Dynojet's correction factors

[BlackICE]

This link seems to imply that Dynojet's HP numbers have a built in correction factor to est. the power loss from the crankshaft to the rear wheels. So that what Dynojet gives as a SAE corrected HP number is more closely related to crankshaft HP rather than RWHP. This assertion seems consistent with the HP numbers often sited for a stock GT, whereby then numbers are close to, or exceed Fords spec 550hp at the crank. Also this site claims tuning on an inertial dyno is inferior to tuning on a load bearing dynos for real on the road performance.

This site seem to have an axe to grind with inertia dynos, Dynojet in particular. I don't know if true, or he is just trying to differentiate his services from others. Dynojets seem to by the most prevalent dynos in use.

Any opinions from the experts?

http://www.germanmotorcars.com/Dyno_load vs inertia_1.htm

 

[Fubar]

That seem very consistent with what I discovered when comparing a DynoJet run to a DynoDynamic run.

http://www.fordgtforum.com/forums/showthread.php?t=4980&highlight=Dyno+Dynamics

The final conclusion was that any single number you get from one of these machines is strictly for bragging. And bragging will get you nothing when you’re trying to push a 3400 pound car off the line.

For tuners, the only thing that really matters is the change from one pull to the next. For that purpose, either machine is fine.

 

[Ed Sims]

Ed's Dynojet results from Whipple

Why does the Whipple hp/torque not come on until after 3250 rpm? What are the 2 measurements for Whipple hp & torque? One is corrected?

Max power = 539.06 Max torque = 489.49 stock with Accufab T-body &
544.30 489.43 Ida exhaust
Max power = 707.02 Max torque = 650.27
727.75 658.56 Whipple 19 lb for 91 octane

I have a little less timing at WOT for open track driving (rather than 100% street use). Dustin Whipple did the tune at their shop in Fresno, CA.


Ed

 

[Black2003Cobra]

The expression for the air-density correction factor in that link is correct, and is used on both inertial and "loaded" dynos. You have to ask the dyno operator for which one (SAE, STD, uncorrected, etc.) you want them to use. (Or if it was done on a DynoJet and you have the run file, you can change the correction factor.) As far as a rear-wheel to flywheel correction factor built into their (DJ) software, I don't know. Perhaps that may be an option. I'd have to check the manual.

It is true that using a "loaded" dyno is better for tuning so that road conditions can be more accurately simulated. DJ does have versions that can add extra trim loads.

Ed - the slope in the one set of curves for under 3750 rpm is just because the operator didn't go WOT until 3750 rpm. (Looks like he just "rolled" into the throttle at the start of the pull, and then went WOT at 3750.) It's not a faulty blower or anything.