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trans Gurus .. how much HP loss ...??

Discussion in 'The Hokey Ass Message Board' started by skipperman, Jun 29, 2006.

  1. skipperman
    Joined: Dec 24, 2002
    Posts: 1,837


    In a turbo 400,350,powerglide,700R-4.....or ANY others you have specs on ( ford..c-4,c-6, AOD,etc) .... what is the parasitic HP loss to turn the trans ?? I've heard as much as 75-80 HP for a 400 .......any body have specs ??

    thanks, jersey Skip
  2. Hebee
    Joined: Mar 15, 2006
    Posts: 41


    Try this website- it offers a good explanation! :D
  3. skipperman
    Joined: Dec 24, 2002
    Posts: 1,837


    hebee... thanks but it's not what I'm lookin' for ... I want to know HOW MUCH HP each trans uses in and of itself ....not the difference between first and high gear ..... I think a 350 uses about 40 and a 400 uses like 75....anybody know the answers ??

    thanks, jersey skip
  4. skipperman
    Joined: Dec 24, 2002
    Posts: 1,837


    C'mon guys ... somebody here HAS to know rhe answer......
    or where i can find it ...

    Thanks, jersey skip

  5. Never Die
    Joined: Apr 22, 2006
    Posts: 174

    Never Die

    If trans loss is measured in HP its not going to be an accurate figure IMHO, transmissions eat up a percentage of HP, not a set number... Bear in mind that HP isn't a measurable number, you don't feel or generate HP, its just a derived number thats based on torque and RPM. A tranny takes an amount of torque to turn it, so the amount of HP it robs changes as the RPMs do. If you go by a percentage of HP lost, the number will go up as the HP does, which is gonna be alot more realistic. Nothing takes X amount of HP to turn, it takes X amount of torque at Y RPMs, and then the HP can be calculated.

    I've only heard numbers for Ford trannys (all I've ever been concerned with) and recall something like 20% for C4 and 30% C6, with sticks being down around 15%, but take those with a grain of salt... I'd figure the TH350/400 difference would be about the same as the C4/6 spilt.
  6. Russco
    Joined: Nov 27, 2005
    Posts: 4,133

    from Central IL

    Im with Never Die its generally accepted that bigger autos IE th400 and c6 will take upwards of 25% or more and newer smaller more efficient ones around 20% there are too many variables to put an exact number of HP loss on a specific trans
    the same trans in a heavier car or on a motor that makes more hp will use more hp just from the slipping of the converter a bit more. Driving the pump, the gear mesh and converter slippage along with just the weight of all the internals have to be turned all cause parasitic hp loss.and the same goes for rear ends as well some are more efficient than others. Hope this helps
    Joined: Jun 3, 2005
    Posts: 8,115


    Through the many years of drag racing We've come up with the following...

    Turbo 400--45HP

    Turbo 350--35HP

    Powerglide- 22/25HP




    These are figures "aquired" over the years to help determine rear wheel HP before the widespread use of chassis dynos. I make no claims as to accuracy but it was pretty damn close when compared to the old "dream wheel" (power/speed calculator) vs a motor dyno sheet. I agree, there has to be some accurate data out there somewhere. I assume you did a general net search?

    Most good hipo trans shops are dyno testing the trans before delivery. I'd assume it's possible some of their sites may have what you're seeking?
    Nailhead A-V8 likes this.
  8. Rand Man
    Joined: Aug 23, 2004
    Posts: 3,582

    Rand Man

    Why do you want to know? If it's for drag racing, nothing lays the power down to the track like an automatic.
  9. squirrel
    Joined: Sep 23, 2004
    Posts: 47,360


    There's a lot to it, if you have a high HP big block and you'ure running a TH400 it could well be "losing" 75-80 hp in the trans. If you're only running a 75 hp 4 banger with the same trans, you'd probably "lose" 10-15 hp (with the engine wide open at the rpm of peak HP) in the same trans.

    Power loss in a transmission is a percentage, and the percentage is higher for some trannys.

    Also when the car is accelerating, you have to "spin up" the parts in the tranny, so if it has big heavy drums and gears then it will "lose" more power to inertia compared to a smaller tranny.

    Generally a big tranny like the 400, 727, or C6 will cost less money to build to withstand a certain power level than the smaller more efficient trannys. It's a trade off.
  10. Bruce Lancaster
    Joined: Oct 9, 2001
    Posts: 21,682

    Bruce Lancaster
    Member Emeritus

    Any numbers out there on semi-modern trans like 200R4 and 700R?
    I know detroit worked on these losses with improved seals and bearings and such when economy started to matter, and I'd think the lockup convertor would help too.
  11. squirrel
    Joined: Sep 23, 2004
    Posts: 47,360


    also the vane pumps in the newer trannys are supposed to have less loss, as the pump gets smaller when less pressure is needed, instead of using a normal pressure regulator valve

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