Dyno Results: Vortech Si Supercharger & 347ci Stroker!

Power Lifting For The Stroker

Our 347ci stroker receives a Vortech Si-trim Supercharger

Our 347ci stroker engine is a thing of beauty. After bolting up our top-end consisting of AFR aluminum cylinder heads and a Holley SysteMax intake with the Holley 80mm throttle-body and Aeromotive fuel rails, our Editor thought it needed one more power upgrade to finish it off. Enter Vortech’s tried and true V-3 Si-trim centrifugal supercharger kit.

Supercharging has been a favorite of engine builders for decades. The legendary World War II airplanes used superchargers to achieve big horsepower, which helped them fly at high altitudes and speeds. The Merlin engines that powered English Spitfires and the American-made Wildcats actually used two-stage superchargers to build amazing power. Still others actually used a combination of supercharging and turbocharging, so for those of you who thought supercharging was a new thing – guess again.

For our 347ci engine, Vortech makes an amazingly compact and highly powerful supercharger that bolts right up. Even such critical things as power steering, alternator mounts and the factory smog pump are all compatible using the supplied drive system. In addition, the standard engine profile is retained so it all tucks under the hood in most cases. If we referred to our AFR’s as a whipped cream topping in our last installment, the Vortech is a great big cherry.

As a quick recap, our 347ci short-block had been completed using an assortment of parts from companies like K1 Technologies, JE Pistons and Wiseco. For induction we used a Holley SysteMax intake manifold with an 80mm throttle-body and used a Holley Batchfire ECU to achieve total fuel management. For cylinder heads, we installed AFR’s Renegade aluminum cylinder heads, which incorporate a combustion chamber that is 58cc and an intake port volume of 185cc (their 165cc intake port volume cylinder heads are suggested for engines that retain the stock piston configuration). When used with a 0.040-inch thick Cometic head gasket and our JE Pistons (-22cc dish), the final compression ratio is 9.2:1, which is very manageable for pump.

Under Pressure
While our engine would have been perfectly fine in a normally aspirated form, we decided to turn up the wick and added Vortech’s supercharger tuner kit as noted above. Because we were using a factory block (bolstered somewhat through the use of ARP fasteners) we decided that to avoid causing block damage and put a limit of 500 horsepower on our dyno test. This would be ample power for our street-bound purposes while delivering excellent durability. That of course that was our plan but, in our zeal, to generate power we decided to test our luck at bit. To cut to the chase, we went well over 500.

The Vortech supercharger kit (PN 4FA218-144L) we used featured a V-3 Si-trim compressor that is built to deliver between 6-8 psi. This kit is designed for the 1986-1993 Ford Mustangs with all of the standard accessories intact including the smog pump, alternator, and power steering. This is a very low maintenance supercharger kit with self-contained oiling system, easy maintenance features and an 8-rib belt to guard against belt slippage. As our boost graph shows, our belt system performed perfectly with no slip anywhere up to our boost cut off point.

Dyno up
Using the tried and true SuperFlow dyno at Westech Performance in Mira Loma, Ca, to test our engine, we enlisted the talents of veteran dyno tech Steve Brule. Our first test would be without the supercharger to get a baseline for normally aspirated power. This was actually the original plan for the engine, but we decided to kick it up a notch with a centrifugal supercharger. An electric water pump was used to circulate the coolant and Hooker Super Comp headers with 1 3/4-inch primary tubing and 3-inch collectors handled the exhaust chores.

We retained all of the original equipment as installed in our previous build, including those pieces from Holley, Comp Cams and AFR. All previous valvetrain adjustments were left intact and total timing was set at 28-degrees.

In all, we made four pulls with the normally aspirated configuration and found the engine to be very consistent offering up figures that would make for a competent street engine. While some “educated” folks had guessed that the 347ci engine would top out at less than 400 horsepower, others, with knowledge of our AFR heads, were confident that the engine would have no trouble making significantly more. In the end, the pundits won out and the engine ripped up the dynamometer hitting 434 horsepower at 5,700 rpm. The torque figures were impressive, the engine achieving a peak of 430 lb-ft of torque at 4,100 rpm. What was equally amazing was the fact that the engine delivered over 400 lb-ft of torque from 3,600-5,700 rpm; a key engine operating range. That is extremely respectable power for a small-block engine of this size, making it excellent for any street vehicle.

Vortech power
The tuner kit from Vortech is extremely reasonable for the street builder, requiring about an hour to install on our dyno engine. In a vehicle, we would expect it to take around four hours tops for the average car builder due to the need to include accessory drives and work around other parts we could omit here. With our concern for block safety, we informed Captain Brule of our concerns.

Using 93 octane fuel and 28-degrees of total timing we fired the dyno while keeping an eye on key dials that could signal engine trouble. We were happy to say that despite taking the engine well over the 500 horsepower figure, it performed incredibly well. We note these things here, because taking time to check the integrity of the engine parts used in the build, component clearances and proper torque specs will make all the difference between celebrating our engine’s achievements and determining which size shovel would be required to remove the remnants.

Boost from the Vortech builds slowly with this system, the engine saw as little as 2.3 psi of boost at 3,000 rpm. In the end the engine would reach a maximum of 6.9 psi at 5,000-plus rpm.

In the end, the engine developed 563 horsepower at 5,000 rpm. Brule believes that the engine would see in excess of 650 horsepower if left to spin higher. Brule went on to say, “If we used an aftermarket block, such as one offered by Dart SHP, this engine could see a lot more power with added boost and higher octane fuel. With the factory block, the engine configuration has more potential than it can safely produce.”

On the torque side of things, the engine developed 594 lb-ft of torque, the curve just flattening out at 4,900 rpm to show that it had peaked. The engine developed 500-plus lb-ft of torque from 3,700 rpm to the 5,000 rpm limit we set for the engine. That’s tons of tire-searing torque that makes it more than competent on the street.

In the end, both supercharged and normally aspirated versions of this engine were impressive in their power output and massive torque bands. Simple to operate and maintain, the Vortech supercharger added over 130 more horsepower and 160-plus lb-ft of torque for a very manageable 7 psi of boost. With a stronger block and the ability to spin it higher in the rpm, the gains could easily have been 200+ horsepower. For any one looking to build a low maintenance, highly reliable, reasonably priced, big power gain small-block Ford engine, we recommend both the normally aspirated and supercharged combinations highly – the choice is yours.

Parts List


Vortech Superchargers
Ford small-block tuner kit, PN 4FA218-144L

Fuel Rails, PN 14106


Air Flow Research
185cc small-block Ford street cylinder head, PN 1388
Combustion chamber size, 58cc
185cc, Intake port volume
Intake valve, 2.020-inch; Exhaust Valve, 1.600-inch
PAC racing springs, 1.290-inch OD hydraulic-roller
Valve spring, 140 lbs on seat
Manley steel retainers, Viton valve seals, 8mm bronze valve guides
Rocker stud diameter, 3/8-inch


Comp Cams
Ultra Gold aluminum rocker arms, PN 19049-16
1.72:1 ratio with 3/8-inch rocker stud
Pushrods, PN 7767
6.500-inch long
0.080-inch wall thickness


42 lb/hr injectors, PN 522-428
80mm throttle-body, PN 112-510
SysteMax intake manifold, PN 300-72BK


Performance Distributors
Black 10mm LiveWires, PN DUI- C9058BK
Ford Hot Forged DUI distributor, PN 18457RD


Cometic Head Gasket
MLS head gasket, PN H2775SP2040S


Spark plugs, PN 3924

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