I've been talking about driveline loss amongst internet 'experts'.

Everyone and their brother has seen the 'Internet Standards' of automatic
and manual transmission loss for stock Fbody.

I believe the numbers are 20% Automatic and 15% manual.

Some will argue that as the engine power increase, so will the loss through
the driveline.

This is where the buck stops for me.

Once you begin to increase engine power, the loss through the driveline should
remain constant given the same axle speeds, fluid temps, clearances, etc.

IE: A 400 HP motor does not lose 80 HP through the SAME driveline that
sucked 40 HP from a 200 HP engine.

A couple of years ago I had a "Negative Dyno" pull peformed. This is meant
to measure the loss from the output shaft of the transmission back to the tires.

How accurate is this test?

Here is my post about the negative dyno:
http://www.domestic-street-scenes.co...&p=41957#41957

 

The "negative dyno" is measuring mainly inertia losses. Think about it... on decel the ring and pinion are running on opposite sides of the tooth.... not representative of what the friction losses will be when they are running on the correct sides of the tooth, nor under the torque level capable of sustaining 400 - 600rpm/sec accel rate.

For a given acceleration rate, the inertia losses are more or less a "constant". But there are also frictional losses, and by definition, frictional losses will be the normal load X the coefficient of friction. Increase the torque transmitted by a gear tooth, or the normal force on the bearing, and the losses are roughly proportional to the torque (and hence the HP) being transmitted.

A bit of a simplification, but that is a fairly clear explanation of why when you increase torque (and in turn HP) you increase the losses on an "absolute" (not a "percentage") basis.

I took the time to measure my drivetrain losses at three different HP levels by running the engine on an engine dyno with full intake and exhaust, then running a chassis dyno immediately after installation in the chassis. Losses increased with HP:

NA: 486 flywheel HP - 61HP drivetrain = 425 rwHP (12.6% loss)
1-stage N2O: 633 flywheel HP - 78HP drivetrain = 555 rwHP (12.3% loss)
2-stage N2O: 762 flywheel HP - 92HP drivetrain = 670 rwHP (12.1% loss)

Drivetrain consisted of a steel flywheel Street Twin, totally "stock" T56, 3" chrome moly DS (19#), 3.73 Strange 12-bolt, 17x9.5" OZ Monte Carlos with 275/40-17 GY GS-C's.

You might want to try a "search" This topic has been discussed before.

 

Those are very interesting results.

I always thought drivetrain loss would be much less.

 

With a TH400 and non-locking, high stall convertor, measured losses were in excess of 21% at the 762HP level. I've seen results as high as 25%.

 

here is oure rwhp cheat http://home.koping.net/u3243a/Tavlin...8%20040903.jpg (the difference is beacuse belt slip)
The right one on this http://home.koping.net/u3243a/Tavling2004/DSC01937.JPG is the engine hp after the dyno have calculate transmision loss (messured on deacceleration)

16-17% loss true a 4l60e(locked converter) and a strange 12bolt.

 

Thanks everyone.

I did perform a search before posting, but I came up with anything but dyno
related posts.

negative dyno pull
reverse dyno pull
inverted dyno pull
http://web.camaross.com/forums/searc...earchid=373917

Obviously, "negative dyno" is the incorrect term. What is the proper term?

Fred,

I can understand that trying to accelerate an object by applying
more torque will create an increase in loss (time to RPM and interia).

That makes perfect sense.

What I would like to confirm is:

Maintaining a constant driveline RPM will not require more power.

You would be amazed of how many articles, or forum users swear that a more
powerful engine uses more power to maintain a constant driveline RPM.

 

It's not the rpm or the power available, it's the power being absorbed or the power required. If cruising at 60 mph requires X hp, climbing a grade at 60 mph requires more hp, so there are more losses due to friction in the driveline.

If you had a chassis dyno which could absorb all you engine's power and hold a constant speed (eddy current dyno), you could simulate climbing a steep hill at WOT and a constant speed. If you monitored rear axle lube temp you'd notice the extra heat generated by the higher power at a constant rpm.

Think drafting at Daytona where the second car in line might not be WOT because of less aero drag. His driveline is transmitting less hp than the leader so there are fewer losses. Rear axle temp is probably lower, as is trans temp.

 

^ Understood.

I still think my question is misunderstood however. I'll try a different angle.

My car has two engines. I can control the engine output using a toggle switch.

Toggle position A activates a 300 HP motor.
Toggle position B activates a 600 HP motor.

The car is currently maintaining a cruise speed of 55 MPH.

At moment 'x' in time, the driveline is eating 20 HP using motor A.

If I were to toggle my switch to activate motor B, does the driveline suddenly
need 40 HP to perform the exact same work?

I don't believe that is the case. I believe the amount of force to turn the assembly
remains constant (as long as the conditions are the same).

 

[QUOTE=Zero_to_69
If I were to toggle my switch to activate motor B, does the driveline suddenly
need 40 HP to perform the exact same work?
[/QUOTE]

i would think no, because regardless of the motor's peak HP capability, both motors are using the same amount of power to maintain that 55mph, because they are just cruising.
the drivetrain couldnt tell the difference between the 300 or 600 engine, UNTIL you tried to accelerate, right?

 

Zero, (may we call you Zero?)

To answer your question, NO, of course not.

If you divide your hp numbers by about 10 and make A an electric, you've basically described a hybrid, haven't you?

It's the power required that remains constant, BTW.

There you go again hanging out on those "other" boards and reading those questionable rags where some of the folks don't know squat about how the world works, let alone how a vehicle works.

FWIW, telling them they are wrong about something rarely causes a change of mind. It's the old DCMWF,MMMU syndrome.

 

You know what the funny thing is Jon (if I may call you Jon?),

Most of the people I'm debating with are quoting from this site, and even
quoting certain members.

The problem is, they are taking bits of the information and applying it incorrectly.

"Well Mr. God at CZ28.com said there was 15% loss in an M6, here's the post..."

It's my calling in life to patrol internet car forums and find the "questionable rags"

Just because I'm not an engineer, or pro engine builder, everything I attempt to convey is swept under the rug.

On the other hand, if you (or someone of your status) was to debate the subject,
there would be no questions asked.

Having said that, I'm not implying that I rank anywhere near the members of
this forum; I'm simply stating, it's not always what you know...rather how
cool your signature photos are.

Here's another example:

A blower on a top fuel motor is said to need 1000 HP to turn.

According to some, the average street motor doesn't make enough power to
spin the rotors.

Try to explain that +60 PSI boost at 12,000 RPM would be just one reason for
needing 1000 HP to achieve that sort of manifold pressure.

Even funnier is showing them pictures of techs cranking the rotors using a lever (by hand) during engine setup.

As always, thanks for everyone's input. No matter how simple my questions
come across, you all seem to slip in a few amazing points of interest.

Signing off until the next world debate,
Zero

 

Zero, yeah, call me anything you wish, except don't call me late for Happy Hour!

You have a better handle on things than a LOT of folks on the 'net and in the real world. Not to say you don't get on a tangeant once in a while.

Bret's (SStrokerAce) signature has a quote I like. It's not original with me, but people keep proving it to me on a daily basis.

Jon

 

i thought it was around 400hp to turn their blower?

that was on that "interesting top fuel dragster facts" someone posted awhile back.

 

Interesting topic.......... I haven’t played with it yet, but it’s my understanding Dynojet’s new software will compute parasitic driveline loss. Always wondered myself as you hear different numbers thrown about, but my feeling it's all academic as rwhp tells ya what ya really should be looking at.


In the middle of changing my combo and have some tuning coming up. Once on the dyno and tuned, I’ll play with the Dynojet software and see what it says and post it regarding driveline loss.

 

the thing is that different dynos types (and even the individual ones if they aren't callibrated) measure different amounts of power that can vary alot. then it goes into what gear you had the car in, and i've even heard the way you tie down the car.
the point is consistency, and while the parasitic loss prediction might make some feel better about themselves on the street, it means nothing on the tracks.