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626HP LS3 Stroker Build - Supersize Me

Who Needs a Power Adder? By Stroking an LS3 to 416 ci, Wringing out 622 hp is Cake

Stephen Kim Jun 5, 2014
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Being normal is overrated. Normal people don’t rebuild their engines until they’ve logged hundreds of thousands miles on the ticker, but where’s the fun in that? As cuckoo as it might seem to your average SUV-flogging conformist, there are plenty of good reasons for a premature rebuild. Perhaps you’ve gotten a bit too greedy with the boost or nitrous and chucked a piston, or maybe that missed shift spun a bearing or two. Fortunately, despite the sheer savagery that the 426 horsepower LS3 small-block already manifests in stock trim, it’s still nowhere near maxed out. Throw in some extra cubic inches and airflow into the mix, and the result is an easy 622 hp on pump gas. It’s only natural for impressive figures like that to elicit some skepticism, so Late Model Engines in Houston, Texas is going to show us how it’s done.

While nitrous oxide kits and superchargers represent far easier ways to make silly heaps of power, there’s just something ultra pimp about doing it all-natural with a big-inch stroker motor. Many engine builders contend that naturally aspirated engines are more reliable than their power adder counterparts. Plus, constantly refilling nitrous bottles can get annoying, and hanging a 100-pound brick off the front of a fifth-gen Camaro with a blower doesn’t do much for its already hefty mass. Furthermore, in an era when the Feds insist on diluting fuel with corn juice, naturally aspirated motors are far less prone to detonation than power adder combos should you get stuck with a bad batch of gas.

Design Philosophy

Anyone can build a motor that makes big horsepower at the expense of drivability, but balancing out both extremes requires much more skill. Since few people plop down over $30,000 on a fifth-gen Camaro to transform it into an uncivilized bucking bronco, a thoroughly engineered engine combination like LME’s 600-Plus LS3 package perfectly complements the car’s refined character. “With any performance engine build, we focus on improving the cylinder heads. As airflow increases and the induction system becomes more efficient, you can use a mild camshaft and still make lots of horsepower,” LME’s Bryan Neelen explains. “When the LS3 first came out, people were over-camming them just like they did with the old cathedral-port LS-series cylinder heads. However, since the LS3’s rectangle-port heads flow so much more air, they can make a smaller camshaft really shine. This approach results in a very broad powerband with excellent drivability, which is why the LS3 and LS7 have become such popular platforms to build.”

Easy Displacement

As we all learned high school Geometry class, the base of a cylinder multiplied by its height determines its total volume. Since internal combustion engines are nothing more than glorified air pumps, and larger cylinders can ingest more air and fuel, increasing cylinder volume—and therefore engine displacement—is one of the best ways to increase horsepower potential. As long as the cylinder heads and intake manifold are up to the job, a larger motor will make more power and torque than a smaller motor at any given RPM. Fortunately, the LS3’s big-bore block makes it incredibly easy to achieve displacement euphoria.

In just 15 years, the development of GM’s Gen III/IV engine platform has progressed at a staggering rate. Early 5.7L LS1 small-blocks were limited in displacement due to their small 3.900-inch bores. Even with a 4.000-inch-stroke crankshaft, boring (or should we say – honing) the cylinders liners out as large as possible netted just 383 cubic inches. Although massive 4.125-inch bore diameters were possible by installing new cylinder sleeves, the process cost upwards of $2,500. Furthermore, re-sleeving a block yielded mixed results, and coolant leaks and poor cylinder seal weren’t uncommon. Things took a big change for the better in 2005 with the introduction of the LS2’s 4.000-inch siamesed-bore aluminum block, which allowed cracking the 400ci barrier when matched with a stroker crank.

Then in 2007, GM took things one step further with the 6.2L block introduced in the L92-powered Cadillac Escalade. Essentially the same block used in the LS3 and L99, it boasts an even larger 4.065-inch bore and makes big-block-like displacement affordable for hoards of late-model enthusiasts. Simply honing the bores out 0.005-inch and installing a 4.000-inch crank increases displacement from 376- to 416 cubic inches. To put this into perspective, the largest motor you could get in a regular production 1969 Camaro measured just 396 ci, and that was a big-block. “The 416 has become a very popular combination to build. When the 6.2L block first came out, it made it possible to build a large-displacement motor without spending a fortune on an LS7 block,” says Bryan. “Even today, the 6.2L block offers the biggest bore size you can get for the dollar. Now that GM is installing it into fifth-gen Camaros, the 416 is getting even more popular.” To transform a stock 376ci LS3 into a 416, LME starts by finish honing the block from 4.065- to 4.070 inches. It then installs a fully forged and internally balanced rotating assembly that features a Callies/Compstar 4.000-inch stroke crankshaft and 6.125-inch connecting rods, and Wiseco 11.7:1 pistons. “You can certainly spend more money on pricier cranks and rods, but from our experience, the components that we use offer the best value,” Bryan explains. “A rotating assembly that’s more expensive isn’t going to make any more horsepower, either. On the flip side, you can also build a motor with a less expensive rotating assembly, but it comes at the expense of reliability.”

Speaking of price, the LME 600-Plus 416 stroker motor will set you back $11,500. That price is even more affordable if you provide your own core block and heads. If you like earning your lunch money on desolate roads at night, a great perk of a stroker small-block is they don’t look much different for a stock motor on the outside. Potential victims will have no idea you’re packing an extra 40 cubic inches.


1. To prep the LS3 block for stroker duty, LME hones the bores 0.005 inches, cuts the deck surfaces down to 9.225 inches, and then align-hones the mains. All sharp edges are also de-burred to stress relieve the block and reduce the potential for cracks.


2. The bulk of the displacement bump in the LME 416 comes from increasing the stock 3.622-inch stroke to 4.000 inches with a Callies/Compstar forged steel crankshaft. It features drilled rod journals for improved oiling, and counterweights that have been profiled for piston skirt clearance.


3. When increasing the stroke of an engine, rod-to-camshaft interference can become an issue. To prevent this, the Callies/Compstar H-beam connecting rods have profiled shoulders for additional clearance. They swing a set of Wiseco pistons that maintain a 1.110-inch compression height when matched with the 416’s big stroke and long rods. Wiseco’s ArmorGlide skirt coating improves lubrication, reduces friction and piston rock, and allows for tighter piston-to-bore fitment.


4. With the crank secured in the block, LME gapped the top piston ring (from Total Seal) to 0.014 inch and the second ring to 0.018 inch. The larger second ring gap allows combustion gases that slip past the top ring to escape into the crankcase instead of unseating the top ring and compromising ring seal.


5. Sliding the pistons in the bores and bolting the rods to the crank reveals the amount of real estate available inside the LS3’s crankcase. Since a stroker crank pulls the pistons farther down the bore, the rod bolts will often hit the cylinder sleeves or oil pan rails at bottom dead center. The bottom of the LS3’s cylinder sleeves are undercut from the factory, making it possible to fit a long-stroke rotating assembly without grinding the block for clearance.


6. Actuating the valves is a custom Cam Motion 235/250-at-0.050 hydraulic roller camshaft with 0.646/0.642-inch lift. That’s a lot of lift for a small-block, but it closely correlates with the peak airflow figures of the cylinder heads to maximize power potential. The cam’s wide 114-degree LSA improves idle quality and decreases the rate of drop-off after peak hp.


7. To endure the rigors of high-RPM and the increased valvespring pressure of the 416, LME opts for a JP Performance billet double-roller timing set. It has multiple keyways cutouts on the crank gear for up to 8 degrees of cam advance or retard.


8. Using a degree wheel, LME verified the installed centerline of the camshaft. It was advanced two degrees to help bulk up low-end torque.


9. Since a stock LS3 utilizes a single-roller timing set, fitting an aftermarket double roller set requires grinding the back of the timing cover for clearance. LME made quick work of this process on its CNC machine.


10. The stock LS3 oil system is already plenty stout, but the LME 416 ramps up the oil flow even more with a Melling high-volume pump. Before installing it, LME radiused the outlet and grinded down all the sharp edges to improve flow.


11. All the cubic inches in the world don’t mean squat without a set of high-flow cylinder heads, and the factory LS3 castings are among the greatest production small-block heads ever built. GM engineers improved upon the already potent cathedral-port LS1 heads by pushing the pushrod passages over to the side, freeing up space for a larger rectangular port with a raised entrance.


12. To maintain valve control at high RPM, LME fitted the heads with PAC dual valvesprings that feature 170 pounds of seat pressure and 430 pounds of open pressure. They’re anchored in place by lightweight titanium retainers to keep valvetrain mass and valve float to a minimum.


13. After a trip through LME’s proprietary CNC program, the factory LS3 cylinder heads flow 365 cfm through the intake ports at 0.630-inch lift. That puts them right on par with the stock LS7 heads at a fraction of the cost.


14. The CNC porting bumps the exhaust port flow up to 235 cfm. Although the LS3 head castings have been criticized for having poor exhaust flow relative to the intake ports, 235 cfm is still right on par with a big-port Gen I small-block Chevy head. Likewise, using a slightly longer exhaust duration on the camshaft addresses the situation nicely.


15. LME’s ported LS3 heads retain the factory 2.165-inch hollow-stem intake valve and 1.600-inch stainless steel exhaust valves. They received a three-angle cut, and LME blended them into the stock 70cc combustion chambers.


16. Sending the lobe lift to the rocker arms are GM LS7 hydraulic roller lifters and 7.400-inch Trick Flow pushrods. The GM hydraulic lifters perform more like solid roller lifters, and can maintain valvetrain stability past 7,000 rpm.


17. In order to tighten up the quench clearance as much as possible, LME sets the pistons to 0.010-inch “out of the hole” and utilizes 0.048-inch-thick GM head gaskets. This yields a 0.038-inch quench clearance. Tighter quench not only produces more horsepower, it also reduces the potential for detonation by improving the homogenization of the air/fuel mixture.


18. Although head studs offer the ultimate in clamping force, head bolts are more than adequate for a naturally aspirated combination like the LME 416. The ARP bolts were torqued down to 70 lb-ft.


19. The LME 416 uses the stock LS3 rocker arms, but with a twist. To enhance longevity under increased valvespring pressure and higher RPM, LME fortified the stock rockers with a Comp Cams trunnion conversion kit. The trick setup replaces the stock pivots with heavy-duty rocker arm trunnions and bearings. At $135, the conversion is a heck of a lot cheaper than a set of aftermarket rocker arms.


20. Since the cylinder heads can only flow as much as an intake manifold will allow, LME matched up its ported LS3 castings with a high-flow Fast LSXR manifold. It features a 102mm inlet, which was matched to a Nick Williams billet throttle body of the same diameter.


21. A testament to the efficiency of the LS3 cylinder heads, the 416 required just 28 degrees of ignition advance on LME’s Superflow dyno. With the air/fuel ratio dialed in at 11.8:1, the motor kicked out 622 hp at 6,200 rpm and 574 lb-ft at 5,250 rpm.

Serious Airflow

Big engines make big torque and improve drivability by taming the adverse affects of a long-duration camshaft. However, they can’t take advantage of their greater power potential unless airflow into the cylinders is increased accordingly. As such, LME has developed a proprietary CNC porting program that dramatically improves the airflow of the factory LS3 cylinder head castings. From the factory, the stock LS3 heads flow roughly 320 cfm of air at 0.600-inch lift through the intake ports along with incredible low- and mid-lift flow numbers. LME’s CNC ports improve upon those already impressive figures by moving 365 cfm at peak lift. Flow wise, that puts the LME LS3 heads firmly into the territory of the vaunted LS7 head castings.

Dyno Time

The enormous airflow LME’s LS3 heads can achieve is more than enough to support well over 700 hp if matched with a big, nasty solid-roller camshaft. However, that would require spinning some serious RPM, and placing undue stress on the short-block and valvetrain. Instead, experienced builders like LME resist the urge to go big in a street/strip application in the name of civility. By matching the cylinder heads up with a mild 235/250-at-0.050 hydraulic roller cam, the LME 416 produces a stout 622 hp at a very reasonable 6,200 rpm on the company’s Superflow engine dyno. Furthermore, with 574 lb-ft of torque on tap, putting around town in traffic or at low RPM is a pleasant, cam-surge-free affair. So while mega horsepower combos are great for single-purpose racing engines and bragging rights, well-rounded combos like LME’s 600-Plus LS3 excel equally both on the street and at the track.

Stroker L99?

Although the LME 416 is built to LS3 specifications, that doesn’t mean automatic-equipped L99 fifth-gens can’t get in on the action, too. Typically, converting an L99 over to LS3 specs involves replacing the stock L99 lifters, lifter buckets, pushrods, timing set, timing cover, and lifter valley cover with standard LS3 hardware. Fortunately, all those components are already included in the LME 416’s build sheet, so there are no additional components that need to be converted over with LS3 hardware. Just drop the LME 416 LS3 in and hit the gas.


Late Model Engines
Houston, TX 77041



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