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

[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