Supercharged 350ci Chevy - Big Power From A Little Blower -

The wheeze is that big things come in small packages. That may work for diamonds and dynamite, but it's not supposed to work for blowers.

Don't let the small size of this blower fool you. We made 504 hp on a stock 350 short-block with Vortec heads, a mild hydraulic cam, and a full street exhaust system.

Don't let the small size of this blower fool you. We made 504 hp on a stock 350 short-bloc

"That blower won't make big power-it's just too small." That was our opinion of Magnuson's new 122ci Magna Charger carbureted supercharger just before we started our dyno test. Jerry Magnuson's company has been building performance versions of the Eaton supercharger for a long time. This blower has made a name for itself making great power in late-model EFI cars like LS1 Corvettes and trucks, but until now, Magnuson had no carbureted version. Plus, the common perception was this blower was just too small to make any real power. After a half-century of giant 6-71 and 8-71 huffers protruding through the hoods of thousands of hot rods and musclecars, it is difficult to accept that a tiny little blower like this could compete. But following the first yank on the dyno handle at Duttweiler Performance, we threw out those old misconceptions and started a new mantra-small is big. Magnuson's new High Helix, 122ci displacement supercharger is about to set the boulevard on fire. With the power our little small-block made, Jerry Magnuson should be buying stock in Firestone, BFG, and Goodyear because this little blower makes enough steam to melt tires at will.

The Magnuson 122 is not much bigger than a loaf of bread. The other important point to make here is the new Magnuson manifold allows this blower to be used with production Vortec heads.

The Magnuson 122 is not much bigger than a loaf of bread. The other important point to mak

Here's the meat of this story: We bolted a 122ci High Helix Magna Charger carbureted-style supercharger to a painfully mild 350ci, 8.25:1 compression small-block Chevy outfitted with almost-stock iron Vortec heads and a mild Crane supercharger-spec hydraulic flat-tappet camshaft. On pump gas with a good supercharger-style 750-cfm Holley carburetor, this little Mouse made 512 lb-ft of torque and 504 hp, stacking a stunning 140 hp on top of the normally aspirated power numbers at the top end. And the blower achieved this amazing feat with single-digit boost numbers. The results were so stout that at first we didn't believe them. And the best part is this blower is the deal of the decade with a list price of $2,395.

On the EFI versions of the Magna Charger, the air enters the blower from the rear, which, according to Magnuson, is even more efficient than air entering from the top with a carburetor. Magnuson also offers an EFI-based package to be used on the early small-blocks.

On the EFI versions of the Magna Charger, the air enters the blower from the rear, which,

We've outlined the parts we used, so you know all the pieces and how brutally simple it would be to duplicate our numbers.

Inside the Magna Charger
The Magnuson supercharger is based on the original Eaton three-lobe supercharger. Most Roots-style superchargers are sized according to displacement, which is the number of cubic inches of air displaced for each revolution the blower makes. For example, the 6-71 GMC blower actually displaces 411 ci of air per revolution. The point of this particular test is that efficiency is more important than size. The Magna Charger supercharger used in our test displaces a mere 122 ci yet makes excellent power. What's new is this smaller blower employs a 60-degree twist to form a helix that creates a more efficient movement of air that reduces the temperature rise. This means the air exiting the blower is cooler than the discharge temperature of a less-efficient blower. Cooler air is denser, and that's where the power comes from.

One trick the Magnuson offers that no other Roots-type blower does is a bypass valve. This simple vacuum diaphragm is connected to the manifold vacuum. At cruise speeds with light load, manifold vacuum is high, which actuates an internal bypass valve.

One trick the Magnuson offers that no other Roots-type blower does is a bypass valve. This

It's also important to note that a Roots-style supercharger, including a Magna Charger, is not a true air compressor. Roots blowers should more accurately be termed air movers, pushing air fast enough through the blowers that it stacks up inside the intake manifold creating pressure, or boost. This is pressure above atmospheric, which improves engine efficiency and power by pushing more air into the cylinders than would normally occur with atmospheric pressure.

Given the above description, this means the discharge temperature from a more efficient supercharger will be lower than a blower that is less efficient for a given outlet pressure, or boost. The discharge temperature we measured out of this blower on our test was a mere 118 degrees F, which is exceptional, but the temperature is also affected by the heat removed from the air with the introduction of fuel into the air stream by the carburetor. Overall, generating 7.2 psi of boost with only a 118-degree air temperature going into the engine is the main reason this engine makes so much power from such a small supercharger.

Here is the bypass valve that feeds inlet air directly to the engine, bypassing the twin three-lobe rotors. This reduces pumping losses and improves fuel economy at part-throttle. At wide-open throttle, low manifold vacuum closes the diaphragm and valve, allowing the blower to make boost.

Here is the bypass valve that feeds inlet air directly to the engine, bypassing the twin t

The Test
The dyno testing was almost too easy. The intake manifold and blower were carefully bolted and torqued in place on the stock iron Vortec heads. The rest of the engine was already assembled, so all we had to do was drop in the Performance Distributors HEI, attach the plug wires, and plumb the 750-cfm mechanical secondary Holley supercharger carb. Almost as easy was installing the blower-drive assembly. We had to finesse the alternator position to ensure it would clear the blower, then we just bolted everything together. The Magnuson kit comes with a large-diameter crank pulley that allows the use of a larger blower pulley to ensure adequate belt engagement to minimize belt slippage-often problematic on serpentine blower beltdrives.

Because this could easily be a daily-driver street package, we limited the timing down low to keep the engine from rattling because our motor is equipped with cast pistons that don't like detonation. This turned out to be a challenge because the Magna Charger wants to make boost right out of the gate, cranking out nearly 5 psi as far down as 2,000 rpm. At 2,400 rpm, the Magna Charger was worth a solid 114 lb-ft of torque over the normally aspirated combination. As you can see by the graph on page 68, the torque curve is amazingly flat, which means the engine will be a whole bunch of fun to drive.

Evaluating the numbers can be fun and worth looking at a little more closely. The addition of the blower increased average torque from a respectable 380 lb-ft to an average of 93 more lb-ft to 473. Also note how close the average torque value is compared with the peak. That means in a car, this combination would be mucho fun to drive with plenty of power at any rpm.

It's also interesting to look at the far-right column-the percentage of power increase. Note how the supercharger tends to do its best job of adding power on either side of peak torque. A normally aspirated engine is most efficient at peak torque, which means the blower can add a greater percentage of power on either side of peak torque.

Quarter-mile Simulation
Just for fun, we plugged this power curve into the Quarter Pro computer dragstrip simulation software from Racing Systems Analysis using a 3,700-pound Chevelle, a TH400 trans with a 2,600-rpm converter, 3.55 rear gears, and a 26-inch-tall by 10.5-inch-wide tire. At 1,000 feet of altitude on a 70-degree day, the simulation reported that the car would run around 11.80s at 115 mph.

Because the engine makes so much torque, we pulled gear out of it all the way down to a set of 3.08s, where it still simulated around 12.00 seconds at 114 mph. Not bad for a full-dress, 3,700-pound street car.

When you consider that the addition of a very compact supercharger on a very mild engine with stock iron heads made an additional 140 hp at the peak of its power curve representing a 38 percent power increase over normally aspirated-that's plenty impressive. The beauty of this combination is that you can drive it anywhere, and there's always power on demand. You never have to open a valve, refill a bottle, or spend additional money to go fast. Even the initial investment is reasonable at just under $2,500. In addition to the Vortec-head manifold, Magnuson offers this same blower in the more traditional 12-bolt intake-manifold configuration.

Of course, this stimulates conjecture on how this engine would respond with a better set of cylinder heads. Imagine bolting on a set of AFR 195, TFS 195, or Dart Pro 1 200cc heads and a slightly more aggressive camshaft with more lift. While that gets into more coin, the power would be ultra-impressive.

Power Numbers
The following chart and graph illustrate the big difference delivered by the Magnuson supercharger.

Test 1 is the normally aspirated 350ci Chevy with stock Vortec heads, Holley 750 carburetor, 151/48-inch headers, and Flowmaster 211/42-inch mufflers.

Test 2 is the same exact engine except with the addition of the Magna Charger 122ci supercharger.