There is no set number. It is a percentage of what horse power you make. The more you make the more horse power you loose. Even the percentages are not carved in stone because there are variables such as valve body, line pressure, clutch material. The biggest of the bunch is your choice of torque converter. The higher the stall speed the more it slips. The more it slips the greater the percentage or number of ponies that leave the flywheel and escape the corral heading for a greener pasture in the form of wasted heat (that is why you need a bigger tranny cooler to match up to your higher stall speed converter).


Larger Dave

 

Well okay. I'm okay with your information . I got onto this HP loss with different transmissions from this below link. scroll down a tad and there is a table listing approximate HP loss for each one ,Except the 700 R. So if there is nothing in stone what are they talking about? Will appreciate some one clearing this up 4 me. Am reading one thing and hearing another. Now am a tad confused . Thanks for any help here. Cornbread....


http://www.hotrodders.com/forum/transmission-information-30771.html

 

Larger Dave is 100% correct.

That thread that you posted up does have a lot of useful info in it but keep in mind he picked up every bit of that data from somewhere else.

In the case of the HP loss numbers, that thread did mention that he got the numbers from a Car Craft magazine but he left out any other details of the article. (like, how did they measure, etc)

I don't know the loss of the 700R tranny compared to others, but it would make some sense that it was more than a TH350, and probably between or a bit closer to the TH400 since I'd believe the 700R to have more parts internally than the TH350.


Sorry I don't have the hard data for you. I did find some hard data for the loss of a standard rear-end at some website of a Testing Institute place long ago. If no one chimes in, you could search for that kind of testing data.

 

For those hp-loss numbers to have any relevance, you need to know what amount of torque and at what rpm they were tested at.
..and was each transmission tested at exactly the same torque and rpm as each other, and what size converter and amount of slippage was factored in.
So, it gets very technical.
The chart has good trivial info however, but there's much more to the story.

Parasitic losses are a constant variable. What you lose in a Powerglide with your engine, with be different to what I lose in a Powerglide with mine.

 

Parasitic losses are a constant variable.

A constant variable?

 

const float *ploss;

(sorry, geek joke)

 

Fun thread. Thanks men.
I remember a press story announcing the 1966 Oldsmobile Toronodo. They claimed that by eliminating the drive shaft parasitic loss the car would save 100(!!!!!) horsepower. As a kid in high school and looking at that drive-chain, I vowed to not read that magazine again.

 

Isn't that like trying to nail down jello ?

 

I highly doubt any of the trans use even 18 HP for parasitic loss at steady rpm. Most of the losses will occur while accelerating the rotating mass, and then it will depend on how fast you accelerate it, how much it weighs, etc.

A powerglide, TH350, and TH400 share the same pump gears and run at almost the same pressures, so the HP consumed by the pump will be almost identical.

 

but,.....TH400 gears are heavier than the TH350 gears, right?

 

The pump gears are identical and interchangeable (except late model TH350C pump gears that are wider).

You are probably asking about the planetary geartrain. Yes it is almost exactly 10 lbs heavier in a TH400. However this doesn't cause any loss of HP at steady RPM. It would only consume HP while accelerating, and then the amount consumed would be almost entirely dependent on how quickly you accelerated it.

Stated another way,
a 12 second ride doesn't lose any measureable (by 1/4 mile ET) HP due to the difference in weight, a 10 second ride usually will start to show minor ET advantages to the Th350 (but at this point the TH400 is usually a better choice).

Also to keep in mind the difference in HP consumed is due to the additional weight AND the greater gear contact. The gear contact is only an issue while in 1st and 2nd gears. 3rd gear the planets are in direct.

 

I'm writing this down as fast as I can!
Did you guys see the story in this months Hotrod about the Fbomb and the drive line choices they made. The writer talks to people from TCI. They suggested and built a Power glide over a TH400. They said the 400 used something like 49 horsepower. I'll recheck, but the mag is in the bathroom. A guy thing.

 

I saw that, the guy from TCI is clueless.

 

Also, when you're got 1300hp, like the F-bomb, you really don't need that low 1st gear. ..and 'Glides are strong.
More so than worry about a measly few hp getting lost along the way.

 

Alright , Heck ,I like that and well put . You leave no stones unturned. :hurray:

 

there are many reasons for using a powerglide. in racing, it is mostly consistency, at marginal tracks when hotlaping your car in bracket racing or nhra super class the glide will give you a more consistant launch and et. that being said the glide is also lighter with less internals, so it does turn marginally easier and only shift once. to take advantage of this you need big power and a low gear with big tires, super gas style. for a normal street driven car the 350 turbo will always be quicker than the glide.

 

One thing; Yesterday, instead of cooking dinner, my brother taped me doing my very first burn-outs on the brand new, first time-ever slicks. Need more air. More practice today. First race tomorrow. This is sooooo much fun! Hope my neck holds up. Whiplash, you know. And I wasn't even wearing the helmet yet. Still lays lots of rubber. TH400 you know. And the slicks are short. (they measure 9.7" wide) At least I have overdrive. Whew

 

Guys,

Don't mean to take this in a little different direction but is it possible that the powerglide's most significant benefit is allowing the engine to remain in a peak hp rpm range for a longer period of time than a 3 speed auto? If this is true the HP loss/gain debate is not as significant.

Thanks,
Bill.B

 

It would seem to me that 3 speeds would allow you to arrive at the peak quicker and remain in the power peak area longer than 2 speeds.

 

I know that you believe you didn't understand what you thought he said but I'm not sure that you realize that what he said is not what he meant. Or something like that.

 

Well thank you everyone for the answers in regard to the 700R horsepower loss issue. Clearly stated that more information is needed . I appreciate the dialouge you wizzards had / have going on . The one reply among the discussion I remember the most. was about the power Glide . Big power big gears and big tires if I remember it correctly. Then something about a 350 TH is good enough. Thank You Again..... .Cornbread