Mizz96Z28

I'm having my heads checked at a machine shop for any cracks and to see if they are warped. I told him to do whatever he can to them by the end of this week and he said he didnt have time to port and polish them but he'd work on the valves. Now I'm assuming he's going to grind them or something along those lines but I was just wondering on average if anyone knew what kind of gains can I expect from this? I know it can vary from car to car and such but I was just wondering a ballpark figure for HP increase if any. Thanks

Myles

NightTrain66

If he has messed with valve jobs and flow benches he probably has his own "recipe" as far as angles and widths but different valve jobs (and back cuts) can pick up cfm at different lifts.

Some could pick up 10-15 cfm at .600 lift and nothing below .400 lift. Some sould pick up 10 cfm at .300 lift and nothing above .500 lift. It all depends. If he has worked with this stuff much, he probably can help you out.

You could have him flow the head before and afetr the valve job and see for your self. A simple thing like going from a 30 to a 33 degree back cut on the valve with the same valve job can cause the head to flow different at ALL lift points. You can pick up 3-5 cfm at low lift but at the expense of the port leveling off at .500 lift instead of steadily climbing to .600 lift.

You can have a port that flows 270 at .600 turn into a 255 cfm head with 3-12 cfm increases at lower lift points just with a different valve job. That same port copuld flow 280 cfm at .600 lift with HORRIBLE low and mid lift #'s by changing the valve job.

These are pretty EXTREME cases but very possible if you change (screw up) the valve job enough.

The valve job is a great way to find CFM if done correct and a great way to lose CFM if done wrong.

NightTrain66