Topic: #46 1969 72cc heads on a 350

[76TAmatt]

I just bought a 76 firebird that has a 350 with 6X heads. The car came with a set of 69 #46 heads off a 400 or 428. I am considering putting them on the 350 along with a better cam. It has a holley street dominater intake and headers already. Would this be worth doing? I know people are going to say build a 400 but I already have that put away for my 76 trans am project. The firebird is a driver and I want a quick fix for a little for power.

[Hitch]

I have the 46's on my 400. They are a small valve, high compression head. Here's a good link to all the pontiac heads to compare:
http://www.angelfire.com/fl4/pontiacdude428/HeadID.html
   
As far as being a better choice, I'll let somone else who knows more about engines chime in.

[72blackbird]

No. 46's are a good choice for a 350p- PMD had a 350 HO in a 68 and 69 Firebird, and it had no. 48 heads (similar chamber size but bigger valves). The small chamber heads will give you a healthy bump in power from the 7.6:1 SCR with the 6x-4's- expect around 9-9.2:1 SCR. I would have the heads serviced first (valve job, guides reamed or liners installed, surfaced, exhaust seats installed). These heads should make at least 300 hp with a good cam like a summit 2800, Crane 283941, or Crower 60916 and headers with a dual exhaust.

[76TAmatt]

I would have them rebuilt. Would it be worth it to have the larger valves installed? I might do some slight porting as using the Jim Hand book as a guide. Trying to keep the cost down for this car. It also came with a new 2000 stall converter. What other things must be change when doing this? Lifters, spings or ?

[72blackbird]

The problem with fitting larger valves on heads going on a 350p is you need to chamfer the top of the block to prevent valve to block contact. The chamfer also has to be at least .200" deep to prevent valve shrouding. Some later 350p blocks are already chamfered, so little has to be  done there. The bore on a 350p is also so tight that 2.11/1.77 valves can hurt flow instead of help it unless your chamfers are large enough- a 2.05 intake is more than adequate with a 1.66 exhaust to improve flow. Some bowl work, guide area and port matching work will yield a noticeable performance improvement.

[76TAmatt]

If I could get close to 300 horse without changing the valves I would be happy. The heads on the 350 are 6X-4 so I would assume it has the chamfer already since them have larger valves. I would save these for my 400 and have the larger valves installed but I am worried about the compression being too high.