if you bore your cylinders out, you will need a larger headgasket :dunno:

 

Incorrect. There is one version of the B20 head that has an 84mm combustion chamber. Using a smaller headgasket than your bore size will raise compression, and it WILL alter the flow inside the cylinder...especially in high comp. or boosted applications.

 

Well, yeah, I can understand using one on that oddball head, but how often do you see those?

For the others with the standard 81mm combustion chamber, it just seems like something super-obsessive. What's the average displacement of a B-series combustion chamber (say, a PR3,) anyway?

 

Well if you overbore the cylinders, you'd go with an overbored headgasket to match. It's not the change in displacement that matters, its the fact that you are going to have material all the way around the circumference of the cylinder disrupting flow as it enters the cylinders from the head, and as the pistons compress it, and as it exits the head. The edge of the gasket in the cylinder will cause a turbulent flow inside the cylinder.

Also, it's a common practice for people who go with an overbore to have the combustion chambers bored to match as well.

 

still off topic, but wouldnt boring out the cylinder head, lower the compression. Now if you go out and spend all of that money on high comp pistons and add a few more cc's to the head, whats the point. it seems the only way to bore the head and keep stock cc is to mill the head... just creates a money hole, or so it seems.

 

yes spotfacing the head to match the bore does lower the compression