318 to stock 340 power level questions.
I realize I will have a port mismatch with the cast iron 340 intake and the 318 heads but it is something I will have to live with.
So, for a came you are recommending one of these?
http://www.summitracing.com/parts/LUN-60403LK/
http://www.summitracing.com/parts/LUN-60402LK/
Both of those are great cams. I agree with the other comments, the 60403 would probably be at the upper limit for an otherwise stock 318, a 60402 would be a piece of cake.
The 60403 goes to .513" of lift on the exhaust, make sure your springs can handle that. Seems like .500" is the cut off for quite a few spring options.
The factory didn't make any production heads with 360 sized ports and a closed chamber, unless you count magnum heads. 308's are open chamber, usually from 65-72cc's. I was fortunate enough to find a set at 65cc's, but from what I've heard most have larger chambers than that.
Magnums are a good choice if you're going to run different heads, they're pretty cheap, flow better than 318 heads, and are usually around 60-62cc's. There's been a couple of magazine builds that have pulled 400 hp out of magnum headed 318's. They do require oil through lifters and push rods, a new rocker set up and a new intake manifold though.
The stock heads are still more than enough to get to 300 hp though. Bigger valves would help, but aren't completely necessary. If the heads are going to be off and getting work anyway, I'd open them up to the 1.88/1.60 size and mill them .030 as suggested, the compression will be better and the larger valves will help the top end.
As far as the port mismatch, Edelbrock's performer manifold is pretty close to having 318 port sizes. The ports are a little larger, but not as big as 360 ports. It would be pretty simple to port match a set of 318 heads to a Performer intake. This is the performer intake, not the Performer RPM or Airgap, both of those have 360 ports. You could also look for an edelbrock streetmaster intake, or a holley street dominator. Both of those older intakes have true 318 sized ports.
