tko-600... .082 or .064 - Page 2

Ron61 · #21 (**permalink**) 09-16-2008, 07:16 AM

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 · #22 (**permalink**) 09-16-2008, 07:58 AM

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 · #23 (**permalink**) 09-16-2008, 08:04 AM

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 · #24 (**permalink**) 09-16-2008, 08:12 AM

Quote:

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 · #25 (**permalink**) 09-16-2008, 08:27 AM

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 · #26 (**permalink**) 09-16-2008, 10:00 AM

Quote:

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...

DC COBRA · #27 (**permalink**) 09-16-2008, 04:12 PM

Quote:

Originally Posted by Slick61

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...

I agree with ya Slick, the .68 just plain sucked when I had the cobra. When I put the .82 in her that was the hot ticket. You should have heard her with my exhaust on her now that was sweeeeeeett!!

DON

Slick61 · #28 (**permalink**) 09-16-2008, 04:47 PM

Quote:

Originally Posted by DC COBRA

I agree with ya Slick, the .68 just plain sucked when I had the cobra. When I put the .82 in her that was the hot ticket. You should have heard her with my exhaust on her now that was sweeeeeeett!!

DON

oy vey... I can only imagine... It's still a little too loud for my ears when cruising around town... most of the curbs are about 6-8 inches high & reflect everything right back to me... gets fatiguing around town, but sounds awesome on the freeway at 80 mph.

DC COBRA · #29 (**permalink**) 09-16-2008, 05:14 PM

Quote:

Originally Posted by Slick61

oy vey... I can only imagine... It's still a little too loud for my ears when cruising around town... most of the curbs are about 6-8 inches high & reflect everything right back to me... gets fatiguing around town, but sounds awesome on the freeway at 80 mph.

Dude it can never be too loud, that means you just getting old and need to stay on the porch HA!HA! But you know BILL said the same thing, it was way too loud.

DON

ng8264723 · #30 (**permalink**) 09-16-2008, 05:36 PM

My Terminator has a 6 speed in it and I cruise all the time in 6th. It's very comfortable the engine is cruising at 1700RPM and is nice and quite. My 70 SCJ with a 428 and stock tires with 3:91's use to cruise (60mph) at 3000RPM. Boy was it loud!! I think a lower RPM at 60MPH would be more comfortable. Having never done autocross I have to ask what is your ave speed?
chris

diegokid · #31 (**permalink**) 09-16-2008, 05:55 PM

I've been using the .82 as stated earlier with a 3.42 rear end. According to the gps at 70 I'm turning about 2450 with the same size tire 295-50-15s. Fith gear feels a natural extension after fourth without the large rpm drop or the higher revving when going from 5th to 4th. Here is a link for looking at different gears. I like this one because you can put any ratio you choose. If I changed anything it would be going to a 3.08 because I'm most likely going to swap to the MT SR Radials with my next tire change. They are a little shorter. If money is no object you could always buy a six speed and have both gears. Also with the 3.42 taking off in 2nd gear is easy if you aren't feeling running through all the gears.

http://www.classicchevy5speed.com/RPM-Calculator.aspx

http://www.secondstrike.com/Technical/GearCalc.asp

cal.cheesehead · #32 (**permalink**) 09-17-2008, 11:02 AM

thanks everyone!

tmareina · #33 (**permalink**) 09-17-2008, 11:47 AM

My 428 with 614hp has .64 5th gear and 3.73 rearend. At 2000 rpm I'm doing about 65mph and it is fine...no detonation. If you want to nail it to go faster you wouldn't do it in 5th gear (enough torque to do so however) BUT you would naturally downshift. I haven't had any problems and love the combo...two seasons now and about 3000 miles.

Tom

JayBar · #34 (**permalink**) 09-17-2008, 07:53 PM

I wish I had the .82 I went for the .64 because I thought it would be a better cruse gear. But on the track (3.73 rear) I wind out 4th at about 130 shift to 5 and it just dies.
Had I to do it again I would get the .82 or better yet get a T56 only about $500 more just a bit wider at the rear.

patrickt · #35 (**permalink**) 09-18-2008, 05:42 AM

Quote:

Originally Posted by JayBar

But on the track (3.73 rear) I wind out 4th at about 130 shift to 5 and it just dies.

If you are so inclined, you can graph the shift points based on the torque/rpm of your engine, your rear ratio, and your tire size. This is my set up as graphed by Performance Trends "Trans Gear Calculator." That being said, the .64 gear is not for the track (a short blast on the salt flats not included). It's a "pleasant cruising" gear only.