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Gen IV Small-Block Build - Budget LS Buildup

Mixing And Matching GM's Gen IV Parts To Build An Affordable, 6.0-Liter L92 Powerhouse

Barry Kluczyk Jun 1, 2008

As the number of GM's production Gen III/IV V-8s proliferates, there's been a corresponding explosion in the number and variety of engine parts released to the public. Generally, they are interchangeable, but there are significant differences, too. And while General Motors and GM Performance Parts have done an admirable job getting crate-engine versions of production motors to market, there's plenty of room for the enterprising engine builder to mix and match from GM's parts bins to build unique, powerful, and-believe it or not-value-driven combinations.

Of course, "value-driven" shouldn't be confused with "cheap," but in the realm of relativity, value can easily be assessed when judged against, say, the list price for an LS7 crate engine. For reference, the LS7 displaces 427 cubic inches (really, it's closer to 428, but who's counting ...) and is rated at 505 horsepower and 475 lb-ft of torque. It also runs about $13,000 over the counter from your friendly neighborhood dealership parts guy-who'll be even friendlier when you order one.

Closer to reality for most enthusiasts are the production-based crate engines, such as the aluminum-block LS2 and the iron-block 6.0-liter engines found in seemingly zillions of GM trucks. These typically run between $3,500 and $5,500, making them good values for those who want to simply drop it in and go.


The used LQ4 donor motor was completely disassembled, inspected, and rebuilt. Here, after the crankshaft and main caps were reinstalled, the crankshaft gear is installed using a 2-inch length of pipe and a hammer.

The engine combination outlined in this story is based on the truck-based 6.0L (364 cubic inches) LQ4 bottom end with a set of new L92 cylinder heads and a four-barrel carburetor. The L92 heads have tremendous airflow for off-the-shelf parts and are a performance bargain from GM Performance Parts. The engine dyno-tested to the tune of 480 horsepower with GM's Hot Cam and a whopping 540 horsepower with the General's racing-derived Showroom Stock camshaft.

And the price for all this glory? About $4,300-that's LS7 power territory for about a third of the price. Yeah, it seems like a value to us, too, and it would have been even cheaper if we hadn't bought two camshafts.

The impetus for the engine came from Bob Cross, a Michigan-based enthusiast who is very familiar with all of GM's latest engine offerings. The engine was destined for a '51 Chevy truck project, and Bob enlisted the help of his nephew Steve Marsa and his friend Cliff Urmanic, who performed the assembly. Dyno testing was done independently at a Flint, Michigan-based performance shop.


The LQ4 engine uses hypereutectic (cast) pistons that have proven to be very strong. They have a dished head that will enable pump gas-friendly compression when used with the L92 heads and their smaller combustion chambers.

Affordable, Easy-To-Build Combo
Building Gen III and Gen IV (alias LS) engines is remarkably easy and time-efficient; only four socket sizes are required to disassemble the engine: 8mm, 10mm, 13mm, and 15mm. Most of the bolts are interchangeable, too, so there's no fumbling with different-size bolts. They also use "dry" gaskets (no liquid, RTV-type sealers), and with their crank-triggered ignition systems, setting engine timing is as easy as plugging in the ignition controller.

The starting point for our value-driven 6.0-liter engine was a used LQ4 engine purchased for only $350. Most of the rest of the parts used to build up the engine were sourced from the GM Performance Parts catalog.

The L92 aluminum cylinder heads were the big enablers of the engine's admirable dyno results. They're the same heads used currently on the 6.2-liter-powered Cadillac Escalade and GMC Yukon Denali, but they are similar to the heads used on the Corvette Z06's LS7 engine. The have huge runners, 2.165-inch/1.600-inch valves, and flow a whopping 310-320 cfm on the intake side at 0.600-inch lift on the top end. They list for $399 apiece-pretty cheap for such a high-flowing aluminum head, in our opinion.


Two camshafts would be tested in the engine: GM's Hot Cam and Showroom Stock cam. First up was the Hot Cam, which boasts 0.525-inch lift and 219/228 duration at 0.050-inch lift on a 112-degree centerline. The Showroom Stock cam's specs include 0.570-inch lift and 239/251 duration on a 106.5-degree centerline. The Showroom Stock cam requires valve relief notches in the pistons when used with the LQ4 rotating assembly.

A stock LQ4 engine's heads have 71cc combustion chambers, giving a compression ratio of about 9.4:1. The L92 heads have smaller 68cc chambers, which bumps compression with the LQ4's stock dished pistons to about 10:1, making the combination safe for pump gas.

Using a carburetor with the L92 would have been almost impossible a couple of years ago, but GM Performance Parts recently released an aluminum intake manifold that fits the heads' unique angle and rectangular port shape. After that it's simply a matter of picking the right four-barrel; there's even a version with cast-in bosses for nitrous or EFI.

To complete the more traditional, carbureted appearance for the engine, the ignition coil packs, which are usually mounted on the valve covers, were relocated to the rear of the engine with a scratchbuilt bracket with Marsa and Urmanic-made 1-inch stock and 3/16-inch tube spacers. Other assembly details included the fabrication of a replacement valley tray designed to eliminate the need for breathers in the valve covers. The tray was made from aluminum stock, with a breather welded to the front for easy access, along with the PCV valve located at the rear of the tray. These custom touches allowed the great-looking Chevrolet-script valve covers from GM Performance to show without the unsightly coils or breathers.


Another one of the easy, time-saving attributes of building LS engines is the drop-it-in lifter trays.

Hot Cam vs. Showroom Stock Cam
From the outset, the plan was to test the engine's performance on the engine dyno with both GM's Hot Cam (part number 12480033) and Showroom Stock cam (part number 88958606). The Showroom Stock cam delivers more lift-0.570 inch versus 0.525 inch-and duration-239/251 degrees versus 219/228 degrees-than the Hot Cam. With the L92 heads' tremendous airflow capability, we figured the Showroom Stock cam would deliver big dividends. It did.

On the dyno, the Hot Cam-equipped combo had a total timing of 32 degrees and delivered 471 horsepower at 6,600 rpm and 417 lb-ft of torque at 5,000 rpm. The Showroom Stock cam put up the big numbers, posting a best of 506 horsepower at 6,600 rpm and just a hair less than 437 lb-ft of torque at 5,400 rpm. By the way, the Showroom Stock cam requires relief notches in the piston, which we anticipated and had cut into the pistons prior to assembly.


Engine building tip: The L92 heads only work on engines with 4.00-inch-orlarger bores, so a stock L92 or aftermarket 4.065-inch head gasket must be used.

But the peak numbers don't tell the whole story. The Hot Cam is the perfect street cam. It has that "idle lope" that everyone wants at 800 rpm but has broad horsepower and torque bands, making it great for propelling a musclecar or hot rod. The Showroom Stock cam is a beast. It idles at 1,400 rpm and has a definitive race-cam sound. It is a wicked cam for a street engine and requires some more compression, a rear gear, and a higher-stall torque converter to make the most of its potential. But boy, it sounds awesome when it's idling at 1,400 rpm.

In the end, Marsa and Urmanic decided to go with the Hot Cam as the final combination. It should prove to be a great street performer, and more than that, it should give these creative engine builders the satisfaction of building a powerful and affordable new-age small-block.



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