69 427 Cast Iron Head Work Plan

[Don W.]

Are there any specific recommendations for the cast iron heads. I have from my other post: port and polish; new valves with 3-angle cut, new design valve springs...Don

[Duke W.]

Re: 69 427 Cast Iron Head Work Plan

Pocket port, port match, chamber relieve, mulitangle valve job. NO POLISHING!

This stuff has been in publication for over 35 years - "How to Hot Rod Big Block Chevies" and the old Chevrolet Power Manuals.

Use OE equivalent valves, but open up the exhaust to 1.88" on L-72 heads". Stainless steel valves on the inlet side are total overkill and a waste of money. Spend it on head work and flow testing.

Get them flow tested before and after.

Duke

[Joe R.]

Re: 69 427 Cast Iron Head Work Plan

Don,

Duke is right on the polishing. It is counter-productive, it actually hurts flow.

Joe

[Don W.]

Re: 69 427 Cast Iron Head Work Plan

I have 70 454 heads; does that change anything on valve sizes?
Right side head GM8T; J 25 9 (= Oct 25, 1969); 3964290; PASS

Left side head 3964290; GM10T; J 23 9 (= Oct 23, 1969); PASS

Don

[Duke W.]

Re: 69 427 Cast Iron Head Work Plan

I'm not sure because I don't know if we're talking about a 390/400 HP '69 or 435 HP.

For early big blocks, the SHP closed chamber rectangular port heads are short on exhaust flow, either OE or massaged. The two "fixes" are longer duration on the exhaust side or enlarging the exhaust valve size to get and E/I flow ratio of about 0.75 with is just right for the OE single pattern cam.

I think the early oval port heads have more "balanced" E/I flow, but there may be a difference in latter open chamber heads.

The only way I can answer the question is to see flow test data for both OE and massaged heads.

Given all the head changesd on big blocks in the first few years, it gets complicated, and I don't have full data on all heads.

See the Fall 2010 Corvette Restorer "Tale of Two Camshafts" article where I discuss head flow issues. The basics apply to any engine. It's just a matter of testing to get the requisite data, then determining if the cam is well matched to the flow data. If not, swapping lobes as I did for the two special small block cams can usually achieve good optimization.

Duke

[Don W.]

Re: 69 427 Cast Iron Head Work Plan

Mine is the 390 HP 427...Don