416ci LS3 Engine Build - Part 1 - Bottom End

Assembling The Beast from the Bottom Up

Jeremy D. Clough Dec 18, 2013 0 Comment(s)
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Since its introduction in the ’97 Corvette, GM’s LS-series V-8 has undergone a process of steady improvement, growing in displacement from 5.7 to as much as 7 liters and nearly doubling in available power, from 345 to 638 supercharged horses. Its strength, compactness, and efficiency have also made it a welcome addition to other vehicles, including older musclecars and even vintage Vettes. While the upcoming C7 is to be powered by an all-new direct-injected V-8, dubbed the LT1, the LS is well supported in the aftermarket and will doubtless remain a strong contender for the foreseeable future.

With this in mind, it seems just and proper to celebrate the latest of the standard-equipment LS engines, the LS3, by seeing how far we can reasonably push one. We’ll start with the bottom of the engine in this article, and follow it up with a second installment covering the top end.

We began with a bare LS3 aluminum block sourced through Street Shop, Inc., a GM distributor, and decided to stroke it from 6.2 to 6.8 liters, or 416 ci. While it’s possible to get more displacement out of an LS3, I was (mistakenly, as it turned out) concerned about rod-angularity issues, so we stuck with a 4-inch crank.

For a bulletproof bottom end, we turned to Lunati. While many suppliers offer complete stroker assemblies for the LS, Lunati, which was founded in the late 1960s by drag racer Joe Lunati, is well known as a racer’s company. With so much experience in the field, the people there not only produce top-shelf components, but they also have a wealth of knowledge that goes as deep as knowing which package of components works best on which track.

They supplied a 4-inch Pro Series crankshaft, along with a set of I-beam connecting rods. Pro Series cranks are forged from certified 4340 steel, with journal roundness kept to a tolerance of 0.0001-inch or less. All of the journals are also drilled to reduce the crank’s rotating mass. This attention to detail adds up: These cranks have been successfully used in engines pushing more than 1,500 hp. The connecting rods, which are subject to enormous strain, are also made from 4340 steel for maximum strength.

A set of beautifully machined forged pistons was supplied by Wiseco. In business now for more than 70 years, Wiseco has the distinction of being the only U.S. company to forge all of its pistons. In a feeble attempt to stay “close to the factory spec,” we specified an LS3-standard 10.7:1 compression ratio.

One of the things we had to choose in building the bottom end was the type of reluctor wheel to use. This serrated wheel attaches to the crank and triggers a pickup that sends information to the car’s ECU. Early LS engines used a 24-tooth wheel, while the LS3 usually has 58. While it’s possible to put a 24-tooth wheel on a later powerplant, doing so will require you to use the older, less advanced engine computer. In our case, we ultimately selected an aftermarket computer from FAST instead of either of the GM units. That said, we still wanted the most precise inputs possible, so we ordered our Lunati crank with a 58-tooth wheel.

For engine machining and assembly, we chose Grimes Automotive Machine, a shop that’s also well-steeped in racing knowledge. On any given day, you’ll find owner Garry Grimes, who raced a Pro Stock Vega through the 1970s, in the shop along with his son Garry Scott and father Hoyt, who’s known as the “Granddaddy of Southeastern Drag Racing.”

Hoyt has been inducted into several halls of fame, including the NHRA Southeastern Division, for his pioneering work in the field, including the first rail dragster in Georgia, the first chain-powered blower, and the 180-plus-mph blow-over crash that ended his racing career and nearly killed him. At 90, he’s still working in the shop on a daily basis, and his experience is just part of the tremendous fund of knowledge that makes Grimes Automotive an excellent choice for a serious engine build.




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