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GM Performance Parts LS Engine - Diy LSX 427
Super Chevy'S Guide To Building A 550-Horse Ls Engine From The Gm Performance Parts Catalog.
Jan 1, 2008
Chevrolet Performance Parts
Detroit, MI 48232
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GM Performance Parts LS Engine - Diy LSX 427
An ls7 forged steel crankshaft, part number 12568820, came next. it delivers a 4.000-inch stroke which, combined with the 4.125-inch bores, gives the engine its 427-cubicinch displacement.
The starting point for the project was the lsx iron cylinder block, part number 19166454, which can be had in most places for less than $2,000. it is based on the Gen iV "ls" engine design, but with provisions for six-bolt cylinder heads. The Chevy-orange paint is standard, too.
The LSX block is delivered in semi-finished form, meaning it must visit the local machine shop for finish work before the engine buildup starts. Ours was taken to Thomson Automotive, where the bores were finished to 4.125 inches with torque plates clamped to the decks.
When it came time to start assembling the engine, the wrench turning was handled by GM Performance Parts' Thom Bates, who started by inserting the camshaft. We used an ls7 cam, part number 12571251, which has 0.591-inch lift on both sides and 211/230 duration specs.
One of the assembly details new ls engine builders will have to get used to is torque-to-yield fasteners. These are one-time-use bolts that, in addition to a traditional torque wrench, also require a torque-angle meter to achieve the correct final torque spec.
One of the toughest jobs of an ls engine assembly is installing the damper, part number 12576652, which is a super-tight fit. We used a tool designed by Thomson Automotive. GM also has a tool for the procedure.
With the rods and pistons assembled, they were ceremoniously dropped into the cylinder block.
With the rods secured, the windage tray was set in place, but we didn't simply torque it down and move on to the next assembly step.
The solution to the rod/windage tray interference problem is adding washers to the attachment studs to serve as spacers. it's all that is necessary to provide adequate clearance.
Next up was the assembly of the rods and pistons. We used the cast ls7 pistons, part number 89018171, and exotic, super lightweight forged titanium ls7 rods, part number 12586258. With our 70cc cylinder heads, compression checks in at 11.0:1-perfect for a modern 93-octane street mill.
Like so many other fasteners on the engine, the rod bolts are torque-to-yield. GMPP's Thom Bates snugged them down and checked the clearance between them all.
On LS engines with more than a 4.000-inch, or greater, stroke, the rod ends will likely interfere with the windage tray. Bates checked this by carefully rotating the crankshaft and noting whether the rods hit the tray. They did.
The oil pump pickup was next. Because the engine can't be primed via a distributor hole like classic small- and big-block engines, it's important to get some oil into the pickup at this stage of the build.
We installed an F-car oil pan, part number 12558762, as it's the most "universal" of the various ls-engine production pans. in other words, it's the one that will retrofit into an older car with the least amount of hassle.
With the short-block assembled, the heads came next. Here, Bates drops on one of the ls7 aluminum heads.
We used GM's ls-series lifter kit, part number 12499225, which includes 16 hydraulic roller lifters. They were doused in oil prior to installation.
One of the unique features of the ls7 heads is offset intake valves, which necessitates correspondingly offset rocker arms, one of which is shown being installed here. Both the intake and exhaust ratios are 1.8:1.
One of the most crucial inspections during the assembly is the squaring of the oil pan with the cylinder block. The best way to get it right the first time is running down the oil pan bolts, but leaving them a little loose; then, a straight edge is used to check that the pan and block are square. When everything lines up correctly, the pan bolts are final-tightened.
The LS7 heads are masters of airflow. They're CNC-ported at the factory and flow approximately 350 cfm through 270cc intake ports. The intake valves are titanium and are 2.20-inches in diameter, while the 1.61-inch exhaust valves are sodium filled. They're all held at a 12 angle.
On all other ls engines, the lifters can be dropped in lifter guides that install two at a time. The provisions for extra head bolts on the lsx block, however, make that impossible. so, they're carefully inserted, one at a time, and held in place with lsx-specific guides that come with the cylinder block.
Our engine builder, Thom Bates, took credit for pushing through at GMPP the ls7 intake assembly, part number 12568976, coming with the throttle body, fuel injectors and fuel rails pre-installed. it makes topping off the engine a much easier, quicker job.
Assembly of the engine was wrapped up with the installation of the water pump, part number 89018053.
On the superFlow dyno at Thomson Automotive, our lsx 427 kicked out an impressive 550 hp and 511 lb-ft of torque (sTP correction). This was with no tuning or external adjustment; the ls7 controller was simply plugged in and the engine was run on its preprogrammed tune. We were thrilled with results, as the performance was achieved with off-the-shelf catalog parts and a by-the-numbers assembly. Our engine was fuel-injected and used drive-by-wire electronics. GMPP has the necessary parts if you'd like to go this route. if you're going carbureted, you can use a regular, old throttle cable.
Surprisingly, the ls7 coil packs don't come as an assembly, even though that's how they installed on the engine. The individual coils and mounting bracket must be purchased separately.
One of the key enablers to making our engine project a turnkey affair was the use of GMPP's new, stand-alone ls7 controller, part number 19166567. it allowed the engine's wiring harness to simply plug into this ECM and-bingo-the engine was timed and tuned from the get-go. it could not have been easier to get the engine up and running.
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