i've done this so many times now, that is just isn't as fun anymore, but here goes.

dynojets are less accurate and more generous with numbers than a dynapack or even mustange dyno. this is because of the 3000lb drum that has to be rolled by the vehicle to obtain power measurements. the flywheel effect of this large mass makes a few extra hp as the effort needed to spin the drum becomes less and less the faster it goes.

other factors to take into consideration are these. if the vehicle is not lined up properly on the rollers, it will greatly skew the results by adding imaginary hp to the vehicle. also, the calibration of the units will effect the way the dynojet registers the numbers.

and finally, the way the dynojet measures power is flawed. they measure acceleration over time to calculate horsepower. they then take this number and correct it back to find a torque figure by correlating it with engine rpm. everyone knows that hp is just a function of torque, so it's odd that they make torque a function of hp.

on a dynapack, the machine measures actual torque. the work that the vehicle is doing to overcome the load being applied at that given time. since there is no additional mass to spin, the readings are much more accurate as the dynapack can measure the amount of load being applied to the axles and calculate work done by those numbers. this is then translated to a hp figure, which has less than 1% deviation from what a dynojet will report.

we have had several examples of this from various cars.
vehicle/dynojet 248c/dynapack
jetta 1.8t/192/190
vortech sc mustang cobra/405/402
bmw e36 m3's/200-210/200-210 (we've done at least 20 of these)
350z/225-240/231-237 (the two we did during the dyno day)
civic si/125-135/130-132 (we've done 10 of these)

we have many more examples too, if you care to see the charts.

the peak hp numbers are on par with the dynojet, but what about accuracy for the rest of the graph? the dynapack is repeatable to .1% and sensitive enough to register a load from the alternator during steady state dynoing. steady state is where we load up the vehicle so it maintains a certain engine speed regardless of throttle position. this is great for tuning because you can see what is happening with the vehicle when you add more fuel, advance ignition, etc, etc.

also, you don't need to worry about tire slip or spin on rollers, which can also skew the numbers on a dynojet as rolling resistance changes as the tires get warm.

dynapacks also don't need any calibration over inputing gear ratios, and the gear ratios are only used to determine proper wheel torque, but hp will always be correct. to get good dynojet results, you need a experience dynojet operator and a properly calibrated machine. note: the newer dynojets have self calibration, but most of the units out there are the older ones that need manual calibration.

also, check this out as far as the consistency of a dynojet.

http://www.factorypro.com/magazine/m...ojet_dyno.html

please don't throw unsubstantiated information out there as fact, because to do so is pure ignorance. i did over a month of research before i decided on a dynapack over a dynojet. and just about all the tuners in japan use dynapack. you buy their cars but don't trust their choice in chassis dynos?

and no, a dynapack doesn't cost less than a dynojet (a lot more actually) so i didn't just just buy the cheap one.