Tremec, toploader, G-Force or T-5 world class?

hi-tech cobra · #1 (**permalink**) 10-12-2006, 10:36 PM

I also posted this on Shop talk...

Which tranny should I get?

Car: Hi-Tech chassis/CSX fiberglass body
Engine: 347 eagle forged stroker
Chassis is already set up for toploader, I will need to notch the cross member if I go a different route.
I don't know the rear end ratio. Does anyone know what Hi-Tech used in their 9" set up?

I could go with a toploader and be done with it since the chassis is set up for it. Although I will probably regret not having the overdrive.
The T-5 world class is appealing because I'm not making crazy hp and it's less $ than a TKO. But will it hold up?
The Tremec TKO 600 would hold up, but I have heard it shifts like a bag of rocks.
The G-Force sounds good too. I just don't know much about it.

Three Peaks · #2 (**permalink**) 10-12-2006, 10:51 PM

The T5 GForce or Gordon Levy's Super Duty T5 would be a great choice behind that motor. It should shift as smooth as the T5's have a reputation for and hold up easily to your horsepower requirements, now or later when you decide to bump it up a bit.....

Excaliber · #3 (**permalink**) 10-12-2006, 11:02 PM

These cars are light so whatever 'rated horse power' a trans may have can easily be increased when used in a Cobra. Of course you CAN break anything if you try hard enough.

I would base MY choice on the ability to get the GEAR RATIOS I wanted in ALL the gears, including that all important 5th OD. Which, in my opinion, would HAVE to be a .8 If the trans does not offer a point 8 gear range, scratch that one off the list.

The fundamental problem with a T5 is the ultra low 1st and 2nd gear ranges. Wheel spin is a serious problem in Cobras and having to low a 1st gear is a VERY common complaint. Followed by having to high a 5th gear, typcially .6 in a T5 with an ultra low 1st gear!

I would like a five (or six) speed trans to have a 1st gear similiar to the same range used in a wide ratio top loader. This is ESPECIALLY true if you plan on a rear gear lower than 3.5, which is all ready borderline to low. Of course a lot of this depends on your engine, small blocks generally need a lower gear, for instance. Be sure to give some serious thought about TIRES to address the traction issue, big or small block.

Finally you HAVE to consider your cam profile when choosing your gear ratios, particular the final gear, 5th overdrive lets say. If your cruise rpm is around 1800-1900 due to a HIGH OD gear combined with a high rear gear BUT your cam likes 2000 or higher, you got a problem. Cruise rpm should fall well within range of where the cam likes to work. This will maximize mpg, mean quieter sidepipes at speed, be less wear and tear on the engine and make the driver a happier person!

Choose wisely my friend, it's tough to 'live with' gear ratios you really don't like. Your not likely to change them later, to much hassle, to much money, so you 'live with it', not a good plan.

Heres the gear ratios for a WIDE ratio top loader. Running these gears with a 3.5 or 3.3 would be just about perfect for most replicas. NOW, throw in a 5th gear OD at .8 and you've really got a nice setup! Of course, thats just my studied and well thought out opinion.

Wide: 2.78 1.93 1.36 1.0 Generally speaking, around 35-40 mph in 1st gear.
Close: 2.32 1.69 1.29 1.0 Generally speaking, around 55-60 mph in 1st gear.
You DON'T want 25 mph in 1st gear or you WILL fry the tires without mercy.

Quite a difference in the close ratio 1st gear, pretty high for a small block, even a big block without due consideration of tire size, rear gear and cam.

hi-tech cobra · #4 (**permalink**) 10-12-2006, 11:16 PM

Thanks for the info.

Is 5th gear in a T-5 .82? I had a big block cobra with a close ratio toploader...didn't like it. I had a 289 with a wide ratio TL, it was better, but the thing shifted like a bucket truck. I'm thinking a more modern trans will be nicer to live with. TKO600 seems to be the favorite flavor right now, but I'm hearing people complain about it. Does the TKO600 shift poorly? Have reliability probs?

Excaliber · #5 (**permalink**) 10-13-2006, 01:26 AM

I think most of the T5's are .6 OD. Yeah close ratio is an interesting trans, most do prefer the wide ratio for the lower 1st gear, especially with small blocks.

I run a close ratio and really like it. It's cool dropping into 2nd at 60 mph and going for it. My big block has a LOT of torque so the high gears are no problem.

Getting the clutch to release properly, a combination of free play, seat adjustment and pedal stroke makes a BIG difference on how easy or hard it is to shift.

trularin · #6 (**permalink**) 10-13-2006, 06:14 AM

I did a bit of "looking" before I changed from my toploader to the TKO600.

Dispite all of the advice you are going to get and there could be much more than this, what you really need to ask yourself is what do you intend for the car.

If you are going to be drivning around town taking on all comers, you may wish to play the gears out for a lower top end that screams to go 80.

Then again, if you are looking for touring about and will see upper speeds, you may elect to use gears that allow for milage ( especially in this day and age ) at cruising speeds without a loss of performance.

It all comes down to intention and design of the car, what are YOU going to do with the car.

There are threads that will tell you about what they did and how they feel about what they did.

May I recommend you determine your intent. There are a good number of cobras that are NOT drag cars and have very respectable topends. There are also a number of cars that are 7 sec street machines.

Just my $0.02

Jimi G · #7 (**permalink**) 10-13-2006, 08:41 AM

I am in agreement with all of you, the T5's low gear will make it hard not to spin the tires in first, and it does have a high 5th of .63, and not only that it is only rated for 330 ft. lbs of torque. It all depends on the rest of your drivetrain, the TKO600 with the .64 5th prefers a 3.73 rear gear or lower, or you might never use 5th gear. With the .82 5th in the TKO600 you have a little more room to play in the rear gearing, I have had customers with Cobra replicas install the .82 with such rear gears as 3.25, 3.55, 3.73, and even 3.90 and all were pleased with the results. What you need to determine is are you going to be cruising on the open road alot at higher speeds (65-80) or more city driving. Also you will need to see what type of RPM range your engine is set up for, that is a major point to consider, because you won't want to get to far out of your cam range otherwise you will be lugging the motor down. As for the shifting, the stock TKO shifters are made by Hurst, but there are several aftermarket companies out there with smooth and quick shifter replacement tops. As for reliability, we units out in veh. that have been there for over ten years, in fact I just spoke with a gentleman that has a TKO600 in a '23 T bucket that has over 1000 hp and a little over 925 ft. lbs. of torque, and it has been there for almost three years without one problem. Hope I could be of some assistance. jimig@standardtransmission.com

Three Peaks · #8 (**permalink**) 10-13-2006, 08:41 AM

The Gforce and Super Duty T5's can be built with the .82 5th gear set up. I agree you need to determine how you will use your car before deciding on at least the gearing. You'll have to live with your choice for quite awhile and you don't want to be changing trannies to see which one works better.

trularin · #9 (**permalink**) 10-13-2006, 09:04 AM

A major point in my first post was the fact that I did make the change. My original design of the car was for a T56, but went with the toploader to spend more on a great paint job. Hence, I changed the intent of the car by changing the transmission.

It was great around town and short trips on the freeway, but cranking around 5000 RPM to go 70 for a long time takes it's toll. So, I went in between on the trans swap and decided on the .64 OD gear TKO600.

Big difference in milage and drivability for long distances.

Thanks again to JimiG for his help.

hi-tech cobra · #10 (**permalink**) 10-13-2006, 11:34 AM

My purpose for the car? Have fun! Drive it around town mostly, an occasional road race event. I don't intend this car to be a serious racer. As you can see from my engine choice (347) I'm not taking the big buck route-a new baby girl and private school tuition for my son helped make that choice for me.
What I want to do is get this car finished and drive it! I've had 2 toploader cobras, and thought both times I didn't like TL's. Maybe they were not set uo right? Does anyone have any experience with a David Key TL? How do they shift? Is it comparable to a T-5 or a TKO600?

What could I expect RPM's to be with this combo:
Toploader-wide ratio
Rear end: 3.54
Tires: 265/50r/15

or this combo:
TKO600-.62 OD
Rear end: 3.54
Tires: 265/50r/15

Three Peaks · #11 (**permalink**) 10-13-2006, 11:56 AM

PM or email me your email address and I can send you an excel based calculator that you can figure out your gear/RPM/speed ratios. You'll have to find out what your tire diameters are and the different gear ratios for the tranny's you want to check but it works great.

bsfx(at)aol.com

Chris Mulvihill · #12 (**permalink**) 10-13-2006, 12:12 PM

Just picked up my CSX yesterday w/a TKO600 .62 OD against a Shelby 427 putting out 523HP. Put about 100 miles on and very pleased w/my trans choice. I've driven Mustangs w/Toploaders and the TKO shifts fine. I also plan on mostly street use w/a few open track days. The Toploader is original as you know, but on the highway the 5th gear is a must have in my book.
My a 2003 Gordon Levy built FFR had a 302 w/a 5 speed and the 5 gear was great on the highway up to Road America (wouldn't every buy anything from Levy again thought).
Always heard good things from guys in my car club about David Keys.

Jimi G · #13 (**permalink**) 10-13-2006, 12:50 PM

If that is what you have planned for your Cobra than I would suggest going with the .82 5th gear in the TKO600. jimig@standardtransmission.com

hi-tech cobra · #14 (**permalink**) 10-13-2006, 01:20 PM

Jimi G,
Is that because you feel the 347 will bog in OD? Does the super duty t-5 have the same gearing as the TKO600?

Ant · #15 (**permalink**) 10-13-2006, 03:54 PM

I went through this saga, and basically couldnt find anything to totally suit my requirements, so I went to a new Jerico Five speed with ratios to suit, a bonus with this trans, or a G-force GF-5R race trans (not a T5 based G-force) is ratio selection, slick changing, low hp loss, and the Jerico has a magnesium case, the bellhousing and trans weigh approx 100Ibs!
I dont really recommend a race box for the street as both those trans really make the car a one driver vehicle and are expensive, plus my application uses a Nascar based engine which has 675bhp and 566ftIbs torque, so my idea was to do the job once......!

As $$$$$$$ can be a concern, and your engine size etc, a good super duty T5 would do but they can be just as expensive as a race box if you get a G-force gearset etc. I would shoot for a wide ratio Toploader and gear the car to suit, but if your car is a cruiser then a T5 might be the answer but dont be rough on it as they arent tough like the Toploader. There is another option that might be slicker changing Richmond make a nice T10 trans which I think is based on the Borg Warner T10 (original 289 trans) these are used in Nascar and allsorts they are 4 speed and if you get the HD version still with syncros they are a slick strong unit.

I dont want to bag a trans like the TKO-600 but they dont last in competiton, which I know for sure!!!! Have unusual ratio gaps, and if you read the CC posts have shifting issues, which hopefully Tremec are working on. I guess in the US the highways are a pain if you have a low geared car, and thats why the OD is so popular, as mentioned there is nothing worse than a high revving engine when cruising. I have a friend who has a ZF 5 speed in his small block Cobra, that may be another option to look at MB/BMW, some of the english supercars use the Tremec T56 trans to good effect but it is heavy.

If you wish look up Richmond Gear and their range of T10 stuff.
Richmond Super T10, P/N1304000070 S Ratio 2.43, 1.61, 1.23, 1.00, 2.35 rev 375 torque, and other gearsets available like the "YY Ratio" 2.88 first etc etc.

Good luck with the Transmission, I think this is the hardest decision with the mechanicals!

Jimi G · #16 (**permalink**) 10-13-2006, 04:26 PM

Hi-tech,

That is exactly what I think, a small block just dosen't have the torque to pull you through like a big block does. The super duty does not have the same gearing, 1st is lower geared and the ratio is a little different. I think the TKO600 with the .82 5th will best suit your driving needs.
jimig@standardtransmission.com

G.R. · #17 (**permalink**) 10-13-2006, 10:47 PM

It is David Kee...not Key

www.4speedtoploaders.com

Excaliber · #18 (**permalink**) 10-13-2006, 10:51 PM

What do you guys think is an appropriate 1st gear ratio with a 3.5 rear gear? Assuming small block with DECENT tires (NOT T/A's, which are a virtual joke when it comes to traction).

347 · #19 (**permalink**) 10-13-2006, 11:34 PM

I am running a 347(238@.050 solid cam, 650dp rpm air gap etc, 337rwhp) with a 3550 tremec (3.27 1st gear and .8 5th) with 4.1's in a 68 mustang coupe with 235/60/14 wheels. My engine does not not make **** loads of power compared to alot of other engines out there.

I went to the drags and all it did was spin 1st, 2nd and half of 3rd. Not a good combination for drag racing. I think its an excellent set up for the street.

It spins up quick and cruises at 2500rpms at 70mph.

In 4th with 4.1's at 50mph it feels and sound like its in third. But I cant have it all.

My box is notchy but its not really a car for a quiet sunday drive so it does not realy matter.

My vote the TKO 600