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By mikeT - 3 Years Ago
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I found a set of G heads for my build . They are not posted and by the thickness of the pads they have not been milled. The engine is for a street hot rod maybe 8.8- 9;1 cr ?
If these were milled .020" with best head gaskets , Block surfaces decked and ARP bolts would I have any problems?
Or should I keep looking for posted Gs?
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By Joe-JDC - 3 Years Ago
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You should be fine with the unposted G heads up to 10:1 compression ratio. I have a pair that was milled down to ~69 ccs for the 2019 EMC 303 Y, and we made over 450 hp with them. We removed them trying to find what was a problem with spring pressures, and found that they were beginning to weaken around the water passages. The compression ratio was ~10.45:1 on the 303Y. I have ported several sets of the unposted G heads, and really like how they respond to porting. I like them for street builds, and think you will be fine at 9.0:1. Joe-JDC
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By 55blacktie - 3 Years Ago
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Joe JDC, if G heads are a nominal 69cc, how much did you have to take off to get to 69cc? What was the open pressure of those springs and at what lift? .025 seems to be the safe number for non-posted G heads, but not too long ago, Ted told me that he routinely posts all non-posted heads, now.
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By Cliff - 3 Years Ago
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Hi Joe, I like your FB picture.
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By Joe-JDC - 3 Years Ago
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Hard to remember just how much was milled off the heads, I ported four sets of heads for the EMC dyno testing, and I would have to go look up all the actual figures, but ~.032-037" comes to mind for the non-posted G heads. More for the 113s. Yes, Ted recommends posting the heads if you are going to build a serious pump gas engine.
The springs were set up at different pressures on different heads, trying to stop a valve float at 6800 rpm, which turned out to the the camshaft, not the springs. The ISKY camshaft we ended up with pulled smoothly to 7300 rpm with the same spring package. Seat pressure at 1.750" was ~145# and over the nose at 365# with beehive LS spring from Comp Cams, titanium retainers, 5/16" radial locks, 1.960"/1.520" 5/16" stem manley valves Joe-JDC
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By Joe-JDC - 3 Years Ago
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Cliff, that avatar is five years old, now. Coming up on our 55th wedding anniversary soon. My youngest son gave that to us for our 50th. One of my cherished memories and one of the most thoughtful gifts we have ever received. Thanks. Joe-JDC
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By 55blacktie - 3 Years Ago
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Thanks, Joe.
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