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I don't really trust the FMX I have now behind my motor, and really need a looser converter badly, so I'm considering buying a C4 and building it up. The Desktop Dyno puts my C at 509 ft-lbs of torque at 3000 RPM and 476 HP at 5500 RPM, on the bottle. The FMX already slips a bit when it gets hot at takeoff, and I don't wanna end up stranded.

Firstly, what era C4 should I be looking for... I see different spline counts on different units, which years should I aim to hunt for.

Do the FMX and C4 share the same flywheel, yoke, crossmember, and driveshaft, or are they different? It will be ratchet shifted (Hurst Pro-Matic) so shifter linkages don't matter.

What needs to be done to a stock C4 to beef it up adequately to hold me? I want to run a 10" converter in it so my stalls in the low 3000 range, and would like to get a shift kit that makes it sorta a semi-automatic valve body like I have now (when you put in drive it does all 3 gears, but if you shift into lower gears it works like a manual shift body). I would honestly ('cause I'm broke) like to find a busted, tired C4 and build it myself (easy trannys, RIGHT?), any good books to check out?

And if you have a busted, tired C4 takin' up space, let me know... The only one I've found local was a 6 banger tranny, and, although free, don't think its proly up to the challange.
 

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If your FMX is already having trouble handling that horsepower..the C-4 will have a harder time..I would switch to a C-6 and be done with it
 

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The FMX, as sluggish as it is, is a BEAST of a tranny. If you are tearing that one up, you are not gonna go ANYWHERE with a C4. I would seriously consider a rebuild for the FMX, or opting for a C6... a C4 is just gonna get eaten alive.
 

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Jason,
If you really want the skinny on a C4 for your app, contact PrairieBronze....he's using the latest permutations...

You'll want the later unit (70-up) to get the larger 26 spline input...I'm still running the early 24 spline one in the race car...light weight and a mild engine get me by *G*

Teebone has a point...I'd suggest you compare the cost/benefits of the C4 vs the C6 since both will work in your application.

I would surmise x-members will be similar but mounts may be different and whether the driveshaft will work will depend on what year and vehicle trans you get. For your app, if the driveline is stock, I'd have it gone through and fitted correctly to the new trans.

This is the manual I used for trans theory in college...it covers the C6 a lot better than the C4 but does have info on both. It is more textbook than rebuilders guide. Do some searching on Amazon and some of the other Mustang forums for recommendations.

I have a number of C4's, mostly in pieces....kinda far from you anyhow..*G*...keep your eyes open, they're out there...also keep your eyes open for a small case C6...I have one case but it's bare (FE and 385 guts will fit)

10" converter should work fine with your combo...

Have fun!
 

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The mount is the same. I wouldn't use a C-4 behind that motor. If you're going to spend the money modifying a C-4 or C-6 to handle the load, why not beef up an AOD instead to get the extra gear?
 

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Going aganst the collective grain here, but (IMO) the C-4 is the way to go. Lighter, less rotating mass, more room underneath...
As Pat says, a 70 up C4 would be best, that unit takes the 164 tooth flywheel, durability won't be a problem. I suggest an automatic/manual valve body and an "H" servo and cover from a C-5. Changes necessary are transmission lines, front driveshaft yoke, flywheel, converter... Don't know about driveshaft length or selector rod. (Make sure you get a floor shift C-4)

(Very simple transmission, build it yourself!)
 
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