Power difference between transmissions

I know that stick transmissions sap less power to operate from an engine than an auto trans.
I wouldn't think the actual # of hp a given trans consumes would vary with a higher or lower HP engine.
(Just throwing up a number, don't know how accurate it is)
If for example a 727 eats up oh let's say 40hp pushing fluid, centrifugal force of the spinning clutch packs, planetaries etc... I'm guessing that it would be 40 hp whether behind a 100hp /6 or a 500 HP hemi, it would still consult that same 40 hp. Right?
Would a shift kit alter that number?
How bout a different stall speed converter?
How about a lockup (or not?) Converter?
How much more HP would a 727 consume vs say an a500 (early, non electronic)?
How much more than an 833 od?
Talking everything else the same with each variable listed.
Same chassis, same engine, same fuel system, same gear, same tires, same driver, same roads and driving conditions?
I have a d150 with a 727 and have an an a500 and an 833od that I "could" put in there. Given the current status of my project it wouldn't be much difference in cost or labor to go either way given what parts I have available at the moment.
I'm trying to decide which way to go. Planning on 3 season daily driver, mostly country roads, lots of open road between...
Truck is 2wd long bed and has a fresh, built up /6 and 3.23s in it. The 727 is it's original trans and is a lock up version.
I'd need an adapter as was used in 60s /6 applications when used with a 727 to run the a500, otherwise everything else I'd need for whichever option I have on hand.

The stick set up should give you the best mileage but the O.D. gear may not be needed much with the driving your planning on doing with the lack of power in direct gear and worse in O.D.
If you're after a lot better mileage I would look at a CTD 12 valve conversion with a manual tranny with O.D.

Don, I don't know if you remember that orange D-150 I had, but when I got it all tuned up and running right it would knock down 23-24 mpg in OD with the 833OD trans.

Unless you rollerize it a 727 is gonna take X amount of power no matter what you do.

Transmissions (and differentials) generally consume a percentage of the horsepower being transmitted through them, rather than a fixed amount like 40 HP.
There is a “brake-away” torque that you can measure. This is what it takes to get an input shaft to barely move from 0 rpm. It is a small fixed horsepower loss, and depends mostly on drag of oil seals and such.

The higher the gear reduction, the greater the percent of loss.
a 2.96 ratio consumes a lower percentage than 4.56 ratio

Straight cut gear teeth consume a lower percentage than beveled or helical gears, but straight cut makes more noise and can handle less peak power.

The “low hanging fruit” of automatic transmission loss was going from a simple torque converter to a lockup type.

Overdrive is a bit tricky,
Adding a set of overdrive gears INCREASES power lost to friction,
but shifting the engine to a lower rpm and raising intake manifold pressure has such a beneficial effect inside the gasoline engine that fuel economy of the vehicle improves.

A light loaded pickup traveling 70 mph with the typical 0.67 ratio overdrive and 3.55 ratio differential
would get a bit better fuel economy with
1.00 ratio transmission gear and differential ratio 2.37 (.67 x 3.55)
but would get worse fuel economy towing a rated weight heavy trailer
using its third gear ratio 1.3 with that 2.37 diff,
instead of 1.00 gear and 3.55 diff.

The 98% efficiency numbers of modern “automated manual transmissions” kind of stun me.
I wonder: is that just in 1:1 top gear at some low rpm? Best case advertising hype that a vehicle seldom runs near?

This is correct. The drive train takes a percentage of power to run. That’s why on a chassis dyno the power consumption number goes up with power increases. It’s not a fixed number.

Chassis dyno numbers get crapped on by many because they don’t understand how they work and how the power used to run the drive train is a percentage and not a fixed number.

And yeah I remember that orange truck, you've been here with it back then.
I like that D150 you have (had?) In your garage down south of here, the last time I was there.
it's much like what I'm working on here except yours looks in better shape than what I'm working on. Which is why I'm working on this one I have... To make it nice too.
Like today's cars they don't make trucks like they used to and those trucks were a whole lot better than newer ones ever will be

Go with A500 you won't be sorry! My power wagon has 3.55's/727 and you can't keep up with traffic with out doing 3K. I had a 90 d150 with a500 with the same gears and what a difference.

Remember the M body with the 2.4 rear gears, it had that crappy ratio working against it in all situations but steady state highway speeds, in which it squeaked out a bit more mpg, still got hit with the gas guzzler tax though. Whereas if it would have had an OD trans and 3.55 gears it would have done better around town and still could have got the same mpg on the highway, Don't hamper yourself with too tall a rear gear ratio.

What's in it at the moment for rear gear is what it came with from the factory. 3.21/3.23
I've had several vehicles with the 3 speed auto and 2.94, and wasn't that bad for all around daily driver.

I've also had a wrangler with 3.07s a 5 speed and a 4.0 inline 6, and 5th was all but useless below 60 or ao

Mileage isn't the biggest reason for these questions, or I wouldn't own all trucks and SUVs...
I'm staying with the /6 for the "different" factor, I've had other vehicles I've removed the /6 for something bigger before, I've also had /6 vehicles I've driven with that motor for years too. Keeping that engine because "nobody else" seemed to over the years. Out of curiosity I want to see for myself "what makes a /6 tick" (besides solid lifters haha) I've done some of the "upgrades" typically done with a V8 to it, just because.
I'm more interested in (with everything else in the vehicle combo staying the same) other ways I can get some more "get up and go" besides swapping the engine for something bigger. And I'm sure I'm not the only one here interested in how much different drivetrain components (besides the engine) take to run, vs a different choice.

Heck, on one of the sites I frequent (FABO I believe) there was someone else asking about added power draw that adding power steering to something that was originally manual steering equipped.
I don't remember the outcome of that thread, and really don't care. (Someone out there apparently does though)
I'm not deleting PS. But I am adding AC. Something else I've seen talked about.
And no I'm not asking about what I am to "compensate" for that. Not at all. More just basic "mechanical curiosity" than anything else.

It seems that manual transmissions make a more notable improvement in lower powered vehicles. This seems to be true for fuel economy, acceleration and the "fun to drive" factor.


Edit: Thanks to the guys who pointed out that automatics draw a percentage of power rather than a set amount. I did not know that!

Newer auto transmissions are a lot better than the old slushy 727.
The 727 rebuilt with torrington thrust bearing and moder TC is better and runs much cooler (so less waste)
I went through a lot of this searching and then got a good deal on an 8HP70 from a newish wrecked RAM - the design wastes much less power with ingenious reduction in spinning gears etc.
My concerns were freeway rpm reduction for mpg and noise (3300 down to 2400), and better acceleration.

https://4wdlife.com/ram/8hp70-transmission
"through intelligent engineering, modern materials, and electronic management system, the overall fuel economy is improved by 11% over old ZF 6HP units and 14% over manual transmissions."

I don't get the "percentage of power" thing. Don't make sense to me. You're not changing what parts weigh, (centrifugal force) or the fluid, it would seem it takes "x" quantity of power to run the trans. No matter what size engine is in front of it. More HP available, less percentage of the whole.

I asked what I did in the most general of terms, I'd think one 727 would eat up the same #of HP as the next, unless that "next" one was modified vs stock (rollerized, whatever)
Or one 904 vs another, or one 500, or one a833od vs another one just like it, etc etc.


But more specifically in my exact case whatever trans I run on this project will be run by a built up /6. I don't see something like that "8hp-whatever" coming close to a possibility.
If I decide the a500 is my trans of choice I'm gonna have to find a /6 to small block trans adapter as it is. The truck currently has it's original and working 727 in it. The only thing I have to do to that is find the leak(not the pan or the input or output shaft seal) and add a mild shift kit so I can stop the converter drain back situation it has. And drive the snot out of it from there.
But I just got an 833od with flywheel, bell housing, pedals, linkage and everything I'd need to swap that in except for a new, fresh clutch which I believe I may have in the attic. And I have an a500 here too, that worked when pulled, that I'd rebuild before I use it just because of age and past maintenance being an unknown.
But being a 500 is '904 based" it seems a downgrade vs a 727 in terms of durability. I don't have a 518 at present. I'd like to run something I have. If it's the 500 is definitely have to do some beefing up just for my own piece of mind.

If I'm gonna make a change from the 727 it's gonna be a change to the least power sucking option I have available and on hand.

A slant six will NEVER ruin an A500.

By all means use what you have - an electronic trans with an adapter ans controller will start at $3k

As far as "percentage of power", consider that the engine only makes ~20 gross HP idling down the street, you can't have negative net power, so loss is not fixed.
Also, gear oils heat up a lot proportional to power/RPM and the 727 thrust bearing makes a lot of heat and proportional to torque (gear thrust) - like 10% of the waste heat.
The 8HP** uses a very thin Lifeguard 8 fluid to reduce its viscosity heating as well.

And in pure physics, power is equal to units of heat per second: 745 watt, is equivalent to 745 joule per second == 1HP

I've killed a couple behind 3.9s and being a /6 is an inline and not a V6 like a 3.9, I figured that the /6 would have more torque especially with the long stroke... If I go a500 it WILL get overhauled, with heavy duty clutches and steels, billet servos with double sealing rings and a mild shift kit like I had to do to the one in my last V6 Dakota got when I had to go inside that one because of the 2-3 shift flare it had.

But I'm wanting to know (relatively at least?) How much power each of these tranny's will suck away from that /6 as compared to each other.
Again... Original to the truck... 727 lockup, then I have an a500 (hydraulic version, taken from a 91 318 Dakota) and a833 OD ... I have all here.//not looking for anything different than what I already have here, for that job.


And a place for each choice that doesn't wind up in the d150.
It wouldn't hurt me to put the a833od in my volare either ... That one will be a stick when finished no matter what. Though I was thinking of a different stick trans for that car, I have this one now. And those were "stock" in that series of car, too. My particular one is a long tail, if a 727 would fit so will the long tail 4 speed ... Another auto to stick conversion any way, so I can work with the different shifter mount location....

Given those 3 choices which would you put into a D150?

Please explain - “killed”.

Burned up

That’s not breaking the trans from power.

Most likely a leak, low fluid, misadjusted throttle pressure, lack of maintenance (misadjusted band/s), etc.

/6 wont “break” a 500.

727 with locking TC?
Rare as hens teeth!

The percentage is because you are acceleration a load. Think it through. It takes more power (a greater number because the percentage stays the same) so it’s not a fixed number but a fixed percentage. (a powerglide is about 19-19.5% and a TF is about 21%). That means that it robs the same PERCENTAGE of power no matter what. 21% of 500 hp is 105 hp and 21% of 1000 hp is 210 hp.

So the percentage stays the same but the actual power consumption number goes up because you are dealing with a percentage of how much hp it takes to drive a gear box.

Look at NHRA Pro Stock and Mountain Motor Pro Stock. One is 500 CID and about 1500ish hp. The other can be some really big CID, BUT the power doesn’t go up as a percentage of CID because friction losses are also a percentage.

So let’s say you are looking at a 500 CID engine and comparing it to a 700 CID engine. At 1500 hp, you get 3 HP/CID. And the 700 CID engine makes 1750 hp which is 2.5 HP/CID. Because the friction losses are a percentage of total hp, the bigger engine makes more hp but is less efficient (2.5 HP/CID rather than 3.0 HP/CID).

If you made the bigger engine even bigger, the flywheel hp would (should) go up but the HP/CID would go down.

i have two on the shelf, big block units from newyorkers.

My son still has one out of an 80 ramcharger that originally had a 360

i was originally going to use one of the lock up units in my humpback project as a kind of fourth gear, but i ended up with two A518's, one of which is a rebuilt unit, and a JW ultra-bell for a big block.
i will use the A518 and the adapter now, for the true fourth gear, and a "kind'a" filth gear with a high stall lock up [expensive] converter.

So, everyone on Moparts contribute $20 and buy a “transmission dynomometer” to test efficiency and power consumption?

https://powertestdyno.com/product/transmission-service-450e-series/

Or maybe give a “shout out” to trans shops that already own and operate units?

Nice
I have seen results from DIY dynos for moto and bike drivetrains that simply use an electric motor input with current meter and generator head on the output, calibrated with a solid shaft.
For a decent HP test one would need an engine dyno - test the engine direct, then with trans.

I would have figured theres a westech/Steve Brule type of person somewhere out there that has already run such tests and that there would be a published list out there "somewhere" that already exists with such info.

In the 80s when I went to a local community college in their automotive program they had a trans test machine, that could be used to test a transmission, usually after a rebuild. It had lotsa adapters for bellhousings and tq converters, I only ever saw it actually get used once in the time I was there, it had a 4 banger (1.6?) Toyota engine to power it, that I remember hearing was donated by a local wrecking yard to power it. It had a bank of pressure gauges that could monitor pressure at any of the pipe plug test ports but I don't think there was any "dyno" function on it to test power used by a given transmission

Are you saying that with no other changes to a car, other than stepping up to 1000 hp from 500 hp the transmission will require more power to move the car?

That’s because there is no trans “Dyno”. There are transmission test stands as you describe here.

A dynamometer measures output. Transmissions make no power.

I found a few references

https://www.researchgate.net/profil...L80-Six-Speed-Automatic-Transmission.pdf
http://spiff.rit.edu/classes/phys216/workshops/w10c/car_engine/efficiency.pdf
https://www.epa.gov/sites/default/files/2016-10/documents/2015-01-0589_0.pdf
http://dirpub.org/images/proceedings_pdf/DIR0517011.pdf

A Mopar trans 845RE/8HP45
https://www.epa.gov/sites/default/f...a-camry-ub80e-eight-speed-auto-trans.pdf

I have one (42RH) behind a 5.9 magnum with upgraded heads, 500+ lift roller, headers, RPM intake and headers. So far I have not broken it though it is fortified with upgraded parts.