GMpart number for ZLX heads

Schonyenko2 · #1 03-08-2002, 04:22 AM

My question is what GM part number is used for the motion ZLX heads? The only open chamber heads that I knew of at that time were 074's which were ZL1 aluminum. Were these prototypes for the LS7 that was supposed to be offered in the 70 corvette?
Also did the 67 and 68 L88s have 12.5 to 1 closed chamber pistons, and a bigger cam but still used 392, 840 or 842al heads? Was the comp ratio and cam size, the difference between the L72, and the L88?
Always wondered why Yenko did'nt put at least a few L88s in something.
Any help on part numbers is appreciated.
Ken

**Stefano** · #2 03-08-2002, 04:29 AM

My understanding is that some of his road race Corvettes had L88's installed?

Chevy454 · #3 03-08-2002, 06:36 PM

I believe BKH's '69 did come from Yenko with an L-88...any others?

Rowdy Rat · #4 03-08-2002, 07:51 PM

<BLOCKQUOTE>quote:<HR>My question is what GM part number is used for the motion ZLX heads? The only open chamber heads that I knew of at that time were 074's which were ZL1 aluminum.<HR></BLOCKQUOTE>

Ken,

That's a good question... To be honest, I never really paid much attention to the so called "ZLX" engine. It was more or less a poor man's ZL-1 that was never installed and sold as a production unit in a car, but was available for a time as a service unit. My guess is that whatever rectangular port/open chamber iron casting was the first released is the one that you'll find.

<BLOCKQUOTE>quote:<HR>Were these prototypes for the LS7 that was supposed to be offered in the 70 corvette?<HR></BLOCKQUOTE>

Not likely on the intended production version of the LS-7 that was slated to be installed in the 1970 Corvette. That engine would have used closed chamber aluminum heads (most likely 842 cstings). This Corvette version of the LS-7 wasn't much more than a 1970 LS-6 with aluminum heads and a slightly different camshaft.

The LS-7 that was available as a service unit was a completely different animal... Much more in line with the ZLX engine you reference. It may have used heads with the same casting as the ZLX since both were of cast iron/open chamber design.

<BLOCKQUOTE>quote:<HR>Also did the 67 and 68 L88s have 12.5 to 1 closed chamber pistons, and a bigger cam but still used 392, 840 or 842al heads? Was the comp ratio and cam size, the difference between the L72, and the L88?<HR></BLOCKQUOTE>

Yes, 1967-early 1969 L-88s used aluminum closed chamber heads (392s in 1967, 842s in 1968-early 1969) and 12.5 to 1 compression ratio. The cast iron 840 heads were never installed in production on an L-88. There were many differences between the L-88 and L-72... From the air filter down to the oil pump. It might be easier to identify what was the same.

Regards,

Stan Falenski

[Edited by Rowdy Rat (03-08-2002 at 02:51 PM).]

**Stefano** · #5 08-11-2003, 03:12 PM

Based on 'The Complete do-it yourself guide to top Street Performance' 1972. "The ZLX 454 Phase III...dyno rated at 575 hp. The ZLX designation indicates the use of open-chamber cast-iron heads, first introduced to the speed field a couple of years back by Rosen on his personal race car. They have since become a performance standard.", Executive Editor, Martin L. Schorr

JoeG · #6 08-11-2003, 03:55 PM

Just some extra info---1969 L-88 opened chambered blueprinted 427 ZL-X---650HP---.585/.605-PhaseIII cam 12.8/1 piston--choice of 850/950/1050 Holley carb- VERY SPECIAL M/P competition engine.---JoeG

Schonyenko2 · #7 08-12-2003, 03:28 AM

I had a conversation with a person who should know ,that told me that before 71 any open chamber iron head, as in ZLX came out the backdoor of GM to only a very select few people. The part # will not appear in any GM parts books as they were experimental iron versions of the ZL1. Comments? Schonye

JoeG · #8 08-12-2003, 03:53 AM

The person you talked to has good info as only a few sets of ZL-X cast iron heads were produced for drag evaluation testing 1969 ---I don't have any GM # for these--JoeG

68l30 · #9 08-12-2003, 06:00 PM

ZL-X heads Motion # 3946028-70 List for $395.95 (pair) in 1970.......

Steve

JoeG · #10 08-12-2003, 07:07 PM

68/30
You are correct, they did have a B/M part # starting in '70,-- but still no GM. part #, at least officially,but there had to be a unofficial GM part# for the few special people who got them [img]/ubbthreads/images/graemlins/beers.gif[/img]

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