To those interested in power output, nothing has the attraction of a supercharger. Forcing atmosphere into an engine makes it take a charge out of proportion to its displacement, and with that, produce power out of proportion to its size. There are many types of supercharger systems used in automotive applications, from turbos, to positive displacement Roots-style blowers, to belt-driven centrifugals. Each has its pros and cons, with turbos getting a nod for efficiency but often presenting an installation nightmare. Traditional Roots blowers are capable of effective low-rpm boost, though they are too ostentatious for some and are no lightweights. Belt-driven centrifugal blowers have become very popular for several reasons. The systems are relatively easy to install, offer increasing boost with rpm, and the bottom line is they make serious power.
The leader in Mopar centrifugal blowers is a company called The Supercharger Store. We had looked longingly at some of its well-designed products at various Mopar events for several years now, and decided to finally take the plunge into the realm of boosted power. The Supercharger Store systems are based on the ATI Procharger line of blower units, superchargers that are well-proven in drag racing and street applications. Most of the ATI blowers are fully self contained, meaning that they carry their own internal lubrication supply, eliminating the need for plumbing pressure and return lines between the blower and the engine. The Supercharger Store has many variations of blower systems and components specifically for Mopar applications, so we had many options to consider when formulating a plan for a blown big-block Mopar.
Popular kits are based on blowers of various capacities, depending upon the boost level and power objectives. Initially we were going to go with a basic street kit, built around the 1,400-cfm D1SC Procharger. Later, we reconsidered the project and settled upon the much larger capacity F1-R, a hotter version of the 1525-cfm F1, rated for 2,000 cfm. This unit would be enough to easily produce high boost in a 440 cubic-inch engine, and yet have the capacity to handle the greater needs of a high-output stroker combination if we later choose to go that route. Boost pressure is dependent upon sizing as well as rpm, and the rpm can be adjusted within the unit's operating range by the selection of blower pulleys. Our intention was to use the F1-R on a typical bracket race/street-style 440, and spin it for high boost. Our engine makes peak power naturally aspirated at roughly 6,000 rpm, with a redline of 6,700 rpm, so those points are established. The drive pulley ratio can be determined by the operating rpm range, the displacement, and the targeted boost. The Supercharger Store has the data to match sizing for the required goals.
Engine ModsOur prospective blown engine was typical of a hot street or strip 440, built on a .030-inch-over factory block, with 10.3:1 compression, Edelbrock heads, and a COMP solid lifter cam. The engine produced a best of 550 hp on the dyno, a very respectable number for a relatively inexpensive and simple combination. This engine would serve to be a testbed of the Procharger's potential, but we needed to make a few changes to prep it for blower duty, besides simply bolting on the blower. We intended to run fairly high boost levels, at which the engine's 10.3:1 compression ratio would be too high, especially on pump gas. To get the ratio closer to the 8:1 ratio recommended by The Supercharger Store, we needed to take a good two points of compression out. A piston change is the obvious solution, but we already had a fine running 440 bottom end, and were not too eager to tear it down and toss out the pistons in favor of custom dished replacements. Our goal was simply to evaluate the power potential of the blower system on the dyno. Weighing everything involved, including the full teardown and replacing the pistons, and then re-balancing the short-block, we weren't too far from building a new short-block.
We found the solution from a company called Flatout Gaskets, makers of unique rubber-coated copper head gaskets, among other sealing products. We had used a set of these copper gaskets in another buildup, and were impressed that they sealed both compression and fluids perfectly, without the aid of O-rings or additional sealant. Flatout manufactures these gaskets in a wide variety of thicknesses, including a 0.125-inch-thick version that can be used as a cylinder head spacer, in conjunction with conventional gaskets. This spacer would add over 30 cc of volume to our combination, enough to drop the compression ratio to 8:1. To aid in the cylinder head clamping, the headbolts were replaced with a set of Milodon head studs. Another point to consider was to ensure the cylinder head alignment dowels in the heads were sufficiently long to accommodate the thick gasket pack. We ended up replacing the dowels in our engine.
The only other change to the 440 was replacing the camshaft with a grind more suited to a blown application. The Supercharger Store recommends a wider-than-normal lobe separation angle to optimize the engine for boost. This is a fairly general recommendation that follows established practice with blown engines, serving to open the exhaust valve sooner, and reduce overlap. In theory, opening the exhaust valve earlier helps deal with the greater volume of gasses produced with supercharging. The reduced overlap is beneficial since overlap scavenging is not critical for cylinder filling with a blower providing the fill. The wider lobe separation is well accepted, so we bit and replaced the cam, going from a 110-degree lobe separation to 114, with no other changes in cam specs. We have not done a back-to-back test of lobe separation angles to verify the benefit, but we'll go out on a limb and say it probably isn't necessary in most cases with typical street cams.
With the engine reassembled, what was left was simply bolting on the blower kit. The Supercharger Store needs to be complimented on the completeness of the kit, since every nut and bolt we needed came in the box, with no runs to the hardware store required. Essentially, an adapter bolts to the damper to take the lower pulley, and then the blower bracket is mounted in place. Next, the blower bolts onto its mounts, and from there it is just a matter slinging the belt in position and plumbing. With their street kits, a blow off valve is fitted to the inlet tube. For high capacity "race" systems, a large, high-flow, blow-off valve is provided, which we got with our kit. The valve needs to be "T-ed" into the induction pressure pipe, and this requires welding an included tube and flange in place.
THE TESTIt was an exciting day when our 440 arrived at Westech for testing. The blower gave the engine a serious look that suggested there was going to be quite a display of power. We trimmed the 440 out with a set of high-flowing TTI stepped headers, and an MSD distributor and wires firing top-notch Denso Irridium plugs. Both exhaust flow and ignition are areas not to be neglected when courting blown horsepower. We plumbed in The Supercharger Store's water injection system (see sidebar), and filled the reservoir tank with a dilute water/methanol mixture, actually windshield washer fluid. It all looked like a go, and sure enough, the 440 fired and settled nicely into an idle. Taking a conservative approach, the ignition timing was set to just 25 degrees total advance, about 10 degrees less than the best normally aspirated power setting.
To establish a baseline before running the engine in the blown configuration, the engine was shut down, and the blower belt and air hat were removed. We ran a baseline and found 421 hp at 5,600 rpm, over 125 hp less than the best numbers this engine has shown before. With the two-point drop in compression ratio, the 4-degree wider lobe separation, and the 10-degree retarded timing, it was not surprising. The belt was reinstalled, and we were ready to try boosted power. Initial problems involved getting enough fuel flow from the carburetor to supply an adequate mixture. Eventually, we installed the largest 4150 carb we had available, a Race Demon RS, with 1,050-cfm venturi sleeves, fitted with power valves at both ends, and very large jets. We were only making short static pulls at a given rpm point and boost level, to gage air/fuel mixture up the range. We were experiencing some variation in boost levels, compounded by a lack of repeatability, which was causing difficulty with tuning, especially at higher rpm. Dyno operator Tom Habryzk suspected belt slippage. We cranked the belt tensioner and continued.
We carried on with the power sweeps and saw quite a bit of boost variation from run to run. Tom pointed out that the serpentine belts could become problematic with high boost and big blowers. To help the situation, the belt was coated with VHT "Track-Bite," and the tensioner wound until the belt was as tight as a violin string. We saw as much as 757 hp at 5,700 rpm and 13.5 psi of boost, but belt slip, even with all of these measures made it a problem to let the engine run up. Finally, the belt skipped a rib, and ended our test session. We later discovered that the blower pulleys were not in perfect alignment, which may have aggravated the situation. We should have checked that, since there are shims from The Supercharger Store to readily adjust the alignment. However, Tom pointed out that in his experience with many large centrifugal blowers in higher boost applications, serpentine belts are often problematic, maintaining that a cogged belt drive is the only way to go.
We conferred with Bob Woods of The Supercharger Store, and he agrees, in fact pointing out that the larger blower kits he normally sells always come with a cogged drive. Chalk one up for experience, we blew it when ordering our setup, and then opting for the larger blower later. We placed an order for the cogged drive, and in a few days were ready for another crack at the dyno. The pulley system directly replaced the serpentine setup, bolting on in minutes, and once again the 440 was ready to run. The cogged drive eliminates all potential for slip, reduces the tension required, and is just plain bulletproof.
Back at Westech, the 440 was again mounted to the dyno, and this time we were ready to let it run for the numbers. The potential had already been shown in our last test session, with over 750 hp on the dial. With the cogged belt drive offering the promise of being able to make full high-rpm pulls without slippage, we knew the 440 would deliver. Deliver it did. We wound the engine up to 6,400 rpm, and the boost just kept coming. A peak output of 878 hp at 6,300 rpm is pretty hard to argue with, especially considering the basic package below. We made several pulls that day, and the power number and boost level repeated like clockwork, run after run. Dialing in more timing than the 25 degrees we started with didn't show an improvement, so that's where we ended up. The Flatout head spacers sealed like a vault, and the 440 showed no signs of distress. For an engine this size, 878 hp is an all-out racing engine's output, but the engine ran just as docile at idle as before--in fact, even more so given the wider lobe separation and reduced overlap. EM
Carb vs. InjectionWe were impressed with the amount of pure horsepower out 440 Mopar made with the blow-through carb arrangement, but the reality is that it took some doing. Initially we had a dedicated "blower carb" bolted to our engine, and the fact is it didn't want to run under boost, no matter what we did at the jet. The carb simply would not provide a working fuel curve, actually delivering less fuel as the boost escalated. We had direct readings of air/fuel ratio and fuel flow, allowing us test through and identify the problems without destroying our engine. We pity the guy who bolts a problem like that on and tries to tune it in a high-powered vehicle. We solved the problem by bolting on another carb, and tuning from there. At best the mixture curve was a compromise, but it was a working one. Generally, you are going to be pig-fat down low to get enough fuel to avoid a lean condition as the boost builds.
Frankly, a carb is a velocity-sensing device, and that is the key variable upon which a carb varies the air/fuel ratio. It does a very poor job of compensation for changes in pressure. That's the plain physics of how it works, period. It will work best at lower changes in pressure, which means lower boost. Outside of that, it will be difficult or impossible to tune the carb to offer an optimal air fuel ratio over a very broad rpm range, with the accompanying broad pressure changes associated with rapidly escalating boost pressure. For a high-powered, high boost engine expected to operate efficiently over a very broad rpm range, I would highly recommend an EFI system.
WATER INJECTIONYou may have noticed that our 440 combination was running high boost, without the aid of an intercooler. It's a fact of physics that compressing a gas (air in this case) produces heat. In practical terms, that means more boost equals more heat in the incoming charge. It's well known that high inlet air temperature saps power and encourages detonation, hence the need for a means of charge cooling, especially with lots of boost. Cooling the air/fuel charge is typically accomplished by employing a heat-exchanging unit known as an intercooler. Essentially, an intercooler is a radiator through which the induction charge is passed and cooled by the temperature differential between the high-temperature inlet air and the cooling medium--ambient air in an air-to-air intercooler.
The system favored by The Supercharger Store is a departure from a conventional intercooler, and actually borrows from technology employed in supercharged WWII fighter aircraft--water injection. Water injection provides a cooling effect to the charge through another effect of physics, the latent heat of vaporization. As a highly atomized liquid changes state to vapor, the process consumes heat. The Supercharger Store's system provides a high-pressure pump that is triggered by a pressure switch, which in turn is referenced to boost. When the boost hits the prescribed pressure level, the pump sends high-pressure water to a fine-atomizing nozzle aimed at the blower intake. Water provides the cooling, and also acts as a detonation suppressant. The kit is complete, with all of the fittings, tubes, an anti-siphon valve, and a fuel cell to serve as the holding tank.
With the water injection properly set up, Bob Woods of The Supercharger Store reports phenomenal power output on pump gas. Various kits are sized with nozzles designed to differ the fluid flow rate for different output levels, with some of the higher horsepower kits featuring two stages of injection, for outputs of up to 2,000 hp. The system can be used with straight water, or various concentrations of water/methanol mix. Bob recommends common windshield washer solution, which contains up to 25 percent methanol. Water injection is far from a new idea, but with the output capabilities of modern supercharger systems, it's an innovative solution for power on pump gas.
Our own observations on the system brought out some aspects that may warrant further investigation. The water/methanol mix is injected into the blower intake, which serves to cool the blower, however, our observation was that the impeller had a tendency to centrifuge the atomized liquid in the blower housing. Injection at the discharge side of the blower may be an alternative worth exploring; in fact we had done some experimentation with such a setup on a pure methanol injection arrangement in a very high output blown Bonneville car. It seemed to work better.
875 HP TIME BOMB?Reading through our adventures here, it is readily apparent that our 440 is nothing more than a stock Chrysler engine, with some "old-school" high-compression SpeedPro forged pistons, basically the old TRW 440 Sixpack replacement street forgings, for those of you who can remember these from back in the day. Our goal was to explore the power potential of the blower system, and in doing this we adapted it to an existing test engine. We made close to 900 hp, with basically all stock bottom-end parts: the block, crank, main caps, and standard 440 connecting rods. We know the factory Mopar stuff is fairly robust, and making power on the blower isn't as hard on the bottom as some other forms of power enhancement, or even making significantly less power normally aspirated. That said, we knew it would work on the dyno and probably not blow up, especially since we would be extremely careful not to detonate it, or lean it out under the controlled dyno conditions. However, it was a calculated risk, and one that you, your machinist, or your engine builder might not want to make.
Would we run exactly this combination on the street, or duplicate it in detail for even a drag racing project? No way. We'd definitely look to build a dedicated blower engine with a host of durability mods. Frankly, we'd consider a partial fill on the block, with aftermarket main caps, preferably with a girdle system, or better yet an aftermarket block. We'd buy the best forged-steel crankshaft we could afford, and the same goes for the rods. We cheated with the head spacers and gasket stack to get the compression ratio down, but for a real world application like this you'd better be thinking about a nice set of custom forged dished blower pistons in the high strength alloy. We'd also be looking really hard at a set of steel rings like the Hell-Fires. Making big power with stock factory components is not the formula for a happy long-term marriage. Sure, some of these kits can work just fine at lower boost on a relatively stock engine, but longevity is a dangerous roll of the dice with anywhere near these boost or power levels.