Originally Posted by HQHolden
Had my engine dynoed a while back and all went well. Got everything up and running and seemed to be going well. Took it to the track and was not running the times I had expected. So took it to a chassis dyno and found a huge dip in power towards the top before it picked up again.
Attached is the printout of both dynos. As you can see the engine dyno shows a smooth power delivery all the way through. Everything I am running on the car was used for the engine dyno, eg water pump, alternator, fuel pump, reg, etc. On the chassis dyno we tried dropping the exhaust system in case there was too much back pressure but it made no difference at all.
So what do you think?
The chassis dyno only shows what power the tire is putting into the ground (roller); this may or may not reflect anything the engine is doing. A lot of mayhem happens inside torque converters, transmissions, u joints, rear axle, and finally the tires.
People who run these chassis dynos like to talk about only 25 percent loss through the chassis and related components, like I wish, it doesn't take many installation sins to double that amount of loss.
If this trend was on the engine dyno I'd be hunting reversion issues related to intake and/or exhaust tuning lengths and/or intake plenum volume, metering inclusive of the air correction jets and emulsion tubes, and ignition. This can be ignition as well, my Harley had a hole in the power curve that was cured with the addition of Nology plug wires all the messing with the carb jetting and ignition module did nothing but move it around a little or lesson it some, the Nology's eliminiate it with no other changes being active. Go figure?
The engine will respond differently to its tuning when on a chassis dyno than it will on an engine dyno and certainly different than either when on the street or track. Being a sucessful racer mostly revolves around identifying these problems and tuning them as much as the constraints allow.
About the best advice I can offer short of being there is to only work one tuning item at a time. This is something that grows geometrically if you start making changes to many things at once. The other is to start with the simple things then work to the complex.