Let’s do some quick, easy math, where your basic 1 + 1 = 2.

We all know that big motors make more power than smaller motors, right? We also know that boost makes more power, too! The question on the table now is, what happens when you combine the two?

The only thing better than one or the other, is obviously both! Big or small, the power output of any internal combustion engine is determined by the amount of air (and fuel) it can process, right?

A rather simplified (air pump) equation we know, but horsepower is basically a function of the amount of air processed by the motor. The more you process (or in our case, force) through the motor, the more power you will get out of the motor. The trick to making power is getting the additional air (safely) into and out of the motor.

Given this simplistic airflow equation, one of the most popular routes to improved performance has long been supercharging. In its most basic form, supercharging involves force feeding the engine more air than it can ingest of its own accord. Like all good things, the problem with any type of forced induction is that enthusiasts tend to get greedy.

Who among us hasn’t reasoned that if a little boost is good, then more must better, right? Wrong! If you can resist the temptation, combining boost with a healthy big block can yield massive power, and, (this being the important part), do so safely and reliably.

man installing carburetors atop a supercharged v8 engine
What could be better than a powerful big block Stroker motor? How about one with boost? (Image/Richard Holdener)

Supercharger Basics

Before getting to the big block build, we should take a moment to better understand the basic principles of supercharging. To start, supercharging is a form of power enhancement that forces air into the cylinders. This is accomplished by installing a compressor (or more accurately an air pump-not unlike the motor itself) onto the motor and using the crankshaft to spin the compressor. The compressor is spun to provide more air than the motor could ingest of its own accord.

The only way to increase the airflow is to pressurize it, the result of which we see as boost. In reality, a naturally aspirated motor runs under pressure even without the supercharger. The pressure we refer to is atmospheric pressure (14.7 psi or one bar). Vacuum is created in the cylinder by the downward moving piston. This vacuum is filled thanks to the atmospheric pressure that exists outside the cylinder. Superchargers (and turbos) only increase the pressure above atmospheric.

More Supercharger Math

Here is a little more (but still simple) motor math to get us started. Suppose our naturally aspirated motor produced a given amount of power at an atmospheric pressure of 14.7 psi. Does it then stand to reason that if we double atmospheric pressure by having the supercharger produce an additional 14.7 psi of boost (above atmospheric pressure), we could then double the power output of our naturally aspirated motor?

In theory (and occasional application) this holds true, but the reality is that the theoretical math and the actual power output often differ. Despite what the math predicts, there are a number of factors working against the theoretical boosted power output.

The major problem with the theory is that the supercharger (any supercharger) requires an input of power to help produce the additional power. Superchargers are driven off the crankshaft and just like any accessory, driving the supercharger takes power away from the engine. Though the supercharger delivers more additional power than required to drive it, the parasitic losses associated with driving the supercharger absorb some of the potential power output.

Let’s try an example to help better illustrate the difficulty we have with the so-called power/boost formula. What happens if we take a theoretical 500 hp NA big block and install a supercharger producing 14.7 psi of boost?

According to the math, we should be able to double the power output to 1,000 horsepower, right? After all, shouldn’t doubling the atmospheric pressure also double the power output? If everything went perfectly, the motor would still not produce 1,000 hp at 14.7 psi since the blower likely required as much as 150 hp (or more) to drive the rotors. The very best you could hope for would now be near 850 hp (1,000 hp – 150 hp).

In reality, the resulting power might be even less on a typical roots blower—like our big block build.

The power/boost formula assumes a supercharger that operates at 100% efficiency (an impossibility). No supercharger runs at 100% efficiency, so in addition to the parasitic losses, we have other factors that might limit the ultimate power production (like intercooling). Despite these obstacles, positive displacement superchargers add huge chunks of power and combining them with big cubic inches is still a time-honored tradition of producing big power.

Supercharging vs. Inlet Air Temperature

One potential downside of running a supercharger is elevated inlet air temperature, as (unfortunately) heat is a natural byproduct of compression. When you install a blower on your motor and pump up the boost pressure (even to just seven psi), you will—in every instance—increase the temperature of the air going into the motor.

Pressure causes heat, and unfortunately, heat is the enemy of performance.

For any performance motor, we strive to supply cool, dense air. The cooler the air, the denser the air. Dense, in this case, means the air is chock-full of power-producing oxygen molecules. The greater the quantity of oxygen molecules, the greater the power production. The obvious answer to keeping things cool on a supercharged application is intercooling.

Many roots supercharged applications rely on an air-to-water intercooler core sandwiched between the blower and lower intake manifold. The downside is this adds even more height to an already tall induction system.

Luckily for blower enthusiasts, the inherent design of the Weiand supercharger already included its own form of intercooling. Perched on top of our Weiand 8-71 blower was a pair of Holley 950 HP carburetors. The fuel supplied by the carburetors above the blower actually helped reduce the air temperature under boost. Basically, the carburetors acted as intercooling for the supercharger.

When combined with a realistic boost level (we ran under seven psi), the combination was very safe and efficient.

The Boosted Big Block Chevy Test Motor

Enough with the theories, let’s get to our boosted big block. The best way to demonstrate the power potential of a blown big block was to combine the two and run them on the dyno.

Starting with a production 454, the four-bolt block was bored 0.060 inch over, honed, and decked to prepare for the trio of forged internals. In addition to the overbore, the displacement was increased via a Lunati Pro Series steel Stroker crank. The Pro Series featured 4340 steel construction, precision tolerances and plasma-gas nitrite heat treating. The Lunati steel 4.25 inch Stroker crank combined with the 0.060 inch overbore resulted in 496 cubic inches.

The Stroker crank was combined with a set of Probe Racing 18cc domed pistons and Lunati 4340 Pro Billet connecting rods. The forged pistons incorporated a single intake valve relief to ensure adequate piston-to-valve clearance for the COMP blower cam. The COMP 300BR-14 solid roller offered 0.652 inch lift, a 255/262 degree duration split, and 114 degree LSA. COMP also supplied the 819-16 lifters and 3110 double roller timing chain. The entire rotating assembly was precision (internally) balanced using a neutral Rattler damper from TCI.

Knowing the Stroker required plenty of airflow, we took a big swing at the induction system, starting with the heads. Airflow Research supplied a set of AFR CNC-ported 315cc Magnum BBC heads. The AFR BBC line of aluminum heads featured a number of impressive features including 3/4 inch thick head deck surfaces for maximum sealing, perfect for our supercharged application. The AFR BBC heads also featured reinforced rocker stud bosses, rolled valve angles (two degrees) to improve flow characteristics, and an exclusive combustion chamber design.

Available in multiple configurations, we chose the CNC-ported 315 heads. The 315cc heads started out life as a set of as-cast 305cc heads, but were then treated to full CNC porting including the already efficient combustion chambers. We ordered our big block heads with 121cc combustion chambers to produce a static compression ratio of just under 10.0:1. The compression choice allowed the motor to run effectively as an NA or blown big block. Though small compared to the other AFR offerings, thanks to the CNC porting, the 315cc heads flowed nearly 390 cfm on the intake and over 300 cfm on the exhaust. These are huge numbers for any performance BBC head, but especially considering the comparatively small port volumes.

NA vs. Supercharged Comparison Testing

Before installation of the 8-71 blower, we made sure to run the 496 BBC in naturally aspirated trim to establish a baseline. For the NA runs, we equipped the 496 with a single plane, Edelbrock 454R intake, Holley 950 HP carburetor and MSD ignition. Additional goodies included Hooker 2-1/8 inch, long-tube headers, COMP 1.73 ratio aluminum roller rockers, and a Meziere electric water pump.

After a few break-in cycles and some fresh Lucas oil, we were rewarded with peak numbers of 651 hp at 6,300 rpm and 579 lbs.-ft. of torque at 4,800 rpm.

Satisfied with our baseline, off came the Edelbrock intake and on went the supercharger. The blower was equipped with a pair of 950 HP carburetors, and pulley combination (59 tooth top/57 tooth bottom) to produce a maximum of 6.5 psi of boost. After dropping the ignition timing down from 40 degrees to 30 degrees, the Weiand 8-71 Street Supercharger produced 4.9 psi at 3,000 rpm and peaked at 6.5 psi at 6,500 rpm.

The boost supplied by the 8-71 increased the peak power output from 651 to 898 hp and torque from 579 to 764 lbs.-ft. Running less than seven psi, the roots blower upped the power ante of the 496 stroker by an amazing 238 hp and 185 lbs.-ft. of torque.

After adding the Weiand 871 to the 496 big block it is easy to see why the big blocks and blowers are so popular.

Dyno Chart: 496 Big Block Stroker, NA vs Weiand 8-71 Blower (6.5 psi)

Engine Dyno Chart
What better proof do you need that big blocks and boost make an awesome combination than these dyno results? The best boosted combos usually start out as powerful naturally aspirated motors. No slouch even before we added the Weiand 8-71 blower, the 496 pumped out an impressive 651 hp and 579 lb.-ft. of torque. Credit for the powerful combo goes to the combination of AFR 315 Heads, healthy Comp (blower) cam, and Edelbrock/Holley induction system—of course, starting with 496 cubic inches didn’t hurt. Replacing the Edelbrock intake and Holley 950 carb with the Weiand supercharger resulted in a jump to 898 hp and 764 lb.-ft. of torque. Even more amazing was the fact that these power gains came with just 6.5 psi of boost. Big blocks are great, and blowers are great, but the combination is positively amazing. (Dyno Chart/Richard Holdener)
engine crankshaft resting on a table
The first step to increase the displacement of the 454 to 496 inches was to add this forged 4340 steel Stroker (4.25 inch) crank (and rods) from Lunati. (Image/Richard Holdener)
dish valve relief in a piston head
Probe Racing supplied a set of 0.060 inch over forged (18cc dome) pistons for the 496 build up that provided a static compression ratio of near 9.8:1. (Image/Richard Holdener)
camshaft on a table
Looking to maximize the power potential of the blower motor, we contacted COMP Cams for a dedicated blower grind. COMP supplied a solid roller cam that offered 0.652 inch lift (intake and exhaust), a 255/262 degree duration split, and wide 114 degree lobe separation. (Image/Richard Holdener)
crankshaft inside a big block chevy v8 engine
After assembly, we had a seriously stout, four-bolt 496 Stroker short block ready for boosted action. (Image/Richard Holdener)
big block chevy cylinder head on table
Topping the Stroker was a set of CNC-ported, AFR 315 heads. Flowing over 385 cfm, the Magnum heads featured a competition, five-angle valve job, 2.25/1.88″ valve package and 121cc combustion chambers. (Image/Richard Holdener)
big block chevy v8 on engine dyno run
Equipped with an Edelbrock 454R intake and Holley 950 HP carburetor, the AFR-headed 496 Stroker produced peak numbers of 651 hp and 579 lbs.-ft. of torque. (Image/Richard Holdener)
big block chevy v8 with intake removed
After establishing the naturally aspirated baseline, we removed the Edelbrock intake and 950 HP carb to make room for the Weiand supercharger. (Image/Richard Holdener)
big block chevy cylinder head with valve cover removed
Installation of the Weiand 8-81 blower required a dedicated lower intake. The port match between the lower intake and the AFR 315 heads was not perfect, but you wouldn’t know it from the results. The perfectionists among you might want to port-match the lower intake to the cylinder heads. (Image/Richard Holdener)
blower and gilmer belt on a supercharged v8 engine
Headlining the swap was the Weiand 8-71 roots supercharger. A hefty chunk of aluminum and steel, consider installation of one of these babies a two-man job. The great thing about Weiand supercharger was not only did it make a ton of power, but it made one heck of a visual statement. (Image/Richard Holdener)
dual quad carburetors on a big block chevy v8
Feeding the Weiand supercharger was a pair of Holley 950 HP carburetors. These carbs were designed specifically to feed the needs of the roots blower. Obviously, Holley did their homework, as the carbs were spot on right out of the box. (Image/Richard Holdener)
belt driven supercharger on a big block Chevy
Boost being a function of blower versus engine speed, we selected a drive ratio to deliver a maximum of 6.5 psi at 6,500 rpm. This was achieved by combining a 57 tooth crank pulley with a 59 tooth blower pulley. Our under-driven 8-71 set up relied on an 8mm cog belt and guided idler/tensioner. (Image/Richard Holdener)
Close up of timing marks on a BBC crank
It was necessary to reduce the ignition timing on the blown application. While the normally aspirated 496 ran best with 40 degrees of total timing, we dropped this back by 10 degrees (to 30 degrees) under boost. (Image/Richard Holdener)
supercharged dual-quad chevy big block on dyno test
With the dual 950 HP carbs feeding the 8-71, the supercharged Stroker pumped out 898 hp and 764 lbs.-ft. of torque. (Image/Richard Holdener)

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Richard Holdener is a technical editor with over 25 years of hands-on experience in the automotive industry. He's authored several books on performance engine building and written numerous articles for publications like Hot Rod, Car Craft, Super Chevy, Power & Performance, GM High Tech, and many others.