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There is no "best" head gasket, but name brands like Felpro and Victor Reinz offer high quality gaskets that should do the job. The most important thing is to get the CR right. You say that your current CR is 10.25, but didn't say how it was measured or what parts (like pistons and head gasket thickness) that were used to achieve 10.25. This needs to be verified because there are several variables that have a significant impact on CR. A set of pistons that claims a given CR doesn't mean diddly-squat because deck clearance and head gasket thickness can yield significantly difference values.

The first thing you should to is search for threads started by me and download and read the compression ratio article. Then remove the heads and ID the gasket and measure its thickness. Measure deck clearance, ID the pistons, and find their dome/dish volume. Now you can use the CR calculator to determine the head gasket thickness to achieve 10.25 that I think is a good target for L-71.

Once the heads are removed you need to carefully check them and the cylinder bores for cracks that might be causing the leak. Don't assume it could only be a head gasket issue, but also inspect the gasket for signs of a leak to help verify that it's not a block or head crack.

Keep us informed as you progress.

Duke

 

Fel Pro is definitely up to the task. Best is an mls type gasket but the regular blue Fel Pros are great. To use the mls everything needs to be flat and have a smooth surface finish.

 

Did you recently add coolant? If it's leaking enough to be running down the cylinder wall it should have all been out sitting that long. Was the oil milky? I did 396 for a friend a few years ago that was supposed to be rebuilt. It had a cracked head like Duke refered to.

 

From my understanding there are the original " Cork" head gasket and the modern upgraded rubber head gaskets. No brainer on the one I would choose for my C2 Corvette.

 

Here's the head gasket and intake gasket I used during my 402 rebuild. They are available from Summit Racing. They worked very well.

· Intake Manifold Gasket FEL 1211

· Head Gaskets Fel 1027 (.039 thick)

 

I would put 8180pt2 Fel Pros on it. They would be available from any parts house or online.

 

The 8180PT-2 is the stock replacement head gasket for the big block.
Options if you wish.
First step up is the 500 series head gaskets, these are tougher than the stock gasket. Biggest advantage is 3x the resistance to detonation failure over a stock gasket due to a Stainless fire ring being used. These are also flat pressed like the performance and marine gaskets so you get a lot for the small price increase. These were initally designed for Hard Working Engines, Heavy Trucks and Motor Homes that were blowing out stock gaskets but this same HD fire ring gives you protection in a Performance engine.

The Performance Gaskets offer even more Detonation resistance by inserting a copper or steel wire ring inside the fire ring. In detonation the head will bounce on the block while accelerating. This causes pounding of the fire ring. Race engines are tuned to the edge for performance and these gaskets give a lot more detonation protection over stock or the 500 series.

The very most expensive and best technology is the MLS (multi-layer-steel) gaskets. These offer the very best detonation resistance and can live for extended periods in detonation. As Robert mentioned your block and head need to be very smooth to run an MLS or the rough block and head surface can cause the MLS to fail quickly. An RA of 65 or less must be acheived with Fel-Pro MLS, other brands ask for as smooth as 20 RA, that is like a mirror finish. Some machine shops can't provide this on a deck surface.

Price wise, you can look them up and compare but from what I remember if the stock gasket is $25 the 500 series will be $35, the Performance will be $55 and the MLS will be $90 each. This just estimates the % of price increase at each step.

I would think the Stock gaskets are safe to 450 HP, maybe a little more if your tune is dead on.
500 Series in the same engine good for 500 maybe more
Performance gaskets good to 700+
MLS has been used at 2000 HP in Turbo engines.

With all this said a bad tune can ruin any of these pretty quick with severe detonation.

On the Big Blocks it is important to make sure you use the early head gasket to match the early blocks. The cooling ports changed on the later blocks.
You can look up prices and make a decision.

PS: There was a note above about Cork and Rubber gaskets, those are Valve Cover gaskets, not head gaskets.

 

Drain the block well before pulling the heads, you can pull the drain plugs from the sides and get the coolant out of the way before the head comes off.
Now when you pull the head there will be no doubt where the coolant came from if you see any in a cylinder.
As you remove the head bolts pay close attention. If you find bolts that are not as tight as they should be it is a sign of overheat gasket damage which leads to blown head gaskets.
Take good pictures with close ups of each cylinder while the gasket is still on the block if possible.
I hope you find something simple to fix.
Mark

 

No such thing as "cork" or "rubber" head gaskets.

 

what concerns me, is how can one tell?
sometimes cracks are so hard to see.
I have also replaced head gaskets on just a guess and it solved the problem.
How can one eyeball a used head gasket to see if it is bad?
also the thicker the gasket, the greater chance of future failure?
and the thinner the gasket, the greater chance of failure if the surface ( block or head) is even a tiny bit warped?

 

Normally if there is a crack big enough to leak you can see it. When I say normally I have never seen one you couldn't. With many years being involved with racing engines cracked cylinders was a norm. With the rings rubbing on the wall the irregularity will show up. Any cylinder that has been run very long with water in it will clean the carbon off of the piston and chamber. The crack will appear as a dark line or you just have the rust trail to follow. Any head warped more than .005" should be resurfaced. Below is a 64 327 I'm helping a friend with. I lapped the deck with a large stone to remove any high spots before I bored the cylinders. As you can see it quite wavy. Blocks are pushed through a huge broach when they are made. This broach shaves the decks, the end pads or China walls, the oil pan surface, and the main cap registers all at one shot. It's not the most precise operation but it worked. They say you are not supposed to use MLS head gaskets with a rough surface finish but I have and never had an issue. I wouldn't suggest it I just did it. In th 60s they used the shim gaskets, 70s up til the 90s .040" thick gaskets, and 90s to date .050" is more normal. I've never seen an issue where gasket thickness was a problem. I've used some .080" gaskets to lower compression in race engines, uh oh time for the .040 quench people to show up.

 

A leaking head gasket will usually show some erosion at the fire ring where the leak is. Cylinder wall/head inspection should be done with a brightly lighted borescope, although only a Magnaflux inspection will show a microscopic crack.

If the head/block mating surfaces pass a check with a machinists bar and .0015" feeler gage then a steel shim gasket should seal. Composition gaskets usually seal with no more than .003" surface warp.

Duke

 

An experienced Eye will see a head gasket failure quickly. Once you see a few you know what you are looking for.

Fel-Pro MLS says it will work on surfaces as rough as 65 RA, Standard tooling to deck a block leaves the deck around a 120 RA if I remember correctly.

Fel-Pro engineering used to tell us to take the freshly decked block and go at it with a piece of machine steel, maybe 2" x 6" wide, 1/2" thick. Wrap this with some 600 grit wet and dry sand paper.

In about 6-10 swipes smoothly across the top of the deck you could get the RA down from 120 to 65 or lower. The sand paper did not remove a lot of material but it took the peaks off the top leaving a better surface for the MLS gaskets.
Fel-Pro taught this method for those that do not cut decks with a CBN cutter that can leave the proper surface. That used to be 90% of machine shops when the MLS came out.
Most shops use a CBN cutter on Cylinder heads so head surface was not an issue, the blocks are what needed a little help if you wanted to use MLS.

MLS is designed to seal at the extremes, an extreme is when you have constant cylinder head movement. This happens in very high compression engines or in detonation. Turbo's, Superchargers, Nitros applications are extreme.
High cylinder pressure makes the head lift and bounce on every combustion event at wide open throttle. MLS can handle this as long as the surface is smooth. A rough surface in extreme conditions will cause an MLS to fail.
MLS is very cool technology when needed, very expensive but offers a lot of protection when needed. I know of 2,000 HP Bonneville engines that run MLS today successfully, in the old days they all had the blocks machined to receive piano wire around the fire rings to help hold the combustion pressure at these levels. MLS is much easier to use than installing Piano Wire grooves in the head and block and making them match.
Engineers say each layer of MLS gives you .001 sealing against vertical head lift. Most MLS for Chevys are 3 layers so they can allow .003 vertical head lift without failure. It takes a lot of cylinder pressure to lift a head .003 when it is clamped down by all the head bolts.
The MLS layers are held together by brass rivets so these gaskets look odd compared to what we have seen the last 50 years.

When installing an MLS you sometimes find with some heads and some blocks the Rivet gets in the way of things mounting correctly. It is OK to cut away the rivet or rivets that interfere. Once installed with head bolts the layers stay where they belong. The rivets keep it properly aligned for handling before install. It is prudent to make sure the rivets are clear before final torquing of the heads. When these first came out we saw some that did not seal because of rivet interference on aftermarket heads and blocks. Easy fix if you look for this.

 

Wow, I was thinking that crack is very rare in a .030 over block. You said this was born in a SS396 375 HP Block???

The pistons in your pictures are TRW/Sealed Power Forged Pistons part L2300F 30 Those are 427 Pistons and your bore with those is actually a 4.280 bore.

The factory 396 block uses a bore of 4.094. A 396 block at .030 would be bored at 4.124. The later 396 became a 402 which is a 396 bored .030 over.
I know pistons are sold for the 402 to be bored .060 over, at that point you are only .090 overbored in a 396.

If someone bored this 396 out to a 4.280 bore it is bored .186 overbore. No wonder it is cracked.

If it really is a 396 block it is now toast throw it away.

If you just want to get it running find a donor 454 block and take your choice to build it as a 427 or a 454. I say this because a 454 block can be had for less than $500 while the 427 blocks are now very expensive. I see people asking $5,000 + for a 427 block today.

If your car is set up for the big block it would be the easiest and least costly fix.

Hope this helps.

Mark

 

Whoa! I didn't read all of the way to the bottom of your post. Mark is spot on that block is toast! It was the day they finished boring it. Get the 454 block bore it .030" use your parts if they are still good. The pistons may not be hurt. I thought we were talking about an original 427 block.

 

Someone took a big shortcut to make a 427 by boring a 396 so thin the cylinder wall cracked on you. If that was your choice at the time you got pretty good bang for your buck.
Cylinder walls as thin as yours must have been will flex a lot while running and that will cost you proper sealing along with short life.
You are not the first to be burned by this. One of my buddys bought a crate GM 350 for his old Toyota Land Cruiser install. After a couple years life and now out of warranty it cracked a cylinder.
When he checked it out he found they took a GM 305 engine and bored it to a standard bore 350. Basically the same thing that was done with your 396 with the same result. A local shop built his replacement engine a .030 over 350 with a nice cam and he has been extremely happy with it since day one. Says it feels 50% stronger than the old engine ever did.
Of course his crate engine was out of warranty when it broke.

As mentioned a 396 crankshaft will bolt into a 454 block and give you a 427 engine and 454 blocks are cheap so you could put your parts into a 454 block and be running for not much money.

Even if you choose new forged pistons, rings, bearings gaskets, oil pump and valve job you should be well under $4,000 leaving lots of room for upgrades like Aluminum Heads to cut some weight off your front end.
And 480 Horsepower today is not a big deal, easy to do with a big block, again for a small amount of money.
Once machined with new bearings, rings and a good valve job the engine would be for all purposes NEW.

If you chose to stay at 454 cubic inches you would have more torque from idle to wide open and it will still look like a 427. You might not want to RPM it as high as a 427 but you could have great power from 0 to 6,000 RPM.
Put 427 decals on it and tell everyone it is a 427 if you wish.

Good Luck, I hope you get what you want. You might check around your local area and see what quality machine shops exist in your area.

Mark

 

The 366 Crank is a forged crankshaft and can be balanced for use in a 396 or 427 as they have the same stroke.
Since it was originally a truck engine with very heavy pistons the change to a 396 or 427 would involve taking weight out of the crank.
Much easier to do than adding weight to make balance so it is not a second quality piece, it is just re purposed for better use!

 

[QUOTE=C2Scho;1599608905] I think that the letter B in the VIN means that the engine was assembled in Baltimore. Thanks to all of you who responded.

C.J. [\QUOTE]

Nope. The "B" in the VIN derivative says the car the engine was originally installed in was built at the Baltimore assembly plant. The engine was cast/machined/assembled at Tonawanda, as were all big-block engines.

 

if that car vin is still around someone will want it as that is a 396/375 engine stamp