The following information as complied from over
3 decades of
supercharging experience on a wide variety of engines. The suggestions and recommendations
below are for gasoline engines to be used on the street unless otherwise specified. The
information is broad in nature and intended to be used as guidelines only.
Blower companies suggest
that the engine block be in good condition and not overboard excessively. Two
bolt mains are adequate for most mild applications with boost levels up to about
7lbs. Four bolt mains are recommended and are considered a must for high
performance systems. O-Ringing is recommended for engines running 12lbs. of
boost or more. When rebuilding, the block should be thoroughly checked, as you
would in any high performance engine build up.
Steel cranks are
recommended whenever possible and are a requirement for high performance engines
spinning high RPMs. Cast cranks are only recommended
when the boost levels are below 10lbs. and the engine is limited to 6000 RPM. When
rebuilding, cranks should not be less then a 10/10 grind and should have all the trick
work as you would for any high performance engine.
Most factory rods will work well for mild
blower systems up to 8-10lbs. of boost. Factory and after market steel rods with
heavy duty rod bolts are recommended and required for high performance
applications. The rods should be magnafluxed for cracks,
shot peened, beams polished, balanced, and bushed to size for full floating pins.
Factory cast pistons are not recommended but may be used in very low
boost (3-5lbs.) applications. Forged, low compression pistons (7-8:1) are the best choice
for performance applications. Higher compression ratios are not recommended because of
overheating and excessive final compression ratios (see the final Compression Ratio chart
in this catalog). Pistons should use full floating pins and double spirol locks or buttons
for high performance applications. In cases where alcohol is used, the compression ratio
of the engine should be between 10-12:1.
Factory heads work well
in most blower applications. The heads should be in good conditions or have a
three angle valve job. After market heads will provide increased performance.
Stainless steel valves are recommended. Head modifications (porting, polishing,
etc.) are not required unless high performance is the desired result. Resurfaced
or shaved heads can cause problems with the blower and manifold. The secret to
Horsepower is cylinder head air flow. More air flow equals more Horsepower.
Choosing the proper
camshaft would be the most important requirement for a blower motor. An improper
cam will cause a variety of problems that can easily be avoided by following a
few simple guidelines. Hydraulic cams are recommended if you intend to drive the
vehicle frequently, require little or no maintenance, and the maximum engine RPMs are kept around 6500 or lower. Roller rocker arms are recommended. Flat tappet
and roller cams are recommended for high performance applications especially where the
engine will see high RPMs. Exact camshaft specifications vary depending on the
performance level you wish to attain. There our ten common different types or
Stages of cam grinds specifically made for blower motors. If you wish to purchase your cam
from one of the many fine camshaft manufactures, we suggest using our camshaft specs as a
guideline. Extremely high lift and long duration cams are recommended for high RPM, high
performance racing only.
The lobe center of the cam will play an important role in determining
the performance characteristics of an engine. Wide lobe centers (112 to 114 degrees etc.)
will create higher cylinder pressure providing more horsepower with cooler burning fuel
such as alcohol and methanol. We have found 110 degree lobe center to produce the best overall power on
Whatever cam you choose, make sure that it will operate and perform
properly in the RPM range required for your application.
Carbs and Fuel Injection
The overall performance of the entire engine package will be determined
by the fuel induction system. Carbs work very well in most applications as long as the
carbs have been calibrated or blue printed by reputable company. Refer to
the carburetor section in the catalog for help in determining the correct carbs for you
Mechanical fuel injection will provide greater performance and throttle
response than carbs. However, these mechanical injection systems can be quite
temperamental and are recommended for the experienced racing enthusiast only.
The ignition system and
advance curve are very important to a blower motors longevity and performance.
The general rule for ignition timing in a blower motor is as follows: Initial
advance at idle should be set 16-22 degrees with the total advance of
approximately 32-36 degrees, all in by 2500-3000 RPM. It is very important to
verify the advance curve. Locked out magnetos or distributors are recommended
for racing applications only. Improper curves may cause a variety of problems
including overheating. Spark plugs should be one or two hear ranges colder than
the recommended stock factory plug (never use extended tip spark plugs). This is
due to the higher cylinder pressure created by supercharging. Higher cylinder
pressure means more heat. Ignition management systems that can vary the timing
according to engine requirements are a good idea to help keep the engine from
killing itself with detonations and to keep performing at its maximum.
The cooling system for a blower motor should be in good general
operating condition. Inadequate air flow across the entire radiator at low speeds is one
of the most common causes for overheating. Mechanical fans and shrouds are highly
recommended. Electric fans are marginal in most cases and may require some experimenting
with location to find the best operating position. A 180 degree thermostat is recommended.
Water flow restrictors may also be used, however, you will have to experiment to find the
size that best works for your system. Stock factory water pumps are recommended and
required in most applications. After market "High Performance" water pumps work
best in the mid to upper RPM ranges and therefore may not have adequate water flow at
lower RPMs to keep a blower motor cool. Three core radiators or larger are
recommended for most applications. Higher performance engines will require better cooling
systems because of the additional heat generated by these types of engines.
Exhaust systems are very important to the
overall performance of the blower motor. The blower forces more air into the
engine than it would normally take therefore the engine must be able to get rid
of more air through the exhaust. Small restrictive exhaust will cause excessive
back pressure, robbing the engine of power and causing additional hearing
problems as well as unusually high boost readings. Large free flowing exhaust
and headers are recommended choices.
The fuel requirements for a blower motor
may vary greatly depending on the application and engine/blower specifications.
Unleaded fuel is OK as long as the engine is setup for unleaded fuel. The "Final
Compression Ratio" of the engine/blower combination is the determining factor in
fuel octane requirements. Refer to the Chart in this catalog to determine your
final compression ratio (Pg. 14). As a general rule, the maximum final
compression ratio should not exceed 12.4 to 1 for 92 Octane fuel. Octane
boosters and higher octane racing fuel will allow you to run a higher final
compression ratio. Final compression ratios should not exceed approximately
24-26:1 for racing gas.
Blower kits and components are directly applicable to most
marine systems. There are very minor differences between the requirements for
marine and non-marine applications.
Small pleasure craft on up to offshore racing engines will benefit from
the increase in torque and horsepower supplied by a blower system.