I've been doing some research to find what mods what produce the best combustion chamber design for my next race A15. I think its silly to bother porting a head if the combustion chambers are not given any consideration.

I was thinking of placing a head gasket on the head and tracing the bore onto it. My block is +2mm so there will be some meat to take off the head around both valve seats in order to let the head breath better, especially when the valve is at low lift. It will ofcoarse have oversized valves fitted though I'm not sure exactly what size I will go.

There is also some performance to be gained by removing some material around the spark plug. The idea here is to get as much fuel+air near the spark to achieve a quicker burn.

I've even heard some people pack spark plugs to align the electrode to the centre of the cylinder.

Then there is the issue of removing or rounding and protrusions to avoid hot spots in the head.

Comments anyone ??

remember that any meat you remove from the combustion chamber will reduce the total CR.

also note that airflow in a cylinder is not the same as airflow outside the cylider. sharp edges to "guide" the airflow either coming in or going out of the cylinder will interupt squish, and cause detonation.

you need to make the chamber as domed as possible - putting the sparkplug at the top of this dome. it doesn't have to be a perfectly hemispherical chamber, just guide the inlet charge as smoothly as possible around the sparkplug.

having a central dish machined in the piston (but don't play around with the squish ring) will also aid in reducing detonation.

i plan on giving this a shot on an A12 i'll be building. i'll be running a high CR /low boost application and am looking at all kinds of methods to reduce detonation.

my theory is - try to have the combustion chamber (including the dish in the piston) as spherical as possible at TDC. a hemispherical dish machined into a piston (instead of a flat bottomed recess) will have more surface area, therefore giving more area for the force of the exploding charge to act on the piston, instead of the chamber walls. more force acting on the piston = more torque.

i'll be trying to get the top of the piston at zero deck, and the dish below zero deck, to eliminate any force whatsoever being exerted on the cylinder walls.

pro-240c dont you think if you have the piston at zero deck at full rpm it may just stretch that little bit further resulting in the piston smashing the head.

sorry i should have mentioned i'm running a 1.5mm copper head gasket.