T5 Hold Up Behind a 408 in 2600 Lb. Cobra?

kschoenefeld · #1 (**permalink**) 11-17-2006, 12:00 PM

I currently have a T5 World Class behind a 351W. It has given me no problems. Think I can keep this tranny when I replace the 351 with a 408, planned on producing 500 HP? Otherwise, anyone with experience with the g-force modified T5 tranny instead of a TKO? Thanks. SB Karl

Buzz · #2 (**permalink**) 11-17-2006, 12:23 PM

I have a non - world class T5 behind a +/- 450 hp/tq 383 stroker in my Unique. I have been expecting it to fail from the day I bought the car (over 4 years now) so I have made no attempt to treat it gently. After years of merciless beatings and abuse, it still shifts as smoothly as ever and now with the recent addition of a Hurst Billet Plus shifter, I can bang my shifts like never before. When I'm in the mood to scare the civilians and stampede the local livestock, I occasionally launch hard enough to boil the tires through first and smoke them on both the second and third upshifts. The ability of the drivetrain to overwhelm the tires no doubt plays a role in preserving the box but it also endures lots of more conservative, but still hard, up and down shifting without a complaint. In fact I like it so much that when it finally implodes or I upgrade the engine - whichever comes first - I will replace it with another T5 from G-Force.

hi-tech cobra · #3 (**permalink**) 11-21-2006, 10:28 PM

What is the 5th gear ratio of your T-5? If it is .63, what rpm's are you turning in 5th gear at say 70mph? People are telling me I need a TKO 600 with a .82 overdrive because the engine will bog with a .63.

My cobra will have a 347 sb, intake Edelbrock Air Gap, and a cam that makes power in the lower rpm range, the rear end is a 3.54. What do you think? A TKO 600 is not really in my budget right now so if a T-5 would work I could get this project flying early.

CHRIS DAMSCH · #4 (**permalink**) 11-22-2006, 07:47 PM

The T-5 should hold up pretty well. There is a guy in the Windy City Cobra Club that is running a T-5 with a very strong 347 and he hasn't had any problems as of yet. He runs it at the drag strip and hard on the street.

I say go with the T-5, you may be surprized. The cobra is light. You should spin the tires before you break the trans.... most of the time.

hi-tech cobra · #5 (**permalink**) 11-22-2006, 08:00 PM

Thanks Chris,
Are the bolts (trans mounting) for the T-5 the same as the Tremec TKO 600?
If so, I will need to modify my cross member as the chassis is set up for a toploader.

54h · #6 (**permalink**) 11-22-2006, 08:09 PM

Just an FYI....the T-5 factory transmission is rated by the manufacturer at handling a MAXimum of 300 lbs/ft of torque. What's the estimated torque of your motor?

hi-tech cobra · #7 (**permalink**) 11-22-2006, 09:52 PM

54h, the engine is not built, I'm guessing torque to be around the 350-375 range. I could go with a world class. The main thing I want to do is get the car on the road. My cobra funds are very limited right now and if I plunk down $1,900 for a TKO it will prolong the project. That's why I was thinking about a T-5 or T-5 world class. The only drawback is the .6 5th gear. Some have said the engine will bog (3.54 rear end). Is it true I'll be turning 1500 rpm's at 70 mph with the .6 overdrive?

Sharroll Celby · #8 (**permalink**) 11-22-2006, 10:11 PM

I have a T5 behind my mildly built 351W (maybe 400 HP), and with my 3.08 gears and the .64 OD, I turn 1800 RPMs at 80 MPH in 5th. A great long-distance cruising gear, and you can always put it in 4th gear to do some accelerating on the freeway.

hi-tech cobra · #9 (**permalink**) 11-22-2006, 11:28 PM

Sharroll,
What do you think my rpm's will be with a 3.54 rear end in 5th gear compared to yours? Will rpm's be more or less?

pmfranke · #10 (**permalink**) 11-23-2006, 12:05 AM

i have a stroked 351 to 402 probably 425 to450hp,3.50, t-5z from summit got it for $1100. the 5th gear is a little tall but not to bad it runs 70 at a little under 2000 rpm.i changed from a 3.00 rear end which was way too tall in first ,i couldn't drive in parking lots with out bucking and shaking,lots of clutch slipage. first now is good for driving in town and in parking lots. Its not perfect because the gap from 4th to 5th is very wide ,.82 is the way to go if possible.Good luck,Peter.

Buzz · #11 (**permalink**) 11-23-2006, 06:24 AM

Quote:

Originally Posted by hi-tech cobra

What is the 5th gear ratio of your T-5? If it is .63, what rpm's are you turning in 5th gear at say 70mph? People are telling me I need a TKO 600 with a .82 overdrive because the engine will bog with a .63.

My cobra will have a 347 sb, intake Edelbrock Air Gap, and a cam that makes power in the lower rpm range, the rear end is a 3.54. What do you think? A TKO 600 is not really in my budget right now so if a T-5 would work I could get this project flying early.

With a 3:54 final drive ratio and 275 60X15 rear tires, I turn under 2000 rpm's in 5th at 70mph. According to the gear speed calculator, the precise number is 1875 rpm. At 100mph, I'm still under 3000rpm. In 5th, around 1600rpm at 60 mph, the car hasn't bogged and still accelerates well enough to easily pass normal traffic. This has come from deliberate seat of the pants testing for my own curiosity as I rarely drive in 5th unless I'm airing it out on a (not very plentiful down here) stretch of open road.