a dynapack dyno in particular uses a hydraulic pump attached to each wheel. restricting the outlet on the pump turns it into a brake, and measuring the pressure the pump builds up turns out to be an accurate measurement of how much torque the engine is exerting to turn the pump. the amount of restriction at the outlet of the pump controls the rate of rpm increase and the length of time it takes for you to hit redline, not your horsepower.

my question is with a brake applied to the drivetrain (dynoing on a dynapack), would mods like a lightened flywheel or UDP show an increase in power?

 

i guess no one knows? i don't think the dyno would show the increase as the engine is being mechanically bogged, i guess you could say, to measure the hp so the effects of any lightening shouldn't be noticeable. i guess you could say the engine is turning at its full capacity but not accelerating at it full capacity making the lightening of components almost impossible to see.

 

Just because your car is lighter doesn't mean that it increases horsepower. Lightening effects only help the car's HP/Weight ratio, improving acceleration and sometimes top speed depending on aero's. So in contrast a lighter flywheel won't add horsepower it will make your car seem a little quicker due to the fact that your car is lighter. You could say the samething about a full gas tank vs 1 gallon in the tank. A full gas tank will result in lower gas mileage during the first part of your tank and the endinding mileage will be higher simply due to the lesser weight, given this mileage difference is only about .5 MPG.

 

true, but a fuel tank doesn't spin at 6k rpm. thanks anyway for the response.

 

well the the purpose of lightened flywheel and UDP are less rotating mass on the motor...allowing it to rev kwiker and have better throttle repsonse...not really a HP gain...maybe a better curve

 

true, again, but say you have two identical maximas except one has a 50 lb wheel and tire combo and the other has a 30 lb wheel and tire combo. its obvious which one would be faster. the reason being is because of less rotating mass. so now the drivetrain is consuming less hp to turn itself. so lets say the the 20 pounds make up a 3% reduction in drivetrain loss. that would mean that both of these ideantical maximas would deliver a different amount of hp to the ground. if both made exactly 200 hp at the crank, taking account the figures noted above, the 50 lb combo would allow max #1 to deliver 160 hp to the ground (a 20% loss) where the 30 lb combo would allow max #2 to deliver 166 hp (a 17% loss). so you really didn't make extra power at the crank, but you freed it up in rotating mass. same theory behind the flywheel and udp. that is what my original question is based upon as a change in drivetrain loss can only take effect if the engine/drivetrain are allowed to spin on the power made by the engine. if a dyno puts a load on the drivetrain i don't think that the loss in drivetrain restriction would be eveident on that dyno. i think i answered my own question.