bhvrdr

I have had a few people contact me about this so I though i'd just make a post. No need for this to become an out of hand dyno post. Just wanted to post the method myself and many industry folks use to calculate your results back to crank power. This is important since most companies advertise in crank horsepower and indeed our cars are rated in crank horsepower. It's also important because dynos can vary by up to 20% from each other for the same car. If we used wheel numbers they would be incomparable.

1. Here is what we need to start out with to get a BEST ESTIMATE of how to convert our dyno numbers back to the industry standard of chp. We need to start out with the factory engine dynod crank hp numbers, the baseline car dyno numbers, and the modified car dyno numbers on the SAME DYNO and using the same car.

E.G. #1

Audi B6 A4

Crank 170chp and 166ctq

Baseline Dyno for E.G. #1

130whp and 145wtq.

Modified Dyno for E.G. #1

165whp and 230wtq


3. We need to calculate the drivetrain loss of THAT SPECIFIC DYNO. Remember, some dynos like the dyno dynamics can read as much as a 35% drivetrain loss for the Audi Quattro. On the other hand, there are some dynos that are reading as little as 12% for the Quattro. Obviously both of these dynos are reading the loss incorrectly but it doesn‼sup>TM</sup>t matter as long as we know how to calculate the loss of that SPECIFIC dyno on a car with a baseline run and a modified run. You can do it two ways. Either divide the whp by chp and use the inverse of the result or divide the chp by whp and use the "correction factor". The result will be exactly the same.

E.G. #1

130whp/170chp = .764 or 76.4% meaning 23.6% was lost to the drivetrain.

Or

170chp/130whp = 1.307 used as the "correction factor"

Here we see that the correction factor is not simply a "1" tacked to the front of the percentage of drivetrain loss. Often companies try and confuse the consumer here. A correction factor of 1.307 = 23.6% drivetrain loss.

Here is a simpler example to show how this is true….

Lets assume the stock car here is a 200chp and 200ctq car from the factory…

Now let's assume the car puts out 150hp and 150tq on the baseline dyno.

The math:

150whp/200chp = .75 or 75% meaning 25% was lost to the drivetrain. Ok we could have done that in our heads.

Now lets do the correction factor method:

200chp/150whp = 1.33 used as the "correction factor"

So here we see that 1.33 is equal to a 25% correction factor.

4. The same exact step for number 3 can be used to calculate the drivetrain loss of the dyno as applied to the torque numbers.

E.G. #1 Cont'd

145wtq/166ctq = .873 or 87.3% or 12.7% drivetrain loss

Or

166ctq/145wtq = 1.145 used as the "correction factor"

5. Now that we have our drivetrain loss calculated from the baseline dyno. We need to apply those drivetrain losses to the modified car's dyno results. So let's assume the example #1 car added a basic chip and injector package.

Remember…

The stock B6 A4 dynod 130whp and 145 wtq. We calculated a hp loss of 23.6% or a correction factor of 1.307 based on those numbers. We calculated a tq loss of 12.7% or 1.145 used as the correction factor.

Modified Dyno of E.G. #1

165whp and 230wtq

So not we apply the correction factor for both hp and torque using either of the methods we choose. We can use the percentage of loss method or the correction factor method.

For hp…

Using the percentage drivetrain loss method (23.6% drivetrain loss in this example):

165whp / .764 = 216chp

Using the "correction factor" method (1.307 in this example):

165whp * 1.307 = 216chp

Hey, it works. Neat.

Now, let's do it for tq…

Using the percentage drivetrain loss method (12.7% drivetrain loss in this example):

230wtq / .873 = 263ctq

Using the "correction factor" method (1.145 in this example):

230wtq * 1.145 = 263ctq

6. So there we have it. We have a stock car that makes 170chp and 166ctq. We received a baseline dyno of that car (baseline dyno was 130whp and 145wtq) and THAT DYNO lost 23.6% for the hp figures and 12.7% for the torque figures. We then went back to that same dyno and did our modified runs and received a dyno printout stated the car produced 165whp and 230wtq. We were able to ESTIMATE the best way we know possible that the car is making about 216chp and 263ctq after the chip and injectors.

Please note that all dynos lose power differently and comparing stock and modified runs from two different dynos is not possible.

Please also note that losses to dynos do not occur perfectly linearly (hence the usual difference between hp and torque correction numbers). Due to this fact it is not possible to be 100% accurate in applying the loss taken from the peak numbers of the baseline to the peak numbers of the modified since often the peaks will occur in different areas of the rev band once the car has been modified. For this reason, we can say that it is a very close estimate but not perfect. Unfortunately nothing is perfect. Not even a MAHA. Not even two engine dynos. There will always be variable that don‼sup>TM</sup>t get controlled for. We need to just make every attempt to control for as many as possible given time and financial constraints.

Cheers! Mike

chelskiSW6

wow, thats a lot of info, thanks for that, ill be doing a search for this post once i dyno

akula-ssh

And calculate correction factors for a few rpm points, which is especially important for a modded car that has a significantly differnt power/torque curve shape from stock?

the senator

i am so glad you are on this board. Thank you.

paul_858

if you don't dyno the car on the same day... here are the potentials...

Additional loss of power due to:
Alignment Changes
Tire Size/compound
Temperature
Fuel
Humidity
Additional wear in vehicle drivetrain

Then as bhvrdr stated, you have to remember that calculations are from peak values... which vary from setup to setup. If we had unlimited funds, we would all reference engine dyno results for analysis, and wheel values for bragging rights.

Tsle

Excellent post Mike, thanks for laying all of that out for all of us.

mcpath

Once you get your vag up and running I can shoot it over. Few months back he posted a awesome write up on logging. I carry a copy of it with my laptop.

bhvrdr

Thanks guys. Glad it is useful.

AggregatVier

Link!?!?

mcpath

I made myself a bible. Using your post and the ross tech m block pages.