Took the mustang to get a custom Dyno tune Saturday morning. I was pleased with the results, but on the way home I noticed the speedometer was 5-6 MPH off. Took a look and the tuner set the gear ratio to 3.31 when I actually have 3.55 in the car. I set the ratio to 3.55 and it corrected the discrepency with the speedometer. My question is, would this have affected the results on the dyno?

 

I am not sure but would dobt it. What mods do you have?

 

Steeda CAI, Steeda Underdrive pullies,GMS 60,000 V Ignition Coils, BBK Throttle Body, 93 octane tune. Manual Transmission.

 

So I guess the questions is, does the dyno use what speed that the car thinks it is going to make its calculations?

 

No. The dyno doesn't care what your speedometer is reading.

 

Bingo.

 

I agree the dyno does not know what gear your car has in it. Your results should be accurate. The speedometer means nothing. They just take it up to a max rpm that you told them to go too!

 

Along the same lines - would leaving traction control on affect the dyno reading? Seems like it maybe could, right?

I took mine to the dyno this weekend and forgot to tell the guy to turn the dyno off. Now, he may well have known that - and it was a mustang specialty store - but they deal with older mustangs, mostly, and I would have felt better just reminding him anyhow, but I forgot. Stupid.

If it would/could affect the dyno result, by how much do you think? Would TCS have to engage (in which case, you'd probably know it).

 

Doubtful T/C did anything to hinder your results unless it was engaged through wheel spin.

 

when I took mine to a dynojet dyno I HAD to have the TC off or the car wouldn't get going. It wasn't the difference between a good run and a bad one. It made the difference of a good run, or no run.

 

Cool, thx guys.