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|