I was rebuilding a 350 using Felpro head gaskets this week and the gasket set came with instructions for drilling enlarged holes for water passages....I have never heard of that and I am far from an experienced engine rebuilder....but it did get me thinking about an engine I had rebuilt years ago that I could never stop from overheating at idle, and I went through it all...is it possible that the issue could be reversed head gaskets or a blocked water passage due to the head gaskets....have any of you ever experienced that as a cause of an overheating problem? Let me know your thoughts. Dino
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Dino Lanno -
I can't answer your question directly, but Felpro offers several different head gaskets for small blocks. What's the part number of what you have and what type of construction is it.
I recall advice about "steam holes", but that only applied to 400 blocks.
Duke -
Duke, it was an 8651tp.. why do the cooling jacket ports have small holes in the gasket but not in the cylinder case or head?Dino LannoComment
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Do you mean 8651 PT? If there are holes in the gasket, but not corresponding holes in the block or heads, maybe those are for the 400 blocks. So it's probably nothing to be concerned about, but let's see what others have to say.
DukeComment
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Do the water jackets in the cylinder case usually match the head gasket shapes or does the gasket have small holes while the case has larger triangular holes for water passages?Dino LannoComment
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The last engine I own that needed a head gasket was my Cosworth Vega that needed new valve guilds a bit over 20 years ago. That engine is somewhat unique in that coolant output from the pump is pumped into the block and all transfer to the head is at the rear of the block. There are no intermediate transfer passages to the head like a SBC.
As long as the gasket has openings that have openings on BOTH the head and block, I think it is okay to use.
If the gasket has openings that are not on both the head AND the block, I don't think it's a concern. They may be just for later block and head castings like the 1970 vintage 400 CID SB "steam holes".
DukeComment
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The holes in legacy SBC head gaskets are generally small and round compared to the raw cast holes in the block and heads. In the days of steel gaskets, the gaskets would erode to the outlines of the passages during their time in service. The LT1 engine in the 92-96 C4 has composite gaskets that tend to erode in these areas as well, but they eventually become compromised and coolant enters the cyls. This is a chronic problem with the LT1 with aluminum heads at about the 100k miles interval.
For the legacy SBC, there was a fad in the 70s era to enlarge the cooling holes between the center cyls at the bottom, and the spark plug cooling holes to increase flow around the center two cyls adjacent exhaust ports. Ever notice that the divider between #4 & #6, #3 & #5 always looks hotter or discolored compared to the other areas of the block and head? This is a result of the concentrated heat from the paired exhaust ports just above this area. I don't know if shops still advocate these modifications or not. I've never worried about it.
The 400 block has 2 additional holes (about 1/8" in diameter) above and below each simeased (Spelling.) cyl wall between the cyl pairs. The 400 block is also 1.125 bore size. I've never used a 400 gasket nor inspected its suitability for use on a non-siamesed block with a 4.030 bore but I don't think a 1.125 gasket would be suitable. Mostly because of the issue described next. (You want to avoid unnecessary holes near the fire rings. They are a potential leak path.)
The gaskets and cyl heads are of course symmetrical and can be installed on either bank. But only the Right Bank has a hole in the block for the water pump bypass passage at roughly the 5:00 position. (Standing next to the engine.) All cyl heads have the corresponding hole for the bypass passage. On the left bank, this passage in the head and gasket is at 5:00 on Cyl #7. There isn't a hole in the block, but the hole in the head and gasket allows coolant to contact the block. This hole is very close to the fire ring, actually, this is the location where coolant is closest to the fire ring anywhere on the gasket. I have had numerous engines over the years exhibit corrosion at this #7 cyl "dead hole" on the block surface, occasionally under the fire ring into the cyl. This is really the only problem area I'm aware of as far as keeping coolant out of the chambers on a Legacy SBC with iron heads.
I don't have any thoughts regarding Dino's overheat at idle being caused by gasket problems, because it is doubtful that they were "gasket problems". My experience has been that an overheat at idle, but the engine stays on temp when the car is moving is a radiator air-flow problem, not an engine problem.
That's enough TL;DR. Cheers.
I found this pic on the Fel Pro site under 8651PT, but this is not a SBC gasket. (Wrong configuration.) But for illustration, it has the "steam holes" that the 400 gasket, and most other engines with siamesed cyl walls have.
732f9f9c-330e-4914-9f35-43eb167ef32e.jpg
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