horsepower loss

[OLE69F100]

Is there a way to figure drivetrain loss? I have a 69' w/c6 and 9" with ? gears. I am wanting to have around 350rwhp. I am just in the beginning of a 390 rebuild so I thought this might be good info to know before selecting parts for the engine.

[71PA_Highboy]

Figure 20-25%. Then you will be safe.

More goes into it, like accessories, tranny type, 2wd/4wd and rear axle, but that will get you close...

hth,

eric

[71 LONG BED]

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

You may want to go with a manual trans...

[ladz]

Hey john where did you come up with those numbers ! I was under impression that the fmx was the largest hp eater .

[averagef250]

I have heard it time and time again that the TH400 is the worst of all of them. Something to do with how GM designed it in the 60's to actually purposefully waste power to protect the rest of the drivetrain behind a hot motor.

A manual tranny running synthetic has the least power loss.

[ladz]

I had that trans in a vega years ago the only way to get to work well i put a converter in it out of a 69 eldorado that had a 472 motor that tranny worked after that !

[Randy Beck]

I put my '69 on a chassis dyno 3 yrs ago in the heat of the summer and it dynoed @ 311 rwhp. The guy running the dyno told me that He would guesstimate 100 hp loss thru the drivetrain. The tranny, drive shaft, rear axle and heavy wheels all take away from the total HP number from the flywheel rating.
A small C4 tranny, alum. drive shaft, and alum wheels will reduce drive train loss and will give you more rwhp.

[ladz]

Did he say how much hp you can pick up by making that change to the drive train ?

[OLE69F100]

Thanks for all the replys Wow I don't think I can afford 350rwhp oh well mabye I can get close. Randy Beck what are the spec on your setup.

[ima71 trucks are older]

I have heard it time and time again that the TH400 is the worst of all of them. Something to do with how GM designed it in the 60's to actually purposefully waste power to protect the rest of the drivetrain behind a hot motor.

not really to protect the drivetrain but for a smooth 1st-2nd shift on land yachts. there are no bands in the th400, it uses overrunning clutches instead. Its also why they are excellent in high torque heavy vehicles. one more reason they take alot of power is the higher 1st and 2nd gear ratio vs the th350.

[71 LONG BED]

Hey john where did you come up with those numbers ! I was under impression that the fmx was the largest hp eater .

I wish I saved the whole post so I could give credit to the right guy, but I didn't. I saw it once on another forum (not FTE ) and saved it for reference. Apparently it was in Car Craft Magazine at one time and was quoted. I just saved the quote.