This started with a reply to a comment in another thread that had a few replies mentioning both steel shim and composite gaskets, but I decided to start a new one rather than hyjack an existing one:

What the heck is with FelPro and their 305 gaskets... I can find them, but I can't find proper numbers about them and they're all listed as intended for stock rebuilds:
Q8510PT- I can't find a bore diameter or a compressed thickness
Q505SD- 3.736" bore, but I can't find a compressed thickness for it either
Z17020- Marine, SS core, but I can't find a bore or thickness

MrG at least gives numbers: 5780- 3.850" bore, and .028" thick, coated graphite composite, but previous experience a lot of the ones that they have listed as that are shims with a coating.

I've never seen anyone list a real stock replacement steel shim gasket for them, if someone knows where to get one I'd be interested in hearing about it. I'm guessing that these have a thickness somewhere in the teens (.01x").

SCE lists some copper gaskets but they require cutting O-ring grooves.

So does anyone have dimensions for any of these gaskets? How about a PN for stock style shims (coated or uncoated) with a diameter close to a 305 bore (3.736")?

For that matter, if I wanted an actual "performance" (this thing will see boost and N2O) gasket for a 305 that is close to the 305 bore diameter, reasonable thickness to give some sort of usable quench with a stock block (lets say <.030" thick), what would you recommend?

In the past, Fel Pro never sold any 305 gaskets with the right thickness or anywhere close. They were always .039 compressed.

The factory gasket isnt a shim really, its some sort of composite with a steel core and its around .020 thick, I forget the exact number. Gm used to sell it, but I dont know if its available that way anymore.

Hang on just a second. The factory head gasket on a LE9 truck engine was a steel shim that measured 3.800 x .015" compressed. The gasket came of completely clean and was very thin steel.

The LB9's and LG4's are not shims.

I know the trucks were shims. I have only played with the LE9s, never the LG4 or LB9. I know about those thin composites you speak of though and I thought they were closer to .028" in compressed thickness.

I measured some years ago, cant find the post but they were in the neighborhood of what is listed here, 0.021.

https://www.thirdgen.org/forums/tech...mpression.html

See posts 9 and 10.

Same with the LU5 (82-83 crossfire), the L69, and the 2 LB9's that I've disassembled (I could have sworn that a friend's LG4 had them also)... I wish I kept some around, since I don't know of any reason why I couldn't reuse them, or at least use them as a pattern for chamber mods.

Come to think of it I don't think I've ever taken apart a factory SBC without a shim in it.

What LB9 did you find a composite gasket in? Sounds like you're almost describing the composite gaskets that GM used in the iron headed LT1's.

Sorry folks, I've been off chasing a girl. Actually, she's a great lady, but back to the topic.
In my 9 years as a professional automotive machinist, 99% of the virgin SBCs I've disassembled had shims. The exceptions being some later engines. I've lost my notes, so I can't give specifics.
Anyway, I never measured my FelPros, I was just satisfied that the bores were much smaller than 4.166". But even in an 11:1 305 bored 60, on a 250 horse progressive hit of nitrous, these didn't fail. The .039" thickness is excellent if you zero-deck the block. This 11:1 nitrous build was zero-decked.
For those of you building 305s but not having them zero-decked, and not using KB 's 334 pistons, I strongly recommend that you use the FelPro steelshims with the 4.100" bore and 0.015" compressed thickness. These are nearly foolproof, and I've yet to see a failed one.

Did you catch her???

Yea, I tend to use those .015" felpro's also, but I'm specifically trying to avoid the crevice volume and want to keep quench reasonable. I was also hoping to find something closer to the 305's bore diameter that I could use to layout some chamber work, so for the time being I've ordered a set of the MRG5780's, but i'm hoping that I find some shims in the 305 that I'm taking apart, I'll probably just clean them up, coat them and re-use them.

BTW, those of you that have seen composition gaskets used, are you sure that they weren't aftermarket? I remember stopping by a friend's house that was tearing his LB9 apart and pulled a head off and found one and we had one of these "see... what did i tell you" discussions until he pulled the other side and found a factory shim

My 3rd gen engines:

'82 & '86 LG4's - both steel shims. Fairly confident neither engine had been apart before.

'87 LB9 - thick composite. Know it had been apart, it had .040"-over dished pistons, one 081 head and one swirlport head.

For what that's worth.

I've got the Felpro shims in now.

I've felt the same way about crevice volume, but I've decided that a 4.100" x .015" crevice is much less of a concern than a 4.166" x .039" crevice. The FelPro steelshims wont cause an otherwise stock L69 to fail emissions or be more prone to detonation.

try looking here http://store.summitracing.com/partde...0&autoview=sku. and before anyone thinks i came up with that on my own FAST355 put it in this post on building a 305 about one year ago. look here for building 305 tips https://www.thirdgen.org/forums/tpi/...tpi-310-a.html.
thanks fast.
I LOVE THAT SEARCH BUTTON

that .028" thickness is too thin for a zero-decked block, and too thick for an un-decked block, you need to be somewhere in between, or building a 334 using the KB pistons and an un-decked block.

according to the link to FAST355 site he used it after boring to 310 and got 356 RWHP and decking it.
but i am a an amature compared to Atilla and Fast and i will not say either of you are wrong - you just have different ways of doing things - ways i am not smart enough to think up myself.
and Atilla - my 081 heads arrived yesterday so i am in the process of practicing how to port and polish them on a junk head. thanks for all the advice on that and thanks to Fast for his advice too.
I will start a site showing pics of progress.

I had a circle track guy, he was only turning 6000 rpm, with good parts, so we tightened his piston-to-head clearance to 0.031" and sent him out. Well, he won, and we had to do teardown, so the officials could verify all his parts met the rules. The pistons had been hitting the heads, hard. Anyone who is skating by with less is one missed shift from disaster.

Tony, I'm not picking on you but it's like you've been about 2 days behind with every response you've made here... look at my post 2 up from that one and you'll see that I even posted that those are the ones that I ordered so I have something on hand if I can't find anything better, and I mentioned them in my first post also.

Atilla, yep, I'm with you 100%, and that is the reason for my original post... now I have a set of the large bore felpro shims and a set of the smaller bore, .028" MRG gaskets on hand. Compression is not an issue since I intend to run boost and spray on this thing (and I sort of expect to carry it home in a bucket sooner or later), so it looks like I have a choice of good quench (I'm expecting to see a stock deck height of .020-.025, so with hat gasket .035-.040" quench) with some mixture contamination due to the crevice volume, or better crevice volume and worse quench (I'm guessing it will end up around .059", .010-.020" more than I'd like to see).

My thoughts right now, WRT to what I want to learn from this buildup that sacrificing quench for a tighter gasket bore will have less of an affect on the things that I'm interested in seeing than vice versa, and if I decide otherwise, well, I have the other gaskets on hand.

Honestly, like I said above, I'm still hoping I pull that 305 apart and find a set of stock shims in there that are in good enough shape that I dare give them a cleanup, spray them down with some copper coat or silver paint and throw them back in.

ok i will go home and sit in a dark closet and hate myself, but please daddy don't spank me again.

With boost and spray, you're gonna need all the resistance to detonation you can get, and you're better off with good quench and slightly higher static compression than the opposite. It's okay for Tony to be slow, he's gotta be tired after 45 years of not porting heads :-)

now be nice atilla. i just got my 081 heads and i was surprised they were not flat and has these round things in them and springs too. when did they start putting valves in the heads?

are you sure your name is cogliandro and not Seinfeld or Leno?

I decked my block, but not to zero. I decked it to put the pistons at about .012" in the hole and ran the .028" compressed gasket with L30 Vortec heads.

see, that's about .040", which is currently widely accepted as a good goal for piston-to-head clearance with steel rods.

I know it is. That is why I did it that way. I wanted to run the composites and still have good quench.

that comment was for everyone else, it's obvious you knew it.

So I think I should run the .015 fel pro steel, if I'm not going to zero deck my block on my 305. I'm just putting a moderate cam in it and will mildly port the stock heads. I don't want to lose compression, so I think the .015 Fel Pro is the way to go.

Old thread, but every third gen I'm seriously considering buying has a tired 305. What about the FelPro 505SD?