The higher the octane of fuel, the more that it resists detonation. So yes you are able to run higher boost. Higher boost also stresses the engine internals. When you plan to run boost like this you should get a good tuner that knows what he is doing so you don't end up with a blown engine.

 

Hes right...the amount of boost depends on your turbo/setup

 

The higher the octane rating, the less evaporative the fuel is. This means its less volatile. Painters use higher or lower octane thinners for mixing paints and other materials to control the curing/drying time. In the same vein, it takes more or less energy to get higher or lower octane fuels, respectively, to burn. When you are running higher boost you are increasing cylinder pressure. Pressure and spark have a similar effect on gasoline. But you want the gas to burn with the spark, not just due to pressure, so that it is timed right with cylinder and value movement and is over all a controlled event. If the pressure is beyond the fuels ability to hold out for burn until the spark comes, it will ignite before the spark (this is why detonation is often called "pre-ignition") and you have an uncontrolled explosion which is usually far more powerful than a controlled spark-generated explosion. That's when things like valves and pistons start to warp and crack. Little pieces of things like spark plugs end up in the turbine, etc. All due to enormous amounts of energy being released in an uncontrolled matter at a rapid rate.

AFIAK there's no all-cases formula for saying "this octane will make this PSI safe". You might be able to formulate one for a specific situation, but that would entail making so many variables into static values that it really doesn't pay to spend the time figuring it out. What tuners do is allow light knock to persist during tuning (mild detonation). When the knock is detected you can tune the engine by backing off the timing (another way to control when burn starts) or change the air/fuel ration to be richer (more fuel, believe it or not fuel is a retardant). Raising the octane is often the quick-fix for knock problems. Its not a tuning solution unless the power you want to make necessitates a particular cylinder pressure that will detonate unless the fuel has a higher octane.

Lastly, 17psi on a stock turbo (I guess that's what you are referring to) will do you no good with an otherwise stock setup. As you get towards 16psi the turbo becomes thermally inefficient and you are just blowing hot air, which defeats the point of trying to compressing it in the first place. So, even if you could possibly have enough octane to offset detonation at 17psi, the air charge would be useless.

jason

 

^^^^ what he said.

re: that last paragraph. I'm looking into picking up a intake temp gauge and will be getting data on intake temp vs ambient for different boost levels to confirm that 17 psi "wall" with the stock turbo and IC.

 

I know that everyone wants to save a buck. Just back the boost to 15.5 or max at 16 psi. It's a lot safer. If you want to go over 16psi. Change the turbo, and back it up with the proper fuel in and proper air in and out. Also don't forget the golden rule. Proper engine and fuel management. If you want no detonation you may have to spend more $ to hp. Quick boost is easy, if you like to leave critical engine parts on the ground. Good luck.

 

if you run higher octane gas and leave the boost the same, theoretically the ecu will increase ignition timing also giving you a bit more power. correct?

 

Probably to a point. Stock ignition only puts out so much juice. Past 100 octane you might run out of spark. May be exhausting unburnt fuel. My have a negative affect on power.