To give you an idea how canted the valves are and the air flow rushing to the backside of the valve and how opening up the chamber on the far side has lots of benefits to flow.




The gap in the intake port divider isn't nearly as bad as your 4.3 head. Looking at it, I am tempted to ask the machinist to shave down the face some to see if it trues up reasonably. Though I don't have a sealed gasket for it (yet..?). I'd have to remove the freeze plugs in the face before hand.


Pulled the valve and springs off the head and did a bunch of measuring today. CC'd the chambers and the pistons valve reliefs (both types are surprisingly within 1cc of each other) as well as measured how far the piston was in the hole and how thick the head gasket is. Crunching the numbers still show I have very low compression, PipeMax calculates it at 8.022:1. The service manual advertises 9.0:1. The chambers have a horrid 76cc's, the pistons have 8cc valve reliefs (much less than I figured), the pistons are 0.034" in the hole, and measured head gasket thickness was 0.047", which is the same as the new gasket I have, so I'm guessing it crushes down to some number, probably around 0.040" for my compression calculation.

My handy dandy home made valve spring compressor worked like a champ.


I also outlined the ports to get an okay estimate of the current port area. Light coat of oil on the port, and a blue shop towel works great. I did the chambers to so I can try and figure out how much compression I can try and gain back by shaving the head.


A pane of glass for some back lighting and traced them out on some scaled engineering paper and can do a rough calc of area here, but I'll probably digitize the shapes to scale and let some computer software calculate the areas. Then I'll average the intake ports together to use as an intake number and then average 1 & 6 exhaust together and then 2, 3, 4 & 5 together for the two exhaust numbers.


Now I can begin the porting!


Edited by TheSilverBuick (06/13/14 09:13 PM)
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Rebuilding an OHC Pontiac 250 with EFI and a Turbo