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Discussion Starter · #1 ·
I have a question for some of you more experienced guys. What is a general rule of thumb for advancing the ignition in relation to octane rating? Like how many degrees can you generally advance when you go from 87 to 89 and 89 to 91, 91 to 93? I believe the highest octane rating within a practical distance from me is 93. I havent played with it much yet but i would appreciate some advice first before i go making changes to it because with my current exhaust i feel i might not notice slight pinging.
Thanks in advance (pun intended :wink: )

edit: i am talking about on the SPI motor btw
 

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I dont have a lot of experience & have never had any of my cars on a dyno; but with our fuel-injected computer controlled machines, I just leave the timing alone. I dont know that there is a co-relation between spark advance and more power for instance- if you dont also change to a different chamshaft profile. Yes, the tendency to 'ping' with overadvanced spark is helped by higher octane - but I dont think you see an increase in torque at the upper midrange; though I could be wrong. Im sure your exhaust valve temps will go up though, along with hotter piston crowns.
 

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When you advance, it may or may not be helpfull.... Your ECU actually changes timing with different fuel. If you put in 95 octane and advance timing 10* there will be no difference in power, just where the power band lyes. If you stick with stock timing and add 95 octane, you may notice a little power boost but none to mention and you wont have the ECU pulling the timing to correct spark and burn ratios.

So basicly if you want to advance run a better gas, and dont expect more power.

I have advanced mine 10* and run 87. I have essentialy relocated my power band from the stock 2-3k to 2.5-4k wich in my opinion is better since i like to run high rpms anyways. It is only a .5k diff but when you are all out WOT it seems to help to pull from other cars :)
 

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Discussion Starter · #4 ·
No you said in another thread you bumped your cam timing 10*. Im talking about ignition timing. If i change my ignition timing my ecu will not adjust it back to stock unless i tell it to. Im not trying to relocate my powerband either im looking for more overall power.
 

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You can sorta rely on a degree of base per octane number over 88, but some motors will let you have 2 degrees "free" for a start.
 

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Discussion Starter · #8 ·
Thank you roadwarrior! I have been messing around with it a little bit and running a 93 octane tune i can deffinitely notice a difference.

Samtheman the SPI motor does not have a distributor it is EDIS so the oringial timing is not really a problem for me if i ever wanted to return to stock.
 
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