How much horsepower does a 727 take to operate..........

[bandit67]

Hi Guys, just wondering how much hp does a stock 727 take compared to a 904 and also a  A833. Anyone know......with GM, the 400 pulls about 42, the 350, about 35, and the two speed powerglide about 25.  Not sure about manuals..........would the later model Chrysler four speed autos be about the same...........J

[RD]

i believe I had seen this in the past, but the overall drivetrain (trans, driveshaft, rear axle) results in a 26% parasitic loss.

the 727 can become less of a parasite with lightened internals, rollerization and increased fluid flow techniques, so on that note, it matters on how you build your tranny.

[Ghoste]

I thought it was less than that?

[RD]

I thought it was less than that?

it may be, i did not mean to sound so definite in that first post.  I was trying to remember and that was the first number that popped in my head.  what did you believe it was?  I know it was not less than 15%.  maybe 15-20?  any idears?

[Ghoste]

No I can't recall.  I'm going through my piles of stuff because I'm certain I've read it someplace but I just can't find it now.  I thought it was closer to 10% but that must be off.
I do have a comparison chart that uses it's own efficiency rating system that places the 727 ahead of the Ford C4 and C6 and the GM TH 350 and 400.

[Mefirst]

To what I heard you will roughly loose about 100Hp, from the crank through the drive train to what is the HP output of the rear wheels..

/Tom

[Paul G]

I have always heard you will lose about 25% on an auto and a bit less with a manual trans. These figures are what GM guys go by. Thas all I know.

[Nacho-RT74]

These figures are what GM guys go by. Thas all I know.

Of course, thats because GMs are on that way

[Rolling_Thunder]

I have always heard you will lose about 25% on an auto and a bit less with a manual trans. These figures are what GM guys go by. Thas all I know.

thats what I have heard as well

[Ghoste]

Interesting.  Is that just parasitic loss in the trans itself or does that include the converter?

[RD]

Interesting.  Is that just parasitic loss in the trans itself or does that include the converter?

I believe the 25% figure comes from the complete driveline behind the engine.  i.e. tq 'verter back to the rear axle.

[Paul G]

It can get complicated if you think too much about it. Say your engine makes 200 HP. 25% loss would be 50 HP. Say you put an engine in the same car, same driveline that now makes 400 HP. Would the loss now be 100 HP? I dont think so. It is just a rule of thumb kind of thing.

[Ghoste]

So obviously converter slippage will make a huge difference in these guidelines as well.  Of course, in the context of a discussion with performance enthusiasts, most of us aren't going to have lock-up converters or even particularly efficient ones, but it does highlight the portion of the original question about modern OD tranny's.  They must be better than the 25% mark, no?

[bandit67]

Yes, the parentage factor is not what I was looking for.  There is a certain amount of horsepower it takes to operate a tranny. That is why GM had three autos and I assume Mopar just had two, 727 and 904. My 67 Camaro came with the 210 hp, 327, and two speed power glide. I also have a much heavier 67 Impala Super Sport  with the same drivetrain.  Seems like they with the lower hp cars, they put in the lower horsepower robbing trannys., unless you or the dealer ordered a different automatice.  The powerglide is smaller in size, weight and has a much lower internal rotating mass.  I just assume Mopar did the same with the 904.   I assume the 904 was standard on the base model 318 cars. Now, at what level of power and torque did they determine that the beefier 727 was needed? And how much more hp does it take than the 904.....10.....15.....20?   Somebody must have published the numbers somewhere..........love the input, thanks all....J

[Ghoste]

I don't think there is one answer really.  I suppose you could determine where they made the 904/727 choice by looking at the powertrain options that called for each.  No big blocks with the 904.  340's were 727.  What about 360?  They were mostly 904 weren't they?  Power loss would less with a 318 than a 360 with a 904 and higher stall speed converter so...

[RD]

there are some, i wont say many because i dont know the exact numbers of people, that are using 904 components in 727's transmission in order to achieve quicker times in drag racing directly because of the lower hp loss rate of the smaller 904 components.

I am not sure there has been an actual study (and if there has, i have not been privy to it) that identified the actual amount of hp needed (or taken) from the engine to operate a 727 or 904 transmission.

But, i do know of ways to facilitate a lower percentage of parasitic loss within these transmissions to ensure a higher HP output to the wheels.

[Ghoste]

If you ever get a chance to see A&A's display booth at a race or somewhere, they have some great setups where you can spin drums and planetaries that are stock and others with their rollerized, aluminum, lightened components.  Significant difference in rotating friction... and price!

[tan top]

To what I heard you will roughly loose about 100Hp, from the crank through the drive train to what is the HP output of the rear wheels..

/Tom

  thats what i have always believed , i know i read something along the lines of  a 727 soaking up as much as 120 horses  in stock form .

[Mefirst]

In my op. the only way you can really get the exact Hp loss through the drivetrain is to first dyno the engine, then do another roller dyno to get the rear wheel Hp...

Other is to use math.. Here are the formulas..

The ET method
This method uses the weight of the car and the time it took that car to travel 1330 feet (¼ mile).

The formula is: hp = weight / (ET / 5.825)3

The Trap-Speed method
This method uses the weight of the car and the speed at which the car completed the quarter-mile run.

The formula is: hp = weight * (speed / 234)3

**NOTE!! When you do the math using both these formulas you will get TWO different HP numbers! To what I hear, most use the Trap-Speed formula, not the ET.. which one of these formulas is the correct one, well thats an academic mathematical philosophical question I can not answer...

To what I can find on the internet there seems to be a common statement that the drive train loss is between 18-25%

I do not think there is an exact mathematical formula you can use to count the Hp loss through the drivetrain.. Reason is there are so many variables one must take into consideration cause of different ways to setup a drivetrain.. These variables are weight of parts, force needed to turn them, friction..etc..etc.. so the only way to get the exact Hp loss is to do the dyno runs.

/Tom

[Paul G]

So if I got this right a 904 being lighter and smaller will actually consume less HP than a bigger and stronger 727. But since the 904 is lighter it can be broken as HP goes up, where the 727 can handle more HP without breaking, it just consumes more power.

[RD]

So if I got this right a 904 being lighter and smaller will actually consume less HP than a bigger and stronger 727. But since the 904 is lighter it can be broken as HP goes up, where the 727 can handle more HP without breaking, it just consumes more power.

Paul, exactly!

That is why when the guys who run F.A.S.T. and such and need the big block 727 to run in that class will use 904 components to lighten the reciprocating mass within the transmission. Less mass equates to less HP needed to move those components.

The negative to this is that the 904 components have to be replaced more often (i.e. trans rebuilt) due to these exorbitant pressures placed on the smaller components.

More mass requires more HP to put in motion, more HP requirements mean more HP loss.

[Ghoste]

In fact, wasn't there a little scandal in Stock Eliminator NHRA racing a fwe years ago where they found the Ford guys were somehow putting 904 guts into their C4's? (or C6, whatever it was)

[RD]

In fact, wasn't there a little scandal in Stock Eliminator NHRA racing a fwe years ago where they found the Ford guys were somehow putting 904 guts into their C4's? (or C6, whatever it was)

for real?  I never knew that! wow... man, does anyone have a link or article on this?

[Ghoste]

I don't know.  I don't even recall where I got that from.  I read it or heard it as track gossip (pits at Norwalk maybe?).  It's one of those questions that's probably better asked at Moparts or Moparstyle or one of the other race focused forums.  It may be pure  caca, for all I know.

[bandit67]

Hmmmmm, I still do not buy the percentage factor because of Paul G comment: a drivetrain using 50 hp from a 200 hp motor  will not jump to 100 hp when a 400 hp motor is installled. Just ain't gonna happen.  A tranny, driveshaft and rear axle/ tires are gong to consume X amount of hp to push said car down the road at sixty miles a hour.  This hp is going to be about the same no matter what hp motor is installed.  Now , I understand  more or less torque effects the stall speed of a converter, but , my original question was how much hp did the stock, as produced , 727 require, as compared to the stock , factory built 904's take.  I know the factory Chrysler engineers must have know and surely this has been published some time...........J