Chassis Dyno Information / Guide / Myths!

[Matt-Rallye]

 Put it on the road and press the pedal, that gives you the best idea

I wouldnt agree entirely...Or at least since having a rolling road, I would certainly never go back to tuning using the road as a "test medium"...For most modifications you havent a clue what is going on / what you have done! But yeah 1/4 mile strip gives you as good as idea of anything with regard to rough power if you know the vehicles weight.

I was talking about using the same dyno at the same place for repeatability of WHP figures. Most good operators set your tyre pressures before you run

Yes this is correct, Using the same dyno for comparisons on the same car is pretty reliable, obviously small changes can occur day to day and with the strap down, on the whole they are comparable. And yes tyre pressures should always be checked.

This is a fantastic write up with alot of useful information but on the highlighted point of 1/4 mile times to indicate horsepower output that just doesnt work in practice.

For example:

If you take a 150bhp 106 gti up the strip with a standard gearbox you can expect a 15.2 at best.

Now take that same 150bhp in the same 106 but with an S1 rallye gearbox (much closer ratio) and you can pull a 14.2 with a decent launch! That 1 second loss might not sound like much but in the world of drag racing it is everything.

I do have some questions about the figures obtained from the RR day i did in hereford as some dont seem to add up but others seem to make perfect sense. just wondering if there can be a reasonable explanation for it?