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Discussion Starter #1
Well, im considering some engine upgrades that should increase power on my already stout 400 thats coupled to the original FMX in my 75 ranchero.

FMX parts are harder to come by these days, and i think ill be near 500 possibly 500 + HP, and as much or more torque, at the crank after the upgrades to the engine.
Also, the upgrades should allow me to more safely run the nitrous kit (125 shot) sitting on my shelf. But that scares me a little because im looking at 11.05:1 comp ratio with the planned piston upgrade. So maybe not on the NOS. Thats a wait and see deal right now.

So ive decided to swap out the FMX for a C6, even though a while ago I said i wasnt interested in that swap. I dont think i would want to use a C4, because of the extra cost of an aftermarket big block bellhousing, the money for which could be used to improve a C6.

Ive heard tale that the C6 uses a lot more power for operation than the old FMX. The highest number ive heard is 25%!!!!! Can that be accurate?

Now, what, if anything, can be done to improve and decrease the power consumption of a C6? Do you folks think im on the right track? Should i re consider the C4 as a COST effective option?

I have naughty wet dreams of a 6 speed manual also;), but who doesnt...thats wayyy outa my ball park right now.
 

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I see your dilemma. If you have a max-dollar budget you can assign, we can look at several options that will get you the greatest improvements now and over time. BTW - the C6 indeed is very strong but a power hog. Actual numbers I've seen are not percentages, but test loads at WOT to 5500 without converter (a variable) where the C4 consumed a peak of 26hp and the C6 consumed 58hp. More than double and why they aren't used so much for racing. Heavy too. Percentage numbers are misleading as the power loss is not power dependent, so more engine HP does not mean more power loss through the trans - if you see what I mean.

David
 

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Discussion Starter #3
Thanks David. I'm not sure on my budget really. It am sure now that I dont want to loose an extra 25 ponies....might cost more to make that power back than to do a c4...

Let's say I want to do it cheap. The rig sees very few miles annually, and I only aspire to do tnt nights on occasion. I'll be wanting a decent stall also.

I have the ability to do most of my own work, but haven't tore down a trans since college, 8 years ago... Should I just stick with the FMX?

I keep ending up back at square 1 when I look at swaps...
 

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There are 5 obvious choices, and two are out (C6 and E4OD) as big, heavy and hungry. The 4R70W/AOD family is capable of great upgrades (and the 4R will handle your 500 hp virtually stock), they are out for converter, controller, and adapter costs and that you have low annual mileage that won't allow recovering costs by fuel savings with the OD. That leaves FMX and C4/C5.

Between those two, I would lean back to the C4, as upgrades to handle 500/500 will be less expensive and more available. If you go bonkers in the future, it can be upgraded even further to handle the added power, whereas the FMX pretty much caps out for support, and even if you can find parts they will be much more expensive. I think the added cost of the core and bell will be more than offset by the reduced cost and availability of the other parts and build support.

I am not saying all this to make a sale. However, if you are thinking of going C4, PM me. I can make you a good deal on a HD C4 core and BB bellhousing. The bigger point is I can meet you and save those shipping costs.

David
 

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Friend ran a hard core built C4 thern went to a hard core Powerglide car went a bit faster but like not worth the money faster. He then went with a fully rollerized C6 and picked up 4/10s in the quarter.
 

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the c4 takes about 25 hp to spin , the c6 takes about 55 hp to spin , the fmx takes about 28 hp to spin. the powerglide takes about 18 hp to spin.
 

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The FMX is pretty tough. If it's a street car only a good fresh FMX would serve ok
Use a good shift kits though..
A roller C6 would do you well. I keep seeing these figures thrown around about how much power C6's use but dont really believe them .. A nice tough streeter i honestly doubt you'd feel a lot of difference ..

For a roller C6 there are instructions posted ay 460ford
Rollerizing a C6 - 460 Ford Forum
C6 trans build for transbrake or manual valvebody - 460 Ford Forum
C-6 Transmission I.D. and rebuild questions.(maybe sticky?) - 460 Ford Forum

or some info here on some i've done

rebuilding a C6
 

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The FMX is pretty tough. If it's a street car only a good fresh FMX would serve ok
Use a good shift kits though..
A roller C6 would do you well. I keep seeing these figures thrown around about how much power C6's use but dont really believe them
theres a performance auto trans shop on the web that dyno tested all the popular autos. i got my figures from that site several years ago and wrote them down. at the time i couldnt find clutch pedals for my 68 t and was going to run an auto. i asked a friend that use to build racing automatics in the 1980's about those hp numbers. he said autos were tested long time ago and the turbo 400 & c6 eat a lot of hp. he said thats why the powerglide was so popular cause it ate the least amount of power. 4 speed manuals with 1:1 4th were tested and ate about 1 hp in high gear.
 

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Discussion Starter #9
Thanks for the info guys, good stuff and appriciated. I decided on the c4. It just costs less overall to end up suiting my needs, and not eating extra power.
 

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Discussion Starter #11
scrnic... Why speak of Efficiency and an Automatic Tranny in the same sentence? That's blaspheme!

Get a stick for efficiency and call it a day. That way the only thing using up power is the asphalt.
Well, efficency relative to a slush box...not ACTUAL efficiency lol... If i swap to a manual, its gonna be a six speed, and that aint in the cards right now. Unless of course you can userp PSIG's offer of the C-4, with a similar priced 6 speed manual and BB bellhousing. Other wise...im sticking with the slushy.
 

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Do to it what ever you can to reduce rotating mass and friction. You probably don't want a real loose converter so your stuck with a heavy converter that's made even heavier by being full of trans fluid. There may be some lightweight guts for the trans and you can definitely rollerize the C6.
 
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