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?

 

Std Fel Pro gaskets come with a bore size of 4.200 for example. You don’t need special gaskets.

 

I can't find any felpro for oldsmobile other than stock bore sizes. The only 4.125 I can find are for chevy motors

 

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.

 

Fel Pro 8171, 4.220 bore
Mr. Gasket 5788G 4.200 bore
Mahle 55047 4.200 bore.

 

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?

 

It’s done all the time, you’ll be fine.

 

If the gasket bore is actually 4.200 it will probably be perfect. Your cylinders are 4.125 and if your machinist left a .030" wide chamfer on the top of the cylinders the actual bore with the chamfer will be 4.185 so the 4.200 is just about perfect.

 

As long as your clamping surfaces are flat and true you will have no problems holding up to 12 to 1 CR with the aforementioned head gaskets.

 

the felpro 8506PT are specifically for the 350 olds and have a 4.130” bore

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”

 

Personally, I would go with cosmetics

 

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.

 

Good choice

 

😂😂😂😂. That’s good. I should learn to post with my glSses on

 

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.