Question about timing - Pontiac GTO Forum
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post #1 of 3 (permalink) Old 07-31-2014, 08:22 AM Thread Starter
 
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Question about timing

So, a little back story, I just bought my 69 GTO with a 400 a few weeks ago. I finally checked the timing as I've been busy with other things, like bolting down the driver's seat. Ever since I got the car it idled rough, felt like it was getting some kind of detonation, overheating and the exhaust smelled like it was running rich. I also had it bog down on me a couple times when hard accelerating from a stop, was hard to start and after it warmed up it would stall at an idle. I found that the timing was set to 4 degrees. I didn't have time to do a full timing job so I didn't disconnect any vacuum lines. I just advanced the timing a couple times until I got it to 14 degrees at idle. What a difference that made. Idles better, doesn't stall, no bogging down, runs smooth, starts easily, feels like it has more power and doesn't smell like it's running rich. So, this brings me to my question...

Why would someone want it at 4 degrees? Other than they just don't know anything about timing an engine, is there a reason you'd want to retard the timing to that point? I read somewhere that you can get better top end performance if you retard the timing a little bit but this engine seems to do a lot better all around now that I have it at 14 degrees.
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post #2 of 3 (permalink) Old 07-31-2014, 09:03 AM
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If we assume that whoever had it set like that did it on purpose (that's a big assumption) and not by accident or by just not knowing how to set it properly, then the only reason I can think of for doing that would be as a band-aid to try to solve a detonation problem.

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post #3 of 3 (permalink) Old 07-31-2014, 12:25 PM
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BINGO. I used to run my '67 GTO at 2 degrees if I ran 92 octane or bumped it up to 4 degrees with 94 octane....but it still pinged. Could never run it at spec (6 degrees initial) unless I ran race gas. Sure ran great with the timing advanced, though. I often marvel at the people out there who run 14-20 degrees initial timing with stock compression ratios of 10:1-plus. Either they're running 110 octane fuel, or they're pounding the bearings out of their engines and just don't know it. I've seen a few of the later!
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  Pontiac GTO Forum > The 1964-1974 Pontiac Tempest, Lemans & GTO > 1964-1974 Tempest, LeMans & GTO Engine Tuning and High Performance

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