Tuning to knock with cast pistons

Once this lockdown is over, I'm looking at putting my car on the dyno to try get the last horses out of the motor. Like a lot of people with un-opened turbocharged nissans. I can't/shouldn't tune my engine to knock and then back it off as every instance of knock could result in serious piston ring land damage. Which leads me to my question, how do i go about tuning my car as safely as possible without leaving too much on the table, without any prior knowledge on what are known safe numbers? For reference my car has an rb25det running 100ron

There is no a exact answer, I guess if the fuel quality is real good, you may be safe with 100ron.

You should not look for knock, what you are looking for is the peak torque.

If in the attempt, the first thing that happens is the knock, you must go back 2 to 3 degrees at a time. As long as your AFR is on target.

Always check you results in final road pace, some times the real load isnt the same that the dyno load.

Yea I'm aware that i should not be looking for knock, the sad reality though is that this car will be knock limited in most areas before mbt. And that knock at say 9psi of boost could be devastating

Hi James,

Ideally we want to be able to tune the engine to MBT, while this is not always possible due to many factors including fuel quality causing knock. We have to find other ways to optimize our ignition timing without hurting the engine.

Knock is one of the biggest engine/piston killers out there, although when understood a little bit of knock during tuning will not destroy the engine.

I am not saying chuck in 10 degrees more than you have and do several power runs on high boost and rattle the thing to pieces.

How you should do this,

The first thing we need is quality knock ears and being able to distinguish knock quickly. Carry out a power run with a safe amount of timing you know won't be close to knock. Ensure fuel mixture is about where you want, maybe slightly on the rich side. After your run, add a small amount of timing, 2 degrees is good as it is not a big jump but enough to show gains. Keep doing this until 1 of 2 things happen. You either reach MBT or you detect knock.

If you're half way through a power run and hear knock, stop. Don't continue the run. You can then either try add some fuel to see if that helps reduce knock and increase power/torque, or you can remove the timing back out. You can also try just remove timing from that one zone and keep the timing in the higher rpm. You will find you will end up removing timing around peak torque (peak cylinder pressure) but ramp timing back in the higher rpm (when we need the spark event to be happening earlier due to less time for the combustion event to occur)

With going up in small amounts of 2 degrees you will pick up knock early at a much less severe state and won't damage the engine, even with cast pistons.

This is an old webinar but a goodie.

https://www.hpacademy.com/previous-webinars/dyno-tuning-ignition-timing/

Also if you haven't I would suggest taking the efi fundamentals course, it has great info on ignition timing tuning and knock.

https://www.hpacademy.com/courses/efi-tuning-fundamentals/

I would also leave a decent safety margin away from the point of knock maybe 2-4 degrees to account for changes in air temp and fuel inconsistencies. You could also run some water meth to add another layer of safety.