hi guys, i was wondering what ppl mean when they say that detonation will occur if we dont put in 91 octane. please tell me because i do not know. thanks,
john

 

it will always occur, but its more likely with lower octane gas. and it means that the explosion in the engine will occur prematurely, causing "knock" or "ping".......

 

Detonation (knocking, pinging) spontaneously occurs when an air/fuel mixture is greatly compressed, for example 10:1. Detonation is bad in two ways: (a) The entire contents of the detonating cylinder ignite at once, sending a wavefront not only down towards the pistons but also up to the valves and sideways to the cylinder walls - a spark plug-ignited cylinder emits a carefully engineered wavefront that pushes mainly down on the piston; and (b) since the air/fuel charge wasn't ignited by the spark plug, the ECU loses some control over the engine.

91 octane gas is less flammable than 87, meaning it's more resistant to high compression without detonation. Some OBD-II engines (like the VQ) work most efficiently with high octane gas but can retard timing to compensate for lower anti-knock indices. The knock sensor and the ECU actually work cooperatively and continuously by keeping the timing slightly retarded from knock. This way each cylinder is maximally compressed and therefore you get the best fuel efficiency.

Hope this helps. I really miss DBM.

 

dbm is/was/always be da shiet...too bad he got bored of the board and left...

 

I'm bringing this thread back up again in efforts to elaborate on what pinging/knocking is.

what kind of feeling do you get while sitting in the car, and how do you know it's happening?

because i'm afraid my car did this today...