318 head porting for the average joe
302 head info.
They are very restrictive as cast and flow a considerable amount less than the 675, 920 etc..without modification.
The picture shows the shrouding and what a simple stone drop can do to help that.
2" nickle chrome stone cut 15 degree bottom, outer edge cut to 45 then 60 above to create a nice transition and not leave a ledge at the chamber wall. Start there if you want to make the most of this casting, followed by a nice 5 angle 75,60,45,30,15.
Doing that will bring the numbers up by 25 cfm! as well as shift the bigger flow to start earlier in the lift range.
Example
Stock cfm........deshroud and perf vj
.100-48...............50-typical closed chamber
.200-87...............106 +19
.300-131.............157 +26
.400-152.............173 +21
.500-166.............179 +13
.550 peak-175.......179
Add porting and you can see numbers jump another 25 cfm from .300 up with 200 by .400 and peaking 210-215cfm around .500-.550. They weren't intended for high lift drag/perf. They do what they do early and don't need much cam lift.
1st pic showing a 5 angle vj vs stock
2nd pic shows a 4 angle vj and was the initial test port for the stock vs vj/deshroud and port.
302 head info.
They are very restrictive as cast and flow a considerable amount less than the 675, 920 etc..without modification.
The picture shows the shrouding and what a simple stone drop can do to help that.
2" nickle chrome stone cut 15 degree bottom, outer edge cut to 45 then 60 above to create a nice transition and not leave a ledge at the chamber wall. Start there if you want to make the most of this casting, followed by a nice 5 angle 75,60,45,30,15.
Doing that will bring the numbers up by 25 cfm! as well as shift the bigger flow to start earlier in the lift range.
Example
Stock cfm........deshroud and perf vj
.100-48...............50-typical closed chamber
.200-87...............106 +19
.300-131.............157 +26
.400-152.............173 +21
.500-166.............179 +13
.550 peak-175.......179
Add porting and you can see numbers jump another 25 cfm from .300 up with 200 by .400 and peaking 210-215cfm around .500-.550. They weren't intended for high lift drag/perf. They do what they do early and don't need much cam lift.
1st pic showing a 5 angle vj vs stock
2nd pic shows a 4 angle vj and was the initial test port for the stock vs vj/deshroud and port.