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Old 07-11-2005, 06:02 AM
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SBO 350, Head Gasket help, with photos

Original Olds 350, 2 dead cylinders thread

Before I re-assemble this engine, I examined the head gasket I found to the block and head. It looks off, yet it's the part # required for this exact engine.

The 79cc Olds #8 heads had their chambers modified to make them 67cc to boost HP. More in spec with the 1970 442. The block is '68-70. But #8 heads are '73-76 ('77 too, when they changed block head bolt size). Concern is the water passage line up. Felpro 8171PT1, for 1968-1976 Olds small block. So why is all this water restricted?? In last photo below, you can see a totally blocked small water hole around #2 intake (manufacturing error, it almost reached). My concern is photo #3.

The 68-70 #2 SBO. The angled notch piston indicates high-compression. Not seen in the pic, but there is also a round notch in the pistons (i.e. '70 W31). Large water jackets. #2 and #8 haven't seen much flame action. You can also see the bent pushrods on #3.

The #8 head. The 79cc are now 67cc, measured with water. All "ovals" are half blocked (block/head issue, not gasket). Top right corner water hole (by #2) was totally blocked by head gasket (gasket's fault, easily fixed).

Close-up of #4,#6. Molten metal added between #4,#6 exhaust ports to add 20HP. Bottom three rectangular holes (below head bolt holes) are completely blocked by gasket. Why have these on the head then?

Felpro 8171PT1. Designed with large top half-ovals (cut by the block) and 4 small holes (these line up) on the cylinder bottoms. Visible is the top right water hole that "missed" totally any water feed. Rectangular head openings, toward the bottom, can not reach the block's water at all.

125 PSI on all odd cylinders. 135PSI on #4, 145PSI on #6. Not only not within 10% of each other, but isn't 125PSI a little low for 67cc chambers & high compression slugs? Other head has same #4/#6 exhaust port divider added, so these heads do match. Is this the 308 degree duration W31 static compression cam bleed off?

Factory rated these motors at 325HP, but actual output was around 375HP, on exhaust manifolds.

At very least I have to fix the #2 intake "almost reach hole". Half-ovals seem by design.

Thanks for any advice


Last edited by 360Camaro; 07-11-2005 at 08:39 AM.
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Old 07-11-2005, 08:33 AM
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When I said "bottom 3 rectangular" openings, it's actually reversed, they sit on top of the engine bores. Either way, I wonder why they are blocked & what purpose they serve. I can't find a picture of a heads off Olds small block on the net to compare my 350 block with.

I realize I can't really open the rectangles since it would just flow the thickness of the gasket, .038" maybe. Can't see that doing much good. Why put full ovals only to use half? It doesn't matter as long as it works, just gives me pause.

So I guess this gasket will be alright maybe (after I make sure #2 medium hole actually reaches the block's water). The #8 head made in 77 uses a different gasket for 1/2 head bolts and only 2 dowel pins.

FelPro 8171PT1
Application: CADILLAC, GMC, Olds. V8, 330, 350(5.7l) (Exc. 1975-76 Omega), 400, 425, 455 Eng., 1964-76

FelPro 8506PT
Application: GM PROD. V8, 350 (5.7l) Eng. VIN B, R, 8, 1977-80

My block casting is certainly '68-70 350, no question. It may have 425 overbore pistons (same pin height), making a 362ci. But the block and head both have 3 dowels pins. So I should relax and put my faith in Felpro right and just install the 8171's right?

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Old 07-11-2005, 09:52 AM
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chevy has done the same thing.they had a big hole in the head gasket for yrs. and lately because many people have been using the pipe plugs and then drill a small 5/16's hole i believe ,now they put a small hole there in the gasket.i think i would feel much better going to and asking those questions.thats all they deal with and should have what you need to here.good luck
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Old 07-11-2005, 11:41 AM
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Actually the "holes" that concern me are the 3 rectangles in the head; the gasket (and block) block them off. So I wonder what's their purpose?

Will try Been thru that site. Useful, but I can't see any pictures, in fact anywhere on the 'net. Will try their forum. Olds just ain't as popular as Chebbies/Fords. Great motor though (large bore/small stroke, on the 350).

Thought this motor was stock rebuild when I grabbed the '75 442 for $500 (new W31 motor/modded tranny, their mechanic took their money & couldn't fix it, 2 stuck valves from sitting). 180HP I thought. Now the wife's car is going to blow away my 360ci 9:1CR SBC Camaro. With 10+ CR we're going to be in trouble at the pumps... or I could kill the timing I suppose.
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Old 07-11-2005, 07:09 PM
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It's not all that unusual, perhaps the holes are a throwback from an earlier design that used them? I know that I've seen similar things...Since the block covers them up, not just the head gaskets, I wouldn't lose sleep over it.

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Old 07-11-2005, 08:29 PM
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Yeah, this is what I finally figured. It seems the cylinders will get most of their cooling from the smaller holes. I did carefully modify the gasket to allow a blocked medium size hole around #2 to get access to block water. Then I put the gasket on the head only to find it's blocked there too So I basically just created a tiny channel (gasket thickness) for water to get to the hole; probably waste of time really.

It's not Felpro's fault at all; it's how Olds made the heads. Knowing they go on both sides of the V8 motor, why create a slightly off-hole blockage that propagates to the other side too, in this case, diagonal medium size hole blockage? Strange, must not be that important.

My SBC build up had similar issue. It runs hot likely because of .060 overbore, among other things. Dual Iroc fans can't really keep it cool for long and it's got A/C. I plan on adding A/C to this 442. Both cars are nearly 400HP.

Can't wait to hear the single pattern W31 308 deg dur cam rumble thru my headers/h-pipe/duals finally on all 8 cyls. Heads are redone and on, motor should be done tomorrow; will put motor/car pics in my gallery here.

Last edited by 360Camaro; 07-11-2005 at 08:41 PM.
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