Oversize bore head gaskets
June 28th, 2024, 01:34 PM
#1
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Oversize bore head gaskets
Having my 350 bored out 68 over to 4.125. Need head gaskets to match bore. Only thing I can find is cometic gaskets but they cost over 200 for set. Any other options out there for 4.125 bore head gaskets?
June 28th, 2024, 02:56 PM
#2
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Join Date: Nov 2008
Location: Central Fl
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Std Fel Pro gaskets come with a bore size of 4.200 for example. You don’t need special gaskets.
June 28th, 2024, 02:59 PM
#3
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June 28th, 2024, 04:49 PM
#4
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Fel Pro 8506pt IS 4.130 bore size. This may or may not work depending on how much chamfer your machine shop put on the bores. Mahle has a gasket too. Not sure of the part number but i have two at the shop I can look at on Monday but they are MLS gaskets. Mark should know the number. I am pretty sure my customer got them from him.
June 29th, 2024, 05:21 AM
#6
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I am going to be running around 10 to 1 or so compression and with boring all the way to 68 over i was hesitant to use head gaskets with bores of 4.2 thinking i would have blow outs between cylinders since will have so much meat machined off of bores. Do you think using 4.2 or bigger gaskets would still hold up in thos build?
June 29th, 2024, 06:12 AM
#8
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I am going to be running around 10 to 1 or so compression and with boring all the way to 68 over i was hesitant to use head gaskets with bores of 4.2 thinking i would have blow outs between cylinders since will have so much meat machined off of bores. Do you think using 4.2 or bigger gaskets would still hold up in this build?
June 29th, 2024, 01:54 PM
#10
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you should be ok with these unless your machinist cut a huge chamfer on the bore.
it’s also not a bad idea to pay the $200 for cometics to get the quench clearance tight as you can…it’s worth it..If you know the final piston to deck clearance.. order them custom
here’s the 8506’s. the 8171PT’s are really 4.250”
Last edited by CANADIANOLDS; June 29th, 2024 at 02:09 PM.
June 29th, 2024, 04:57 PM
#12
Old(s) Fart
Join Date: Mar 2007
Location: Northern VA
Posts: 47,682
The stock bore in both the 425 and 455 Olds motors is 4.125". Head gaskets are larger to allow for overbores. Yes, 350s and 455s can use the same head gaskets.
Today, 07:10 AM
#15
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Join Date: Dec 2006
Location: Melville, Saskatchewan
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Stupid spell check, I just had to😁. You have great recommendations here, as said most Oldsmobile V8 head gaskets are larger than your bore due to having the same gaskets for the larger bore 455. I have set of Mr Gasket MLS that are 4.100" to match my 4.100" bore. They looked spot on but will check the cylinder for a chamfer BillK mentioned to make sure they cover properly as I am planning aluminum heads this Winter. With iron heads, nearly any head gaskets will work, no dissimilar metals to worry about. Unless you are 0 decking the block, you will probably be in the 9 to 1 compression range.
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