Small-Block Vortech Supercharger - Blow Through

A Street-Friendly Centrifugal Blower For The Carbureted Crowd

Mike Petralia Mar 1, 2002 0 Comment(s)
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If you want to build a reliable, honest-to-goodness 575hp, everyday small-block, this is how it gets done. There's nothing trick or outrageously expensive about it, either. Just assemble a quality motor using strong parts, top it off with a good breathing top end, boost it a few psi above atmospheric pressure with a blower, and you're going to come out with a winner. That's exactly what Southern California-resident Doug Kruse wanted for his screamin' red '57 Chevy, and he went to the experts at Vortech Superchargers to help him get the results he wanted.

What Kruse and the guys at Vortech were after was a very streetable, blown small-block using a centrifugal blower boosting air through a good old-fashioned carburetor. The reason for sticking to a carburetor was simple: it's inexpensive and most people already have one. Besides, there are already enough EFI centrifugal blower kits out there, and Vortech really wanted to build a blow-through carb system.

What's a blow-through system you ask? Basically, superchargers increase power by sending more air into the engine than it could normally ingest. How the supercharger sends this air into the engine determines its basic operation. For instance, a Roots blower-like the 6-71s we're all familiar with-draws air mixed with fuel through the carburetors to boost it in the intake manifold, hence a Roots blower is typically referred to as a draw-through design.

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A modified Holley 750 double-pumper feeds this stroker, making it all the more outstanding in the world of centrifugal superchargers.

Whereas a centrifugal blower pulls its air right from the air cleaner and pressurizes it as it goes into either the carburetor, like in Kruse's case, or the intake plenum of an EFI motor, where it mixes with fuel just before it enters the cylinder head runners. So a centrifugal blower on a carbureted engine can be referred to as a blow-through design because it "blows" boosted air through the carb. There are also centrifugal systems using carbs in a draw-through fashion, but that requires mounting the carb way off the intake manifold, and it is a nightmare to plumb the system that way.

Building The Beast
To start out, Kruse knew he needed a strong, but not overbuilt, bottom end. So he searched locally for an engine builder that knew a thing or two about putting together a strong street combination. He met engine builder Ernie Nunes from C.A.R.S. in Thousand Oaks, California, through a friend at the Ventura County Chevy Club and contracted with him to build his motor. Nunes runs a 9-second Vega with a juiced small-block, so Kruse felt he'd get the job done right.

For both power and durability Nunes built a 383 stroker using a 4340 Eagle crank and 5.7-inch Eagle H-beam rods with 9:1-compression SRP pistons to keep costs down and quality high. File-fit moly rings and bearings from Sealed Power ensure that Doug's blown stroker won't let him down on the open road. Nunes finished off the bottom end assembly with a complete Milodon oiling system that would fit in Kruse's '57 Chevy.

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Here's a close-up showing the carb and all the connections going to it. All joints leading into Vortech's blow-through box are sealed to prevent any dirt from getting into the engine.

Blower motors can treat a typical camshaft two ways. It'll either make tons of power with the right cam, or the engine will just make decent power with the wrong cam. The good thing about blowers is that it's hard to over-cam the engine with one. Overlap is the key, and staying away from too much of it is the best way to make blown power. So Nunes chose a custom Comp Cams hydraulic roller profile with 276/280 degrees advertised duration, ground with a 114-degree-lobe-separation angle to keep overlap down.

Edelbrock products were counted on to feed the fuel into the fire, and a set of out-of-the-box Victor Jr. heads with 2.08/1.60 valves and a Victor Jr. intake were bolted on to give the blower some breathing room. Kruse found out the hard way that these heads feature raised exhaust ports, so that meant his old headers would no longer fit and new ones had to be fabricated. Since Kruse likes to show as much as he likes to go, he sent the entire upper assembly off to The Polishing Shop in Newburry Park, California, for the royal shine. Then, Nunes had a friend of his set up the 750-cfm Holley double-pumper carb to work with the blower by boost-referencing the power valve and calibrating the metering circuits the way he felt would provide the best compromise between power and economy.

To The Dyno We Blow
While the engine was being assembled, Kruse made good friends with the guys at Vortech Engineering and trucked the finished motor over to their shop for a few days of bashing on their new DTS engine dyno. Vortech's dyno guy, Mike Reagan, dialed the engine in while making several combination changes to see what would and wouldn't make power with the new carbureted blower system. The kit responded well to a bigger carb than the 750 Doug originally supplied.




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