[oldman]

Originally Posted by Nabush

Where did I say the dynojet were not repeatable ? I perfectly understand a fixed mass to rotate will provide repeatable measurements. After all, what should I know, I only have a Master in engineering and a PhD in physics...

Ah vitae, I always say engineers have the slow cars. Last time two German PhD came and talked to me about direct injection in a diesel, I was installing a stereo and boom box playing 99 luft balloon (as fate would have it). They said your nothing like we envisioned from your writing. Great guys, they do like the Fredericksburg beer garden. As an aside if you get a chance to watch the mock invasion of an island at the Nimitz Museum, it is something to see.

Originally Posted by Nabush

The issue I see with Dynojets is that the pulls are really short for most of them, you don't load properly the engine, which is obviously an issue with turbo engines.

I have noted that in my post, the Mustang dyno is better at tuning because of the load. So we agree

Originally Posted by Nabush

Moreover for tuning the adjustable load of a Mustang dyno is very usefull even on an NA engine to look for knock and or simulate very high loads.

It is common knowledge that most of the time Mustang Dyno, properly setup, yield lower numbers than dynojets by few % (max 5% ?) . There is no science behind the words " heart breaker" but yet they come from experience of several users.

Once again I agree. I was and am addressing that an as measured dynojet number is dead on 100% accurate no cheating possible. Does it reflect the real world? No as noted more eloquently by you, but I did refer to it, the load especially on street fuel is the same as on the street. Back in the bad days (the 80s and early 90s) many boosted cars would run more boost in the lower gears vs drive as the engine would be spinning against less load, meaning less chance of detonation. Hence the 1000 HP Supra, take that car off the dyno put 93 octane in it and try to drive it on the street and your down to 600 HP. That why the Supra crowd don't even place in the top 20 ever in the pump gas shoot outs. Because the engine is just too small for the octane limit of pump gas.


The nut of the problem is the 100% accurate dynojet numbers get corrected to SAE which is meaningless on a FI engine, secondly it was meant to be used under very small variances say 2 to 3% Then enter in STD and STP aka Unicorn HP and now the reading of a 100% accurate dynojet is so far off nobody knows what HP / torque the car is actually making. Of course the tuners could print the correction factor applied (CF) but then that would drastically undercut their HP claim. To make matters worst you have shops, that just manually enters false data into their dyno so that all their cars are like 10% more HP than any other dynojet.

Not to be outdone, the Mustang dyno guys (since this is a fully programmable dyno) can and do come up with fanciful numbers themselves. So as you have stated "properly setup" does not bring customers into the shop. At least the dynojet can display as measured, no cheating possible. I know how to run a dyno have made many dyno runs.

Oh and FWIW, I've worked my way through 3 college degrees by building cars and engines. BTW and make more money the Dean or Chair of my department. Too bad these guys can't teach, much less build cars.

Nutshell if there is ANY doubt and the shop has a dynojet, just ask for numbers uncorrected aka the actual HP the car made to the wheels.