Wow, brought back from the dead.

From the data I have seen over the years, a properly calibrated Mustang dyno that hasn't been altered by the owner is quite consistent with OTHER mustang dyno's. Dynojets are probably the MOST consistent shop-to-shop dyno I have ever seen, when compared to the other popular brands out there.

The biggest variance is with weather correction. SAE J1349 is the standard, STD J607 is outdated and shouldn't be used and can inflate the numbers. Even with the proper SAE weather correction being used, these numbers can vary from a few different things. A lot of shops have their electronic weather stations die and then they just use their local weather data to manually 'punch in' to the dyno computer. This can be a problem unless your shop is at zero feet above sea level.

Local weather barometric pressure already factors in for elevation. Thats why you will see baro values roughly the same at 5500' elevation cities as a city at sea level. The weather stations on the dyno's output ABSOLUTE barometric pressure which is a raw value and doesn't have the elevation correction factored in.

Another thing that can mess up weather corrected readings is the location of the weather station. If its mounted on a wall near the dyno and an exhaust tip is pointed directly at it, it will make the air temp readings go up a great deal and make the weather corrected values inaccurate.

We have tested our dyno with multiple vehicles that were JUST dyno'd on a dynojet with SAE corrections and they have always have been 13% higher than our mustang dyno, same as numerous other reputable Mustang dyno's around the country, with minimal variation.

I looked at the OP's first comparison and on the Mustang Dyno using SAE weather correction vs. the DJ without the weather correction. The DJ had all of the weather parameters on the bottom of the page so I did the calculations and the SAE weather correction value would have been 0.961. So this is what the closest A-B comparison would be:

Mustang: 286whp/299wtq
DJ (using last pull): 329whp/336wtq

multiplying the MD results by 1.13 (adding 13%) gets you in the overall ballpark of 323whp/337wtq. It's not an exact science but it generally gets you in the right area.

Since DJ's are so consistent across the world, if the comparison between a mustang and a dynojet is very close, the error is most likely from the mustang dyno.

-Jamie

 

These percentage differences, are they the same regardless of power level? In other words will you see 13% more with an 800bhp car on a dynojet vs mustang?

 

Lets not forget about hitting different load profiles on an eddy current dyno that you would typically not hit on an inertia dyno (especially for turbo applications).. The timing and fueling changes effect power output as well..

 

No it usually will plateau, but this percentage rule is not much of a rule.. You are comparing a dyno that calculates output via speed vs. time to one that uses a load cell or torque disc (eddy current mustang)

 

Yes the load will have effect too. Ramp rate or step test on any dyno gives different figures. I think some used badly assumed inertial factors. Inertia test will be more prone to skew from lighter -> heavier wheels.

 

So why is there such a discrepancy between dynojet numbers and Mustang dynamometer numbers?

 

because race car

 

pretty much

 

Wow, pretty significant difference there

 

Interesting they wernt using a correction factor or smoothing.

 

Great thread, I hit over 300 oh Johns Dyno back with my stocker so I was very happy about that.

 

Guys just concentrate on gains vs baserun in the same dyno shop.

Comparing numbers from different dyno shops even of the same type is as stupid as using drugs.

Stop losing your time