Forum » Practical Dyno Tuning » Torque /knock relationship !!

Torque /knock relationship !!

Practical Dyno Tuning

Discussion and questions related to the course Practical Dyno Tuning

Page 1

Hello to all ,

Is knock and torque related linearly ?!

I mean if I am tuning by dyno without any knock defection tool can I observe the torque drop at dyno graph and use it to determine knock or tell that torque falls because detonation accure at that point ?!

In theory, the torque increase should taper off and even drop as detonation point is neared, but not always - cheap insurance getting something to either hear or detect it.

Andre went into more detail in one of his tuning videos - have a look for it.

In my experience on engine dynos, torque will continue to climb as you hear knock from the engine from advancing spark (torque goes up but you start hearing it rattle, mostly at steady speed and load). In actual chassis dyno tuning doing WOT pulls, typically you're going to add spark in 1 or 2 degree increments and once you see it pick up only a few horsepower you stop adding spark, or if you trust the knock sensor you stop when the knock system is pulling timing.


Thank you .

It depends a little on the engine you're tuning. I group engines into one of two groups - Those that are knock limited and those that aren't. With a knock limited engine you will find the torque will continue to rise as you reach the onset of knock and keep adding timing. On the other hand with an engine that is not knock limited then you can safely tune to MBT and you're immune to knock.

In short though there is a theory that we can just use the torque output from the dyno and stop when the torque plateaus. The theory is that when the engine knocks the torque naturally drops off. The problem with this theory is that usually an engine will start knocking lightly on perhaps 1-2 cylinders and this can still show a net increase in torque. this is why I strongly advise the use of knock detection equipment instead of solely relying on torque output from the dyno.

Is torque drop because of ecu retard spark after it detect detonation ?

I may be corrected on this, but I believe it is because - when the engine doesn't detonate/pre-ignite first - the torque is basically a result of the cylinder pressure balance after and before TDC. When the ignition point is a little retarded, not optimised, there is less mean pressure before but also less than the maximum potential after TDC so despite what onemight think, net torque is less than optimal. As the ignition point is advanced towards the optimum, the mean cylinder pressure before TDC increases but as the mean ATDC increases more, the net effect is a torque increase. If the ignition point is advanced past the optimum, the mean pressure BTDC increases more than that ATDC and the torque drops off.

ECU spark retard is a slightly different thing, but the effect is it does retard the ignition point to after (depending on the specific setup) the optimum timing.