nitrous_bob

is your thought that the "better" gas will last longer as it sits for short spells ? it really doesnt make any difference. the octane doesnt make gas any better, or last any longer. use an additive like "stabil" for that

people waste a lot of money on higher octane that makes their car actually run slower....albeit safer, but if your not making big compression or boost its a moot point

dawson1112

87 octane fuel reaches full combustion slightly faster than 93 octane. This allows for greater advance in timing, advancing the timing starts the combustion process a bit sooner . If you advance too much on 87 the combustion of fuel creates an explosion that acts like a hammer on the pistons, by increasing the octane you can slow this action creating more downward force on the pistons . Regardless of the fuel you make more power running a 12 degree base timing as apposed to 10, reason being as the piston comes close to tdc it starts to create pressure , fire to late and the combustion of fuel is wasted on a piston that is already starting to drop pressure , fire to soon and the combustion is wasted on a piston that is still making pressure, find the sweet spot on each particular engine ( and each engine will have its own characteristics ) now your getting the most downward force from the combustion of fuel.

Ive played with the timing of a lot of different engines some engines will tolerate 14 even 16 degrees of base while others max out at 12. Variations in the manufacturing process have a great deal to do with how much advance you can run. Remember when a machinist runs a part they have a +/- tolerance , some machinists will like to stick to the + side while others will like to stay on the - side of things, depending on the particular machine the parts are being ran in, how well it was set up and the quality of the tooling being used. Its often easier to start on the - side of the tolerance and as the tooling wears the measurements will start to creep up to the + .


Your best bet is to start at 12 , run it through out the rpm range . If you get no pinging go up to 13, and so on till you start to get some pinging then back it off 1/2 degree till it stops.


I meant that 93 allows for greater advance due to the slower combustion..... Thanks darkmach1 for catching that..

darkmach1

^Did you say that 87 allows for greater timing advance than 93?

dawson1112

lol No that's not what I meant , 93 allows for greater advance..... Wow should wait till I had a few cups of coffee before spouting off hah ha thanks for pointing that out don't know how that came out like that..

darkmach1

Good, I was like lol wut!?

StalkerGT

I have it at 14 right now with no pinging at all...when I get gas again I'm gonna put 89 in it and see what it does