Rules for 2013 - Crank power vs Dyno

[Chrispy]

Continue dyno discussion here:

This is NOT off topic. The rules specify the use of manufacturer/crankshaft horsepower and torque for Touring classes and dyno horsepower and torque for Super classes. I disagree and believe crankshaft results should be used for both (even if calculated) to allow ease of transition between Touring and Super classes. So we need to understand what the dyno results mean and how to perform a mathematical conversion to crank torque and horsepower. I have yet to hear anyone reveal (except my guess) how the dyno torque numbers are calculated.

That part is not off topic.

Dyno results are effectively crank power minus drivetrain loss and dyno manufacturer variance. Known dyno's can use a fixed multiplier to calculate crank power. Right now we are assuming 15% for all RWD results and 20% for all AWD vehicles, obviously that isn't perfect since there is a large variance between a Dynojet and a Dynodynamics. Dynojet reads roughly crank minus 13% and a Dynodyamics closer to crank minus 20% for a RWD car. The part that is known is that the dyno gives results that directly correlate to crank power, the part that is unknown is by exactly what percentage, and whether the results should be corrected for atmospheric conditions.

So here is your conversion formula:

Generic for either HP or torque
Crank power = wheel power * 1.15

The specific multiplier needs to be determined by dyno brand and configuration/calibration as indicated above.

The Super page doesn't necessarily need to use the same formulas as the touring page since they aren't being directly compared to touring results, however it would be fair to consider a dyno correction factor.

[blindsidefive0]

The authors hear this point loud and clear - different dynos yield different results. Part of this conversation went down the rat-hole of "how" those results are calculated - see Bruce/Alex's discussion of what exactly is being measured. Frankly, we care little about the mechanics and more about the practical results - dynojet and mustang dynos will give you different figures for the same engines.

Paddy is working on this for "version 1.1" - we hope to include in the rules different adjustments based on different dyno types.

It should be noted again that dyno sheets are not required. In the case of a protest, documentation for power figures would be helpful, but we are looking into data loggers that measure longitudinal G-forces to estimate power if needed. However, getting these dyno figures right will help folks estimate their true power in the case of engine swaps, engine re-classes, and super classing.

[Stynger]

So here is your conversion formula:

Generic for either HP or torque
Crank power = wheel power * 1.15

.

I was told by Nick Crank power = wheel power / .85

[Chrispy]

So here is your conversion formula:

Generic for either HP or torque
Crank power = wheel power * 1.15

.

I was told by Nick Crank power = wheel power / .85

Same thing, just the inverse.

[Stynger]

So here is your conversion formula:

Generic for either HP or torque
Crank power = wheel power * 1.15

.

I was told by Nick Crank power = wheel power / .85

Same thing, just the inverse.

Do the math and tell me it's the same.

[WillM]

Les is correct, and I'm sure Chris just had a brain fade.

Both of these cannot be true:

CP = WP/.85
and
WP = CP * 1.15

However, both of these can be true:

CP = WP/.85

WP = CP * .85

...and I believe that is the intent.

[Chrispy]

They are both approximations and are both approximately the same. Since 1/0.85 approximately equals 1.15.

The intent was to add or subtract 15%, so the true math is multiply by 1.15 or divide by 1/1.15 (0.8696).

assuming 15%

CP = WP * 1.15
WP = CP / 1.15

You can switch the multiplier for a divide if you have the inverse.

CP = WP / 0.869
WP = CP * 0.869

[TroyV]

Don't screw with 3PO.

[brucesallen]

And torque? I am pretty sure that the displayed chassis dyno torque is a calculated value of the engine shaft torque in lb-ft derived by calculating wheel horsepower * ( 5250/(engine RPM)) and thus, the displayed torque is also reduced by 15-20 percent over the true shaft torque.

I have a query in to one of the chassis dyno manufacturers. I hope they have an engineer on staff.

By the way ft-lb is a measure of WORK. Torque is measured in lb-ft (or in newton-meters in metric)

[agrabau]

Bruce do you know what a load cell is?

Also your statement above is incorrect.

Alex

[agrabau]

This post is from Steve Nichols, one of the owners of Dyno Dynamics. This will save you time sorting through emails from engineers.

http://forums.evolutionm.net/evo-engine ... amics.html

[agrabau]

And in the interest of this thread and providing factual information, dyno numbers of nearly all types can be fudged, changed, manipulated.. whatever you want.

Enter the wrong wheel speed and do the math. Enter falsely hot weather into the computer, see what happens. This is why I suggested shootout mode for Dyno Dynamics shops as it is a "locked" mode with no opportunity to change numbers.

Dyno Dymamics shops differ. Kaizen has cars making 30 more whp than our cars but I'd bet my life that they aren't faster on the road... Go figure. When we got our dyno we used it in the same manner as KTR did but other shops have bowed to social pressure and entered larger correction factors to make up for what starts as a lower-reading dyno. It's nothing to fault, just a different standard.

So, if you want to waste a bunch of time and google stuff, "Dyno Dynamics Correction factor" would be a good one. We almost never enter one above 1. This means actual output isn't multiplied. Some shops multiply by a correction factor of 1.2 which in a 300whp STI would be... wait for it... 60whp.

[Chrispy]

This post is from Steve Nichols, one of the owners of Dyno Dynamics. This will save you time sorting through emails from engineers.

http://forums.evolutionm.net/evo-engine ... amics.html

Thanks, the non-linear losses are important to note.

I presume that shootout mode locks the correction to 1 but still gives SAE weather correction?

[agrabau]

That is my assumption Chris. Matt knows for sure but is on his way home from Road Atlanta. I will ask him as soon as he gets back. Shootout mode is the standard in Australia where they run big dollar dyno competitions and require normalized readings.

[naschmitz]

By the way ft-lb is a measure of WORK. Torque is measured in lb-ft (or in newton-meters in metric)

Torque is a force. Work is force times distance.