One of the features of some aftermarket heads is a more pronouced heart shaped combustion chamber and altered valve pockets, which affect swirl in the combustion chamber. Correctly done, a good combustion chamber design speeds combustion providing more pressure at the top of the stroke by burning the charge faster and possibly more completely.

An indicator of this is the optimal ignition timing. The quicker the combustion the less advance that is needed.

Could you specify what cylinder head, compression, and peak ignition timing you are using? Ideally, people with a variety of heads (AFR, ET, Dart, Patriot, TEA, Cartek, CNC LS6, stock) will chime in.

Thanks,

David

 

i run a set of 5.3s that LPE did for me.they CNC'd the combustion chambers,i couldn't tell a big difference in shape from stock.anyway,with 11-1 CR i'm running about 25*total advance.(93 octane)it doesn't seem to like more,but i do need to play with the tune a little.i was thinking about this the other day,i hope more people chime in.