I'm completing a 408CI build-up and need some quidance. I'm using a Vortec iron heads w/64cc chambers, 2.02/1.6" valves and pocket ported. The pistons are dished (-12.5cc) and they are down in the hole .025".
I want the best chance of running 91octane pump gas. Would it be best to tighten up the piston to head distance to .040", increase the quench and increase the compression ratio to ~10.7? Or use a thicker head gasket lower the compression to ~10 and lose the quench?

I'm installing a solid roller with 249/254@.050, 107intake centerline and 111LSA.

 

I'd really consider some different heads.

 

10.7 will be close to the limit on pump gas, but if it's in good tune and the cam has enough overlap to bleed off some of the cylinder pressure you might get away with it. Deck heights of -.025 plus a .040" gasket is a lot. Tightening it up will raise the compression but it will also be more resistant to detonation. Keep in mind you want to keep a minimun of .030" of piston to head clearance.

 

that's a very large cam, look up your dynamic compression ratio, and go with that, rather then the static. Remember, bigger cams need higher compression to work well. I think keeping your quench distance right is most important, you can always use sanding drums in the chamber and polish it, and gain a few cc's of volume. win win.



but yea, vortecs are (arguably) the best factory head made, but you're building something a lot more powerful then the factory put out. Why go with a giant SBC motor, a huge cam, and mediocre heads?

 

Yeah. I know there are better heads for this application but I own these.
I was given the cam and had the short block.
They do flow pretty well:
Intake/Exhaust
.100 72/78
.200 128/135
.300 188/170
.400 231/183
.500 258/187
.600 260/191

My car is heavy (3650lbs). So I want to make a lot of torque down low. the smaller ports shold do that.

 

Top ping or not to ping. Go with the quench. 10.7:1 may not be enough compression with that big of a cam. Like was posted above you need to check you dynamic compression ratio. Should be at least 8:1 for good performance on 91 octane. I bet you are not close.

 

Yeah. I hear you. I'm going to proceed with a .015" head gasket and see how it goes.

Thanks for the help.