Words And Photos: Richard Holdener
Adding a supercharger to any motor is a surefire method to increased performance, but what happens when you want to make serious power? A supercharger is best thought of as a multiplier, as boost supplied to the motor increases the output as a percentage of the existing power. The reason for this is that the normally aspirated motor is already running under atmospheric pressure of 14.7 psi. Knowing this, if we double the pressure applied to the motor by adding an additional 14.7 psi of boost, we can (theoretically) double the power output. There are several reasons why the actual output differs from this simple mathematical formula, but know that the boost will increase power in direct proportion to the existing power output. What this means is that if we add 14.7 psi to a 300-horsepower motor, we can get 600 horsepower, but if we do so to a 400 horsepower motor, we get 800 horsepower. This also works in smaller (or larger) percentages, as adding 7.35 psi will result in an increase of 50%. Likewise, adding 10 psi can result in a gain of 68%, since 10/14.7=.68.
The uptake of understanding this formula for boosted applications is that we should make every effort to increase the power output of the normally aspirated motor before adding boost. One of the tried and true methods of making more power is to Go Big! All things being equal, bigger motors make more power than smaller ones and (according to our formula) that extra power now gets multiplied by the boost. To illustrate this boosted logic, we applied the concept to a big block Chevy. While boost can be applied to a stock-displacement 396, 427 or 454, we decided to (you guessed it) go big with the displacement. Dart made things simple for us by supplying a complete short block that checked in with no less than 540 cubic inches. Right off the bat, the displacement alone put us head and shoulders above a typical 454 (to the tune of almost 90 power-producing cubic inches). The Dart 540 short block combined a 4.50-inch bore with a 4.25-inch stroke. The Sportsman Big M, 4-bolt block was precision-machined then stuffed with a 4340 forged crank, matching 4340 forged I-beam rods (with 7/16ths cap screws) and a set of Mahle forged flat-top pistons. In short, this big beast was ready for some boost.
Already sporting the necessary displacement, what the Dart motor needed was big flow and a big cam before the big blower. Airflow is critical for any motor, but all the more so for a big-inch stroker. The 540 was topped with a set of Dart Pro 1 335 heads. The Pro 1 featured 335cc intake ports and 129cc exhaust ports. Thanks to full CNC porting and a 2.30/1.88 valve package, the Pro 1 heads offered impressive flow numbers. Intake flow checked in at 397 cfm, while exhaust flow was equally impressive at 280 cfm. Our Pro 1 heads were configured with a Vasco-Jet spring package allowing a maximum of .790 lift. The 250-pound seat pressure was designed to work with our custom COMP solid roller cam. Looking to maximize flow through the Pro 1 heads, the COMP Cam offered a .742/.715 lift split, a 271/280-degree duration split and a 112-degree lobe separation angle. The cam also featured a revised 4-7 firing order swap. Working with the heads and cam was a set of COMP hardened pushrods, multi-index, double roller timing set and 1.7-ratio, Ultra Pro Magnum roller rockers.
The 540 long block now needed an induction system. In normally aspirated trim, the 540 was run with an Edelbrock 454 R intake and Holley 1050 Dominator carb, but once we added boost, the 540 received a Weiand Team G intake designed to accept the 1000-cfm, 4150 blower carb supplied by Carb Solutions Unlimited. Starting with a Holley carb, the CSU was modified specifically for blow-through applications. Additional components used on the 540 test motor included a compete Moroso oiling system, MSD ignition and Meziere electric water pump. After the break-in cycles, the conventional oil was replaced with Lucas 5W-30 synthetic and we ran the motor normally aspirated before adding boost. The 540 demonstrated just how successful going big is, as the big block started thumping out some impressive peak numbers. After dialing in the carb jetting and ignition timing, we were rewarded with 770 hp at 6,700 rpm and 663 lb-ft of torque at 5,600 rpm. Considering the static compression was below 9.0:1, these peak numbers were pretty encouraging. Now it was time for some boost.
Adding power with boost is a tried and true method, but adding boost to a combination that already makes over 750 horsepower requires careful blower selection. Obviously your typical 750-horsepower, stock small-block blower was out of the question, so we stepped up to something bigger. The V4 Mondo XX from Vortech was just what our big block needed, as the blower was capable of supporting over 1,400 hp and 29 psi. We had no intention of taking full advantage of the available 65,000-rpm impeller speed or 1,950 cfm, but we hoped to run the blown big block right smack dab in the middle of the 78% max efficiency island.
Hooking up the blower was a simple matter of bolting on the mounting brackets, installing the cog pulleys and clamping down the discharge tube. The tube was configured with a high-flow blow off valve. With only minimal tuning to the CSU carb, the supercharged big block thundered out BIG power, with peaks of 1,197 hp and 953 lb-ft of torque at just 11.4 psi. It was all very matter of fact, with no drama, no belt slippage and very little tuning. Such are the benefits of Going Big!
The graph looks like any other power curve when you add a Vortech centrifugal supercharger. It is only when you look at the scale to the far left that you start to get impressed, realizing that the 540 offered 770 horsepower in normally aspirated trim and almost 1,200 horsepower with the blower. Making this all the more amazing was the fact that the power gains came at less than 11 psi. That’s what happens when you go big with a big block and big blower.