Quote:
Originally Posted by Irace86.2.0
If you max out timing in ideal conditions then won’t it be risky in less than ideal conditions like on a track or on a hot day because then the engine has no wiggle room to adjust timing?
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I over simplified it, and I'm assuming by “max out” you mean no timing left to pull? If so then, Yes sort of.
As boost increases heat exponentially increases once it hits the tipping point of the octanes abilities you start pulling exponentially more timing, and like I mentioned the inherent risks of running more boost increase, so it’s recommended to not just throw all the boost at it even if you technically “could”.
Hypothetically, Say going from 8 to 10psi you drop from 19 degrees timing to 17 degrees timing. Say 1 psi is 4% whp, 1 degree of timing is 2% whp so you still have a net gain of 4%, but say the “threshold” of 91 is at 10psi, meaning going from 10-12psi your timing to not have knock goes from 17 to 13 degrees. 8% gain from boost but 8% loss from timing so You gained no power, but now have the added risks and increased temps of more boost for no benefit. Then you go 12-14psi but timing goes from 13 degrees to 5 degrees. And now you just lost power. As you see because the heat increase is exponential so is the timing being pulled to accommodate. This is why it’s technically possible to run say 14psi with 91 but highly not recommended, and running 10psi would be ideal as you make max power still, but still have some safety wiggle room for error/increased temps from driving hard, at 12psi you still make peak power but with basically no wiggle room. And at 14 psi you might actually lose power and have zero wiggle room.
So the ideal “threshold” of the octane is when you can still make max power but at the lowest boost level for highest margin of error. And if you drive hard like tracking that threshold decreases because your temps will obviously be a lot higher.