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Small-Block Vortech Supercharger - Blow Through

A Street-Friendly Centrifugal Blower For The Carbureted Crowd

Mike Petralia Mar 1, 2002
Sucp_0203_02_z Small_block_vortech_supercharger Belt_drive 2/14

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.

Sucp_0203_06_z Small_block_vortech_supercharger Modified_holley_carb 3/14

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.

Sucp_0203_07_z Small_block_vortech_supercharger Carb 4/14

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.

Sucp_0203_20_z Small_block_vortech_supercharger Timing 8/14

Ignition timing is critical to running any blower. Too much will kill the engine quickly. Vortech's Mike Reagan sets the total timing to 38 degrees for the baseline motor-only dyno pulls (note the missing blower belt). All boosted power pulls were made with 30 degrees total timing.

When Vortech installed an 850-cfm Demon double-pumper into its carb box, the blower made just about the same boost as it did with the smaller carb but cranked out 47 more ponies at peak. This blow-through supercharger system seemed to want lots of air, which is not that unusual for any blown engine. Typically, blown motors will make more power with bigger carbs than they would naturally aspirated. However, as you'll note in the last dyno power pull we've listed (B), the engine did not like the bigger carb down low and made considerably less power between 3,000 and 4,000 rpm. That's most likely due to the larger venturis' of the Demon carb not getting a strong enough signal at that low rpm to begin working efficiently. It's not that the Demon carb was inefficient; to the contrary, this just proves that there is always some compromise involved when making the best power on any engine.

Blown power is the best kind there is, and Vortech's new carbureted kit makes it that much more approachable for the average car nut. This kit means there's substantially less cost involved when compared to building a blown EFI motor, and tuning can be accomplished with a timing light, vacuum gauge, and screwdriver, instead of a laptop computer. Next, we'd like to see Vortech integrate an intercooler with this system for even more power and streetability. That'd be the ultimate in power-per-dollar for any hard-core blow-hard.

Baseline Power(normally aspirated)
Vortech first dyno'd the engine without the blower belt and left the carb box open. Centrifugal blowers are the only types of superchargers that allow testing like this, because you can't remove a Roots blower and test the engine without it.

3000 215 376
3500 253 380
4000 304 400
4500 352 411
5000 393 413
5500 395 377
5900 403* 360
*MaxHP 403 @ 5900
MaxTQ 415 @ 4900

Blower Power Pull (A)
The first couple blower pulls utilized the modified Holley 750 carb. This test represents the best power made with a 6-inch diameter crank pulley and a 3.47-inch blower pulley, meaning the blower was 173 percent overdriven.

3000 213 373 8.8
3500 269 403 9.3
4000 338 443 9.7
4500 409 478 10.5
5000 452 474 11.4
5500 497 475 11.8
5900 526* 469 11.9
*MaxHP 526 @ 5900
MaxTQ 482 @ 5100

Check out how the simple addition of the blower added almost 125 horsepower to this otherwise very mild small-block! That's a bolt on worth an incredible 31 percent increase in power that'll work on just about any carbureted engine!

Blower Power Pull (B)
This pull represents the best power made on full-kill. Vortech installed a larger 850-cfm Race Demon carb and a replaced the 6/3.47 pulley combination with a big 7-inch crank pulley and smaller 3.33-inch blower pulley boosting the overdrive ratio to 210 percent.

3000 180 315 9.7
3500 240 360 10.6
4000 349 458 11.5
4500 420 490 11.1
5000 484 508 10.9
5500 533 509 10.9
6000 573* 502 11.7
*MaxHP 573 @ 6000
MaxTQ 517 @ 5300

Note the drop in low-end power from 3,000 to 4,000 rpm compared to power made with the smaller carb. The bigger carb more than made up for it with 47 more peak horsepower on the top end. There's always a trade off in power somewhere.


Comp Cams
Memphis, TN 38118
Holley Performance Products
Bowling Green, KY 42101
SRP (Sportsman Racing Pistons)
Huntington Beach, CA 92649
Vortech Engineering, Inc
Channel Islands, CA 93033



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