Thread: pre-detonation help

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Hi guys a friend recommended this site for some chevy tech help so here I'am.

I have recently rebuilt chevy 350 in my 1979 C10 and I just swapped intake maifolds from stock to an edelbrock performer and she runs great the only problem is when I gun the throttle it responds very quick but theres also some pre detonation knocking and was wondering what could be causing it. I was thinking it could be too running rich/lean? or should I just drop the money for some more octane fuel? Any help is greatly appreciated.

more info:
rochester quadrajet carb (recently rebuilt)
edelbrock performer intake
hooker competition headers

Take a little ignition timing out of it and richen up the mixture a little before you go to a higher grade fuel.

79C10 - What is your compression ratio?

OK guys - Help me out with the theory -

Pre-detonation is caused by excessive pressure before spark as opposed to pre-ignition caused by over advanced timing?

Throttleing up advances timing perhaps to a pre-ignition state?

Would pre-detonation occur at lower RPM also or only when reved up?

So you need to ritchen mixture or use a slower burning fuel to handle pre-detonation?
OR
Spark is occuring too soon so retard the timing to handle pre-ignition?

Which would you try first?
I'm guessing timing.

Bert

ALRIGHT!

Now I see why no one replied to my previous post -
Its nothing more than novice-babble and misunderstood semantics on my part.

Did some web research and realized that.

Detonation occurs AFTER ignition as a result of advanced timing raising the chamber pressure to quickly instead of a slower controlled burn initiated later in the engine cycle. I suppose excession compression ratio could cause a similar result.

Pre-ignition on the other hand is a result of chamber combustion before a spark occurs. This could be caused by either a glowing spark plug, residual carbon embers or overheated metal, like a valve within the chamber.

Pre-ignition is more likely to occur closer to BDC because the spark required to ignite the mixture is proportional to the chamber pressure. That is, more spark is required as chamber pressure increases. For some reason I though it would be the other way around.

Pre-ignition causes catastrophic engine failure very quickly whereas detonation can be tolerated for a longer duration.

SO detonation could be remedied as TECH suggested, by either retarding the timing a bit or a ritcher mixture - maybe a little of both. If on the other hand its caused by a high CR, higher octane could be the solution.

OK - Back to the books - Bert