Gearheads love horsepower. Many of them lust after an ultra high-power supercharged engine to build an extremely radical ride. Every once in a while however, someone comes along who just wants the sound and glory of a blower sticking through their hood. To hear the whine of it as they motor down the road is their ultimate source of satisfaction. They like the power it brings, but they're not looking for the max. They want a blower motor on a budget. That is where this engine comes in.
Typically, when talking about high-performance engines, using the terms "blower" and "budget" in the same sentence is considered an oxymoron. However, the crew at Hardcore Horsepower LLC has worked many late-night hours seeking the best combination of supercharged power, sights, and sounds for the street while keeping the total price relatively low.
The foundation for this budget blown engine is a reconditioned Chevy block with four-bolt main caps and ARP bolts. The block is CNC-machined to ensure the most accurate dimensions, and the factory one-piece rear main seal is converted to a two-piece design to make crankshaft and oil pan selection more plentiful. The machined block is then washed and professionally blueprinted for assembly with new cam bearings, brass freeze plugs, and hardened steel dowel pins installed.
The stroker crankshaft used in this 383 is an internally balanced Scat-9000 iron piece straight out of the box with one important modification. Small-blocks that run belt-driven blowers have a bad habit of spinning the harmonic dampener right off the crank. To prevent this, an extra keyway is cut into the crank snout and a matching keyway is cut into the dampener. Most high-performance dampener manufacturers offer double-keyed blower units.
Wiseco's Pro True blower pistons are forged from 2618 aluminum and feature coated skirts and full-floating pins to keep them reliable. The pistons hang on 6.0-inch Scat 4340 forged I-beam connecting rods with bronze bushings in the pin end and 3/8-inch ARP rod bolts in the big end. Wiseco also supplies its GFX moly-rings, which are file-fit to each bore. This engine will not be run at high rpm or high boost levels, so there's no reason to add the expense of H-beam rods or larger-diameter capscrews. The pistons and rings take the brunt of abuse in a blown engine, so extra money is spent on them instead.
Canton Racing supplied the 6-quart-capacity oil pan without side kick-outs making it easy to clear big headers. The pan also features a built-in crankshaft oil scraper, trap doors, and a windage screen for oil control and power. The oil pump is a high-volume Melling unit with a welded pick-up tube for added protection. The pump was bench-tested at 60 psi before installing and later rechecked in the engine to confirm that it was consistent.
In keeping with the budget theme, World Products S/R Torquer iron cylinder heads were used. The small-port World castings are stronger and can support higher power levels than OEM units. Bigger ports are not necessary for this type of engine, and the Weiand blower manifold matched up perfectly. To ensure a good seal, Mr. Gasket's Solicor head gaskets, which are derived from high-boost diesel engine technology, were installed. Mr. Gasket also sealed the intake to the heads with polymer Ultra Seal III gaskets. These high-density gaskets are developed for steam, oil, and chemical resistance and seal well with the low clamping loads typical of an aluminum manifold. Their high torque retention and high blowout resistance make them ideal for supercharged engines.
Most customers want their supercharged engines to surge like high-power drag cars. Traditional blower cams are ground with a wider lobe separation angle, which actually creates a smoother idle in a motor like this. Instead of running a blower cam, they choose an Erson hydraulic stroker grind with an advertised duration of 296 intake/306 exhaust and 0.503/0.503-inch net valve lift with 1.6-ratio rockers. The cam has a 110-degree lobe separation angle with 4 degrees advance built in and just enough overlap to make it sound great idling around and not affect driveability. The cam is big enough to make good power, but being a hydraulic flat-tappet, it's easy on the wallet.
Comp Cams High Energy 1.6:1 aluminum rockers were installed for durability and ease of adjustment. These low-friction rockers keep oil temperatures down, and their poly-lock nuts are easier and quicker to adjust than OE-style friction nuts.
No one builds a 6-71 blown engine with the intention of concealing it under their hood, but not everyone wants the glitz and glamour of a polished unit, and there's been a mild shift toward the retro look of cast blowers (Weiand refers to them as "satin"). Cast blowers are also less expensive than polished kits, but the cast finish can present a few problems.
No matter how good the foundry is, there will always be some inconsistencies between castings made from different batches of aluminum. With this many cast parts at the center of attention, it's easy to spot the differences. Cast parts are also harder to clean than polished parts, and some over-the-counter degreasers actually damage the finish of raw cast aluminum. To make everything appear the same and keep cleaning easy, all of the cast parts were painted with aluminum-color engine enamel.
Most people assume that it's the rotors and gears inside the blower case that creates the classic blower whine we all love. The noise is actually the result of air being trapped between the blower belt and the blower pulley's teeth. Weiand's 8mm drive pulley configuration used on this engine has more teeth than the older 1/2-inch pitch design so it's better at making the ultra-cool blower sound.
The fuel system is a critical aspect of any blown engine. This engine's owner requested dual inline 600-cfm Holley vacuum secondary carbs for a clean look and presumed lower cost. The carbs had to be heavily modified to work with the blower, and after analyzing how much time and money was expended on them, it would be better to run blower-specific double-pumpers side by side instead. The upfront costs of running the double-pumpers seemed higher, especially when adding the price of linkage and fuel lines, but it actually cost about the same amount to modify and run the vacuum-secondary carbs.
A blown engine requires roughly twice as much fuel as a stock engine would. If you still have a stock tank, the pickup may need to be enlarged and bigger fuel lines run. A minimum 3/8-inch-diameter fuel line is recommended for blown engines up to about 500-550 horsepower. A 1/2-inch or larger pickup and line is required for anything more powerful. Avoid reducing line size anywhere before the regulator, but it's OK to step down one size smaller from the regulator to the carbs. It is also a good idea to increase your fuel pump and filter capacity to about 125-150-plus gallons per hour. Electric pumps are most popular, but there are high-capacity mechanical pumps that'll work too.
Maintaining wide-open throttle fuel pressure and flow at the carbs is critical. To keep the budget in check and the finished engine looking cool, they hung a billet Mallory regulator between the carbs on a custom-made bracket. The linkage connecting both carbs together had to be tweaked a bit to allow for adjusting fuel pressure. j
After the engine was completed and test-fired in the shop, it was trucked over to Tommy's Auto & Machine in Springfield, Tennessee, and was bolted onto its Superflow 901 engine dyno. As the power runs began, the blower's whine could be heard far out into the street and several visitors stopped by the dyno cell to see and hear what all the noise was about. They all agreed that for $12,000 this is one awesome blower motor that would be hard to beat on the street.
This engine required almost no tuning, except for a few timing adjustments on the dyno. The Mallory digital distributor allows easy adjustments for boost retard and it has a programmable ignition curve, which can be changed from a laptop or handheld programmer. The proper timing curve is critical to making a blown street engine survive on pump gas.
The dyno pulls started out conservative, keeping revs low and monitoring boost and air/fuel ratio while periodically checking the spark plugs every couple of runs. Only on the last few dyno pulls of the day did they run the engine up to its 6,000-rpm redline, where they made just shy of 550 hp at 8 psi boost.
|Budget Blown 383ci Street SBC test|
|Max TQ: 558.6 @ 4,500 rpm|
|Max HP: 548.1 @ 5,800 rpm|