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Discussion Starter · #1 ·
I've always been told automatics usually cost you 20%-25% of your flywheen hp. How much parasitic loss is there with an FMX transmission? Anyone ever do an engine dyno and then a chassis dyno to see? Is parasitic loss just a constant % or does it change throughout the power band? Thanks in advance.
 

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I was told ~20HP for the FMX but I wonder if that is correct after a shift kit and new higher stall converter are installed. And I wonder if a set of 3.25 R&P gears will offset that effect. I noticed yesterday when I was shifting in manual the car took off like a spotted ape and actually spun the open geared rearend when I shifted into second. Either that or one of my belts squealed. LOL
 

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From a thread on Hotrodders forum below. I find it odd that the C6 is that much more than the FMX and C4 has more loss than the FMX



Just in case you're curious, power loss for various auto transmissions:
Please remember these are approximate values, and were provided by Car Craft Magazine.

Powerglide_____18 hp
TH-350________36 hp
TH-400________44 hp
Ford_C-6______55-60 hp
Ford_C-4______28 hp
Ford_FMX______25 hp
Chrysler_A904__25 hp
Chrysler_727___45 hp
 

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Discussion Starter · #6 ·
Really, thats it?!?! I dont think that 25hp sounds right...these cars must lose a ton of hp from the tranny to the rear wheel then; something like 40-50 hp.

A 69 Mustang with an FMX and 351w-4v would run something like 15.0 1/4 miles...say the car weighs 3600 lbs with the driver it would be making something like 210-220 rwhp for those times. Dang Bias Ply tires I guess ;) 25hp sounds good to me! Thanks guys.
 

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Discussion Starter · #7 ·
Those numbers vindicate the FMX as a pretty darn good transmission. Long live the FMX :drunkies:
 

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6t9mach1 said:
Dang Bias Ply tires I guess ;)
You got that right! I have a Hotrod article from the early 80s where they took an unrestored Hemi Roadrunnuer and an unrestored Buick GSX and put slicks on them. Back in the day, both cars were right about 13.5s on stock tires....with slicks they were hitting the 12.5 range :burnout:
 

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I have no idea. If it were done correctly, it would be an engine dyno and then a dyno hooked up to a short driveshaft (if that's possible). Subtract the two HP/TQ numbers and you have the parasitic loss. You have as much info as I have unfortunately.
 

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I'm just wondering because it was mentioned if it's constant throughout the rpm band, and I doubt it is, but.. I'd liek to see loss from idle and then up. I still have a hard time believing a 60's transmission only loses 25hp..
 

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Believe it or not, the FMX was the basis on the AOD trans design. They share very similar internals, so there must have been something good about them ;) They weigh a freakin ton though, the one downside. I doubt weight was a consideration in the tests.
 

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If you could get a lock up torque converter, that would sure cut the loss since it would be direct drive in top gear. I, too, have heard parasitic loss about 25HP, with some loss in gas mileage but not much, but that is hearsay; I have a T5 in my bucket.
 

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Actually they do not way a ton. The are just a bit more then an AOD. Remember most of the trans is aluminum.
 

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It still has the aluminum bell and tailshaft. I've been down this road before in past discussions, but the only data I've found with trans weights are below:

Transmission Weights
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AOD (without converter or fluid) - 150 lbs
AOD stock torque converter - 34 lbs
C4 (without converter or fluid) - 110 lbs
C4 torque converter - ? lbs
C6 (without converter or fluid) - 140 lbs
C6 torque converter - 30 lbs small block, 31 lbs big block
FMX (without torque converter, unknown fluid level) - 160 lbs
FMX torque converter - 32 lbs
Ford-o-Matic (pre-FMX), cast iron case - 228 lbs
 

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those numbers are correct as far as Drive train loss.

Remember its not the dead weight of the transmission that has anything to do with the loss of horsepower its, the internals.

A C6 inside has a lot more rotational mass then a FMX or a C4, but at thats because the C6 is more heavy duty.

Calculation of HP loss through a percentage isn't very accurate. if your losing 20% of 100HP why should the parasitic loss be even higher at 320HP it should remain about constant. so there is a big debate about DTL using percent calculation.

Those numbers are a very good starting point to calculate your DTL loss for the transmissions tested.
 

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I think it DOES remain consant, percentage wise. I don't think if you're losing 20% at 100hp, you're still only losing 20hp at 320hp. I think you are losing far more than that. It's not a mechanical (you know what I mean) coupling between the engine and the rear wheels.
 

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Discussion Starter · #20 ·
I just found this online...I thought that I would share it. Pretty interesting. Link
 
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