Re: Cracked Heads
Many years ago I went through cracked heads on a four banger. I was informed by a number of engine shops that it was a chronic problem with this brand of vehicle. I pulled the cracked head and checked it out on my bench. I concluded the ports in the head were undersized on purpose to reduce the flow and run hotter so as to improve emissions. The reduced flow through the head allowed carbon to build-up in the ports. As carbon built-up in the ports, the head started to run hotter and eventually the head would crack. My solution was to mildly port the head to improve flow. Problem solved and I never cracked another head in about 250,000 miles.
Pinging/pre-ignition can also be caused by carbon build-up in the head's combustion chamber. The fact that there is a carbon build-up in a particular part of the combustion chamber indicates a " flow dead-zone", i.e. poor flow through the combustion chamber. A mild porting improves flow during the valve overlap duration (i.e. when both intake and exhaust valves are open).
Hope this helps.
Best regards,
CJR
