C6 trans behind a 302 block

[Harris]

I'm in the process of making some mechanical changes to my 66 JCF. A local builder tells me he has a C6 we can build to go in my car. I've never heard of this before, C4 yes-C6?
My engine will put out around 450-475 HP. Plan "B" would be a Tremec. Any comments?

Thanks,
Haris

[Randy Resetar]

I would go with the tremec. Automatic cobra's don't have a good resale value.
RR

[PSB]

A C-6 is a heavier duty transmission than a C-4. Go with the C-6. Or even better yet, go with a built AOD, then you get overdrive too.

Pete

[Sizzler]

a C6 is heavier duty, but also sucks up more energy from the engine during power transmission to the rear wheels (and weighs more). I'd get a built C4 or a built AOD. My opinion.

[Ron61]

Harris,

The C-4 any time. Four of the people here have automatics and three have the C-4s with light shift kits in them and one has the C-6. The guy with the C-6 has complained about all the weight since day one. The local drag racers are running buit C-4s in their drag cars because of the weight difference and they take anything the C-6 will. As stated above, if you are concerned about resale the automatic may be a little of a problem to get as much for.

Ron

[GREENSNAKE]

Hey Larry! I just pulled my c-6 out tonight Bought a Built C-4 The C-6 was fine but wanted a little more power Plus its lighter Get about xtra 35 hp by switching Good thing Bout Auto is that you Dont get tired as fast as a guy shifting gears all day plus I took mine down to the track ran consistant! kick ass drag set up! Lonny

[Excaliber]

I suppose some day when my knees give out or my leg "goes bum" on me I'll have to consider an automatic. Other than an "injury" it leaves me totally baffled why you would even consider an auto for a Cobra.

On that note, you can without a doubt damage a stock C4. At the very least it MUST have a shift kit and 2nd gear (was it clutch or band that drives 2nd, been so long I forget?) HAVE to be beefed up. It's "banging" second to many times that will lead to less than "crisp" shifts into 2nd over time. That is THE weakness of the C4. The "planetarys" (gears) are OK. An increase of "line pressure" and friction materials should do that trick.

Hmmm,,,,I wasn't aware that it was "easy" to bolt a C6 onto a 302, by the way!

Ernie

[GREENSNAKE]

The C-6 Came Stock in 1985 F-150 & 250 With 302 in 1985. Ford Made it Easy! (greensnake)

[aumoore]

Ford put a C-6 into some 1978 F100 trucks with 302's. My father still has his and he has wore out two motors but the tranny has never been touched. Close to 300K on the clock. Great for truck duty and if you have a bib block but I hear a built C-4 is better for drag racing.

[TheShadow]

GreenSnake

How do you get 35 HP more by using a C4. I only have past experience with the C6 and it never broke. Ed

[Excaliber]

,,,TheShadow,,,,good question!

I can see the weight thing, skeptical about hp gain that high. Drag racers are looking for EVERY advantage, not always the "best" way for reliabilty or strength. C6 is WAY tougher than C4, but C4 maybe OK built "right". Tough call what to do there.

Ernie

[Ron61]

Ernie,

I am not sure what they do to the C-4s but a cop I know runs one in his all out drag car with a 900+ horse motor and he has ran it for three years with no problems. I know he did have the whole insides worked on at a pretty good transmission shop. He said his times and speed have improved mostly to the less weight.

Ron

[Sizzler]

The following values are for illustration purposes only, though I’ve actually seen/heard them associated with the equipment:

C-6 25% loss between flexplate and rear wheels
C-4 15% loss
5.0L 350 horsepower at the flexplate

difference between C-6 and C-4 is 10%, or 35 HP for the 350 HP engine.

This is how you can lose 35 HP by using the C-6 instead of the C-4.

I’ve never actually dyno’ed an engine and then rear-wheel dyno’ed the exact same engine after installing a transmission, so I can’t verify the losses. This is a constant (shades of SB vs BB) point of discussion in benchracing rear-wheel dyno results…trying to back into what the engine is actually putting out HP-wise.

As for using C-4’s in drag racing. Yes, racers use them. They also rebuild them and/or examine them regularly. Drag racing is also a much different class of use than street driving. I’ve taken this position with oiling mods, and I also think it applies to transmissions. The C-4 can be built. Torque is the killer of transmissions. If you use a C-4 behind a high-torque, make sure it is built to withstand such treatment.

I’d still pick the C-4 for your situation. You’ll ‘gain’ effective HP at the rear wheels and reduce the weight of the vehicle. All good things.

[Harris]

Thanks to all who responded. I am a medically retired sheriff's criminal investigator. Three years ago a car ran into the back of my unit on the freeway. My left leg is 30% paralyzed. Thats one of the reasons I'm going with the C4 auto.
I love driving my Cobra-the automatic will make it even nicer.
Harris

[Tim Votaw]

Guess I'll weigh in with an opinion here. I have to use an automatic, too - lost leg in Vietnam.

After a lot of deliberation and research, I went with an AOD specially-built by Lentech out of Ontario, Canada. They built it to an 800 fwhp spec, including a lot of forged parts, solid shafts, extra kolene & kevlar clutches, etc. They built a valve body designed to allow me to decelerate the car in downshifting, such as desirable on a road course or a bit of spirited driving on backroads.

I haven't installed it yet - waiting on a new 427W from Performance Eng., then out comes the 408 and the Art Carr Extreme AOD, which is no slouch, either.

My point, I guess is that the AOD can be made to do double duty and live, whereas I'm told the C4 has to reach a point in its modifications where it no longer is fun or friendly on the street in order to kick butt on the strip. I don't profess to know much about C4's, so I defer to others, but I chose otherwise for the reasons stated above.

TimV

[PSB]

I also have an AOD from Lentech. I have their Street Terminator Plus, which is rated to 800HP.

Pete

[GREENSNAKE]

Hey Sizzzler ! Ty for Doing the Math for Shadow guy how to get 35hp (Greensnake)