Today it's not uncommon to see superchargers finding their way onto just about anything short of a lawnmower. Blower companies offer bolt-on kits for virtually every application, be it an EFI-induced late-model or a carburetor-fed classic. For many enthusiasts, adding an extra 100 or so ponies is enough to get their blood flowing.
While most of the above-mentioned applications will easily receive the added horsepower with little or no modifications, there is a lot to be said--and gained--by planning an engine that is to receive added boost.
With that in mind, the following story is intended to shed some light on what it takes to beef up the base starting point of a supercharged engine. Speed-O-Motive, our resident gurus from Day One with regard to the Danger Mouse Series, walked us through their rendition of a boosted engine.
BUILDING THE BEAST
Any motor that's going to use a blower must be built strong or it won't live long; that means if you're looking at having upwards of 500 hp and 500 lb-ft of torque, a solid foundation including a well-machined block, forged crank, splayed four-bolt main caps, and a set of good aftermarket connecting rods swinging the correct compression ratio forged-aluminum pistons is the optimum starting point. Speed-O-Motive deals with blown applications on a daily basis, and for that reason they offer a stout crank and connecting rod combination. Outside of those exceptions, the sky's the limit for everything else. As for blowers, in this case we chose to use a small Roots-style huffer rather than a more common centrifugal, and these little blowers respond well to just about any bolt-on performance parts.
Beginning with the block, Speed-O-Motive's experts CNC-machined all the critical areas. The GM Performance Parts block was decked and squared, and the Milodon splayed main caps were align-honed for straightness. Cylinder boring and honing were accomplished with torque plates in place to duplicate the distortion created when the heads are bolted down. The rotating assembly, consisting of Speed-O-Motive's forged one-piece rear seal stroker crank (PN#DG318SLD), 4340 forged I-beam and bushed connecting rods (PN#SOMCRS5700I), JE 8.5:1 coated forged pistons and rings, Clevite 77 bearings, TCI Rattler harmonic balancer and flywheel was precisely balanced to within a 1/2 gram by Speed-O-Motive's technicians. Blueprinting such as this is essential when the additional loads of a boost induction system are applied.
When considering what parts to use to build a blown engine, cylinder-head design is critical. Better airflow means more power--so the bigger the better. Since the blower is trying to pack as much air as possible into the cylinders, you may as well give it every opportunity to do so with a great set of cylinder heads. In this case we went with state-of-the-art Air Flow Research 210CNC heads. These CNC-ported, 23-degree angle-plug aluminum castings offer 210cc of intake airflow coupled with fast-flowing 80cc exhaust ports. The combustion chambers are 76cc and are also fully CNC ported. Intake valves are huge 2.08 inches in diameter and exhausts are 1.60 inches. And as an added bonus for blown engines is the fact that the deck thickness is a whopping 3/4 inch!
One of the coolest things about running a blower is that you can run more camshaft timing. The blower will tend to tame the cam, making the engine idle better, and with more vacuum, too (which is great for power brakes). For this build we chose a COMP Cams custom hydraulic roller that featured conservative figures on a 114-degree centerline (230-degrees of duration at 0.050-inch valve lift on the intake with 0.560-inch lift and 244 degrees and 0.600 inch on the exhaust side). Making the valves open and close is the job of Isky valvetrain components. Roller rockers and hydraulic lifters (coupled with one of their HR Rev kits that helps gain a little more engine speed and top-end power) are connected by stout pushrods from COMP Cams. Complementing the outstanding design and flow capability of the heads are the Beehive valvesprings and retainers from COMP Cams.
With the long-block built rock solid, the ancillary items need to be up to snuff, as well. For our 383 we added a complete Milodon oiling system to keep all things lubricated and moving smoothly, and a COMP Cams timing set to coordinate cam to crank movement. A Speed-O-Motive cover and TCI pointer make timing chores easy. Rounding out the front of our "Iron Warrior" is an Edelbrock aluminum water pump. Of course, an engine is only as good as the fasteners that hold it together and the gaskets that keep the fluids inside doing their job. ARP supplied all of the good nuts, bolts, studs and washers, while Corteco gaskets sealed it all up.
COST OF POWER
With a stout engine as a foundation, choosing a form of induction system becomes a personal preference, limited only by your desires and wallet. While not as cheap as a nitrous kit, but usually less expensive than most centrifugal superchargers, the Weiand 177 Roots mini-blowers are perfect if you want around 600 hp in your daily driver. While they can be made to work on more complex EFI machines, about 99 percent of the time these little blowers are installed with a carb sitting on top of them. Since there are plenty of them out there, we chose to put one on top of our 383 stroker. Rounding out the upper end of the engine is a Carb Shop-prepped Holley 850 double-pumper and a set of Holley valve covers for a clean look.
Finally, converting that boosted mix of air and fuel into power and torque is the job of a coordinated ignition system. Here, MSD fills the bill with everything from the low-profile billet distributor (PN#85551) and coil (PN#8207) to a rev-controlled ignition box (PN#6200) and beefy plug wires (PN#31229).With regard to being built tough, all in all, when we hit the dyno to see what this real Danger Mouse was made of, we felt confident that it went together with a combination of parts that would not only hold its own in the power department, but for a long time to boot.
While the crew at Speed-O-Motive was putting this engine together, there were bets going around as to how much power it would make. The magic number everyone agreed upon was 600 hp, but a few holdouts hoped for more like 650 ponies. On the best pull of the day we walked away with just over 650 hp and 612 lb-ft on a livable 10-psi of boost. But note: All this power was made on Shell Performance 105-octane unleaded fuel, not on pump gas. Lower boost pressures around 5-6 psi could probably live on 91-octane, but anything over 10 psi from these high-winding little Roots blowers, and you'd better run some good juice. We also used Quaker State's Q-Racing synthetic motor oil to make sure the higher oil temps associated with running extended boost would be easily managed. Just for kicks, we also ran the engine on regularly available 91-octane pump gas, limiting top rpm to just 5,000 to keep blower temps down, and still managed a whopping 615 hp and 556 lb-ft at 6-psi boost; not at all bad for a Roots-style, street-worthy small-block on pump gas. Totally awesome for a great street-fighting machine!