In the last decade as the octane rating of gasoline decreases and the demand for more horsepower increases, there is more of a possibility for detonation. Forged piston made for blown systems are highly recommended. Also using 8.5 to 9.1 compression ratio and less blower boost will keep the engine cooler. When you run a lower compression engine and raise the boost levels, this elevates the temperature of the air charge to your engine, requiring you to buy higher octane gasoline to suppress detonation.
A camshaft profile that has been designed to work with a supercharger system will provide more horsepower and torque. If you have a secret application, BDS recommends a hydraulic or flat tappet profile camshaft.
The amount of boost and the RPM at which boost starts is controlled by the throttle, blower size and drive ratio, engine size, camshaft profile, and exhaust system. All of these factors determine the breathing capability of the blown engine. Boost should only be measured at the wide open throttle at 6,000 RPM. If there is only part throttle, the blower cannot get enough air to overcome the demands of the engine. Only when the blower can get enough air will there be boost.
Exhaust pipes get red-hot for two basic reasons. Either the ignition timing is incorrect or the engine is running extremely lean. There are other causes but these are the two most common, ignition timing is extremely critical. Blown motors love advance. Without enough initial timing advance, blown motors will run hot and the exhaust pipes will glow in the dark. Blown motors should run as little as 16 degrees or as much as 26 degrees initial advance with the total advance of about 32-36 degrees at 2500 RPM to 3000 RPM. Specific timing requirements depend on the compression, blower drive ratio, engine load, camshaft, and fuel octane.
Overheating of a blown motor may be caused by a too high compression ratio, too high blower drive ratio, improper timing, poor water flow through manifold, or an inadequate and inefficient cooling system.
Ignition timing deals with the time at which ignition occurs during the compression stroke. Retarded timing ignites the air/fuel mixture closer to maximum compression than advanced timing. Higher compression at the point of ignition means hotter temperatures form the burning of the air /fuel mixture and this translates into a hotter running engine.
There are many reasons why an engine will backfire but the most common problem with blown motors is holding the throttle open while cranking the engine over. It is better to give the throttle a few pumps (2), and take your foot off the accelerator before turning the engine over and count slowly to ten. When the engine does fire and begins to run, quickly catch the throttle and raise the engine idle at about 1500-2000 RPM until some heat can be built in the motor, about two minutes. Trying to engage the engine before enough heat is built usually results in an engine that spits, sputters, backfires, and/or dies.
BDS recommends using a self-contained system, using a 80-90 weight heavy-duty gear oil lubrication. Contaminating the engine oil in the motor with 80-90 wt. oil can cause some engine lubrication problems and increase the likelihood of detonation.
Testing with gapless rings in a supercharged engine shows excellent increase in performance.
Both styles of rods are well suited for blown applications. Steel rods are generally used on motors that must produce a long service life. Aluminum rods are generally used for engines seeking high horsepower output and not long service lives.
Blower whine can be increased or decreased by tightening or loosening the blower belt tension. Caution! Improper belt tension can cause severe belt, blower, and engine damage. It is not recommended to adjust the belt to get the sound you want. Worn pulleys and belts as well as mismachined pulleys can contribute to blower whine.
Idling problems with blown motors are usually a result of a severe vacuum leak, improper ignition timing, or improperly adjusted carbs or fuel injection.
Black sooty plugs are a direct result of too much fuel. The carb or fuel injection is not properly adjusted or set up for your engine, correct your fuel delivery system.
Only use a heavy-duty 90 weight gear oil lubrication which is a non-detergent oil and basically no synthetics. They are too thin.
Yes. On mild street motor applications, the BDS intake will work with the oval port cylinder heads by using the rectangle port gaskets. The difference in the intake port openings has a small effect on performance with mild motor applications. For high-performance racing applications, always use rectangle port performance heads.