Big block open chamber heads

[Steve Antonucci]

Hello,

I have a question for the big block crowd:

In my efforts to restore a 69 L/71 to its former glory, I had elected to use
the original pistons ( stock dome height ). After reading many posts here
along with great direct input from several NCRS.org members, I have since
changed my position.

My '840 cast iron heads are closed chambered design. I would like to go to
open chamber instead, to lower the compression ratio. I have been advised to
acquire head castings 14096188 or 6272990 for my L/71. My question is simple.
Can anyone tell that these heads are not '840 castings from an external
observation? I'm not trying to fool anyone here or mis-represent anything. I
just want the engine to look original while I'm having fun driving it on
unleaded fuel. If I ever decide to sell, I will also sell with the original
heads - promise.

Now, this leads me to my second question: Last summer, I restored my L/89
( 396/375hp ) for my 69 SS Camaro. I used the '842 aluminum heads ( yes, closed
chambers & stock piston dome height ). I am now wanting to replace those heads
with open chamber aluminum heads as well. I have an opportunity to purchase a
set of Chevy 14011077 aluminum castings from a friend, but I know nothing about
these heads other than that they are open chamber design. Again, are the
visually correct ( from an external glance ) for my 69 application?
Furthermore, are they of the correct configuration to work with Mark IV engines
in a street application? Any issue I should know about with these heads?

I really wish I had learned of this site before I spent the time & money
building these engines. Never too late though!

My thanks to all of you for a great forum for information!

Steve

[Ted S.]

Re: Big block open chamber heads

Mortec shows 14011077 is shown as open chamber 118cc for Mark IV. Just out of curiosity which pistons and cam did you use in your L89? Have you considered changing cams to bleed off some of the compression? What problems are you having? What PSI cranking compression are you getting?

If you do the DCR calcs on an L78 with the factory cam/pistons/heads it should run on pump gas due to the late intake closing fine. The DCR calc comes in below the 8:1 number for cast iron heads. The comp cams 11-106-3 cam has the intake closing at 86* ABDC which sure bleeds off alot of compression.

[Clem Z.]

Re: Big block open chamber heads

open chamber aluminum heads 14011077 have a totally different extrenal shape around the exhaust ports

[Steve Antonucci]

Re: Big block open chamber heads

Hi Clem,

Is this difference noticeable with the exhaust manifolds, accessory
bracketry, etc. installed?

Also, are there any functional differences with the aluminum heads in
question?

Steve

[Clem Z.]

Re: Big block open chamber heads

the closed chamber heads have a flat look to the area around the outside of the exhaust ports on the top surface of the head and the open chambered heads have a round look to the same area. i do not understand what you mean 'functional difference".

[Mark #28455]

Re: Big block open chamber heads

The 077 heads can definitely be identified by their external appearance. Closed chamber heads have a flatter external top to the exhaust port. Open chamber heads were prety similar through the mid 1970's. When they changed to the 077 "D port" casting, the Winters logo was different and the texture of the head is different. My later 077 heads also have a smaller temp sender hole. By the way, the later 842 casting heads are also different from the vintage heads.

[Steve Antonucci]

Re: Big block open chamber heads

Clem,

By functional difference, I mean how the exhaust manifolds mate and bolt
up against the exhaust side surfaces. Will the heads look out of place.

Steve

[Mark #28455]

Re: Big block open chamber heads

Functionally, the 842, 074 and 077 castings are externally interchangeable - all the options, manifolds, etc will bolt up. Piston dome styles MAY not be interchangeable. The original closed chamber pistons may hit the open chamber heads (on the big pop ups) Yes I know the open chamber is BIGGER but the closed chamber has a little more clearance in one spot! As far as I know, all the current production (TRW, JE, Keith Black) closed chamber pistons will fit the open chambers too and will drop the compression by about 3/4 point.

[Clem Z.]

Re: Big block open chamber heads

every thing will bolt up OK,it is just the cast part of the heads are different.

[Joe L.]

Re: Big block open chamber heads

Steve-----

The 14096188 and 6272990 are cast iron castings which are very similar, if not identical, in external appearance to the 3919840 castings. Either of these castings are used to manufacture the GM PART #6260482 cylinder head which is the GM SERVICE replacement for 69-71 SHP big block applications with open chamber heads. This head is still available from GM in bare form only.

In general, closed chamber pistons will work with the above-referenced heads and will produce a compression ratio significantly lower than the same pistons used with closed chamber heads. However, whenever using such pistons with these heads you need to check for proper valve-to-piston clearance by using modeling clay on the piston domes and subsequently test fitting the heads.

The GM #14011077 aluminum heads were the GM SERVICE replacement heads for 1969-71 SHP big block applications with open chamber heads. These heads were NEVER used in PRODUCTION for any application, whatsoever. Their external configuration is very similar, but not identical, to the original 3919842 and 3946074 aluminum cylinder heads. As Clem and Mark have pointed out, the external shape of the exhaust port area is somewhat different. Otherwise, though, they are very similar. Contrary to popular belief, though, the 14011077 castings DO NOT use hardened exhaust valve seat inserts. As with all aluminum cylinder heads, the intake and exhaust valves do use seat inserts. However, these inserts for the '077' head are plain, nodular cast iron. Also, unlike more modern aluminum cylinder heads, the '077' heads do not use interlocking valve seats; the seats are simply pressed into machined areas in the aluminum substrate material.

The 14011077 casting heads will work perfectly for 1969 applications. As before, if they are used with closed chamber pistons, compression ratio will be significantly reduced.

[Clem Z.]

Re: Big block open chamber heads

the exhaust seat in the 077 heads formed a venturi effect to help with the exhaust flow. we added this type of seat to CI BBC heads and even SBC heads by machining the venturi into the seat area.

[Steve Antonucci]

Re: Big block open chamber heads

Great info Joe!

Any guess as to how much the 14011077 heads might reduce the compression
ratio from the '842 heads?

Steve

[Joe L.]

Re: Big block open chamber heads

Steve-----

The change from the 107 cc '842' heads to the 118 cc '077' heads will reduce the compression ratio from 11:1 to about 9.8:1.

[Patrick H.]

Re: Big block open chamber heads

Steve,

Stupid Question #348:

Why change?

Are you going to be putting so many miles on the cars that making them work on "modern" gas will be a problem if left in stock configuration?

Just wondering. I've followed plenty of the threads here too regarding pump gas and compression, and I believe I'd rebuild one as original.

Just my $0.02, and wondering if it's really worth the hassle you appear to be prepared to go through.

Patrick

[Steve Antonucci]

Re: Big block open chamber heads

Well Patrick,

The only stupid questions are the ones left un-asked!

I initially felt the same way, but all of the threads about detonation got
my attention. With all of the $$ I put into the short blocks for both of
these projects, I didn't want to even think about ruining my pistons & bores,
or any other internals.

I thought the heads would be a good compromise to lower compression and
possibly allow me to run on unleaded fuel at the same time. But, if the
heads are going to stand out as incorrect, I'm not sure I want to go that
route.

It's time to ponder some more - I guess!

I welcome any other thoughts on this subject. I know many of you faced the
same decisions while in the restoration mode.

Steve