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TJay74 · 11-19-2016, 01:27 AM

ok, so here is what we have found in logging data on the truck LT1 engines. The 5.3 trucks knock like crazy on 87 octane, they show to really need 91/93 octane to not knock.

The 6.2 trucks show knock events on 91, so they do benefit to have 93 octane as well. The 6.2 trucks state in the manual to only use 91 octane, you can use 87 in a pinch but it is suggested to get back to 91 ASAP.

With that the GM powertrain testing is done on 91 octane as it is available everywhere in the USA where 93 octane is not. As EFI-Tuning said, 93 wont make more power per say, it just keeps detonation from happening which will cause the ECM to drop you into the low octane table which pretty much takes 15° of timing away instantly.

Octane is a fuels ability to resist detonation. Detonation happens with timing is advanced too far and a sharp edge on the piston gets too hot. As the fuel is injected into the chamber and the piston comes up on compression stroke the hot edge in the chamber ignites the fuel charge, then the spark plug ignites the fuel charge as well.

Now instead of having one singular flame front moving across the combustion chamber, you now have 2 flame fronts. They move across the chamber and collide, that collision is what causes detonation and makes the pinging sound. The occurrence of detonation is likened with taking a ball peen hammer and smacking the top of the piston, if it happens enough or is severe enough it can damage the piston/valves and leave small marks on them.

The cooler the weather and the incoming air is, the less the chance of detonation unless the timing is just advanced way too far.

I have a station a mile from my house that carries 100 octane pure gas, I get it for $7 per gallon. I mix 6 gallons in my truck with the rest being 91 octane, brings my octane to around 93/94. I do the same thing in our Audi SQ5 as well. So far no detonation has been seen in either of them, now that it is cooler out I can run 91 and will be fine.

11-19-2016, 01:27 AM	#20
TJay74 Drives: 17 Camaro SS 1LE & 16 Sierra AT CC Join Date: Nov 2016 Location: Norman, OK Posts: 2,424	ok, so here is what we have found in logging data on the truck LT1 engines. The 5.3 trucks knock like crazy on 87 octane, they show to really need 91/93 octane to not knock. The 6.2 trucks show knock events on 91, so they do benefit to have 93 octane as well. The 6.2 trucks state in the manual to only use 91 octane, you can use 87 in a pinch but it is suggested to get back to 91 ASAP. With that the GM powertrain testing is done on 91 octane as it is available everywhere in the USA where 93 octane is not. As EFI-Tuning said, 93 wont make more power per say, it just keeps detonation from happening which will cause the ECM to drop you into the low octane table which pretty much takes 15° of timing away instantly. Octane is a fuels ability to resist detonation. Detonation happens with timing is advanced too far and a sharp edge on the piston gets too hot. As the fuel is injected into the chamber and the piston comes up on compression stroke the hot edge in the chamber ignites the fuel charge, then the spark plug ignites the fuel charge as well. Now instead of having one singular flame front moving across the combustion chamber, you now have 2 flame fronts. They move across the chamber and collide, that collision is what causes detonation and makes the pinging sound. The occurrence of detonation is likened with taking a ball peen hammer and smacking the top of the piston, if it happens enough or is severe enough it can damage the piston/valves and leave small marks on them. The cooler the weather and the incoming air is, the less the chance of detonation unless the timing is just advanced way too far. I have a station a mile from my house that carries 100 octane pure gas, I get it for $7 per gallon. I mix 6 gallons in my truck with the rest being 91 octane, brings my octane to around 93/94. I do the same thing in our Audi SQ5 as well. So far no detonation has been seen in either of them, now that it is cooler out I can run 91 and will be fine.