Dyno Ramp Rate

Hi,

I have a question regarding the optimal ramp rate setting for vehicles that have a more "aggressive" torque curve. An example would be the torque curve of a turbocharged vehicle compared to a n/a or a supercharged vehicle. The ramp rate as I understand, is the rate at which the rpm or mph increases in relation to time (ex: 25mph/sec) which is a linear relationship. But on the road with a turbocharged vehicle for example, the torque curve can be far from linear which would mean the ramp rate would also be non linear. In my mind if you set a linear ramp rate on the dyno for a vehicle that would normally exhibit a non-linear acceleration rate this would mean the dyno run would not accurately load the vehicle as it would on the road.

Is this a neglible situation or am I completely wrong in my thinking?

Thank You!

hello, the ramp rate doesn't really matter too much as long as it gives the turbo time to spool up for power runs most tuning is done using steady-state where each load and Rpm zone is tuned where ramp runs are used to confirm the power and improvements under full acceleration. i generally do a 8-10 sec ramp run with all my tuning and only go longer if I need to check for an issue like if a customer is complaining the car goes off song after half a lap or that kind of thing but often this sort of issue can be found under steady-state, example holding at 6000 rpm for 30 sec under full power on an rb25 engine to test for a misfire, I found that my fuel flow meter on the dyno showed the surge tank was running out of fuel. and was able to then see the lift pump was not supplying enough fuel to the surge tank, this could not have been found on an 8-10 sec ramp run,

you will notice the different length ramp runs produce different torque curves and ofter different hp readings this is because of the generated and spool up time so I try and stick to the same 8-10 sec runs to keep it consistent, for your information I use a dynopack hub dyno for my inhouse tuning but have a vast amount of experience with most dyno platforms and they all differ on the way the software controls the dyno, some inertia dynos need a 15 sec run just to complete a power run, so it is a bit of a asking process to find what works best for the dyno being used

Awesome, thank you!

Excellent post, Ross.

I suspect there's some confusion between the different types of chassis dyno's, and how they "ramp run" differently. Possibly because if you're used to one, the other may be unfamiliar.

You CANNOT do a constant acceleration run on an inertia type because the inertial mass (roller, etc) is fixed, and the acceleration rate is proportional to the applied torque (power, in context of the tuning) - as the torque increases, so does the acc'n rate, and the power is extrapolated from the torque that gave the change in roller rpm.

With chassis dyno's that use an electrical, or water, resistance, the resistance (load) can be adjusted to control the acc'n rate. This means as the torque increases or reduces, the load can be adjusted electronically to maintain the same rate of change of rpm, or speed, or hold it at a specified rpm..