Technical Transmission horsepower losses

Had 2 f100s
Both with FEs. The one with the c6 got around 4 less mpg than the one with the manual

 

Man this thread intrigues me!
I don’t doubt gaining a couple thousand RPM by switching transmissions.
An interesting experiment would be to activate the AC idle solenoid with the AC unhooked and see what the RPM gain is. I believe an AC unit pulls 2 to 5 hp. If the RPM increases a like amount then we could reasonably ***ume the Auto draws 2 to 5 HP at idle.
Dan

 

Are lock up converters available for older transmissions?
Dan

 

I saw a car at a show this summer with a stock flathead, automatic and AC. I roughly calculated that he had maybe -10 HP at the rear wheels.

 

Hahaha, that´s a good one^ he probably had two buddies push him to the show

 

Neighbor put a c6 behind a flathead.
Lost so much hp it only moved backwards

 

Yes, and it has a AWD transfer case hanging off of the tail.

 

If you stay on the starter, it's a hybrid!

 

Older than what?

1979--1984 GM offered the TH350C. It had a lock up converter.

Other than that, no, but adapters are made to put newer transmissions on older engines.

 

Thanks, I know Chrysler 904s had lock up TCs in that era also, didn’t know if there would be a way to make a lock up TC work with out the corresponding transmission.
Dan

 

We need someone to build a multiple bolt pattern bell housing hooked to a large electric motor so each transmission could be run on a dyno with nothing but a drive shaft. Run each one through its gears up to a set rpm or speed, then run just the electric motor. It would be the only fair and accurate test of drag each one has. It would be an interesting test.

 

Powerglide and T400 are available with lock up converter, used in drag racing .

 

Back when I was kickin' **** and takin' names at the weekend quarter mile, the only legitimate "testing" was a freshly printed time slip. Everything else was ********.
I do recall that it was commonly believed that shedding 100 pounds from a vehicle could yield about a 10th of a second off the time. I forget how many car lengths a 10th was worth at 100mph through the lights. Those manuals were easily 100 pounds lighter than those autos. So even if 2 cars had identical HP, the lighter one had the edge.

 

The valve body played a part in 904s lock up circuit. The trans. case is machined for each specific valve body.

 

Don’t think Ive ever cruised in an old ride and said “dang this transmission sure is eating a lot of hp”

 

You might need to in order to pull a hill.

 

I'm sure this is true of you and many others. There are also people who want to find every little bit of giddyup possible.
Each to their own.

 

As far as being quicker. Back in my street racing days I could beat 383 4 speed road runners by 3 lengths in a quarter while 383 Automatic Roadrunners would normally beat me by three lengths. That was identical cars except for transmissions. There are more things involved than just power loss to the rear axle.

I don't argue the point that there is more power loss between crankshaft flange and front driveshaft yoke with and automatic than a manual though. Also that there is more power drain with the bigger heavier automatics rather than the smaller simpler ones.

 

Drag racing gravitated toward automatic transmissions. Probably not because they were slower.

 

An automatic would gain most times in racing. It took a lot of skill and coordination to speed shift a standard transmission fast & without miss shifts

 

No matter how fast you shift a standard four speed you always have the time you’re not applying power between shifts. With an automatic you don’t have that, you’re applying power the entire p***. I’ve seen enough side by side videos of automatic vs manual and you can see the manual car drop back at every gear change. Back in the early 60s the SS Mopars were faster with automatics than manual transmissions. However I don’t think it was that way with the Thunderbolts, quite a few of them were converted to four speeds they had a Lincoln automatic…
Now the C4, turbo 350 and the 904 are used behind big inch big blocks because of their efficiency. But you will pay big money for a C4 that can handle a 1000 hp.

 

The day before this thread started I fired up my old Buick and drove her out of the weeds. A 53 nailhead with a DynaFlow. Out on the road tromped on it and thought, man, wonder where all my horsepower is going?

 

Don't confuse hp loss with performance in an automatic trans. What I mean is the torque converter multiplies torque so you gain back some percentage (or more) of the loss of the pump and rotating parts. Also don't forget a manual trans also has some loss with rotating parts and flinging fluid around. Both trans have bearing friction. A high stall converter allows an engine to reach max torque transfer for longer period than a slipping clutch generating heat.

Overall I think it's easy to understand a larger automatic has more internal loss. But manual trans also has some loss, less than an automatic. But that loss isn't a direct proportion to performance. Likely the biggest effect of automatic vs manual is going to be found in steady state cruising conditions.

 

I think for a lot of us, the reality is, "How many more years will this bum knee push this pedal in?"

 

For me it’s drivability and the auto’s get driven more than the manuals. My wife won’t/can’t do 3 on the tree so if we take “old oily” I get to do all the driving. I have an equal mix of manuals and autos with the autos mostly C4’s and 1 700r4. The manuals are ford 2.77 and T5 and T170 and a few I have no idea what they are 4 speeds. Of the autos the only one thats confusing is the green dot. With the manuals the column shift is always difficult for just about anybody who has not driven one daily for a few years.

 

The car makers must have thoroughly tested their transmissions, producing graphs of power consumption vs. rpm vs. load. Strange that this information never seems to have leaked out.

 

Regarding any change in idle with a C4 transmission to T5 transmission swap behind a 351W, my idle only went up about 200 RPM with my swap. Stock converter on the C4, very healthy lopey engine (about 12 in/Hg vacuum at idle.

 

You are correct. This is the reason the Lenco was developed. Right?

 

It is and now they put a torque converter in front of the Lenco.

 

Good point. It would be interesting to see figures for different manual 'boxes.

But what is it in an automatic that eats power? Depending on the type of planetary, there might be between three and 12 times as many gear meshing instances per gear, and each of those suns, annuli, and planets will have its own shaft, bearings, perhaps oil seals, etc. So that's friction, fluid drag, etc. That is also what makes for many automatics' greater torque capacity. The torque capacity of any given iteration of an automatic is more likely to be determined by the holding torque of internal clutches and brakes than the strength of hard parts. That makes some of them relatively easy to beef up to a ludicrous amount.

So an automatic with relatively great performance potential, but kitted out with gentle I'm-not-really-driving-a-car-at-all clutching, will probably not be very energy efficient. That might be why heavily stoutened C4s appear to be gaining popularity over C6s in Ford circles.

Automatic transmission hydraulics are mostly but not entirely hydrostatic. Spool valves don't seal positively and will leak down over a period of time, but it is not unusual for VBs to have arrangements of check valves and relay valves to counteract that somewhat. So while it isn't quite accurate to say that the pump keeps clutches etc. pressurised, the pump does replenish pressure leaked down all the time. But that represents much less of a loss than the pressure required to engage the gear in the first place. If pressure leakage could be solved entirely the pump would spend most of the time pumping ATF around in circles through the regulator(s) against minimal resistance. Still, all that stuff has bearings etc. Point is, the pump works harder while shifting than the rest of the time.

I took a bit of a dive into that a while ago.

The biggest energy drain is a slipping unlocked torque converter. That is virtually the only reason automatic transmissions have ATF coolers at all. That is why the fluid outflow from the converter is typically direct to the cooler, and from the cooler to the pan, pump, and everything else. If a converter isn't slipping it might as well have no fluid circulation through it at all. And TCCs are a lot simpler than I thought they were! They don't have actual engage pistons but are kept engaged by ordinary operating hydraulic pressure inside the converter. To disengage the TCC the fluid flow is reversed to that the inflow is between the clutch frictions, moving them apart. That could potentially be done purely hydrostatically.

Converter slippage is simply hp converted into heat and radiated into the atmosphere. Torque multiplication is why early automatics typically had one ratio fewer than the manual alternative, but slippage is why it was accompanied by a slightly taller final drive ratio.