427-Vette
Forum Newbie
Posts: 12
Loc: Ireland
Reg: 12-11-09
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12-11-09 02:25 PM - Post#1822141
Hello guys,
I am building a 427 motor and am working out my static / dynamic compression ratio. I have read that most chevy heads cc more than the advertised volume, my heads are 3904390 '67 427 Corvette heads, the chevy spec. cc is 98.4cc,
I have measured mine twice to be sure, and both times came out the same at exactly 112cc.
Thats 13.6cc over the factory spec, is this normal for these heads, or have mine been modded ?Anyone familar with these 3904390's.
Any info really appreciated !
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Impala65SS
Valued Contributor
Posts: 3355
Loc: Sweden
Reg: 08-23-07
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12-11-09 04:34 PM - Post#1822207
In response to 427-Vette
My, that really sounds a LOT!
100-101cm³ is more like it. They are identical to 702's, btw.
Have you measured ALL the chambers? I have never seen a head, and less so a pair, with identical volume within one cm³.
Are they ported?
Hi perf valves installed?
Valves pounded after years without lead?
How did you stick the plate with the filler hole to the head deck surface?
How large is the filler hole?
What fluid did you use?
What sealing precautions did you do?
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427-Vette
Forum Newbie
Posts: 12
Loc: Ireland
Reg: 12-11-09
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12-11-09 04:44 PM - Post#1822213
In response to Impala65SS
They have manley valves, I sealed the valves with some marine grease, used a glass plate with a 1/4" hole, greased and clamped down with a "G" clamp, have only checked one chamber so far, but done it twice as I was suprised with the result, not sure if the valves have sunk as I have nothing to compare it to, starting to wonder if someone has machined them to de-shroud the valves a tad, but again I have no other heads to compare.
I will take a picture and post it, they have had some minor porting. I used hydraulic fluid thinned out with about 10% synthetic thinners as the fluid
Edited by 427-Vette on 12-11-09 04:46 PM. Reason for edit: No reason given.
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427-Vette
Forum Newbie
Posts: 12
Loc: Ireland
Reg: 12-11-09
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12-11-09 05:17 PM - Post#1822227
In response to 427-Vette
Here are some pictures of what I have,
thanks for the reply !
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Impala65SS
Valued Contributor
Posts: 3355
Loc: Sweden
Reg: 08-23-07
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12-12-09 06:27 AM - Post#1822435
In response to 427-Vette
They have manley valves, I sealed the valves with some marine grease, used a glass plate with a 1/4" hole, greased and clamped down with a "G" clamp, have only checked one chamber so far, but done it twice as I was suprised with the result, not sure if the valves have sunk as I have nothing to compare it to, starting to wonder if someone has machined them to de-shroud the valves a tad, but again I have no other heads to compare.
I will take a picture and post it, they have had some minor porting. I used hydraulic fluid thinned out with about 10% synthetic thinners as the fluid
From what you are telling us - it's pretty much the way I do it, anyway.
The chambers looks definitely unmolested in my eyes. There is obviously no polishing of the chamber done anyway, that would have taken a couple of cm³. Some grind down the front quench surface to mimic the 063,215,802,290-heads, not here though.
-If someone went through the trouble to unshroud, what looks like standard 2.06/1.72 valves (albeit aftermarket valves as you said), with a factory appearing method (radially) - that would perhaps explain a higher volume. It seems farfetched, though.
Reinstalling std low perf valves will nominally set the volume back maybe 0.8 (exhaust valve seat cut at depth 0.020") to 1.1cm³ (intake at 0.020") - but if there is an additional 30° cut, to unshroud the machined valve recessment, it will subtract another 0.5cm³ or so per valve. The additional cut is hard to calculate, since the chamber surface is irregular. It's just a guess.
What did you use to measure the volume with? I use a 200cm³ syringe which I carefully knock all the bubbles out from, and then make sure I start filling up on a definite mark every time.
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motorman
Super Senior Member
Posts: 5019
Loc: south western pa.
Reg: 01-25-00
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12-14-09 08:17 AM - Post#1823772
In response to 427-Vette
depends how far they "sunk" the valves doing the valve job. check each chamber to see what you have.
| retired race engine builder,former NASCAR tech inspector. new corvettes owned 1959,1962,1963,1964,1965, 1966,1997,1999,2002,2005, 2008 plus 30+ other chevy cars and trucks along the way |
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427-Vette
Forum Newbie
Posts: 12
Loc: Ireland
Reg: 12-11-09
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12-17-09 02:51 PM - Post#1825779
In response to motorman
Thats a good point motorman, I will check the rest of the chambers
thanks !
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