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Stroker 426-inch LS3 that Makes 638 horsepower!

Displacement Chase: Going big with a 638hp, 426-cubic-inch carbureted LS3

Aug 23, 2016
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It’s all about the right tool for the right job. For a street car, you want an engine that makes its grunt in the lower rpm range where it spends most of its time. For a ride that’s going to hit autocrosses and road courses you might favor EFI over a carb due to its superior lateral fuel management. But if you’re going drag racing, then high-rpm power coupled with the simplicity of a carburetor is hard to beat. That’s the logic Tim Lee used when coming up with this build. He wanted an engine for his drag car project and knew that upper-rpm power was more important than low rpm driveability and that it’s hard to beat a carburetor when it comes to building a drag-centric quarter-mile-at-a-time engine.

Tim also knows the value of displacement and weight so the plan gelled into stroking an aluminum Chevrolet Performance LS3 block to the tune of 426 glorious cubic inches. That’s a gain of 50 torque-producing cubes all in the lightweight package of an LS3 engine. With this combo, the 427-inch number is far more common. But, since Tim was starting out with a fresh block, he saw no need to hone the block out to 4.070-inch just to get a cooler sounding displacement number, and we have to agree. After the choice of a stock bore and a 4.100-inch stroke, the rest of the plan was straightforward. A bulletproof high-lift valvetrain would work in concert with high-flowing heads to get as much air through the mill as possible. It’s a combination that, when done right and paired with the proper torque converter, can really make a Chevy fly down the quarter-mile. So follow along as we assemble the right tool for a very fun job.

Ls3 427 Engine Build Dyno Stroker 2/22

01. The starting point for our 426 LS3 build was this 6.2L block from Chevrolet Performance (PN 12621769). Since the block was new, we decided not to mess with it and leave the bores at the factory 4.065-inch diameter. We did send the block over to Custom Built Motors (CBM) to have the cylinders notched for stroke clearance. You can do it by hand, but it’s tedious work.

Ls3 427 Engine Build Dyno Stroker 3/22

02. The biggest pain about starting off with a new block is that it’s missing all the “stuff” needed to build an engine. This block plug kit from Comp (PN 251) made life a bit easier and sealed up all the water and oil ports.

Ls3 427 Engine Build Dyno Eagle Forged Crank 4/22

03. The key player in any stroker build is the crank. To make our displacement goal we went with a 4.100-inch Eagle 4349 forged steel crank with a 58x reluctor wheel. The non-twist forgings were heat treated, X-rayed, sonic tested, and magnafluxed to ensure they were perfect. Later, they were shot-peened and stress relieved for enhanced durability. The journals were nitrated and precision ground followed by micropolishing. Cross-drilled and chamfered oiling holes were also on the features list.

Ls3 427 Engine Build Dyno Torque Main Studs 5/22

04. The crank was installed with a set of Clevite main bearings and the factory main caps were torqued to spec.

Ls3 427 Engine Build Dyno Comp Camshaft 6/22

05. This engine will see some action at the dragstrip but we still wanted it to have decent street manners. Given this, we opted for a big cam but not so big that the car wouldn’t be able to be driven to the track. This Comp stick spec’d out at 243/251-degrees duration (at 0.050-inch) and lift of 0.624/0.624 with a 114 LSA.

Ls3 427 Engine Build Dyno Mahle Piston 7/22

06. For slugs we grabbed eight fully coated Mahle Motorsports forged pistons. They were perfect for the 4.065 bore of our stock Chevrolet Performance LS3 block and built to play nice with our 4.100-inch stroke crank and 6.125-inch rods. The -4cc volume should yield us a premium gas friendly 11.1:1 compression ratio.

Ls3 427 Engine Build Dyno Eagle H Beam Rod 8/22

07. Rods take a lot of abuse so we paired up a set of Eagle H-beam connecting rods (PN 6125O3D2000) with our Eagle stroker crank. These 4340-certified rods are much stronger than stock, yet lighter in weight. Like the crank, they’re fully tested, shot-peened, and stress relieved. They came fitted with 230,000 psi rated ARP 2000 rod bolts.

Ls3 427 Engine Build Dyno Ring Compressor 9/22

08. With the rings file fit and installed, we slid piston and rod assemblies into the cylinder bores.

Ls3 427 Engine Build Dyno Chevrolet Performance Oil Pump 10/22

09. It was then time to install a Comp double-roller timing chain, with a four-pulse sprocket and a new Chevrolet Performance high-volume oil pump. We used the spacers that came in the timing chain kit to move out the oil pump so that it would clear the wider chain.

Ls3 427 Engine Build Dyno Comp Link Bar Hd Lifter 11/22

10. Our cam had lift numbers of 0.624-inch, but to move more air we decided to go with 1.8 ratio rockers. This meant our actual lift numbers would be right around 0.661-inch. To handle the extra abuse of the higher lift we dropped in a set of Comp heavy-duty short-travel lifters (PN 15956HX-16). The XD lifters are built to take the extra abuse of high-lift cams and incorporate tool-steel internal parts.

Ls3 427 Engine Build Dyno Improved Racing Pick Up Tube Hold Down 12/22

11. We then flipped the engine over to install the Moroso steel oil pan and pick-up tube. On the tube we decided to try this cool widget (PN EGM-500) from our friends over at Improved Racing. The factory tube is secured by a single screw, which can cause a poor seal of the O-ring due to uneven pressure on the flange. This brace adds clamping force to the other side of the tube, which makes for even pressure all around the O-ring. For around $20, it’s cheap insurance.

Ls3 427 Engine Build Dyno 13/22

12. In terms of power output, heads can make or break a build. For this engine we went with a set of Trick Flow GenX 255 LS3 cylinder heads (PN TFS-3261T004-C01). The big 255cc intake ports should easily feed our stroked LS3, and these square-port heads work on engines with 4.000-inch and larger bores. The heads have 69cc combustion chambers and are completely CNC detailed. This equates to more airflow and better combustion. These heads also feature valve angles that have been changed from 15 to 12 degrees for more piston-to-valve clearance.

Ls3 427 Engine Build Dyno 14/22

13. To seal the deal we installed a pair of Fel-Pro PermaTorque MLS gaskets (PN 1161L-053, 1161R-053) over the ARP head studs (PN 234-4317).

Ls3 427 Engine Build Dyno Trick Flow Ls3 Heads 15/22

14. With the gaskets installed we could then set the Trick Flow GenX 255 heads in place and secure them with the ARP hardware. We bought the six-bolt version head since we see boost and an upgrade to a Chevrolet Performance LSX iron block in our future. The standard head-bolt configuration head is only $40 cheaper. These heads came with titanium retainers, 2.165-inch stainless intake valves, and stiff 448 springs.

Ls3 427 Engine Build Dyno Crower Ls3 Trick Flow Shaft Rockers 16/22

15. Remember when we said we wanted more lift so we specified a 1.80 rocker? According to Trick Flow our heads were good-to-go with LS3 rockers up to 0.625 lift. But our cam was well above that with our 1.8 ratio factored in. This meant we needed something a bit more special in terms of rockers. Given this we picked up some Crower shaft rockers specifically designed to work with the unique layout of the Trick Flow LS3 heads. These stainless steel 1.8 ratio rockers will stay rock-solid steady at high rpm and are optimized to be as light as possible at the tip. Comp 7.400-inch hardened pushrods rounded out the valvetrain.

Ls3 427 Engine Build Dyno Trick Flow Intake Carbureted 17/22

16. The plan for this engine is drag racing, so we topped the 426 off with a Trick Flow R-series single-plane aluminum intake manifold (PN TFS-32600111). The design is perfect for engines that live in the 3,500 to 7,500 rpm range. This intake also has bosses for installing nitrous as well as extra material in case custom port work is desired.

Ls3 427 Engine Build Dyno Holley Hp Ultra Carb 18/22

17. To feed in fuel and air we topped the intake with a Holley Ultra-XP 850-cfm carburetor (PN 0-80844HBX). Besides looking great in its grey anodizing, this carb is built to perform right out of the box. Features like 6061-T6 billet aluminum metering blocks, improved higher-capacity fuel bowl design, Pyrex sight windows, integrated bypass valve, and hand-adjustable primary and secondary curb idle screws are just a few of the features of this next-generation carburetor.

Ls3 427 Engine Build Dyno Westech Eddie Motorsports Billet Valve Covers 19/22

18. The taller shaft rocker system meant our factory valve covers were a no-go, so we grabbed a set of taller, billet valve covers from Eddie Motorsports. We also installed a TCI Rattler damper, a dyno-friendly Meziere electric water pump, and a set of Hooker 1 7/8-inch LS swap headers. Once in the car, the LS engine will stay cool and conserve power with a high-flow Meziere electric water pump (PN WP333S) that weighs just 10.3 pounds yet still pumps 55 gallons per minute!

Ls3 427 Engine Build Dyno Msd 6010 6012 Coil Pack Control 20/22

19. Even with a carburetor we still needed coil packs to put fire to fuel. Enter the MSD 6LS Ignition Controller. This box plugged into our LS engine’s cam and crank sensors to properly time the coil firing. It also had some cool features like a two-stage rev limiter and a vacuum advance curve. There was even a step retard in case we want to try some nitrous. This model is for 58x reluctor wheels, but they make a 24x as well (PN 6010).

Ls3 427 Engine Build Dyno 21/22

20. After some break-in pulls on Westech Performance’s Superflow 902 dyno we started making power pulls. Once Steve Brule did a jet change the pulls became very consistent with a best blast of 638 horsepower at 6,500 rpm and 553 lb-ft at 5,500 rpm! The long, flat torque curve is exactly what we were looking for and this should be a solid performer at the track.

Ls3 427 Engine Build Dyno 22/22


ARP (Automotive Racing Products)
Ventura , CA 93003
Don Lee Auto
Cucamonga, 91730
Trick Flow Specialties
Tallmadge, OH 44278
TCI Automotive
Ashland, MS 38603
Westech Performance
Mira Loma, CA 91752
Improved Racing
Orlando, FL 32828
Mahle Motorsports
Fletcher, NC
Eddie Motorsports
Rancho Cucamonga, CA 91730
Meziere Enterprises
Escondido, CA 92029
Eagle Specialty Products, Inc.
Southaven, MS 38671
Bowling Green, KY 42101
Chevrolet Performance
Southfield, MI 48034
MSD Performance
El Paso, TX 79936
Competition Cams
CBM Motorsports



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