Today I went out and got some hi octane gas(that i should be running with the 12.1 compression) since my z28 was out. I got 5 gallons, poured on the fuel cell. Fired it, let it idle for a few, then drove it around the neigborhood...It ran completely different....ran real good....still alittle rich but I was crisper on the throttle...ect....
so my dumb question is: Running the high octane gas in it cause that much of a difference? I was told to run 114....or 92 with octane boost due to the compression....and i havent....good ol no ethno. 87....

 

Ya you need the high octane with the high compression. The higher octane burns hotter for a bigger explosion. I bet that thing is hard to start hot on pump gas.

 

Yeah it is hard to start.....huh and i just thought it was the tune messed up causing that. learn something new everyday

 

your knock sensor will detect knock with cheap gas and retard the heck out of your timing

your engine will run hotter too

no benefit in cheap gas

 

should have the knock count from before on your data log. do another and compare.

 

I will do that tomorrow. The knock count on the last log only increased when I reved it, I assume thats the retarding of timing.

 

was it your knock count that was wayyyyy up there.

 

Yeah. It jumped when I started the car then stopped...then I reved it and it jumped again then stopped.

At start up it jumped to 4140 and when I reved it to 4000 and it went to 4496 and stayed there till I shut it down.

 

Just to sort things out. High octane and low octane gas have practically the same energy level, with low octane having a bit more. High octane gas actually burns at a lower temperature than lower octane gas and does not produce a bigger explosion. In a spark ignition engine fuel is not supposed to explode in the combustion chamber, but is expected to burn in a very fast and controlled rate. If the fuel explodes it will cause knocking, and in the worst case it will case cause engine damage. As compression is increased the fuel will burn at a faster rate increasing cylinder pressure and combustion temperature. If the pressure and temperature get high enough all the fuel in the chamber will detonate instead of burning. Being that a higher octane fuel will burn slower and at lower temperature than the lower octane fuel, detonation will be held in check.
A high compression engine using low octane fuel will be harder to start when hot because the high compression and heat in the combustion chamber is causing the fuel to light up too early in the compression cycle (before the spark plug fires) and attempt to push the piston back in the wrong direction.

 

^^^ A very concise and easy to understand explanation of the difference between high and low octane fuels.

I have also read that higher octane fuel burns at a slower rate, and thus produces the expansion forces for a longer time, which results in more power per burn cycle (all other conditions being identical) than lower octane fuel.

Now, the difference in burn rates is measured in micro-seconds and thus not something that a person could detect without the proper equipment.