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Max safe Boost vs Octane

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Hey :)

What are common guideline in terms of boost vs octane ?



There isn't a rule you can apply to every situation as there are so many variables. Turbo, compression, cams, exhaust, and air temp are all factors that will play into the knock sensitivity of the engine and how much boost you can run. That being said, here in New Zealand on our locally delivered 98 octane pump gas I find that the majority of engines will only want to see around 22 psi. You can run more than that but this will usually require the timing to be retarded rapidly top prevent knock. From here you just go around in circles adding boost, removing timing, and making no more power. Testing will show what works for your own application though.

Hey Andre, thank you for your answer.

Let me see if I understand,

1 - Start at low timing - around 10deg ?

2 - Keep AFR @ boost 11.5-12.0

3 - Add timing until knock or no power increment.

4 - add boost and retard timing (probably because knock occurs), until adding boost at such retarded timing does not add power (?) - this is the point to stop for this engine with this fuel ?

Thanks !


Essentially yes. As the boost increases there will be a natural tendency for the timing to retard even if you're not knock limited. The denser charge in the combustion chamber basically burns faster. You will almost certainly be knock limited though and then it's just a case of finding the point where more boost doesn't really gibe you an advantage. It sounds a little complex and clumsy but it becomes very clear when you're actually doing this on the dyno.