ZL-1 & L-88 head design clarification
 

Hello,

I am doing some research into building an L-88 engine for
a project. I know the L-88 in 1967 used a different head,
but I'm not sure what it was. I'm trying to determine
which heads were used in the 3 year L-88 program, which
heads were used in the ZL-1 program, and how the cross-over
between the L-88 & ZL-1 programs worked ( if at all ).

I've been told the L-88 ( 68 through mid-1969 ) may have
used the '842 closed chambered heads. Sometime in mid-
1969, the ZL-1 came into being as did the '074 open
chambered heads. Is this where the cross-over happened?

Here are some questions:

1) Were all L-88's equipped with aluminum heads?
2) The ZL-1 was open chambered, but when did the L-88 go
that same direction? Was it also mid-1969?
3) Where does the whole LS-6 program fit into all of this?
4) Does anyone have an example of a closed chambered L-88
piston, open chambered L-88 piston, ZL-1 piston that they
can post pictures of?

I thought this would have been easy to figure-out. https://www.yenko.net/ubbthreads/imag...emlins/eek.gif

Steve

Re: ZL-1 & L-88 head design clarification
 

The L-88's all were aluminum heads from the factory. The 69 switch over from the 842 closed chamber design to the 074 open chamber design was around serial # 21,000 (if my memory serves me well) But as a side not the L-89's did not change to the 074 they were all 842. Hope this helps, Rich.

Re: ZL-1 & L-88 head design clarification
 

Also the L-S6 for the Corvette was the 454 version of the L-89 but they had aluminum open chamber design heads.

Re: ZL-1 & L-88 head design clarification
 

The L88 head was also made in steel as a parts replacement item.
If you went to the parts counter at a Chevy dealer and ordered an L88 long block, it would come with the steel heads. I have a CE stamped 512 block, and on the inside of the head is stamped L88.
The casting # for these heads is not listed in all of the Chevy parts books, like Colvin's.

Re: ZL-1 & L-88 head design clarification
 

[ QUOTE ]
The L-88's all were aluminum heads from the factory. The 69 switch over from the 842 closed chamber design to the 074 open chamber design was around serial # 21,000 (if my memory serves me well) But as a side note the L-89's did not change to the 074 they were all 842. Hope this helps, Rich.

[/ QUOTE ]

Rich,

The L/89's refers to 67-69 - correct? Would an L/89 454 in
1970 have the '842 heads? https://www.yenko.net/ubbthreads/imag...lins/dunno.gif

Steve

Re: ZL-1 & L-88 head design clarification
 

[ QUOTE ]
The L88 head was also made in steel as a parts replacement item.
If you went to the parts counter at a Chevy dealer and ordered an L88 long block, it would come with the steel heads. I have a CE stamped 512 block, and on the inside of the head is stamped L88.
The casting # for these heads is not listed in all of the Chevy parts books, like Colvin's.

[/ QUOTE ]

Andy,

What was the casting number for the steel L-88 heads? I've
never heard this before. Love to know more. Also, what
made them different from any other rectangular port big
block head of that same production period?

Steve

Re: ZL-1 & L-88 head design clarification
 

The L-89 in '70 was only for the 396. The L-S7 that never made production would have had the open chamber aluminum heads. (Which over the counter could have steel heads also.) The L-S7 was to replace the L-88.
P.S. The L-89 in 70 was closed chamber.

Re: ZL-1 & L-88 head design clarification
 

Steve, I wish I had taken photos of the casting numbers when the covers were off. The "HI PERF" is there, and the dates are March and April of '69.
They also have the "half moon" casting mark, indicating a closed chamber, square port application.
Difference between them is the amount of grin on your face at WOT. https://www.yenko.net/ubbthreads/imag...ns/naughty.gif

Re: ZL-1 & L-88 head design clarification
 

Here is the casting mark.

Re: ZL-1 & L-88 head design clarification
 

They are not just 840 heads? I would think they would be since 842 and 840 are vitually the same save the material.


Jason

Re: ZL-1 & L-88 head design clarification
 

I think the open chamber iron heads are #990.

Re: ZL-1 & L-88 head design clarification
 

These '69 cast iron L-88 heads...I picturing them to be very similar to the ZLX head - open chamber cast iron...

Re: ZL-1 & L-88 head design clarification
 

I see we are talking about 69 version heads. They are 990s.


Jason

Re: ZL-1 & L-88 head design clarification
 

[ QUOTE ]
Here is the casting mark.

[/ QUOTE ]

Andy,

Where exactly is the "half moon" casting mark on the head?
Front/rear face?
STeve

Re: ZL-1 & L-88 head design clarification
 

Rich, I believe the last LS-6 Corvettes produced in -71 got the first open chamber iron heads, similar to the #074 aluminum head.

Re: ZL-1 & L-88 head design clarification
 

All Chevy casting marks are on the front face of the head.

Re: ZL-1 & L-88 head design clarification
 

Closer view.

Re: ZL-1 & L-88 head design clarification
 

That rectangular port/open chamber #990 cylinder head was not around in 1969 or 70. That and the similar #188 are what came on the newer crate LS-6's and LS-7's. I've seen reference to this so-called cast iron ZL/X head and would like to know what the casting number is. The earliest cast iron rect. port/open chamber head I know about and have owned were 1971 dated #026. They are also listed in Colvin's book as standard issue for the 1971 LS-6 Chevelle. A car that never happened so they must have been over the counter service pieces. The 1971 Corvette LS-6 all used the aluminum rect. port/open chamber head #074, the same as found on the 1969 L-88 and ZL-1 Corvette.

Re: ZL-1 & L-88 head design clarification
 

According to Colvin, there were 3 #'s starting in '67 that had this "half moon" casting mark, all square port, hi perf applications. (Mechanical lifters).
The first was '67 only, #3904391, and had no temp sending unit.
The 2nd was the #840, and was installed in '67, '68, and '69. It was also cast in '69 as a #291, with a tapered spark plug seat. The #291 was also used in '70, since the 512 block was used in '70 for the 454. The only difference was the crank being stroked for the extra cubes.
The '67 L88/9 aluminum heads (#392) was identical to the #840, except for the casting metal.

Re: ZL-1 & L-88 head design clarification
 

[ QUOTE ]
According to Colvin, there were 3 #'s starting in '67 that had this "half moon" casting mark, all square port, hi perf applications. (Mechanical lifters).
The first was '67 only, #3904391, and had no temp sending unit.

The 2nd was the #840, and was installed in '67, '68, and '69. It was also cast in '69 as a #291, with a tapered spark plug seat. The #291 was also used in '70, since the 512 block was used in '70 for the 454. The only difference was the crank being stroked for the extra cubes.
The '67 L88/9 aluminum heads (#392) was identical to the #840, except for the casting metal.

[/ QUOTE ]

So, the #3904391 is the '67 L-88 head then? Did I read
that correctly, or read something into that? https://www.yenko.net/ubbthreads/imag...lins/dunno.gif

Steve

Re: ZL-1 & L-88 head design clarification
 

I have read reports about new 1971 LS-6 Corvettes beeing sold with the iron head, for 600$ less than the aluminum head versions. They were the last ones produced.
Is this wrong ?

Re: ZL-1 & L-88 head design clarification
 

I'm not sure about the '70 heads, but the '67 L88 was a square port head, and the ZL1 or later L88/9 were round port.
I'm just going by what the Corvette guys and Colvin say.

Re: ZL-1 & L-88 head design clarification
 

Maybe on the exhaust side, the intake sides were all rectangular.


Jason

Re: ZL-1 & L-88 head design clarification
 

Guys,

I had often heard that the '074 ZL-1 heads, with their
round exhaust ports, we an ineffective design concept.
The amount of power required to take advantage of this
port design was impractical. In my research on building
big block engines, the '077 ( over the counter ) heads
seemed to get the thumbs up due largly in part to their
"C" shaped exhaust port designs. Can any of you support
or refute this information? I see the '074 heads on ebay
all the time and often wonder why people will pay big bucks
for them if this it truly the case. https://www.yenko.net/ubbthreads/imag...lins/dunno.gif

Steve

Re: ZL-1 & L-88 head design clarification
 

[ QUOTE ]
I have read reports about new 1971 LS-6 Corvettes beeing sold with the iron head, for 600$ less than the aluminum head versions. They were the last ones produced.
Is this wrong ?

[/ QUOTE ]
I think so, the NCRS tech manual / judging guide, makes no mention of an iron head version. 1971 LS6's were only delivered from late February to early June of 1971. I have the earliest known vin # parked in my garage (a GM press car), it, as well as some mid to late May vin #'s, are all aluminum head versions.

Re: ZL-1 & L-88 head design clarification
 

The #077 over-the-counter aluminum cylinder head is much superior to the factory installed #074 production head. That giant round exhaust port makes for a poor intake-to-exhaust port ratio. The #077 head has a beautiful D-shaped exhaust port with a cast in vane on the port floor. It also has a little bit smaller intake port to try to compensate for the big blocks' infamous 4 good/4 bad intake ports. Both heads do tend to suffer from valve guides that like to move around unless they are pinned at the valve spring seat. People like to pay more money for the #074 head because it is considered more correct for an aluminum head L-88.

Re: ZL-1 & L-88 head design clarification
 

Hi Mark,

Well, thats goes with what I have often heard about the
'074 heads. Only question I have about them is this:
If there were so few L-88's and even fewer ZL-1's, why are
so many of these heads on ebay all the time. I see 3 - 4
sets per month on average. There aren't that many real
cars, so where did all the heads come from? Over the
counter race stuff? More to the point, are they over the
counter race stuff that really didn't work and have been
collecting dust forever? https://www.yenko.net/ubbthreads/imag...mlins/hmmm.gif

Steve

Re: ZL-1 & L-88 head design clarification
 

The 074's were sold over the counter for years.