After measuring deck clearance I realized I got gaskets too thick (0.040); also have a question about the coolant passage.

First, this is an L98 383 with 3.75 stroke and 6” forged rods and forged flat top, short skirt pistons. Heads are AFR 190 with a 74cc chamber. Measuring clearance at piston 1, rocking piston back and forth, the tightest clearance is 0.015”. So if I understand rightly that quench should be .035-.045,
.020 gasket sets static compression to 10.63:1 and
.030 gasket sets sc to 10.39:1.

So my question is which is better?

Secondly, does it matter that this coolant passage doesn’t exactly match the hole in the gasket?

 

So what is the piston to deck?

Jebby

 

GM gaskets are .026, just about all the rest are .040. I think either way it will be fine with 10ish compression. Mine is .047 @ 11.3:1 and it works fine on pump gas with a ~230 cam.

The cooling port alignment looks like it’s off by more than a little. I’d try a different head gasket set.

 

Found the dcr calculator and plugged in numbers. Smallest 4.030 gasket I could find at Summit is an .027 thickness. Cam is XR276HR-10. if I set crank advance at 4, that sets quench at 0.042, CR at 10.47:1, and DCR at 8.42.

So then only question left is setting the timing chain gear angle. The calculator uses crank angle and that if the cam maker presets angle then double it to get crank angle. Comp presets to 4 degrees. So that would be crank angle of 8, right? So do I retard the gear 2 degrees?

Heres the calculator numbers:

 

Regarding the port, the only 4.030 gaskets I could find at Summit are the Cometic MLS. They say the port should be drilled to size so I guess I can just do that. Ive got a tool that “nips” steel so I think I can do a custom cut.

 

0.015”

 

The calc doesn't use crank angle....it uses gear phase angle....the crank is always a constant.....the gear phasing determines the advance or retard of the cam......so for your purposes....plug in 4 degrees.....same thing.

Mahle makes an excellent .027 thick gasket that is just right for a 4.030 bore.......I recommend it.......I keep them in stock now.....

Jebby

 

Awesome, thanks! So since Comp “bakes in” the four degrees, I should just set the timing chain gear to the zero dot, is that correct?

 

Yes.

Jebby

 

​​​​@STORMIN NORMAN Where do you find those GJ .026 gaskets? P/N? Google is useless.

 

Because they are not .026...they are .028.......I bet it is made by Mahle.....they are an OEM supplier.....

CHEVROLET 5.7L/350 Chevy small block Gen I Chevrolet Performance Head Gaskets - 0.028 in. Compressed Thickness (in.) - Free Shipping on Orders Over $109 at Summit Racing

Jebby

 

So isn’t it important to choose head gaskets the same bore as the cylinders? I see now I wasn’t finding a good selection because I was limiting my search to 4.030 bore.

 

OK, so I appreciate your patience as I ask all these questions - you guys are a wealth of knowledge I haven’t been able to find anywhere else.

So then as I look at all these gaskets I see that each manufacturer seems to have their own take on the coolant holes. And for that matter, even the heads aren’t a one for one match.

Here’s the AFR 190 heads.
The heat riser makes it legal in California.


AFR 190cc Street Heads w/ heat riser, 74cc chamber

Here’s the Cometic gaskets (.027” thick, 4.030 bore)


Cometic MLS Head Gaskets C5399-027

And here is the Chevy Performance gasket you linked to Jebby.


Chevrolet Performance Composition Head Gaskets 10105117

…and of course the block (1989 L98)


1989 L98 head hole pattern

So my point is this; what holes are required and how big do they have to be? There’s a LOT of variation between all those head gaskets out there!

 

The Cometic doesn't have enough flow area IMHO on that block.........the GM gasket uses the correct two hole setup.......Fel Pro performance gaskets (like the 1003) have a third hole to promote even more flow........they actually have instructions to drill the hole yourself on older blocks.....and it works.....you see, the two exhaust ports are right next ot each other, right there.....and get hotter than the two outer ports......running extra water through there balances the heat.....my 406 loves it.....
In this application I would run the GM gasket.......or......the Mr. Gasket 1134G, which is made by Corteco which used to be "Detroit Gasket".....Edelbrock sells a similar composition of gasket. It is an excellent piece and the last 383 (385) I built has these...as it was 4.040 bore and the Mahle fire ring is just a C-hair too small.....the 385 is out there running and cooling perfectly......
CHEVROLET Mr. Gasket 1134G Mr. Gasket Ultra-Seal Head Gaskets | Summit Racing
I have never ran a Cometic gasket on a roller one piece block so do not know all the details on that......

Jebby

 

Typically, a head gasket bores range is from 0.030 to 0.060 larger than the cylinder. And in some cases as much as 0.100 bigger.

Keep in mind the cylinder head is probably the second hottest part of the engine (next to exhaust manifolds). So, think about the expansion of that thin metal gasket being pounded on by heat and pressure. You sure don't want that gasket expanding into the travel of the piston or creating hot spots for detonation.

Another thing about head gaskets selection is a somewhat common term of "Steam Holes". Not sure but, I think those are related to the 400 block only.

 

Though the Mahle and the Mr. Gasket show 4.100 bore....I can confirm that both are much smaller, the Mahle at 4.030 and the Mr.Gasket at 4.040......
I had spec'd the Mahle gasket for the 385 build and I set it on to find it was just a bit smaller than 4.040.......others would have assembled it...not me, I looked again and ordered the Mr. Gasket....to my surprise, three days later I set it on and it just cleared the bore at 4.040.
So....now knowing that....these two gaskets have become penciled into my notebook as viable options.
BTW....to those swear to a brand of gasket as opposed to another....let me tell you that if both head and block surfaces are flat and have a shiny finish after milling.....a damn piece of posterboard and a twist tie as a fire ring will seal this ****.....most of the gripe the novice bitch about involves old factory milled decks and blocks.........
Sealing engine parts is like a paint job.....about 80% prep and 20% what you use to seal it.......motorcycle engine cases and a lot of new automotive engines like the 2.4L Ecotec GM.....have NO gasket between some surfaces......RTV only.....the surfaces are machined so nice that only a paper thin coat of RTV is necessary......I have built DOHC 750/900/1100 Honda engines have exactly one gasket on them....the head gasket.....all other pieces had a thin coat of Hondabond 4, thinned with reducer....spread on with an acid brush......
Why am I saying this here? Because these .020 something thick gaskets seal very well.......as long as everything is flat......the .015 steel shim gaskets are the same way......if your deck and heads are ****....use the .041 Fel Pro stuff......which will seal most anything...

Jebby

 

Thanks Jebby, I settled on the Fel Pro MLS at .026 (want to stay within 35-45 quench and deck is .015.). Both the deck and head are fairly shiny so I think it meets Fel Pro's 30RA spec for MLS. I like that it has the extra flow in the center.
Fel-Pro Performance PermaTorque MLS Head Gaskets 1142026

 

Yes, that's the one I was thinking of.

 

For the sake of wrapping this up, here's the one I settled on.:


Fel-Pro Performance PermaTorque MLS Head Gaskets 1142026