Hey, I`m going to change heads on a 1978 L-82 to Brodix 1021004, and need some advice in picking the right head gaskets. Have read some threads about it, and find the 0.015 inch gasket recommended in one of them. The bore on this engine is 4.00 - and the gaskets I can find at Summit with 0.015 inch compressed thickness are with oversized bore. The best fit I can find so far are some GM performance gaskets with 0.028 thickness. Does it matter if the gaskets are oversized in bore - or should I be pleased with the GM´s at 4.00 bore and 0.028 thickness? The intake is a 2101 performer. Please guide me here.

 

The .015 gasket is a steel shim gasket and I doubt Brodix would recommend that, though you could pose the question to them. They're probably going to point to a traditional fiber composite-type gasket. I'm not sure what you mean by overbore. Head gasket bore size will always be larger than a standard cylinder bore size and most off the shelf gaskets are made from standard to minimal 30 over, then they usually get specialized beyond a 30 over.

 

O.k. - by "overbore" I ment that the diameter in the gasket is slightly larger than the cylinder bore. The only gasket I can find with bore diameter equal to cylinder bore is the GM gasket. Other recommended gaskets are with lager bore. My question was if this matters - could I for instance choose this gasket:
http://www.summitracing.com/parts/FPP-1043/

 

Yes. That gasket should work fine.

 

Thanks for the advice.

 

The felpro fpp-1094 .015 gasket is rubber coated compatible with
iron/aluminum, its not a regular steel shim gasket, you can buy a regular steel shim .015 gasket but there for iron/iron.

The thickness of the gasket makes the bigger difference in volume not the dia. for instance a 4.100 .026 = 5.4cc, a 4.100 .015 = 3.2cc.

4.100 .039 = 8.5cc, 4.100 .041 = 9.0cc.

if you were to use a gasket as big as 4.200 .041 = 9.3cc
if you the same 4.200 in a .039 = 9.0cc.

a 4.166 gasket at .041 = 9.1cc, 4.166 at .039 + 8.9cc.

if your pistons are down in the hole (factory) block has not been cut the least gasket you want is the #5746, 4.100 .026 = 5.4cc
or better yet the FPP-1094 4.100 .015 = 3.2cc,

If you just want to kill yourself off for compression slap on the 4.100 .041 = 9.0cc or the 4.100 .039 =8.5cc. or you can keep getting a litte worse 4.166, .041 = 9.1cc or 4.166 .039 = 8.9cc.

Not much sense in spending $1000.00 to $2,000.00 for aftermarket heads with smaller 64cc chambers looking for more compression then add back another 5.9cc of volume in your cylinder picking to thick of gasket. .039 or .041 thick gaskets belong on a ZERO decked block. You know what used to be just racers doing it. Someone that needed a little taken off the block say .010, .015 would use the 4.100, .026 5.4cc gasket.

Chevy back when there was nothing but iron heads block used a
.018 steel shim gasket built engines over the yrs in the millions that way both in high compression and low compression versions. If your block is strait, heads strait the gasket holds. You don't walk in a machine shop they find one or the other is warped a little they don't say well you have been using a .015 or .018 gasket don't worry about it we will save you some bucks just throw on a.041 gasket. I do not unstand this FEAR factor of a .015 gasket.

Full gaskit kits will generally come with a .041 gasket is it because its a better gasket NOPE its in there because if someone has a cut deck does not know it they use a .026 or .015 gasket they end up with piston head contact not good. the .041 gasket covers anybodys behind. The person with the pistons factory down just looses some compression he could have had, may not even know any better. You need .035 piston to head clearance, even a zero decked block the .041 gasket covers it. .039 .041 gaskets belong on ZERO decked blocks.

Why did chevy put the pistons down in the hole use a .018 gasket.
This allowed if something happend the block needed decking in a rebuild not a problem .026 gasket fixes it back up. If they would have done things more ideal performance wise tried to get closer to a zero deck, then there would be no room for rebuilds the owner would need another block. No one would want a piston sticking .010 .015 out of the bore.

 

O.k. - so the GM performance gasket at 4.0 * 0.028 may be a good choice?

 

Unless someone has took a lot off your deck you should be able to use the .028 gasket. .035 is the minimum recomended piston head clearance. Your piston would only need to be down .007 in the hole to meet that requirement.

PROBLEM performance wise is your pistons are probably at least .028 .032 down if your block has never been decked.

Pistons down like this is why the .018 steel shim gasket from 1955 to in the MILLIONS of engines built .028 down + .018 gasket = .046 piston head clearance, plenty of clearance.

If you use thicker then original gaskets.

.028 down + .028 gasket = .056 piston head clearance, .032 + .028 = .060 piston head clearance. You really want to mess up the volume .028 + .041 = .069 piston head clearance, .032 + .041 = .073 piston head clearance.

.028 down .015, 3.2cc volume gasket= .043 piston head clearance .032 down .015 gasket = .047 piston head clearance.

You only need .035 piston head clearance.

Thicker is not better it will not give any more durability and will cost
compression. But you don't have to believe me CHEVY used .018
thick gaskets on MILLIONS and MILLIONS and MILLIONS of engines
from cars to pickups to light trucks a few put in boats.

 

Thanks - starting to get it now. As my engine is only 25.000 miles, I presume the block has never been decked. Will measure when I get the heads off, according to the numbers you gave me. If no suprises, the 0.015 gasket that gives the best compression will be my chice. Thanks a lot again.

 

Just trying to get you to stay away from the .039 .041 gaskets
they are bad killers of compression they range from 8.9cc to 9.2cc
roughly.

 

Got it now, and looking forward to the winter work. Bought the Brodix K180 heads with ´
CNC´d runners and chambers on my holidays in US this summer. Also got Scorpion rockers, ARP head studs, Brodix girdles and new Brodix valve covers. Already got Pypes racing 2,5" X-pipe, full length headers and a 2101 edl. performer non-egr intake. Hope this build will give some more power. Anything else to go for without touching the bottom end?

 

Interesting thread! I wish I had read it a year ago. I completely rebuilt my 74 - 454 last year. I used the felpro blue .039 head gaskets. The block was not decked. Would I gain noticeable compression if I went back to the original style steel shim that came on the engine? While this new motor runs as smooth as honey....it is very tame.

Thanks.....

 

yes! my 72 355 went from 9.17 to 9.67:1
1/2 a point! But u will want to do the math on your bb

 

Don'y forget a good Cloyes double roller timing chain, and a new Harmonic ballancer.

 

I would recommend an RPM Airgap manifold. but thats just my preference.

 

I forgot to mention I bought the Cloyes double roller. What are the benefits of a new harmonic balancer, and which type to choose?

 

Does the RPM airgap get me into another rmp range, am I loosing low end torque, and getting high end hp? Do I need a drop-base?
Have considered this air cleaner for connection to the stock intake ducts: http://www.ramairbox.com/models.html - model 14*3@110.

 

the air gap will be less low rpm torque than a 2101.
the cut down divider can cause unwanted changes in a street car, see my story http://community-2.webtv.net/MATTGRU/carb/

 

Red it, an see your point. When I installed the performer intake I was unsure what base to use, so I ordered two, with and without the center diverter. After some thinking, I mounted the one with diverter, as the open base gasket would ruin the two-plane concept.