Interestingly enough, HPtuners logs engine torque on LS2/LS7 motors. I noticed this some time ago and started logging it a while back. I never really paid to much attention to this since the cars are on our dyno, so I have my HP and TQ reading right there. Today I'm playing around with a 06 Z06. On our Mustang MD-1100SE dyno, it made 431.8rwtq (horrible weather in chicagoland today, hot and humid), and yet the torque reading in the scan read 533lbs/tq. That's 101.2lbs/tq loss through the drivetrain, or 19%. Assuming that the torque reading in the scanner is accurate, it kind of ruins the 15-17% drivetrain loss that is currently accepted for manual transmissions.

 

I looked thru tons of dynos over the last year (comparing mods).....I found (average on C6s)... manual 12% loss......auto 17%.

 

If the numbers from GM are correct, I lost 16.5% in my A6. Some say 10% on M6, some 15%. I'm surprised there's not a calculator of sorts to give more accurate drivetrain losses with each individual tranny(A4,A6,M6).If the Z lost 19%, then the auto must be over 20%, right?

 

Gee, I wonder why they don't rate it at 533 lb/ft of torque then? Could it be that those numbers...

a) are not accurate - just some relative reference point

b) the readings are calibrated as a "gross" number, not taking into account losses of the alternator, power steering pump etc (like in the "old days".

c) both of the above.

It's hard to say the "15 - 17%" losses currently accepted are not valid when they are not based on the 533 you saw.

 

I would trust the Dyno. I don't believe the "Calculated" torque numbers are accurate since they are just an algorithym from ECU and sensor inputs. I know, on the cars I work on currently, the Laptop number is bogus..

 

Car had headers and Corsa catback. I never usually look at the calculated torque from the scan, the one time I did, I noticed a huge difference and thought it odd. I'll take my dyno readings over the calculated torque anyday.

 

What kinds of losses are you seeing for an A6?

 

I just ran my base '07 Z06 on a Dynojet and it pulled 445.0 HP. That calculates to a 11.88% loss of HP. Pretty darn close to 12% as mentioned earlier in this thread.

 

I did the same. Came up with a factor of .88(12%)Manual
.8475(15.25%) auto's (my $.02 worth )

 

My 07 MN6 dyno'd at 353.39 stock - about a 11.7% loss.

 

Assuming that the 400HP advertised by Chevrolet is accurate.

 

I used to log the same info on my WS6 and it was always interesting to see what torque the computer said the car made. I remember it showing something similar at around 100 or so difference to the wheels.

One thing in general not directed towards Mike, but people need to remember, not every drivetrain is the same on every car. Different amounts of friction, different types of fluids, placement of various pieces in the drivetrain and materials used all effect "drivetrain loss". You cannot use a general percentage to calculate flywheel power and be accurate.

 

I'd have to look at some old logs with the A6's. I don't remember when I started logging calculated torque. It should be interesting since there's no 1:1 drive ratio through the transmission.

One thing to remember as well is that I'm using a Mustang MD-1100SE loaded dyno. Same car (04 GTO M6) made 422rwhp on our dyno, made 458rwhp on a DynoJet two days later. That's an 8% difference right there. This can be attributed to Mustang Dyno's power absorption by adding resistance to the vehicle during the dyno pull. I have had two nearly identical builds, one in a C6, one in a GTO. Both were A4's with cam, headers and procharger, both had the same stall Vigilante TC. The C6 (according to our book values from Mustang) had a weight of 3375, made 535rwhp, and had a total resistance (PAU force) of 446lbs. The GTO had a book value of 4000lbs, made 485rwhp, and had a total resistance of 688lbs. Both cars had the same amount of boost, same injectors, same cam, same AFR, and the same amount of spark. As far as engines go, they are about a close to each other as you can get, but that extra 242lbs of resistance accounted for 50rwhp at the rear wheels.

Now if you're figuring you're seeing a 10%-12% drive train loss on a DynoJet, then it could be assumed that I would see a higher drive train loss on my dyno. Add 8% to the 10%-12% and I'd be between 18% and 20%. That 100lbs of torque loss between the scanner and the recorded chassis dyno is 19%, and that falls right in between the 18-20%. Now I understand that this is mostly assumption, and until we have accurate data of what the scanner says compared to what an engine dyno says compared to what a chassis dyno says, we can assume whatever we want. None the less, I think this is some good food for thought.

 

That is some very interesting information. So if I understand you correctly, for a manual 6 speed, you could loose up to 12% on a DynoJet and up to 19% on a Mustang. The A6 could end up being between 25% to 32% loss depending on the equipment used. Now I have to do more mods just to keep up with the loss ratio!!!

I am very curious now to see what your actual data for the A6 shows. This is pretty important information you are providing. I hope other Tuners contribute to this thread as well.

 

You are 100%correct on this. Don't forget "wear" as this makes a much more inefficient power transmission.
Rule of thumb: @ new,perfectly mated straight cut gears will reduce torque between 2 aligned shafts by 7%. Now, 2 helical cut gears changing direction (such as a rearend) will reduce about 11%. This is for perfectly mated, "machined as a set" gears. Worn gears will only escalate the reduction. You are also correct in oil being critical to efficiency. Ok, now I'll get off of my tribologist & mechanical engineering soapbox.

 

You aren't seeing a higher drivetrain loss from one dyno to another.
If it is a test of one particular vehicle...

Nothing about the drivetrain has changed!

It's just the way each dyno is set up to measure power.

I think people get way too concerned with estimated flywheel numbers.

All that matters is the power that actually makes it to the ground.

 

which a mustang loaded dyno provides... power your car is actually putting down to the ground cause its putting a load on... right???

 

If I understand your question correctly, then yes.

Any dyno provides a load, even an inertia dyno, like the typical dynojet.
It's just the difference in how each reads the output from the vehicle.

I look at it this way when it comes to drivetrain loss.

A stock c6 z06 rated at 505 flywheel hp, dynoes around 450 rwhp, for a drivetrain loss of 50 or so hp.

A stock c5 z06 rated at 405 flywheel hp, dynoes around 350rwhp, for a drivetrain loss of 50 or so hp.

Therefore, my estimate for a manual equipped vette is a loss of 50 or so hp thru the drivetrain.

Even if you increase the engine hp by turbos or nitrous, for example, the drivetrain loss remains the same.

Now, there are certainly instances where this may differ, say if the car gets a rear diff gear change, which changes the amount of torque produced at the rear wheels.

Also, an auto will potentially lose more torque to the wheels because of slip in the transmission/convertor.

Remember, a dyno measures torque at rpm.
HP is just a calculation derived from that torque.

 

If a stock 2002 Z06 with 405rwhp made 350rwhp on a DynoJet then it has a 13.5% drivetrain loss from the Crank to the rear wheels.

Same car made only 340rwhp on a Mustang Dyno, and shows a 17.1% loss from Crank to rear wheels.

If the drivetrain stayed the same, then which is the correct drivetrain loss?

As far as dyno loads, DynoJets have a constant load, basically the rotating mass of the drums, where Mustang dyno's are loaded by a computer controlled magnetic brake.

 

Get your a$$e$ off the dynos and go run your cars at the track!!!!!!! Enough math class already!!!