How accurate are dynos? Accurate as in... if i did a run with car X, got 300hp, waited for the car to cool down and did another run. Would you get exactly 300 again? What's the +/- factor? If its + or - 10hp, then couldnt you say that if you did a run and got 300hp, then added an intake and got 310, that that's not really proof that the intake added 10 hp?



edit* why cant i fix the damn title to "are" instead of "or"

 

The rule we work by is 2 runs within a hp ,you do however need to get the car to working temp first tho .

 

The key is that the car and environment are at the same state for each run. I think most people are content with starting the dyno run with the coolant temp being at the same point each time, though I think ideally you need to look at oil temp. And to really get into it, tranny fluid temp too. The viscosity of the oils is going to change with their temperature, effecting the power to the ground.

You also need consistent air intake temps. So if the ambient air temp is significantly different, then that will effect the dyno readings. Same deal with humidity.

The more variables that are the same, the better data you will get.

 

Yeah definitely many variables/factors play into how the dyno will read, well, actually more on how the car will run. Someone might run a car in the afternoon, get a reading, get some "slight" mod done, then dyno again late in the afternoon while temps are cooler, and think he gained more than he actually did from the modification alone.

 

load bearing dynos are more accurate than anything else.

 

In the case of an inertia dyno, it depends how many teeth are on the speed gear.

In the case of a load bearing dyno, it depends on sensitive the load cell is.


In either case, the dyno is going to be more accurate than the power output of the car from run to run.

 

Dyno's as many a internet battle have found are only a tool to referance performance gains in isolation . The single biggest factor I have found is that the operator is the biggest variance to the whole test cycle .

Correct load and boost profiles as well as elasped time are factors we use the Motec to help with . Many a EVO in the UK suffer from a 40 second dyno test to peak power with 60 degree intake temps logged !!!! The usual answer was you need a bigger intercooler !!!!!!! How times change .

 

they are just reference if you are making power or not. as of accuracy it always depends which one you use so no real answer here.