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416ci LS3 Engine Build - Part 1 - Bottom End

Assembling The Beast from the Bottom Up

Jeremy D. Clough Dec 18, 2013
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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.

One of the things that was eye-opening to me was the labor and tooling required to build an LS properly. Hailing from the custom gunsmithing business, I was under the impression that engine building was mostly just assembly. I was wrong. The LS isn’t the old-school SBC, and to assemble one correctly requires a great deal of precision measurement and fitting on virtually all of the components. The specialized tools required to measure the various small, but critical, dimensions cost more than many complete engines.

The first step was machining the block and preparing it for assembly. Since LS3 blocks can vary considerably in bore diameter, ours was machined so it would be the correct 4.070 inches after final honing. The total height of the rotating assembly was measured, and the block deck machined to leave the piston 0.010-inch “in the hole.”

Decking the block ensures a smooth surface for cylinder-head mounting as well as the correct compression ratio. It also establishes a “true deck,” with both sides of the block cut to the same deck height; this eliminates the problem of uneven forces acting on each cylinder bank. Otherwise, as Scott pointed out, the engine will run, but the question is how well—and for how long.

With that done, the cylinders were honed to remove any taper and to meet the finish diameter. While some shops simply mount the block in the machine and go to town, Grimes uses a torque plate to simulate the pressure of having heads installed. Otherwise, while the bores may be round when honed, they can distort when the heads are torqued down, leaving the cylinders out-of-round. Since this engine is a stroker, the block also had to be clearanced with a little U-shaped notch near the base of each cylinder, to make room for the longer stroke of the connecting rods.

Once the bores were done, it was time to measure and hone the main bearing caps. Since one of the caps was a little large, giving too much clearance, it had to be shortened at the bottom mounting surface and then re-honed. The bearings were then installed in the caps and measured for crank clearance.

We should note here that GM assembles engines using “torque to yield” bolts. These are torqued to a set value, then turned an additional distance, measured in degrees, to stretch them. Needless to say, they’re a single-use proposition, which gets pricy considering the number of times a bottom end should be assembled and disassembled during blueprinting. Accordingly, we opted to ARP fasteners throughout, along with studs on both the bottom and top ends.

With that, the block was done, and it was time to turn to the rotating assembly. While we ordered the crank with the 58-tooth reluctor wheel installed, Grimes checked the wheel’s position to make sure it was indexed properly, and used a dab of weld to make sure it stays in place. The crank itself proved to be within the NASCAR tolerance from the factory—a strong showing for Lunati—but it had been balanced with reciprocating parts a little heavier than the ones we were using, necessitating a rebalance.

The other parts—the pistons and connecting rods—were numbered by cylinder with an electric pencil, then weighed and prepared. The pistons, crisply machined and carefully deburred, came out of the box looking too beautiful to be consigned to an existence where they’ll likely never seen again. The passage where the wristpin passed through the piston was honed, while the I-beam connecting rods were measured and cleaned. The rods also had their caps repeatedly removed and re-torqued to check for both the proper amount of bolt stretch and the roundness of the rod ends.

The assembly was relatively straightforward. With the block on a rotating stand, the pistons and rods were laid out in order of installation. First, the crank was washed and installed in the block, and the thrust (the forward-and-backward play of the crank in the block) was set by measuring and adjusting the clearance on the thrust (center) bearing. While it may seem counterintuitive, race engines require more clearance, to allow for greater expansion due to heat.

“You’re going to beat on this thing, right?” Scott asked me as he measured the play with a dial indicator.

“Yes,” I answered, having decided at the beginning that an engine like this would have to live at least part of its life on a racetrack.

“Good,” he said, pulling the thrust bearing to take off a little material.

The pistons were then installed on their respective connecting rods, with a spiral lock on each side of the wristpin to keep them in place. The rings were then installed after being file-fitted to each cylinder; their ends were also verified to be square to one another and carefully beveled. With each of the pistons fully assembled, they were slipped into a piston-ring compressor, a tapered sleeve that compresses the rings so they don’t snag on the block when the piston is placed in the cylinder.

As I watched, Scott deftly slid the first piston through the compressor and down into the number one cylinder, carefully guiding the lower end of the rod so it didn’t nick the crank; he then carefully installed the cap and torqued it into place. All of a sudden, the block was starting to look like an engine.

Once the rotating assembly was torqued into place, we switched to the top end—including the cam, timing set, lifters, heads, intake, and front and rear covers—which we’ll cover next month. The last major bottom-end component we added was the oil pan, which goes on after the front and rear covers have been installed.

As an industry leader in LS retrofits, Holley was a natural source for the right oil pan. Intended to provide maximum ground clearance, Holley’s cast-and-machined aluminum pan has a total capacity (with filter) of six quarts, and it uses a standard LS3 dipstick and tube (not included). The kit comes with most of the other major components required to install it, including a sump baffle and pickup tube; you’ll need to provide a windage tray. We used one from a truck, and followed the included instructions to clearance it where necessary.

Since the LS uses the main cap bolts to mount the oil pan, we stacked washers on the main cap studs to get the spacing correct, keeping clearance between the rotating assembly and windage tray minimal for best oil scavenging.

With the pan in place, we tightened the front and rear covers, and tapped and screwed in the engine-plug kit provided by Comp Cams.

In our next installment, we’ll seal up the top and put the fire to it.

Sources Comp Cams (800) 999-0853 www.compcams.com Grimes Automotive Machine Alpharetta, GA (770) 475-5272 Holley (270) 782-2900 www.holley.com Lunati (662) 892-1500 www.lunatipower.com Street Shop, Inc. (256) 233-5809 www.streetshopinc.com Wiseco (800) 321-1364 www.wiseco.com


Wiseco Performance Products
Mentor, OH 44060
Comp Cams
Memphis, TN 38118
Holley Performance Products
Bowling Green, KY 42101
Lunati Camshafts
Olive Branch, MS
Street Shop, Inc.
Athens, AL 35611
Grimes Automotive Machine



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