Technical Transmission horsepower losses

Curious if there are any definative percentage numbers on power loss of various transmissions. The internet is all over the place (as usual).

I was always taught that automatic transmissions have a lot of power loss when compared to manual transmissions, everything else equivalent.

I personally have replaced about 10 automatics with sticks over the course of my lifetime of playing with cars. I have no dyno, so results are seat of the pants only.

Testing that I did was: (1) run a 1000 miles with the auto and keep fuel records, (2) run three timed zero to 70 speed runs, and average the results. Then the transmission change and repeat the tests. My findings gave 15 to 35 percent BETTER fuel economy with the sticks; and significantly lower 0 to 70 average times; although the 0-70 results were skewed by the fact I replaced the automatics (2 speed or 3 speed) with 4 speed manuals. All of the automatics I replaced were pre-1980.

Do any of you who might run transmission shops or specialize in transmission repair have any hard data?

Thanks.

Jon

 

Let' see if @justp***inthru has a feel for the subject of transmission horsepower loss.

 

These numbers were published years ago from Car Craft Magazine
Don't know if that's really accurate or not.
Larger/heavier transmissions, that have more rotating m*** like Turbo 400, C6, 727 etc are going to gobble more HP than lets say a Powerglide that has only 3 major internal parts.

Powerglide_____18 hp
TH-350________36 hp
TH-400________44 hp
Ford_C-6______55-60 hp
Ford_C-4______28 hp
Ford_FMX______25 hp
Chrysler_A904__25 hp
Chrysler_727___45hp

Bill

 

With an automatic, you have 2 @additional hp losses when comparedto a manual. #1 is torque converter slippage. In cruise mode, lockup eliminates that but otherwise, you are experiencing it. #2 is driving the pump. The pump is a constant drain on hp and the bigger the transmission and pump, the more the loss.

An additional considerations is that an automatic has more rotational m*** that must be accelerated. With a manual, you can use a light flywheel and clutch combo. A torque converter plus the drag of the de energized clutches, the planetaries, etc. would be noticed on acceleration.

This is a great simplification but you get the idea. I dont know if anyone has ever truly measured these but NHRA had separate cl***es for 4 speeds and automatic back in the day because automatic are inherently slower than a skillfully shifted manual.

 

Any statement that a particular transmission uses some number of HP is very misleading. It's a percentage...it's not a fixed number. For a simple example, my TH400 equipped truck idling in Park is making ZERO hp, it's doing no work. I put it in drive, don't touch the gas pedal, and the truck stars moving! So, there's no way it can be ****ing up 44 hp! Now, put it behind a 450 HP engine running full out, and 44 hp sounds reasonable. Put a TH350 behind a 350 HP engine, and 36 HP sounds reasonable. You really have to tell us ALL of the test conditions when you post stuff like this. Maybe they were all behind the same engine? I don't know.

Modern automatics are generally as good or better than manuals in the same modern car, both mileage and performance. The older ones, not so much.

And it can be a lot more fun to drive with a manual. It can also be a lot more of a PITA, if you're making a LOT of horsepower.

 

Jim is right. Part of it is rpm, part of it is load. It's complicated.

 

I participated in a fuel economy trial 20 years back with 2 ford falcons one with a c4 and one with a 3 speed . Same motors and same diff ratio and same tires. One got 18 and the other got 20 average 50/50 country roads and in town. The C4 was the winner around town and the 3 on the tree did better on the longer drives.
No idea of actual HP drain

 

I’d ***ume the numbers above would have come with dyno pulls, which would show peak loss between transmissions., can’t be a constant steady state loss.

 

Are you gettin like me???
Are you sure about the "20 years ago", as the last Falcon was produced 55 years ago?

Bill

 

When you look at numbers like that it can be deceiving. Some automatics had lock up converters which helped with overall mileage. Back in the mid to late sixties, the super stock Dodges and Plymouths that ran Torqueflites were faster than their 4 speed counterparts.

 

The last Ford Falcon was produced in 2016.

 

Not with a C4 or manual 3 speed transmission.

 

and there are still some American ones from the 1960s on the road, that you can take for a test drive, if you talk nice to the owner. He didn't say they were new cars 20 years ago.

 

That is NOT what you wrote.

 

Mine reliably gets 32MPG on the freeway, and ain't exactly slow.

 

I would ***ume the later transmissions would be better.

The best percentage on fuel economy I got came from swapping out a C-6 behind a 390 CID. Right at 40 percent improvement. Remember, that 40 percent is with testing, not a guess. As the stick was a 4-speed with a granny low, the performance numbers were difficult to measure. Normally do not use first gear in the truck.

Jon

 

On our ch***is dyno, superflow says a 20% loss for drive train with an automatic.

 

one way to know for sure that there's more loss in an automatic, is to notice that automatic transmissions have oil coolers, manuals don't.

More heat means less efficiency.

If you could measure the heat output, it might give you an indication of how much power is being lost.

 

I believe it’s pretty much accepted that a C6 has higher hp losses than a C4 same with a 727 vs 904 or th400 vs th350. The question is how much and at what speed or input level. I do believe an auto with a lock up converter will have close to if not the same economy as a manual. A lock up converter is directly coupled like a clutch set up the only difference would be any extra parasitic losses in the auto do to weight etc.
A fun project would be bolting up all the above mentioned autos to an engine with dyno data sheets and seeing what the actual loss is. Also compare to say a T10 or such.
Dan

 

Remember that in an automatic, you also have to run a pump to pressurize fluid, to keep the clutches engaged. That's a parasitic loss that a manual does not have.

Another advantage of the smaller lighter automatics vs. the big heavy ones, is the energy it takes to spin the heavy parts up to speed. Then there's the weight that you have to accelerate.

But to make up for it, a torque converter can multiply torque at the launch, putting more of the power to use, vs heating up a manual transmision clutch by slipping it.

 

Remember that in an automatic, you also have to run a pump to pressurize fluid, to keep the clutches engaged. That's a parasitic loss that a manual does not have.

An answer to this^^^ is really the answer to the original question. I’m sure the engineers that worked with said autos know the answer or at least have a good ballpark figure. Like you said above if we knew how much heat was generated we’d know how much extra power may be required. I do know that transmission coolers aren’t very big and not sure what the delta T is but I’m thinking the waste heat isn’t a big power number at least for stock or mild performance stuff.
Dan

 

All I know about transmissions hp costs when I comes to an automatic to any standard trans swap is if you take out an automatic and don’t touch the idle screw on the carb before starting when you start the car your idle will be 2 to 3000 rpm in neutral.
Costs in your wallet to have any automatic in the past for sure.

 

Here’s a very good article. Apples to oranges type test, but manual 4-sp Buick 455 had a 12% better loss in power in drive train vs Ford 347 with auto.

https://www.hotrod.com/how-to/ccrp-0311-drivetrain-power-loss

 

I love my Turbo 400's, but there's no doubt they **** power. I had one in a 2000 lb. roadster that I built, and I remember how hard it became to push around in my shop when I installed the driveshaft!

 

My 1974 Chevy 1T 454/T400 4 door dually got 7 mpg empty.
My 1974 GMC 1T with a 454/4-speed and a 20 ft steel bed got 10 mpg empty.
Both were 2 wheel drive.
That's my only 'real world' data.

 

New transmissions like the Ford 6R80 I am using in my build with a double overdrive and lightning fast shifts are more economical with fuel. I’m using one because my old arthritic knees can’t handle a clutch pedal anymore

 

I thought I made a mistake one time but then I realized I was wrong.

 

Put it in neutral.

 

My A now has a 6L80e.

 

Ahead of the Hemi?