You will find lots of hate on this one.
Putting 305 heads on a 350 was a good way to bump compression back in the day when compression was low, and aftermarket heads were almost “unattainable.” Those days are long gone, and decent heads (be they aftermarket or Vortec) are cheaper than getting work done on old heads. And 305 just don’t flow all that well stock.
Having said that, the point of this build is CHEAP. I ain’t spending a lot on this engine. I already had a set of 305 heads. I have a die grinder and theories on porting. Labour don’t cost me nuthin’. Let’s see what happens.
First, because I am upgrading the cam and valve springs, I pulled the studs and machined the heads for screw-in studs. Four studs didn’t want to be my friend, and were a bugger to remove (one required milling out, once it sheared off).
Holes were tapped 7/16″ UNC.
Bosses machined 0.400, and counterbored 0.125″
ARP studs installed, polylocks will be used
Next, I spend a considerable amount of time porting the heads for flow. The OCD in me likes this.
The edge surrounding the valve seat was smoothed with a surfacing disc and a couple old valves machined down to almost flush. Pics to follow.
Intake and exhaust valves were back-cut 30°, lapped, the exhaust valve edges radiused, and the heads reassembled (pics to follow) with new o-rings and added umbrella seals.
I used Howard’s Cams valve springs #98212 (115@1.780″, 340@1.250″) and ditched the exhaust valve rotators. This required .015″ shims under the exhaust spring and +.050 keepers for the intake (for the taller installed height of the spring). Summit Racing’s website is incorrect on the installed height of these springs.