Tranny HP losses -- FWIW

Clay Thompson

New Member
This has been discussed and I ran across the following info in a totally unrelated websearch.

Just in case you're curious, power loss for various auto transmissions:

Powerglide 18 hp
TH350 36 hp
TH400 44 hp
Ford C6 55-60 hp
Ford C4 28 hp
Chrysler A904 25 hp
Chrysler 727 45 hp

Here's the source:

http://h-body.org/library/hbodyfaq/hbodyfaq-10.html

What do you think about the 200 4R, about the same, more or less than the PG?
 

chris718

Active Member
ithink they are close but it depends on what gear you are in .w/ a2004r in 2nd , third and fourth you must pull thru the 6 lo clutches and in 1st 2nd and third the 2 od clutches
.this is obviously increased if you use our 4 clutch od pack.apowerglide must pull thru the 5 or 8 lo clutches,and the 5 or 8 hi clutches in 1st gear and then the 5 or 8 lo clutches in 2nd.surface area of friction paper is more with a glide so it could be higher however tests have shown the friction materials when compared show different parasitic losses up to about 5500 rpm and then remain constant.now a2004r must rotate the hi drum against engine rotation in1st gear and then doesnt spin in second ,aglide must drive the hi drum with the engine increasing absorbtion of the hp available at the fly wheel .i guess its all dependent on what gear your in ,but at a cruise speed in final drive id say theyre just about equal.
 

chris718

Active Member
we tried to do atest on a dynojet but the car had to go to the bathroom and never recovered .will be getting to it soon and will post results
 

BuickV6

New Member
I believe it is more accurate to use a percentage. Is'nt the same tranny is going to lose more power behind a 500HP motor as oppossed to a 200HP motor?
 

chris718

Active Member
interesting question .look at it like this .a ten pound block that must be moved 10 feet requires a certain amount of energy to be created and consumed to transfer the 10 pound block 10 feet. if the amount of energy required to move the 10 pounds 10 feet is 10 horsepower and the power source creates 500 horsepower then 490 is left over for power transfer after absorbtion. if the amount of energy required to move the same 10 pound block 10 feet is 10 horsepower and the power source creates 600 horsepower then 590 is left over for power transfer after absorbtion .now although this seems logical to some and not to others i believe regardless of power created ,power consumed will be the same and expressing it as a percentage would only be useful when we want to know how much of a percentage FOR A SPECIFIC APPLICATION has been absorbed verses what is created .and this is useful to some extent .mechanically speaking ,and idea expessed simply allows it to be understood and accepted easier than the pschobabble i just typed .JUST KIDDING .i hope you have found this info useful.
 

Irid

New Member
It's not a straight power loss, i.e. "just 10HP" if you want to get technical. Frictional losses through the drivetrain increase under load, yaddah yaddah yaddah. But that's getting picky.

Most nascar techs I've dealt with throw around percentages, and they lose about 8% through their trannies. It's been cheaper recently to find power there than to make it with motor tricks, where they're really pushing (and cheating too ;-)) already.

Would be interesting to see someone engine dyno their car and then throw it on a dynojet chassis dyno.
 

The Radius Kid

Active Member
Originally posted by Irid
It's not a straight power loss, i.e. "just 10HP" if you want to get technical. Frictional losses through the drivetrain increase under load, yaddah yaddah yaddah. But that's getting picky.

Most nascar techs I've dealt with throw around percentages, and they lose about 8% through their trannies. It's been cheaper recently to find power there than to make it with motor tricks, where they're really pushing (and cheating too ;-)) already.

Would be interesting to see someone engine dyno their car and then throw it on a dynojet chassis dyno.
Percentage is the way to go when describing losses due to the transmission.
As the load goes up,so does the friction due to gear "sliding" and attendant trans fluid heat increase.
What also needs to be remembered,is that as the fluid heats up and the viscosity decreases,the friction across the hypoid of the teeth,increases as well.
This compounds the problem.
 

6PacktoGo

Moderator / Curmudgeon
FWIW.

Rotating mass has a least as much effect as friction.

The pump is a big factor in horsepower loss. More than you think.

So is the helical cut on the gears.

While it may be a very small factor heat effects of viscosity on fluid vs. friction on helical gears has not shown any real effects in racing automatics.

If I had about 3 hours, and it wouldn't waste the bandwidth, I'd go through all the work I did on reducing horsepower loss a few years ago. I spent nearly ten years working on automatics in record holding class cars.

Here are a few things to think about: In a non transbrake equipped PowerGlide for a class car (like a small block Super Stock car), I ran a low volume pump, a roller bearing between the pump and direct drum (the rest of a PowerGlide is already roller), an aluminum direct drum, an aluminum direct hub, straight cut planetaries, an aluminum planetary ring gear, four direct clutches, two reverse clutches, and a low pressure valve body. Eventually, I rifle drilled the output shaft.

We even had some transmissions that had small pieces of o-ring glued to the lugs of the steels to keep them off the clutches when not applied. Alto has been looking at making those for a year or so.

I built a 400 with straight cut gears and aluminum drums and reaction carrier, along with a low volume low pressure pump, a low pressure valve body (the valve body doesn't regulate pressure like a PowerGlide does, but had to be modified to work with lower pressures), along with a custom set of roller thrust bearings, and it was nearly as quick as a basic Glide with an aluminum direct drum. It was nearly as light too. It was within a couple hundredths in an A-B-A test in a 396 powered Super Stock Camaro.

Years ago, one of the advantages of a 200 was the fact that the stamped drums were lighter than the cast drums of other three speed boxes. With the advent of aluminum drums, that advantage was lost. There are still plenty of 200s in fast class cars.

In many class cars, we found that the RPM drop when using the super low gear sets in PowerGlides was not a major factor, as it just put the car back "on the converter" using some of the torque multiplication of a good converter to make up for a slight lack of gear. I had a bunch of cars running 2.08 and 2.18 low gear sets. I even had a 1.98 low gear set in my Super Gas Camaro.

The big thing to remember is that when you get into all the trick stuff in transmissions is that like anything else, nothing is free. You can spend $1K to get 0.05 ET reduction. You can also reduce the time between overhauls by a factor of 10 to make the same gain. A lot of that stuff is great for class cars under severe restrictions due to rules, where a couple hundredths is a huge advantage, and can give you the record. But in the case of fast street cars and drag cars running under open rules, most of it isn't worth it. Beyond getting the right box and the right converter, you won't find huge gains anywhere. But you can spend plenty of money and create plenty of work.
 

chris718

Active Member
the info i gave you was based on engine dyno and dynojet results and sean at dynojet was in disbelief at what steve brie ,chris kokkonis and the crew of rampage racing discovered on their chassis dyno call them .stick shifts are used in nascar and direct drive power transfer in a manual transmission cant be compared to an automatic transmission because of the torque multiplication of the fluid coupling verses the direct transfer of a dry clutch .as far as power losses thru thru the rpm range the same motor may produce a diferrent torquu curve because of transmission absorbtion when using different transmissions but it is barely recognizable .if you read several times what i wrote you may understand better what i am trying to present .the main topic is differences in power losses from a constant power source with non constant power absorbers .ie different transmissions . another thing to note is these results are based on direct drive in hi gear .in first and second gear the different weights of direct drums ,the unapplied friction disks that must be driven thru ,and the added inertia of a steel drum over a stamped steel drum proved to be overwhelming challenging hence the direct drive results .also power loss can be calculated by using the drive shaft as input as opposed to the engine giving very good power absorbtion numbers .
 

BuickV6

New Member
Dyno the tranny?

Chris, Alan, anyone

I always understood it to be like this: say you had a turbo engine that you engine dynoed at 245 net crank HP with accessories. Then say you dropped it in a GN with a 2004R and it lost 44.1 HP or 18% for a 200.9 WHP at peak in 3rd gear on the chassy dyno. Now lets say before you took it off the engine dyno on another run you cranked up the boost etc and it made 490 net crank HP. Likewise if you also crank the boost on the chassy dyno it should lose roughly 89HP or 18.+% for about 400 WHP on the chassy dyno or at least much closer than the same or constantish 44.1HP that it lost when the engine was making less power. Is this correct does this jive with anyones experience? Assuming this is true then a % for estimating tranny loss would generally be better than a fixed number. Also I don't know that 18% is the best number just a guestamate. :)
 

chris718

Active Member
CRANKING UP THE BOOST YOU WOULD STILL ONLY LOOSE THE 44.1 HPWR IN HI GEAR .THIS WAS ESTABLISHED ON A DYNOJET MACHINE .THE POWER REQUIRED TO DRIVE THE TRANSMISSION WOULD BE THE SAME .THEREFORE A PERCENTAGE WOULD GIVE YOU A FALSE NUMBER sorry bout the caps .
 

dynoman

Well-Known Member
When I use to dyno snowmobiles on my Dynojet track dyno ( chassis dyno for snowmobiles ) , you would get approximately 50% of the motor HP @ the track due to drive train losses . Every sled I dynoed , from 90hp fan cooled 2 strokes to 210+hp turbo 4 stroke sleds it was the same 50% loss a the track regardless of motor HP. And yes I did have sleds motor dynoed & then track dynoed ......... 50% loss .
 

Nigel

Active Member
I would say an unlocked torque converter would be a percentage of output, but increasing to some degree with HP as slip will increase. The rest of the tranny will be close to a fixed loss based on RPM. At some point though the increased torque will increase load and friction for a given RPM, I can't speculate on how much.
 
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