Technical Transmission horsepower losses

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.

 

Transmission dynamometers exist.

 

Is there any published data?
Dan

 

I was talking to one of the mechanics at Freddy Brown racing transmissions about two years ago. He said they don’t even rebuild manual race boxes because of the damage they sustain.

 

I am not sure that much of anyone besides a few people here concern themselves with our ancient tech.

Both of my vintage cars have modern transmissions. One a T56 and the other a 6L80E (built to 1,000hp spec).

 

Oh I have.

The Roto-hydramatic "Slim Jim" behind my 394 Olds was the worst transmission you could imagine. The only way I could describe it is if you had a transmission that was basically a garbage bag full of mol***es that could somehow shift 3 times. It choked the life out of the big torquey engine.

I wound up putting a Chevy 350/700R4 in it. People scoffed at the idea of swapping it with a smaller engine, with the same hp but substantially less torque. The current combo would eat the old 394/slim Jim for breakfast.

 

One measured data point for this discussion.

My avatar runs an N/A 327 Chev (Dart heads) and TH350 with a basic shift kit and 2500rpm stall convertor. It weighs 3726lb with the driver onboard. It is a grocery getter, parts chaser, tow car and gets flogged routinely at the local drags.

a) It was engine dyno'd at 396HP.
b) It was ch***is dyno'd at 246HP (39% driveline loss).
d) On the Great Black Dyno it can run in the 13.3's in the quarter. Typical best run time slip below.



As an aside, I would appreciate ****ysis of the time slip (other than my poor reaction time... was concentrating on launch). I don't know how to ****yse a timeslip properly, buy would love to learn to (any good references?). It rarely wheel spins (prepped track), and suspect it needs more convertor to get any quicker.

Edit: By "I don't know how to ****yse a timeslip properly" I mean I understand what the numbers are, can use an online calculator, but struggling to see where the problem is:
a) I know my reaction time of 0.435 seconds is abysmal. It's normally better, and should be pretty close to zero if I practiced enough. This does not effect ET on a timeslip though.
b) I have no idea if a 1.978 second 60' is good or not for the type of car I am running. Online calculator says it looks OK for a car my weight and flywheel HP (1/4 Mile ET Calculator), but if I use rear wheel HP then my times all look awesome.
c) I have no idea if a 5.636 second 330' is good or not for the type of car I am running.
d)I have no idea if a 8.626 second 1/8 mile is good or not for the type of car I am running. Online calculator says it looks OK.
e) I have no idea if a 11.2 second 1000' is good or not for the type of car I am running.
f) An ET of 13.398 and 102.49mph seems slow. Calculator says I should be doing 12.7 seconds@112mph.

Cheers,
Harv

 

Since its an all round car performing many tasks, I'd put an overdrive automatic in it and lower the rear gear a little if its not real low already. The lower first gear in the OD trans will help whether you change the rear or not........but you'll still have a good all around driver instead of a lot of slippage from a higher stall speed.

 

My bad - forgot to mention the rear is a 3.08:1 BW78 with a truetrac centre.

cheers,
Harv

 

Well no wonder it rarely wheel spins.

 

In high school I had an old Chevy pickup with a 327/m20 Muncie. Made the mistake of buying $20 in gas from Casey's and got like 7 gallons of water lol. Anyway after it refused to stay running let alone barely start I slammed it in second and cranked that poor starter to drive it the 2 miles to the vo tech building lol

 

The wildlife seems to have traction problems:
Just when you thought the drag strip at Eastern Creek Raceway couldn't... | TikTok

Cheers,
Harv

 

I had the exact same thing happen with my local Casey’s in July of this year. My daily driver would hardly run after I filled up, it didn’t help that I had been down to an eighth of a tank when I filled up.

 

I verified it was water in the gas years later. It never would start again until there was ice on the ground and snow on the hood. Then it'd start right up. Which is normally backwards for a holley carbed 327 owned by a 16 year old. Then whenever the snow and ice melted it'd go back to not starting. Happened that way multiple times before I just drained the tank and put fresh gas in. Didn't put two and two together till years later. Basically it would only run when all the water in the gas froze and floated to the top allowing what little gas there was to actually get to the engine lol

 

This seems odd, accepted belief is that the FMX uses more power than the C-4, and why you can buy C-4s beefed up to take north of 700 HP.

 

Mph is a little off. 13.30’s are normally around 104-106 mph. If you use slicks the your ET should come down a few tenths but the mph will probably be the same. Now the fellow beside you is the opposite. 11.77 @ 120.00 mph is way off. I run 11.00’s @119-120 mph.

 

Here's a dyno sheet from my 289' Mustang with a T5 transmission and a 3.55 limited-slip rear end.
You can clearly see the engine, red line, and wheel horsepower, blue line, and the power loss in, "P-Schlepp", is also shown.

All of this is in DIN hp, which is similar to US SAE net horsepower.
Regards, Harald

 

If you look at the NHRA Stock cl*** National Records, you'll find that the automatic cars are generally quicker than the stick cars. Modern torque converters are really good. For example:

K/S 11.53 113.30
K/SA 11.21 117.66
G/S 11.3 116.43
G/SA 10.6 122.98
Q/S 12.69 108.80
Q/SA 12.6 104.32

 

Pretty sure it's not just a simple percentage of loss, either. A TH400 behind a 1,000HP engine isn't eating several hundreds of HP in loss.

Side note: 727 clutchflite is pretty thrifty, once going. Its turning a pump and the rest of the guts are all spinning together as one, when in high gear. While a 4 speed would still be churning a cluster and the other speed gears on the main.

-rick

 

It’s all about the money you put in them, a lot of billet parts and roller bearings that are not available for the FMX but are for the C4…
I’ve had an AFX behind a 351 4V that held up for years, no problem with plenty of abuse.

 

What is the percentage for a standard?

 

I said HAD. A lot has changed. That was in the late 60's and early 70's, I think. Today's automatic transmission technology is different. Lots of technology development, plus you never lose power to the driveline.

 

The FMX is a stronger ******, but the question is what HP is used by what ******, don't think the FMX would use less.

 

15%. Those are there standard numbers, in reality they of course vary depending on transmission type.

 

I wonder how the use of 80W90 vs. ATF in a manual transmission changes this.
And how much difference in drag there is between the 1:1 gear ratio (high gear) and say second gear.
Although the cluster gear is turning in both, in high there is no power transmission through the cluster gear.