hey, i've seen on some built heads, on the combustion chamber is welded up and grinded down and it looks like a clover leaf. im curious as to whats the advantages/disadvantages to this? i think its called the squish areas that are welded up, correct?

 

I think that is done to make very high compression levels. The CR can only be raised so much with pistons. Then metal is added to the head by welding, and that is grinded to get the CR desired.

 

Advantages:
- higher percentage of potential quench area
- smaller head cc equals higher compression with a given piston volume
- higher power potential

Disadvantages:
-welding in aluminum can easily weaken overall combustion chamber strength
-cost
-if not done properly, is useless

That third disdvantage is the biggest one IMO. The real benefit here is for larger quench area, but people seem to miss the fact that the pistons must mate up to the new chamber shape in order for this to work. If the clearance between quench pad and piston crown is larger than about .06" (according to KB Pistons data), the point is lost and additional compression carries with it the usual limiting factors of detonation and possible pre-ignition. Overall I think this is an overly expensive and questionably beneficial practice, which is why it's so uncommon. But then again, additional quench (something 4 valve pentroof chambers are inherently bad with) can have payoffs if everything else is properly optimized to take advantage of it.

 

so from what im getting, this would be for something all out race where every little bit counts? thanks