Dyno Operation

So I was tuning my own car for the first time on a mustang dyno. The owner of the shop said he usually uses third gear for 5-speed cars. We did a few pulls in third gear and all seemed fine. So I pressured him to do a pull in fourth gear and he did one pull. Well as you can guess everything was good but the ramp up took a long time as opposed to third gear and seemed to put the engine under more load over time than needed. My question is: Does the owner of the dyno need to adjust the ramp rate thru the dyno itself to speed the process or should I just forget about fourth gear and continue to do full power pulls in third gear? I did not operate the dyno or vehicle as they didn't allow it, but I sat in the passenger seat and concentrated on the lap top and afr's. BTW I dyno'd prior to watching "dyno set-up and operation" webinar..

-Ernie

I've never used a Mustang dyno so I'm not familiar with how they function unfortunately. What you're explaining is typical of an inertia dyno (I believe however the Mustang dynos use a power absorber) as the dyno simply uses a roller of a large fixed mass. The torque multiplication of the gearbox in the car affects the torque produced at the wheels and hence this affects how quickly or slowly the roller is accelerated. For useful results it's important to choose a gear that produces a similar acceleration rate to what the car will actually see in 4th gear (I choose the higher gears as this is where the engine will be more heavily loaded on the road/track and where we really want to be sure the tune is correct).

So in short, on an inertia dyno you'll need to select a gear that achieves a reasonable acceleration time. As the engine power increases, you find you'll need to use a higher gear as naturally the roller will be accelerated faster due to the increase in torque. If the dyno uses a power absorber then you need to manually select a ramp rate to achieve your desired acceleration speed - I'm not sure how that's achieved in the Mustang software and it may be best to discuss this with the operator.