Seems there's a correlation between higher compression and higher (than othwerwise expected) horsepower out of these heads. My view is If you can't run pump gas abouve around 10.75:1 or so anyway you might as well jack the CR as high as it is practical...I think I'll shoot for 12:1 which I think is where a 414 will come up zero deck with a no dish Flat top and a 64cc head.