head work vs flow?

On a stock stroke motor 460 that has to pull vacuum 15in at 900 rpm , flat top motor, how much can u gain by doing head work ? i'm useing c8ve-a heads different people say different things.. the cam will not flow enought and so on .. so i'm wondering from you guys with 460 experience...
will i gain power by bowl blending or mild port work?? What kind of valve job?? Is there a specific cutback on the valve to gain flow???
thanks

In head porting the low hanging fruit is blending (for about 1-1 1/2" in the port) and throat sizing.

Concentrate on the short side radius just under the valve seat on the int. and exh, and unshrouding the intake valve in the chamber. That along with a good valve job, (Serdi, Sunnen, or Rottler machine able to machine radius exhaust seats) will get you the most bang for your buck.

Yes you will gain substantially in power with a good port job. Camshaft design for a vac engine will dictate the amount you will pull. The more flow the more go. Given two identical style heads ie. DOVE, one ported, and one stock untouched, even vac limited the ported head will make more power.

Just about all the work you do inside the port will be useless IF the valve job isn't done correctly.

If you have to meet a vacuum rule, there are some other things that will help also.

1. Spread the LSA or lobe seperation angle on your camshaft. In other words the same cam on a 114 LSA is better than one on a 110 LSA because of reduced overlap.

2. Run fairly tight valve stem to guide clearance.

3. Run vacuum advance at idle and high idle.

4. Tune and adjust your carb with a good accurate vacuum gauge hooked up.

Hope this helps,

Charlie

Even in a 15" vacuum rule combo fully ported large valve heads will outpower as cast every time provided the valve job, port work etc are done well...

Since the cam will be somewhat limited good flowing high velocity ports are the key here along with a specially ground cam to allow good wheel speed / rpm while still meeting your vacuum rule.

Dual plane intake
locked out timing
additional vacuum advance at idle
high static c/r
Wide lobe sep angle with additional exhaust duration for high rpm power

All of the above will allow you to maximise duration and still meet vacuum requirements.

Some good info you guys listed.

Have you thought about a full radius, 5 angle, or 3 angle valve job to help flow? Anyone know just how big of a gain you could get from it in this type of situation?

I have found that a radius cutter like the TFS serdi works well on the iron head intakes as it helps low and mid lift flow significantly when coupled with an .080" wide back cut, however the exhaust seem to prefer a 3 angle with a wide 45 degree seat located just outside of center of the valve itself. When the exhaust bowl is properly shaped and opened up there is little if any of the 60 degree angle left. The bowl walls really end up being hand radiused into the top of the 45...

I back cut the exhaut valves in the passenger car heads but not the iron cj heads which like more of a tulip shaped exhaust valve.