318 head porting for the average joe
Years ago when I was doing a 318 block , stretched to 4.04 bore std 340 kb243's I worked some 273 head with a 1.88/1.50 valve combo. This is a pick of one of the ports 'chamber side' sitting on the 4.040 bore I was scribing the far side for deshrouding. The major detail her is i did not deshroud the lower ssr side of the chamber... instead I played the boundary game and only put a slight angle on it. .so there was no smooth ramp.. it was a gap and 30 degree lip. Also the valve job 'shop did it' has a ledge around it... bad. The port in this pic from 10 yrs ago flowed around 223-227cfm.. BUT the ledge around the valve and the lower chamber shrouding around the ssr ' I believe'...killed the low lift. .300 was only 160's iirr. I'll have to look at my log book.
I wasnt happy or where I wanted with them. In the end it got a .473 lift solid and ran great, just could have been better! Take away... a lip or ledge around the valve is never good unless something else is messed up.
Let me throw this in..
Years ago when I was doing a 318 block , stretched to 4.04 bore std 340 kb243's I worked some 273 head with a 1.88/1.50 valve combo. This is a pick of one of the ports 'chamber side' sitting on the 4.040 bore I was scribing the far side for deshrouding. The major detail her is i did not deshroud the lower ssr side of the chamber... instead I played the boundary game and only put a slight angle on it. .so there was no smooth ramp.. it was a gap and 30 degree lip. Also the valve job 'shop did it' has a ledge around it... bad. The port in this pic from 10 yrs ago flowed around 223-227cfm.. BUT the ledge around the valve and the lower chamber shrouding around the ssr ' I believe'...killed the low lift. .300 was only 160's iirr. I'll have to look at my log book.
I wasnt happy or where I wanted with them. In the end it got a .473 lift solid and ran great, just could have been better! Take away... a lip or ledge around the valve is never good unless something else is messed up.