Quote:
would knocking down the pinch work to kill off the swirl on the heads and decrease the flow?
In my opinion, it is a ballancing act. Removing the rounded pinch completely will all but eliminate the swirl effect. When I have ported these I have tried to retain the the overall shape of the runner but also increase the cross sectional area. I have talked to some (and experienced it myself) that removed the pinch all together and their quarter mile times went backwards.
I think in almost every performance application you want to open it up from as-cast, at the very least, removing the valve cover bolt bulge and smoothing the pushrod and divider wall. (Remember these were designed for an OEM application that almost never see more than 4500 RPM). On more serious motors, I have moved the wall over as far as possible but kept the round shape with an increased radius.
The larger the dispacement or higher the RPM range, the more increasing the cross section will help.
My understanding is that the 308 exhaust bowl (and short turn) is based on the W2 design.
Note: I am not a cylinder head design expert. I am offering my opinion only.
It would be great if one of the chrysler engineers that worked on this head would chime in. (I wont be holding my breath)
Last edited by Rapid340; 01/29/10 10:35 AM.
