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454 Chevy Big Block Build - Ask Anything

LS Defined
Ken Swinson; Wailuku, HI: I am a dyed-in-the-wool Chevy fan, particularly the small-block engines. I got totally away from the hot rod scene for many years, mostly because of financial constraints. In my younger years, I did lots of customizing, engine swaps, and engine performance enhancements and owned some very hot cars. My question is this: In numerous articles, the technical writers refer to Chevy engines as LS engines. What is the difference between former Chevy engines and the LS engines? I think this is a question many of your readers would be interested in seeing published.

Jeff Smith: Let's see if we can do this succinctly. The LS series of engines debuted with the '97 Corvette, later in trucks, and now represents the standard for domestic GM pushrod V8 engine performance. This was a clean-sheet-of-paper redesign, so there are few commonalities to the original small-block (Gen I) or even the short-lived Gen II LT1/LT4 engines. The bore spacing, which is the distance between the cylinder bore centerlines is the same at 4.400 inches. The LS engine family actually uses the same hydraulic roller lifter as the earlier production small-blocks, and except for one bolthole, the bellhousing pattern for the LS engine (also called the Gen III/Gen IV) is the same. The original LS1 346ci 5.7L engine was designed as an aluminum engine, so the block was reinforced with deeper block skirts to add strength along with cross-bolted main caps that use a total of six bolts to retain the caps to the block. The gerotor-style oil pump is mounted on the front of the crankshaft to eliminate load on the camshaft, but it now spins at engine speeds so the pump can possibly drain the sump under continuous high-rpm engine operation. The crankshaft flexplate/flywheel pattern is also different compared with either the one- or two-piece rear main seal versions of the Gen I small-block. Using a far more sophisticated fuel injection system, perhaps what really improves efficiency is the distributorless ignition system using a coil-near-plug ignition that employs a separate coil for each cylinder. This single step not only dramatically increases ignition power at high engine speeds, but also creates far more accurate ignition timing, since proper spark advance is now not affected by all the clearances of a spinning distributor, rotor phasing, and other built-in ignition timing inconsistencies that afflict the typical distributor-style ignition system.

The LS series engines also enjoy a far more efficient cylinder head design with intake ports either of a cathedral- or rectangle-port design. The lowliest stock 4.8L head still enjoys a 15-degree valve angle that is far superior to the old small-block 23-degree angle. Along with properly engineered combustion chambers that reduce timing requirements, this effect combined with production compression ratios of more than 10:1 and excellent airflow from the ports all make for a very powerful engine. There are several truck and SUV variations that are built with an iron block, but most performance applications come through as all aluminum, which really adds to the performance advantage. A typical all-aluminum block for a small-block Chevy will reduce engine weight by roughly 50 to 60 pounds but that is a costly upgrade, since most aftermarket Gen I blocks will cost around $4,000.00. For less than that, you can purchase a complete used LS engine that is already all aluminum. The real advantage for the Gen I small-block is that the price for most parts is far less than comparable LS engine pieces. But other than cost, it's hard to beat the late-model engines for performance, efficiency, and weight. That's why you're seeing so many LS engines swapped into older performance cars. It just makes good sense.

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