On Jun 26, 2005, at 5:38 PM, Lehanover@aol.com wrote:

Everything affects everything. Unless there is a need to operate the engine well above 9,000 RPM, there is no need to modify the exhaust port to any great extent.
 
Later closing the exhaust port (Port cut taller) extends the open time and increases overlap with the intake ports. This is quite helpfull at very high RPM. The same for early opening of the port. (Cuting it lower) there is little to be lost here at high RPM. The available work left in the charge has been reduced to near zero, and the late opening is to help sound by allowing more complete expansion before the charge is released. Radiusing the opening lip of the port gets flow started along a smooth curve where much of the flow stays along the bottom of the runner. There is some interest in removing the exhaust flow completely before uncovering the intakes. Adding the radius along the opening line and up the sides of the port does that.
 
Other than removing tooling marks and smoothing the top of the port there is not much to do. You don't want flow from the top of the port in either direction. So leave the top as per factory. I would reduce the chrome and iron  around the port in all directions just s few thousandths to avoid any possibility of snagging an apex seal. Just a 16th of an inch or so is fine.

Lynn, would it not be accurate to say that lowering the opening of the exhaust port lowers the effective compression ratio? I have been thinking that this may be desirable in a turbo engine.

Hans Conser