Head gasket bore question?
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Racer
Joined: Jul 2010
Posts: 261
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From: Manahawkin NJ
Head gasket bore question?
I have a stock bore 350. It was suggested that I use a Fel Pro 7733pt2. the bore is listed at 4.125 with a .039 compressed thickness.
Wouldn't it make more sense to use a gasket with a smaller bore? Would it be better to use a GM Performance 10105117. 4.00 bore and a .028 height? BTW the heads a Pro TopLine Cast Iron votecs.
Thanks
Tom
Wouldn't it make more sense to use a gasket with a smaller bore? Would it be better to use a GM Performance 10105117. 4.00 bore and a .028 height? BTW the heads a Pro TopLine Cast Iron votecs.
Thanks
Tom
Drifting
Joined: Jun 2010
Posts: 1,781
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From: Oxford Ohio
The 4.125 bore is Std 400 cu. I suspect that the larger 400 bore is universal for the 350 and 400 so two part numbers to stock are not required.
Personally I'd find a gasket the correct size for the 350. You'll have a few thousands any way for over bored 350's. A .060 over 350 would have a little over .030 space in there anyway. The 4.125 gasket would have twice that.
Personally I'd find a gasket the correct size for the 350. You'll have a few thousands any way for over bored 350's. A .060 over 350 would have a little over .030 space in there anyway. The 4.125 gasket would have twice that.
Race Director
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From: Corsicana, Tx
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Generally you're looking for about .040" over bore size for the gasket.
JIM
JIM
Le Mans Master
Joined: Sep 2001
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From: Unreconstructed, South Carolina
regarding gaskets for 350 blocks ... heck ... most do Not have a round hole anyway ... I really dunno how they measure those diameters ... but most are advertized 4.100 to about 4.170 and 4.166 is quite common.
Routinely blocks' bores have a lead-in chamfer cut around bore & that makes bores' diameter at deck even bigger ... never ever allow gasket to hang over edge-into bore & not into chamfer either. That's why gaskets're bigger than block bore itself.
10105117 is a great gasket for 302 or 327 or 350 blocks (referred to as 4.00" bore) and that gasket has bigger hole than 4.00" ... but
Unless your 350 block has been decked more than about 0.010"
I suggest felpro 1094 with iron heads ... thin rubber coated steel shim 0.015" thick x 4.100 ... about 3.2cc.
fyi typical sbc400 gasket has advertized bore 4.200. Suggest do Not use a 400 gasket on a 350 block. Suggest do Not guess on this stuff.
Routinely blocks' bores have a lead-in chamfer cut around bore & that makes bores' diameter at deck even bigger ... never ever allow gasket to hang over edge-into bore & not into chamfer either. That's why gaskets're bigger than block bore itself.
10105117 is a great gasket for 302 or 327 or 350 blocks (referred to as 4.00" bore) and that gasket has bigger hole than 4.00" ... but
Unless your 350 block has been decked more than about 0.010"
I suggest felpro 1094 with iron heads ... thin rubber coated steel shim 0.015" thick x 4.100 ... about 3.2cc.
fyi typical sbc400 gasket has advertized bore 4.200. Suggest do Not use a 400 gasket on a 350 block. Suggest do Not guess on this stuff.
Racer
Joined: Nov 2004
Posts: 485
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From: Oakville ON
Jackson on head gaskets
Thanks
Le Mans Master
Joined: Sep 2001
Posts: 7,739
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From: Unreconstructed, South Carolina
Super-sharp pics of block's super-clean, no-paint ID stamp pad can often tell if block has ever been decked.
Measure it yourself. With Head OFF motor. Carefully verify piston is at very top of its stroke. Then measure from block's deck to top of piston crown (as close as is practical to its edge but Not atop a Piston's chamfer). Measure several times-positions to help identify any measurement error. When new factory OE sbc Average about 0.025" 'down in the hole'.
sbc needs some 'gap' between top of piston and flat surface of head. The gasket provides some. This gap area commonly called quench or squeeze. A value of 0.040" is widely accepted as ideal. It can be less but heat-expansion Requires some. Any more than about 0.050" and any "stirring" benefit of a tight quench begins dropping off.
Merry Christmas y'all
Last edited by jackson; Dec 25, 2010 at 10:08 AM.
