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Re: Ignition and spark plug gap questions Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Wed, 24 Jan 2001 12:56:49
In Reply to: Ignition and spark plug gap questions, Erwin Timmers, Wed, 24 Jan 2001 12:20:11 Members do not see ads below this line. - Help Keep This Site Online - Signup |
Remember - the manufacturer's recommendation for plug gap covers a wide range of applications (read - lots of different engines in lots of different cars). They call out a plug gap that should work OK with all the applications.
You, on the other hand, have just one engine to worry about, and a pretty interesting one at that. A non-turbo engine basically runs at the same compression ratio throughout it's operating range (some variation due to valve lift and in some cars, adjustable valve timing). A turbo engine runs at low compression with no boost, high compression at high boost, and everything in between.
A bigger gap is good because you get a longer spark, which improves the flame-front dynamics and fuel burn. But it's harder to make a long spark than a short one. When the compression ratio is high (say, under boost), it's even harder to make a long spark. So if the gap is too big, you may not get a spark under high boost conditions - the problem you were seeing. So make the gap smaller, get decent spark under high boost, and misfire goes away.
Does this produce some compromise at low compression conditions? Yes, some. But it would take someone with A LOT more experience than I in engine combustion to determine what the loss is. Basically, until someone comes out with a variable gap spark plug, you're stuck with the gap that works.
Personally, I don't think the difference between 0.7 and 0.9 is going to be noticable at low power (low compression) conditions. I think 0.9 may give you problems at high boost. Yes, it may be fine today, but if you're on the hairy edge, it may show up the next time you pull out to pass.
My advice is to use what the engine manufacturer recomends. They know more about that particular engine than the spark plug manufacturer does. The spark plug gap from Delco must cover a range of cars, and therefore is a compromise.
, Wed, 24 Jan 2001 12:56:49 <-- Viewing This Message
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