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  • Make 625 hp with a Junkyard 5.3L Truck Engine

Make 625 hp with a Junkyard 5.3L Truck Engine

Adding a Magnuson blower and carburetor to an old truck 5.3L gets you over 600 horsepower.

Jeff Smith
Nov 20, 2020
Photographers: 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. We had rescued a 5.3L truck engine orphan out of the junkyard and made 433 hp, a gain of 97 hp with nothing more than 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.
Photo 2/4   |   02 Junkyard 5 3 Ls Engine Out Of Truck To Make 625 Horsepower Magnuson Supercharger
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 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 5.3L 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 5.3L Pieces

Our previous build relied on a long-duration camshaft, a good set of cylinder heads, and lots of rpm to make 460 hp. It's all pretty mundane stuff in the LS by current standards, and anything less than 500 horsepower out of pretty much any LS engine barely raises an eyebrow these days. 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.
Photo 3/4   |   03 Junkyard 5 3 Ls Engine Out Of Truck To Make 625 Horsepower Edelbrock Cnc Ported Heads
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. As with our previous baseline tests, we controlled ignition timing with an MSD LS1/LS6 timing controller. Compression also remained the same at 9.5:1.
Photo 4/4   |   04 Junkyard 5 3 Ls Engine Out Of Truck To Make 625 Horsepower Edelbrock Cnc Ported Ls Head
For camshaft specs, the Comp Cams XER273HR-14 features advertised duration numbers of 273/279 intake and exhaust, 224/230 @ 0.050 duration, and 0.581/0.592 lift ground on a 114-degree lobe separation angle. It's a good performance grind, but certainly nothing that's exotic or that would impose severe restrictions in everyday street use.

Runnin' on Alcohol

One limitation of any supercharged engine is the octane rating of the fuel. Basically, almost any supercharged pump-gas engine will respond with more power by using a higher-octane fuel, which allows the engine tuner to dial in maximum boost and optimize the ignition timing. With current pump premium at a mere 91 octane in California, this is a significant limitation. Sure, we could pump that up with 100-octane unleaded race gas, but we decided instead to load it up with E85 that sports roughly a 105-octane rating if the ethanol and fuel have been mixed properly. In past supercharged dyno adventures, we've seen major power increases from this renewable resource fuel.
Supercharged (and turbocharged) engines are where this ethanol-based fuel really shines because it offers both a high octane rating along with a high latent heat of vaporization (see sidebar), which—when combined with boost pressure—can produce serious horsepower numbers. Even though our current 5.3L engine is small, the Gen III engine's superior valve angle and excellent airflow numbers (especially the exhaust side) foreshadowed better horsepower numbers.

Evaluating the Numbers

In case you haven't jumped ahead to peek at the power curves, on pump gas this little 325ci managed to crank out an excellent 562 hp at 6,400 rpm with a maximum boost of just a touch more than 10 psi around peak torque and 8 psi at peak horsepower. This neo-327 also pumped out an excellent 514 lb-ft of torque peak and never made less than 456 lb-ft of torque. We tried more timing, but a max of 19 degrees was the limit on 91-octane gasoline. Consider that this is a simple, cast-piston 5.3L engine. That makes this 562 hp even more impressive, equating to 1.73 hp/ci. Not bad for a tuned-up truck engine.
Our last magic trick involved replacing the Holley 750 gasoline carburetor for a Quick Fuel 850-cfm E85-version fuel mixer. Then we merely filled the dyno gas tank with 105-octane E85 and began playing with boost and adding timing. The higher octane allowed us an additional 5 degrees of ignition timing (to 24 total) while also adding 1 to 2 more pounds of boost. That may not sound like much, but this was worth as much as 102 more lb-ft of torque at 3,000 rpm over the gasoline-fed version. This massive torque gain is because at lower engine speeds, there's more boost and more time for the fuel to cool the air. Remember, this little blower is only 122 ci. This is why the boost trails off at the higher engine speeds.
From 3,000 rpm up, the E85 delivers a consistent 60-plus horsepower over the 91-grade pump gas. Peak power jumped to 625 hp at 6,400, and there's probably more waiting to be uncovered. If 625 hp and 592 lb-ft of torque doesn't impress, check your pulse.

Latent Heat of Vaporization

One of the big advantages of running E85 with a supercharger is alcohol's ability to chill the incoming air. This phenomenon is called a liquid's latent heat of vaporization. As an example, if you spread rubbing alcohol on your skin, when the alcohol evaporates, it pulls heat away from your body. Creating a change in state from liquid to vapor at a constant temperature requires energy, which feels like a cooling sensation on your skin as heat (energy) is removed. Because we have to use roughly a 25 to 30 percent greater volume of E85 (85 percent ethanol) compared with gasoline, and since ethanol has a higher latent heat of vaporization, it can drastically lower the inlet air temperature compared with gasoline.
Now let's add the fact that superchargers heat the air as it is compressed, often driving up the temperature by 80 degrees or more over the ambient inlet air temperature. Even pressurized, hot air is less dense than cool air at equal pressure. If we substitute E85 as a fuel, the large volume of fuel combined with its excellent latent heat of vaporization drastically reduces the discharge temperature from the supercharger. This greater density provides additional power even at the same boost pressure because more oxygen molecules are packed into each cubic foot of air pushed into the cylinders. Plus, the air temperature entering the cylinder is cooler, reducing the engine's sensitivity to detonation. Now add in the benefit of a 105-octane fuel on top of that, and you can see why supercharged engines really like running on E85. This is the same basic reason why the '60s turbocharged IndyCars used methanol.
To put this into perspective, a typical 8-71 supercharged, gasoline-fed engine at 10 psi of boost could easily see an intake manifold air temperature under the blower (depending on the blower's efficiency) of 150 degrees F or higher. In comparison, on a recent Gen I small-block test, a 122ci Magnuson supercharger at 10 psi using E85 fuel recorded an intake manifold temperature of 90 degrees. If you accept the old rule of thumb that power improves 1 percent for every 10-degree reduction in inlet air temperature, just this air temperature reduction alone is worth 6 percent of power. At a 500-hp level, that's 30 hp. Plus, with E85 you have the luxury of running idealized ignition timing because of E85's higher octane rating. The combination of these two factors is why this 5.3L engine made roughly 60 more horsepower on E85 versus 91-octane gasoline throughout virtually the entire power curve from 2,000 to 6,400 rpm.

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