c-6/302 compatability

[DonB]

A friend gave me a low mileage 3o2 from a 93 Ford Pick up. I had a local shop go thru it and build it to my specs. He went to dyno it and asked me what it came out of. He then told me that I would have to run a C-6 instead of the C-4 I have already. He was told that the crank was balanced differntly. Can anyone tell me what the differnce is? Also can anyone recommend a C-6 and torque converter. Thanks

[blykins]

A small block C6 should work fine. The only thing I can think of is that the flexplate you have is for a C6....I was looking through the Jegs catalog and they offer different flexplates for a C4 and a C6. Apparently your rotating assembly was balanced with this flexplate...

If this is the case, you can remove this flexplate, buy a C4 flexplate and have the one balanced to match the other.

How much hp is your engine putting out? That would dictate how stout the tranny needs to be.....and your cam specs and rearend ratio dictates what stall you should use on the torque converter.

[DonB]

Is there someone that specializes in flex plates/ balancing that you know of? I'm running just over 300 hp and 310 ft/lbs torque and I plan on upgrading the rear end to either 350or 373 rear gears. I'm getting a lot of differing opinions on which way to go. The engine builder suggested the 3.73's other guys that I've talked to told me that the 3.50's would be better on gas and for any distance travelling.

[Woodz428]

Crank balance is irrespective of the trans. a C6 will work fine, and a C4 will too, and if you want to get really funky a FMX. It is, as already stated, a flywheel difference. The 302s changed balance ,I believe, in the early to mid 80s, but it was not at all related to the trans.

[blykins]

Any machine shop that does balancing should be able to do this no problem....The guy that assembled the engine should be able to do it.

Your engine builder probably has acceleration in mind....the others you were referring to probably had economy and low rpms at speed in mind. This will just come down to your preference. I'm running a 3.70 9" Ford with a 4-speed Toploader.

You should be fine with the C4, especially if this is just a street car. You need to grab your cam specs (mainly duration) and maybe someone on here can help match a stall converter to your cam. I've never ran an auto.....I just know enough to be dangerous.

[blykins]

You know, if you're really at the point where you can juggle between trannies right now......I'd think about buying an AOD so that you can have an extra gear. The C4's and C6's are only 3 speeds.

[Woodz428]

I agree with Blykins, that extra gear is a nice advantage. The AOD is a little bulkier, so you might want to verify space available.

[lovehamr]

It sounds as though Don's engine builder is refering to the 28oz balance of the earlier flexplates (flywheel) as compared to the 50oz balance no doubt used in his 93 vintage engine. Does anyone know if there were any C4 trannys used after the intro of the 50oz balance? That question actually may be moot because any flexplate for the AOD, as blykins suggested, would most certainly be 50oz. And all of this talk is just skirting the issue of overkill with the C6. How much does your car weigh? How much HP? The C6 was intended for 3.5K# cars with over 350hp. In a Cobra type car this would be massive overkill with a tranny that probably weighs 100# more than the AOD. When was the last time someone saw a small block C6? As far as I know only 4V Cleveland cars would have had them, everything else would have come with the C4 or FMX (kind of a beefed up C4). Makes them kind of rare today anyway. All of these factors point to the AOD as the most logical, and the easiest, choice.

Steve

[Woodz428]

The Small Block C6 isn't all that rare. I have 2 and know where another 2 or 3 are. They came behind some engines in big cars and pick ups/vans. But ,as you said,it is a bit of overkill.

[DonB]

You Guys have given me a lot to think about. Does the harmonic balancer have anything to do with the weight of the flex plate weight? I thought that the guy that built the engine said that he had to swap the harmonic balancer because of the application that the engine was formerly in. (a '93 pick-up)

[blykins]

Yes. They need to match or the assembly will be out of balance. You could probably balance it with odd matched parts, but it would take a lot of weight.

Usually you match a 28 oz balancer with a 28oz flywheel....50 oz balancer with a 50 oz flywheel....etc...

[427sharpe]

Stick with a well built C4. The C6 is a heavier duty trans, but it also loses more power to parasitic loss than a C4. Most trans builders offer a reasonable C4 that will live very well behind the engine you describe. Almost any reputable builder has fixed the inherent C4 weaknesses (bands and clutch packs). Art Carr comes to mind immediately. The FMX would be my absolute last choice for a performance trans. I would be wary of any off the shelf AOD as well, because they were known to lose the OD (burned governor) if the plastic linkage clip fell out of adjustment.
If you want to go with an AOD for the overdrive, get one from a good performance builder. It will have all the HD goodies, as well as a shift kit to bring the rpm shift ranges up, and make the shifts crisper, with less slippage which will give a lot more life behind a performnce motor (or in a perfromance car). Makes the car a lot more fun to drive as well!

[trularin]

Balance the entire rotating mass.

Then, if automatic is in your plans, AOD with over-drive.

My $0.02

[DonB]

I appreciate the info. I hadn't considered an AOD because of all the bad press I'd heard(at least in regards to any kind of performance usage) . I guess I'm heading back to the engine builder to see what he bolted to the back of my 302. Thanks. Don