I recently had my car dynoed at turbo tech, and they did the pulls in 4th gear. Well, my car doesn't make a whole lot of power, and it took about 19 seconds of full boost to run from 2,000 to 7,200 rpm. I kept getting a little pinging starting at 6500 rpm even though the fuel and ignition timing were fine.

It seems that since I'm using a tiny eclipse intercooler, under such prolonged boost, its getting heat soaked thus causing the detonation/pinging. It seems to me that they should be dynoing it in 3rd gear, so that it's not under max boost for so long- I'm never full throttle for 20 seconds straight on the street or track! Any input?

 

Dyno runs are done in the gear that has the ratio closest to 1. In most cars that is 4th gear.

 

a lot of places do them in 3rd gear as the diffrence in power will be minimal and it is a lot easier o the engine.

 

How does the gear ratio affect the dyno?

 

From practical experience it doesn't have much effect. At a friend's shop we dynoed the same car in 3rd and 4th gear and there wasn't much difference in HP.

 

it doesn't make much difference, but here's the math involved.

If you do a dyno pull in a gear closest or equal to a 1:1 ratio, you are basicallt taking the power straight from the input shaft to the ring and pinion, and the other gears are jsut hanging around. makes the parasitic drag less, so to say.

 

If the gear doesn't make that much difference, then wouldn't it be smarter and or safer to do the runs in 3rd gear? Otherwise I might be unnecessarily pulling timing at or above 6500 rpm in order to stop the detonation while on the dyno- because in real life operation redlining 1st through 4th gears doesn't even take 19-20 seconds like it does on the dyno. Is my thinking correct?