1988 4.3L OMC timing adjustment question.

[houstonnoob]

I have 1988 4.3L OMC and would like to know if I need to reduce my timing because I am using 87 octane fuel?

OMC Manual for 4.3L timing spec:
6 BTDC - with 89 AKI or higher
1 BTDC - with 86-88 AKI

My current timing is dead on 6 BTDC, should I reduce it to 1 BTDC because I'm using lower fuel grade?

 

[Reinell-BRXL-191]

Re: 1988 4.3L OMC timing adjustment question.

86-88 AKI (91-92 RON) Normally Anti-knock indexes are 3-4 points lower than the RON index we use... So, as suggested, you would need to run premium at 91-92 in order to have the timing set advanced to 6 degrees - But, most have not adjusted their timing for these lower RON fuels, and are not having any issues. It all depends on many factors regarding the motor maint, running conditions, including engine temps. If not experiencing any knock, your engine can run on lower octane fuels, but you are leaving horsepower on the table, and also running the risk of detonation during any high engine temp conditions... I would reduce the timing myself. it's a couple minute adjustment.. if you have a timing light and a wrench.. why not?

 

[houstonnoob]

Re: 1988 4.3L OMC timing adjustment question.

86-88 AKI (91-92 RON) Normally Anti-knock indexes are 3-4 points lower than the RON index we use... So, as suggested, you would need to run premium at 91-92 in order to have the timing set advanced to 6 degrees - But, most have not adjusted their timing for these lower RON fuels, and are not having any issues. It all depends on many factors regarding the motor maint, running conditions, including engine temps. If not experiencing any knock, your engine can run on lower octane fuels, but you are leaving horsepower on the table, and also running the risk of detonation during any high engine temp conditions... I would reduce the timing myself. it's a couple minute adjustment.. if you have a timing light and a wrench.. why not?

I've been running 87 Octane (Ron) couple fuel tank now since the engine has been fully rebuild and no detonation. I was just curious after reading through the OMC manual. Since I don't experience any detonation, what about running like 4 BTDC sound? Wonder how much of power I'm loosing from this. Just a thought.

 

[Levinz11]

Re: 1988 4.3L OMC timing adjustment question.

I run mine at 8* and use 89 octane. No adverse affects at all.