IQ52
Well-Known Member
Chassis dynos are a funny thing like engine dynos. They are good to test changes like tunes or part swapping but you will get different results on different dynos. I even experienced vastly different results on back to back pulls on a chassis dyno.
We went to 'Chrome in The Dome' at Pocatello, ID one year when they were dyno testing diesel trucks. We took the Demon that had been on other chassis dynos and thought we'd beg them to let us run on the dyno with our car. They let us pay the fee and on we went.
Whoa, we went to 7,000 RPM pretty quick and way down on horsepower at 620 RWHP.
Having had some experience on dynos I asked if they had changed the load on the dyno before my pull. Sure enough the operator had lowered the load for what he thought the average car needed on his dyno. He thought the dyno would stall my engine with too much load and it wouldn't be able to reach full RPM.
I asked him if we were making more horsepower than he expected would he please set the load for the diesels he had been running on that day......then we made the second pull.
Presto, now we were back into the 680's for RWHP. A third pull verified the second pull.
What happened?
If you rev your engine in neutral in your driveway you're going to get lots of quick RPM but you engine isn't making any torque so there isn't going to be horsepower because horsepower is function of RPM and torque. The engine has potential torque but that torque isn't realized until a load is applied to the engine. Put your transmission in gear with your foot on the brake and start to rev the engine and the left front of the car is going to start to lift.....now you are making torque and horsepower.
The first pull on the dyno that day the engine had more torque available but the dyno wasn't applying enough load to bring out all the torque.
Some dynos have a big weighted drum that the car or truck spins and the load doesn't change on those dyno's. They calculate the horsepower by how quickly it spins the weighted drum up to the full engine RPM. This dyno was different and the operator had control of the load.
We went to 'Chrome in The Dome' at Pocatello, ID one year when they were dyno testing diesel trucks. We took the Demon that had been on other chassis dynos and thought we'd beg them to let us run on the dyno with our car. They let us pay the fee and on we went.
Whoa, we went to 7,000 RPM pretty quick and way down on horsepower at 620 RWHP.
Having had some experience on dynos I asked if they had changed the load on the dyno before my pull. Sure enough the operator had lowered the load for what he thought the average car needed on his dyno. He thought the dyno would stall my engine with too much load and it wouldn't be able to reach full RPM.
I asked him if we were making more horsepower than he expected would he please set the load for the diesels he had been running on that day......then we made the second pull.
Presto, now we were back into the 680's for RWHP. A third pull verified the second pull.
What happened?
If you rev your engine in neutral in your driveway you're going to get lots of quick RPM but you engine isn't making any torque so there isn't going to be horsepower because horsepower is function of RPM and torque. The engine has potential torque but that torque isn't realized until a load is applied to the engine. Put your transmission in gear with your foot on the brake and start to rev the engine and the left front of the car is going to start to lift.....now you are making torque and horsepower.
The first pull on the dyno that day the engine had more torque available but the dyno wasn't applying enough load to bring out all the torque.
Some dynos have a big weighted drum that the car or truck spins and the load doesn't change on those dyno's. They calculate the horsepower by how quickly it spins the weighted drum up to the full engine RPM. This dyno was different and the operator had control of the load.
