Ping (detonation) vs AFR

Philip Lochner · Post by **Philip Lochner** » Mon Jul 17, 2006 3:03 am

Is there a relationship between Air fuel ratio (AFR) and pinging? I understand that higher compression engines combined with too advanced timing and too low octane fuel would be more prone to ping but can the AFR also contribute? If so, which way, richer = more ping or leaner = more ping

keithmac · Post by **keithmac** » Mon Jul 17, 2006 4:26 am

I believe if you run a richer mixture the engine is less likely to ping, up to a point. I`ve got detonation issues on boost, going to try a richer AFR (10:1) and see what happens. I think the extra fuel acts to cool the combustion chamber, heat is one of the causes of detonation.

FoundSoul · Post by **FoundSoul** » Mon Jul 17, 2006 5:11 am

keithmac wrote:I believe if you run a richer mixture the engine is less likely to ping, up to a point. I`ve got detonation issues on boost, going to try a richer AFR (10:1) and see what happens. I think the extra fuel acts to cool the combustion chamber, heat is one of the causes of detonation.

This is true-- and the extra fuel will also cause the combustion process to slow down a bit as the overly rich mixture won't burn as efficiently/fast.

I'd lean towards reducing your spark advance though rather than going overly rich to compensate for too much advance.

keithmac · Post by **keithmac** » Mon Jul 17, 2006 5:48 am

Spark`s already 7 to 8 DBTDC, can`t retard it anymore as it flattens the engine responce/ ability to rev.

FoundSoul · Post by **FoundSoul** » Mon Jul 17, 2006 7:06 am

There may be something else going on then... preignition due to a hotspot maybe? Plugs that are too 'hot' of a heat range?

keithmac · Post by **keithmac** » Mon Jul 17, 2006 8:41 am

Plugs are 2 grades colder than stock, I`m out of ideas really. Going to 8:1CR when I change pistons, 9:1 at the mo. The VW 16v has a tendancy to ping at full load/ low rpm anyway so shoving 12psi through just exagerates the problem..

FoundSoul · Post by **FoundSoul** » Mon Jul 17, 2006 9:43 am

The lower compression should help alot then if that motor is known for ping issues.... Is it head design? Anything else that should be cleaned up while you're in there?