine lugs too badly. Believe me... 3000 rpm on the highway sounds FABULOUS! It's not as fatiguing as it would be around town. If you want mileage, slow it down to 65 mph... it's mostly aerodynamics (or lack thereof).

... and you can still hammer it around town...