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5 3L Truck Engine with 625HP - Make 625HP With A Junkyard 5 3L

Think Small-Displacement Engines Can't Make Power? We Used A Supercharger And E85 Pump Fuel To Prove That Wrong

Photography by Ed Taylor,

This is the age of horsepower. Power masters build giant-cube big-blocks and play with exotic CNC-machined billet blocks with custom bore centers, tomato can-sized bores, and yard-length strokes. But on the other end of the scale is a new army of small-displacement production V-8 engines capable of amazing power numbers. Back in the Apr. '08 issue ("Add 120+ HP"), we rescued a 5.3L truck engine orphan out of the junkyard and made 433 hp, a gain of 97 hp with just an intake, a carburetor, headers, and a cam. Then we bolted on a set of West Coast Racing Cylinder Heads-ported (WCRCH) stock 5.3L heads and made 449 hp. Finally, we added a set of WCRCH CNC'd Edelbrock heads, and the power jumped to 460. We made this power from a used and totally stock rotating assembly, displacing a mere 325 ci. Little motors rely on rpm to generate horsepower numbers like this, and this effort was no different, spinning 6,700 rpm. This is great power, but we weren't satisfied.

Then we heard rumors of big horsepower attained by bolting one of Magnuson's superchargers to 5.3L truck engines. So we decided on a carbureted Car Craft version using a Magnuson 122 supercharger. As the plan came together, we knew we'd need a different camshaft to take maximum advantage of the supercharger, but other than degreeing-in the cam, that was about the extent of our internal engine modifications. We also retained the CNC-ported Edelbrock heads because their added airflow would really make our 5.3 motor shine.

We'll run through all the details on this test, and after you've digested the data, you'll see what a little motor with a simple supercharger can do on both 91-octane pump gas and a large shot of alcohol. If 1.9 hp/ci sounds interesting, read on.

Parts in 5.3 Pieces
In the April test, we relied on a long-duration camshaft, a good set of cylinder heads, and lots of rpm to make 460 hp. This month, we refined that combination to bring the peak horsepower rpm point down with more conservative camshaft timing. The specs can be found in the Cam Specs chart, while all the other valvetrain components (except the valvesprings) were retained, including the rocker arms and pushrods from the previous flogging. Comp has introduced a new, stiffer beehive spring that we wanted to try, which increases the over-the-nose pressure to keep the valvetrain happy. To keep the supercharger testing simple, we retained the WCRCH CNC-ported Edelbrock heads fitted with 2.00/1.57 valves in a fully CNC-machined combustion chamber. Of course, the big change was the Magnuson 122ci carbureted supercharger.

We also retained the Hooker 1 3/4 engine-swap headers along with a pair of Flowmaster 2 1/2-inch mufflers from the previous test to minimize the variables. But in hindsight, it's more than likely that a 3-inch exhaust system (or open headers) would have unleashed even more power. Again, we controlled ignition timing with an MSD LS1/LS6 timing controller. Compression also remained the same at 9.5:1.

You may remember that our first foray into the world of the Magnuson superchargers was with a Gen I 355ci, cast-piston, 8.2:1-compression motor with iron Vortec heads. That simple little motor made 504 hp on pump gas in the Sept. '06 issue ("Big Power From a Little Blower"). This Gen III motor would make much more.

CAM SPECS
CAMSHAFT DURATION (Adv.) DURATION (0.050) LIFT LOBE SEPARATION
(degrees) (degrees) (inches) (degrees)
Comp Cams, intake 273 224 0.581 114
XER273HR-14, exhaust 279 230 0.592
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