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The Zl-1 Engine's Rebirth - Awesome Aluminum

The Story Of The Zl-1's Rebirth

Barry Kluczyk Sep 1, 2001

ZL-1 Nothing gets your Chevy nerves tingling like the mention of this legendary piece of big-block history.

For those who need a reminder, the ZL-1 was an aluminum version (heads and block) of the Chevy Mark IV big-block. Designed for racing, it appeared on the scene in 1969, displacing 427 ci and making more than 500 hp. An instant powerhouse in drag racing and, later, in Can Am road racing, the ZL-1 also found its way into a handful of '69 production cars-the rarest of the famed COPO Camaros. These cars were sold mostly throughout the Midwest, like the famous Illinois dealership of Fred Gibb. There were even ZL-1-powered Corvettes.


The ZL-1 aluminum big-block (PN 12370850), is newly cast from 356-T6M alloy, but cast from the same tooling as the original blocks and retaining the original 3946053 casting number. The four-bolt block incorporates several new features, compared to the first ZL-1s, including screw-in plugs and stronger cylinder liners. Altogether, it weighs 110 pounds, which is about 12 pounds more than it did in 1969.

The best figures put the number of ZL-1 Camaros built at 69 and the number of ZL-1 Corvettes at just two. To be honest, there weren't that many built for racing, either. A couple of hundred, maybe. Those lucky enough to get their hands on one usually enjoyed success at the track, but it was a rare animal, even in its heyday.

From the start, the ZL-1 was intended as a race engine. The street versions were de-tuned just enough to make them somewhat livable on the street-or, at least, on the drive to the dragstrip. With more than 500 horses and solid lifters, the ZL-1 427s were touchy and required constant valve adjustments. But, the all-aluminum motor saved about 100 pounds, compared to a big-block setup, which was a welcome benefit to nose-heavy Camaros and Corvettes.

Although the engines saved weight, they added cost. The ZL-1 just about doubled the price of the Corvette-same for the Camaro. Buying one for your race car wasn't cheap, either. By the mid-'70s, the expensive, exotic ZL-1 race engine faded away.

Throughout its production run, though, the casting of every ZL-1 aluminum engine block was handled by Winters Foundry. Known for its trademark "snowflake" logo, Ohio-based Winters has been a longtime supplier to General Motors. While the ZL-1 history dates back more than 30 years, the last few blocks were poured 20 years ago-just a footnote in Winters' records. It was a footnote, however, that didn't go unnoticed by some fast-thinking GM Motorsports personnel.


One of the most significant upgrades since the ZL-1, which was last made in the '70s, is the switch to O-ringed, screw-in water jacket plugs and rear cam plug. The originals were brass parts.

In the early-'90s Winters was changing its casting process from the more traditional sand-cast method to a permanent-mold setup. The company, after deciding to clear out some of the old sand-cast tooling, sent a memo to GM asking if any of the old tooling was wanted. When the list reached the desk of one Motorsports staff members, a particular seven-digit casting number, 3946053, piqued his curiosity. After a little research, it was discovered to be the ZL-1's tooling. After discussing the finding with a block engineer and fellow performance zealot at GM Motorpsorts, a road trip to Canton, Ohio, was planned to examine the tooling.


A couple of things to note here: Splayed, billet-steel, 4-bolt mains are an upgrade from the original ZL-1. Also check out the engraved cap. The enthusiastic staff at Schwartz Machine in Warren, MI, who finish each raw casting for GM, began etching each main cap with the "ZL-1" logo. GM didn't ask them do it-they just did it because they understand the history behind the block. They engrave the rear cam plug, too.

The pair found the tooling gathering dust in a corner of the foundry. It hadn't been used since the '70s. Though dusty, it was in excellent condition. In fact, with an estimated 300 blocks poured altogether, it was almost new compared to tooling used to make blocks by the thousands.


With super-strong "G2" steel liners fitted, the ZL-1 has 4.25-inch bores, which can be stretched to 4.30 inches. According to GM, the block can handle a 4.375-inch stroker crank, too. There are plans for 4.500-inch-bore ZL-1 block in the future, also.

Arrangements were quickly made to have the ZL-1 tooling shipped to the foundry that makes current, aluminum GM Racing small-blocks and heads. During the next couple of years, the ZL-1 tooling was cleaned and revamped. Improvements were made on a few of the block's design details before pouring the first "new" ZL-1 block.

The biggest improvements included screw-in, O-ringed water jacket plugs and splayed, four-bolt 8620-billet steel main caps. The lifter valley was also modified to accept Gen VI-type roller lifters.

Overall, quality and serviceability of the block were improved. This better version of the ZL-1 offers brand-new blocks from the tooling of the originals. The best of both worlds, wouldn't you say?

No, the best would be some sort of ZL-1 crate engine. But it's not available... Well, not yet anyway.

Oh, wait. We weren't supposed to mention that!



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