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

[RD]

well no one knows, its a mystery. 

question, why do you want to know?  does it really matter? 904's do not take as much to run as 727's.. how much, well I do not know.  sorry i could not answer that for you.

[bordin34]

So if a 727 can take 100hp to operate and you have a 74 318 with 150hp than it only get 50rwhp.

[RD]

So if a 727 can take 100hp to operate and you have a 74 318 with 150hp than it only get 50rwhp.

no, to use the 25% parasitic loss theory the equation would look like this:

150hp x .25 - 150 = 112.5 hp to the rear wheels

[bandit67]

RD, I can't really say why I want to know........my head is full of useless knowledge and I am always adding to it.  I my  younger days I spent alot of time , effort and money changing things to something  'better", that really wasn't for a certain application.  What I am saying is that for some low hp stock restorations that will be only street driven, built as driver, the 904 may be a better choice.  For my first adventure into the world of Mopars, I bought three Chargers, a 71,72 and 73. Still trying to decide as to how I wish to set each one up as they become road worthy..........and that is why I have found this site so invaluable. No one knows it all, but as a group, the info and help here is priceless.............I learn something new here everyday......thanks to all................J

[John_Kunkel]

I don't have the answer but it isn't a percentage of the available horsepower. At a given rpm the parasitic loss is going to be the same whether it's hooked to a /6 or a blown Hemi.

If the loss is in the 100 hp range as some suggest does that mean when a 100 hp engine is attached to a TF the car won't move?

[skyhawk61]

    In an article appearing in Mopar Muscle dated December of 2001, Steve Pilic, a former Detroit powertrain engineer and Dynotek Dynojet chassis dyno operator reported that (quote)" a Torqueflite street car shows 75% of its flywheel engine-dyno number at the rear wheels.  Some of this loss is through the drivetrain, and some has to do with the different correction factors relating to engine dyno versus chassis dyno."

    Mopar Muscle-December 2001, page 20.

    He didn't mention if the 904 and 727 were different, though I suspect the lighter rotating mass in the 904 would show a lesser amount.

[RD]

I don't have the answer but it isn't a percentage of the available horsepower. At a given rpm the parasitic loss is going to be the same whether it's hooked to a /6 or a blown Hemi.

If the loss is in the 100 hp range as some suggest does that mean when a 100 hp engine is attached to a TF the car won't move?

that is a good point...

now if we look at it from this perspective:

if a 600 hp motor is mated to a 727 and a 300 hp motor is mated to the same 727 which of the two would enable more HP to the wheels proportionately?

would you not think that the 600 hp motor would have an easier time at spinning the 727 than the 300hp motor?  and if so, would the ability of the 600 hp motor have a disproportionate lesser value of HP stolen from the transmission because of it would be able move the transmission internals with more ease due to this larger amount of HP?

so, theoretically, if a 727 would steal 15% of hp from a 300 hp motor, would not the percentage of hp lost in that same 727 be less when mated to a 600 hp motor because the engine has the ability to move the internal components with more ease?

i know this has nothing to do with the original question, but what do you all think?

[John_Kunkel]

     Some of this loss is through the drivetrain, and some has to do with the different correction factors relating to engine dyno versus chassis dyno.

This is a monumental issue and it's way over my head. On the Viper (manual trans only) forums they constantly refer to the "correction factor" as a reason for high/low chassis dyno readings.

Back to the original subject, I still don't think that the hp loss through the TF can be expressed in a fixed percentage or hp number; there are too many variables.

[Paul G]

Is the power consumed by the trans linear? Meaning does the trans consume the same amount of power at 2000 RPM as it would at 5500 RPM?

[RD]

Is the power consumed by the trans linear? Meaning does the trans consume the same amount of power at 2000 RPM as it would at 5500 RPM?

not to get too newtonian, but when mass is in motion it will want to stay in motion, so i believe the hp stolen is proportionately less at higher rpm fundamentally speaking, but other factors that may be involved are heat and fluid dynamics.

[d72hemi]

OK this is a bit of "apples vs. oranges", but the magazine "Muscle Mustangs & Fast Ford", (I can't get any Mopar mags where I am at, so I read what I can) did an article (Feb 07, pg 140) comparing a C4 to a Tremec 3550 (5 speed).  The MT made a larger flatter tq curve on the chassis dyno with 27 lb-ft more peak tq at 300 lb-ft. The HP was also linier, but it peaked at 290 12 HP less than the C4. The C4 was at 302 hp and 273 lb-ft of tq. Over all the Tremec was 2-3 tenth quicker and 4 MPH faster in the ¼ mile.

Over all I did not like the article, testing was done on 3 days in a month window, along with multiple suspension changes. I feel that the ¼ mile times should have been on the same day, preferably under controlled conditions such as on a "1/4 mile chassis dyno" (or what ever those are called) to lessen the variables. I also found the small dyno graph (nearly unreadable) annoying.


Ian

[andy74]

damn, you guys are making my brain hurt! ive been thinking of this all night

[John_Kunkel]

Is the power consumed by the trans linear? Meaning does the trans consume the same amount of power at 2000 RPM as it would at 5500 RPM?

It's hard to say. The pump is a constant displacement unit, the faster you turn it the higher the output and the higher the parasitic loss. Higher speed also means higher frictional losses and higher losses from windage but the flywheel effect from the converter and the internals will likely compensate for some or all of it.

If the transmission is in a lower gear you need to take into account the frictional loss and pumping loss from the geartrain but the gear reduction multiplies torque so it might be a tossup again. 

[Ghoste]

If the fluid is hot enough, is there an rpm point where the converter begins to slip more from shearing the fluid?

[JB400]

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.

Old as dirt thread, I know, but I wanted to correct this.  Given the example provided, the 400 hp engine would lose 25 hp. The 400 hp engine is twice as strong as the other engine, so it'd lose only half as much parasitic loss from the same drivetrain.

[1974dodgecharger]

I still say 30 to 35 percent loss with 727 tranny.

[BSB67]

I still say 30 to 35 percent loss with 727 tranny.

How much loss with a manual transmission?

[ChargerST]

Some food for though:

Horsepower is a function of rpm and torque - you can't say a tranny takes x amount of hp to turn. A 100 hp engine will still accelerate a car equipped with a 727 - although not very quickly or fast. It takes less hp to run the tranny at low rpm. As the rpm go up, you need more hp to accelerate further. The percentage loss seems correct to me as it will be measured at different rpm.

Let's say a 25% (100hp) loss for a 400hp engine was measured at 6000 rpm. The very same tranny could show a 50hp loss with a 200hp engine - but the rpm would only go let's say up to 4500. Relative loss would be the same but absolute loss is quite different - as are the rpm when measured.

Makes sense?

[John_Kunkel]

And, yet, some sources claim an average loss of 15% through the entire drivetrain.

[cdr]

And, yet, some sources claim an average loss of 15% through the entire drivetrain.

the Hellcat is around 13%

[flyinlow]

15% MT & 20% auto  are the numbers I have heard.

I will skip the water pump, alt. and PS. pump, most street cars have those so we have to pay that Piper.

MT loss: trans bearings, transferring torque from the input shaft to the output shaft thru angle cut gears , u joints running at less than straight angles, torque turning 90* thru hypoid gears that must slide teeth past each other and the rear axle bearing. Some fluid drag losses.  I would think in top gear at WOT the hypoid gears are the biggest drain.

AT loss: converter slippage , trans pump, bearings, u joint angles, hypoid gears, rear axle bearings and some fluid drag. The auto had one advantage in top gear the whole clutchpack-drum-planetary assembly spins as one big straight thru unit.  I would think its a toss up between the converter and the hypoid gears for biggest loss.  

Autos usually have coolers ,manuals don't. I think NASCAR rear axles have coolers.

35 % was mentioned . If you have a 500 HP (crank) engine ,at  peak HP the losses would be well over 100,000 watts of heat generated to powertrain loss.....So don't floor your 500HP car for long periods of time.

[1974dodgecharger]

I still say 30 to 35 percent loss with 727 tranny.

How much loss with a manual transmission?

I rebuilt my tranny, whole rear end, and I'm an amateur on the lowest scale.  My 383 day ode on engine stand at 500hp. My power to rear wheel is 383hp with my manual.  I say 25 percent and yeah I'm sure a better build can do 20 percent loss.  I saw guys claim 600hp with their 727s and only put down 300hp at bests and there is a YouTube video with a blown 440 with nearly 700hp put down 450hp to wheel......and I like to go to Dyno sessions a lot and saw roughly same results over and over with our classic  molars that's why I think a lot of folksy ONG like Dyno especially old classics results r always disappointed. 


I'm doing another Dyno session in 2 weeks to tune my methanol and nitrous together to see what I get and how much is gained each one and test my cut outs.

[BSB67]

I still say 30 to 35 percent loss with 727 tranny.

How much loss with a manual transmission?

I rebuilt my tranny, whole rear end, and I'm an amateur on the lowest scale.  My 383 day ode on engine stand at 500hp. My power to rear wheel is 383hp with my manual.  I say 25 percent and yeah I'm sure a better build can do 20 percent loss.  I saw guys claim 600hp with their 727s and only put down 300hp at bests and there is a YouTube video with a blown 440 with nearly 700hp put down 450hp to wheel......and I like to go to Dyno sessions a lot and saw roughly same results over and over with our classic  molars that's why I think a lot of folksy ONG like Dyno especially old classics results r always disappointed.  


I'm doing another Dyno session in 2 weeks to tune my methanol and nitrous together to see what I get and how much is gained each one and test my cut outs.

How much additional hp loss for the driveshaft, rear end, and axles and tires?

The car in my sig, what do you think the rear wheel hp is?  

Here is more info, if that helps:

http://508charger.yolasite.com/

[cdr]

I still say 30 to 35 percent loss with 727 tranny.

How much loss with a manual transmission?

I rebuilt my tranny, whole rear end, and I'm an amateur on the lowest scale.  My 383 day ode on engine stand at 500hp. My power to rear wheel is 383hp with my manual.  I say 25 percent and yeah I'm sure a better build can do 20 percent loss.  I saw guys claim 600hp with their 727s and only put down 300hp at bests and there is a YouTube video with a blown 440 with nearly 700hp put down 450hp to wheel......and I like to go to Dyno sessions a lot and saw roughly same results over and over with our classic  molars that's why I think a lot of folksy ONG like Dyno especially old classics results r always disappointed.  


I'm doing another Dyno session in 2 weeks to tune my methanol and nitrous together to see what I get and how much is gained each one and test my cut outs.

How much additional hp loss for the driveshaft, rear end, and axles and tires?

The car in my sig, what do you think the rear wheel hp is?  

Here is more info, if that helps:

http://508charger.yolasite.com/

oops #1

[68pplcharger]

I'm not sure if anyone has mentioned this yet, but this is simple physics. F=MA or force = mass times acceleration. i.e. the percentage loss is always the same no matter the horsepower. the faster you accelerate a mass( 727 gear set) the more power it takes because you are performing the work faster (horsepower= 550 foot pounds/ second). I won't go into the details any closer than this simple explanation. I can elaborate further if needed, but i think this covers the Cliffsnotes...  

25% loss is the general rule for any Automatic trans

[cdr]

tires on a chassis dyno can make a big difference , on my Motorcycle dyno a street tire designed for a cruiser, low speed tire, would dyno 5 hp less & 5 lb torque less than a high speed tire, so at 100 hp, 5 hp loss is a lot on a 500 lb motorcycle.  

[68pplcharger]

tires on a chassis dyno can make a big difference , on my Motorcycle dyno a street tire designed for a cruiser, low speed tire, would dyno 5 hp less & 5 lb torque less than a high speed tire, so at 100 hp, 5 hp loss is a lot on a 500 lb motorcycle.  

That is true because you can add or subtract rotating mass depending on the wheel/tire combo

[Kern Dog]

I wonder how difficult it would be to rig up a test for spinning a trans, drive shaft, axle and rear tires. ALL of this driven by some electric motor with the only goal to be the determination of the power required to get it all up to speed. THIS would highlight the exact amount of power loss any engine sees.

It would eliminate many variables. It seems that most transmissions would have similar numbers, same goes for drive shafts and axles. The one variable might be tire and wheel, since smaller and lighter tires/wheels would require less HP to spin.

[1974dodgecharger]

tires on a chassis dyno can make a big difference , on my Motorcycle dyno a street tire designed for a cruiser, low speed tire, would dyno 5 hp less & 5 lb torque less than a high speed tire, so at 100 hp, 5 hp loss is a lot on a 500 lb motorcycle.  

U r correct cdr.....the dyno operator. On my car always tell me if u want bigger numbers I would n3ed to ditch ky 20s in the rear......he said I probably have. 20hp loss....no big deal to me im not chasing the numbers purely. ..

[metcoll]

my 440 bored 30 over with six pack pistons, lunati 240/250 @50 520/547 cam 452 heads that were rebuilt mild porting standard valve rpm intake 750 dbl pump holley through headers which would should dyno 440-450 on engine dyno...we put it on a dynojet and dynode 330 @ the wheels...this is through a 727  with 4200 stall & 4.56 gears..

[Kern Dog]

My 440/493 with Edelbrock heads, 2" headers and a 292/509 cam was close to the 500/500 engine that the MOPAR dealers were selling at one time. MIne should have made 500 HP at the crank but only registered 369 at the wheel through a 727, an 8.85 with 4.10 gears and a 28" tire.

[BSB67]

tires on a chassis dyno can make a big difference , on my Motorcycle dyno a street tire designed for a cruiser, low speed tire, would dyno 5 hp less & 5 lb torque less than a high speed tire, so at 100 hp, 5 hp loss is a lot on a 500 lb motorcycle.  

U r correct cdr.....the dyno operator. On my car always tell me if u want bigger numbers I would n3ed to ditch ky 20s in the rear......he said I probably have. 20hp loss....no big deal to me im not chasing the numbers purely. ..

No estimate on my RWHP from my earlier  question?

[cdr]

oops #2   

[1974dodgecharger]

I still say 30 to 35 percent loss with 727 tranny.

How much loss with a manual transmission?

I rebuilt my tranny, whole rear end, and I'm an amateur on the lowest scale.  My 383 day ode on engine stand at 500hp. My power to rear wheel is 383hp with my manual.  I say 25 percent and yeah I'm sure a better build can do 20 percent loss.  I saw guys claim 600hp with their 727s and only put down 300hp at bests and there is a YouTube video with a blown 440 with nearly 700hp put down 450hp to wheel......and I like to go to Dyno sessions a lot and saw roughly same results over and over with our classic  molars that's why I think a lot of folksy ONG like Dyno especially old classics results r always disappointed.  


I'm doing another Dyno session in 2 weeks to tune my methanol and nitrous together to see what I get and how much is gained each one and test my cut outs.

How much additional hp loss for the driveshaft, rear end, and axles and tires?

The car in my sig, what do you think the rear wheel hp is?  

Here is more info, if that helps:

http://508charger.yolasite.com/

hard to say I like to estimate it as a whole with 727 and whole rear end etc...with a run of yours at 11.67 e.t.  with those 3.23 gears im sure you have more than 500HP....engine wise.

[440]

I'll take a Stab at BSB67's car and say about 430 - 450 RWHP?

[BSB67]

I still say 30 to 35 percent loss with 727 tranny.

How much loss with a manual transmission?

I rebuilt my tranny, whole rear end, and I'm an amateur on the lowest scale.  My 383 day ode on engine stand at 500hp. My power to rear wheel is 383hp with my manual.  I say 25 percent and yeah I'm sure a better build can do 20 percent loss.  I saw guys claim 600hp with their 727s and only put down 300hp at bests and there is a YouTube video with a blown 440 with nearly 700hp put down 450hp to wheel......and I like to go to Dyno sessions a lot and saw roughly same results over and over with our classic  molars that's why I think a lot of folksy ONG like Dyno especially old classics results r always disappointed.  


I'm doing another Dyno session in 2 weeks to tune my methanol and nitrous together to see what I get and how much is gained each one and test my cut outs.

How much additional hp loss for the driveshaft, rear end, and axles and tires?

The car in my sig, what do you think the rear wheel hp is?  

Here is more info, if that helps:

http://508charger.yolasite.com/

hard to say I like to estimate it as a whole with 727 and whole rear end etc...with a run of yours at 11.67 e.t.  with those 3.23 gears im sure you have more than 500HP....engine wise.

So I've gone back and re-read your posts (and many of the others) to see why you think 30 to 35%.  I really don't have any science or theory to add to this thread that has not been already been kicked around.  

Your last response is what made me go back to look at your other posts, as your last post shows that you are not that much of a student on this subject. Please don't take offense, as I think you have indeed made some good observations, but have come to the wrong conclusion.  It sounds like most of your info/observations come from observing chassis dyno results, probably at events?  Is this correct? If it is correct, my conclusion would be different than yours.  Instead of a 30 to 35% power loss, I suspect that people (owners) are wrong in what they believe is the actual engine hp output to begin with.  There are several possible reasons for this: 1) They are guessing at engine hp (magazines, buddy's stuff, someone told them, they figured....) 2) the engine dyno results were somewhere between happy, and very happy (pretty common),  3) there are other non-drivetrain parasitic losses going from the engine dyno to the car (water pumps, fans, power steering, 4) The exhaust systems are usually different, possibly way different between the engine dyno and chassis dyno, and finally, 5) the in-car engine tune-up is not right.   These can add up to large hp discrepancies that some explain away as drive train losses (way better than saying that my "500" hp motor actually makes 450 hp).   And all of this is assuming that both dynos are being corrected to the same standard conditions.

Before chassis dynos got so popular, people would actually run their cars at the track.  Because the car normally performed below expectations, just like on chassis dynos today, the excuse was "poor traction" (verses drive train loss).  Of course, mph is independent of et, and no matter how poor the traction, you can get fairly accurate hp info from the track mph.  Back then with track data, as today with chassis dyno data, people find excuses to explain the results, verses accepting the reality that their engine simply does not make the power they thought.

So here is my observation.  When I have good engine information, good engine dyno information, good engine chassis dyno information, and actual track data w/ atmospheric data, they usually align and show the hp loss due to the drive train is 17% to 23% on auto cars.  I'm sure there are cars outside this range, but I would say that these would be the exception.

[Volaredon]

1st post here. been wondering the same thing, found this forum via  a Google search to see how much power loss thru a 727 vs 904.
I  recognize some of you guys from FABO, the /6 forum, Moparts, etc at which I have posted for years.
My truck; 85 D150, "SLANT 6" (yeah I know) but it has a 727. 3.2 geared 8-1/4
I'm asking because I am tired of guys saying to "ditch that 727 and put a  904 in there".   a 727 oughtta be all but "unkillable" behind a slant. So I want to leave it there. it IS a truck, it will be mostly daily driver but sometimes pull a light popup camper or utility trailer with a garden tractor and a push mower or 2, ~30 miles at a  time..... (though my camp trips are 10x that far from home) I have a replacement slant in the machine shop as we speak waiting for teh "Tim Taylor... more power" treatment. Keeping the /6 "just because" most people wouldn't.  Unsure at the moment the extent I will build it up.... thinking of adding a draw thru home brew, junkyard parts sourced turbo setup.... that idea is still out for debate.  I have burnt up more 904s in daily driver use than I care to remember in plain ol' daily drivers, I have always had better service from 727s in general....
but if (as some say) it takes 100 hp to run a 727 then how does this thing accelerate (at all) and even pull itself at much more than a crawl? The stock slant only has about 100hp to begin with.  my new one will be hopefully about double that.
I have also heard various percentages of engine power, is the answer? so lets pick a number. 25% seems a commonly heard figure. So then a 727 robs 25 hp from my slant, where  it would consume 100 hp from a 400 hp big block? (assume for just a minute, that I could yank the slant and drop in a big block and bolt it up to this same trans, though we all know it can't happen) so chassis, tires, gear, trans and converter would all be the same  between the /6 and a BB. That does not seem logical either.  Each drum, planetary weighs the same no matter which engine is in there. It takes the same amount of HP and torque to overcome band friction and get things moving from a standstill. Right?  In this scenario, same TC so same amount of fluid being displaced and such so that should stay constant, right?  Aerodynamics the same, as we're still talking the same 85 D150 no matter which engine is in there.

I plan to retain the 727 and the 3.2 gears. Unfortunately I know of no A518 or 46RH that was cast with a slant 6 bellhousing. so "if" there were to be a trans swap down the road, it would be to something with an OD gear.... meaning probably a manual of some sort.  Otherwise the 727 stays.


Since this is my 1st post here, a little about me.  53 yo, from Kankakee IL, I work as a fleet mechanic for the miserable state of Illinois.
I had a Charger as my 1st car.. a '76 Charger SE (basically a Cordoba)   I tried in vain to buy my brother's '68 when he went to sell it... my favorite Charger is a toss up between that '68 and the '73-74s.  and have never owned anything besides a Mopar.  Hope I don't have to either.  Newest vehicle owned to date... (still have, its the wife's daily) an 01 Durango with a  360. Have never, and hope to never own a FWD anything.

[XH29N0G]

Volaredon, 

First off, someone else will know about the 727 vs 904.  I don't.  But there was one thing about your post that struck me and that was the 100hp loss (compared to a loss that is proportional to rotations).  My assumption is that (1) the loss for any given (constant) rotation rate (speed) should be the same regardless of engine, but the loss will (2) vary with rotational speed (3) might be different for different gears, and (4) vary a little bit with the rate at which the rotational speed increases during acceleration. 

Point 1 would mean you would be pretty near 0 HP loss at low RPM and is why you can move and point 3 is what lets you drive in 3rd gear without losing as much power. 

[BSB67]

As rpm and load go up, the power consumed by the transmission will go up too.  Is it linear?, I don't know.

Going from an engine dyno to a Mustang chassis dyno, mine lost 21%.

[cdr]

As rpm and load go up, the power consumed by the transmission will go up too.  Is it linear?, I don't know.

Going from an engine dyno to a Mustang chassis dyno, mine lost 21%.

Hey Russ, what all was on the engine for the Flywheel dyno, ? stock ex manifold, water pump, fan ,, ECT

[BSB67]

Good question. No fan, no alternator, minus full exhaust.

[c00nhunterjoe]

While i cannot give you a hp number, i can tell you that going from a traditional heavy duty 727 to a protrans, it is worth 2 tenths in the quarter mile on a 10 seconds car.