mustang_302
07-29-2006, 05:28 PM
How much horsepower will a supercharger add to my engine?
Although some manufacturers claim a specific horsepower increase, superchargers actually add horsepower as a percentage gain (percentage of an atmosphere). Assuming an engine with a compression ratio of around 9:1 running pump gas,if a supercharger gives your engine 14.7 psi of boost (another atmosphere) that will essentially double the output of your engine, everything else being equal. After adjusting for thermal and mechanical energy transfer, if an efficient centrifugal supercharger is generating 7.5 psi (approx. 1/2 an atmosphere), you will see around a 35-40% gain in horsepower and torque at your non-supercharged maximum horsepower rpm. If detonation forces you to use an ignition/timing retard system, you will of course see less of a gain because backing off several degrees of timing will greatly reduce an engine's power output. At higher boost levels, the heat generated by compressing air will produce diminishing returns as the boost is increased, although the use of intercooling or racing fuel can avoid this scenario of diminishing returns. Assuming the use of intercooling to run higher boost levels while maintaining reliability, a 100% increase can generally be achieved at around 17 psi on an engine with 9:1 compression running pump gas.
Basic Building
Engine Specifications
The following specifications are general guidelines offered to aide in
building an engine for street use. For more detailed specifications regarding your specific application or for "strip only" use, please consult a professional engine builder.
Pistons:
Forged pistons recommended for all applications. Cast and hypereutectic pistons can be used but should be limited to lower horsepower (approx 450-500 hp) applications.
Compression ratio:
For pump gas (91-93 octane) applications, a compression ratio of 8.5:1
to 9:1 is recommended for boost levels of 8-10 psi. Higher octane fuel
will allow you to run higher boost levels, approximately 1 psi for every
2 points of octane. To determine the maximum boost level for your
compression ratio (using pump gas), refer to the enclosed compression
ratio chart.
Heads:
The same rules for normally aspirated engines apply to supercharged
motors. Higher flowing heads will help generate more horsepower than
stock heads. Supercharging produces a percentage gain in horsepower; by starting
with more base horsepower a modified motor will receive a larger total hp gain
(from the same percentage gain).Porting, especially on the exhaust side is recommended. Aluminum heads will allow you to run approximately 1 psi more boost than cast iron
heads due to their ability to dissipate heat.
Cam:
Lobe separation: 112 to 116 degrees
Split pattern: Exhaust duration and lift approximately 10 degrees and .010, respectively, greater than intake. Install cam straight up. Contact a cam manufacturer for lifts and durations that best suit your application.
Crankshaft and rods:
Cast up to 450 horsepower, forged for higher horsepower or for rpm
levels above 6,000 rpm.
Exhaust:
Headers are recommended. The size of headers are dependent on whether you are wanting to create more low end torque or high rpm horsepower.
Intake manifold:
Dual planes are recommended to improve low end torque, however may
require staggered jetting for good fuel distribution with carbureted applications.
Carburetor:
Holley double pumper w/ mechanical secondaries.
cfm 600 (#4776) for up to 500 hp
cfm 650(#4777) for up to 650 hp
cfm 700 (#4778) for up to 750 hp
cfm 750 (#4779) for up to 900 hp
All carburetor’s will require removal of the choke assembly and choke
horn, replacement of the floats with the solid nitrophyl floats and jetted to suit your motor.
Fuel pump (carbureted applications):
Your fuel pump must be capable of supplying the proper amount of fuel
flow at the maximum operating pressure. To determine maximum operating fuel pressure requirement, add your maximum boost pressure to your initial idle fuel pressure.
Example:
psi 8 idle fuel press.) + (10 psi boost press.) = 18 psi max. fuel press.
multiplying this figure by 1.2 (20% safety factor) gives us 21.6 psi
To determine required fuel flow, multiply your total expected horsepower
by a bsfc (brake specific fuel consumption) of .65. This will give your
fuel flow requirement in 1bs/hr. To convert to gallons per hour, divide
this figure by 5.87.
Example:
(boosted hp500 ) x (.65 lbs/hr/hp bsfc) = 325 lbs/hr fuel flow
lbs/hr325/ 5.87 lbs/gal = 55.4 gals/hr fuel flow
Therefore, a fuel pump capable of providing a minimum fuel flow of 55.4
gals/hr at a pressure of 21.6 psi is required.
This can be accomplished by an all electric high pressure-high flow fuel
pump (i.e. SX #18201, B.G. 400, Magna-Flow 250 or similar type fuel
pump) and a return style, boost sensitive fuel pressure regulator
Mallory #4309 or similar). Or by using a boost referenced mechanical fuel pump only (up to 500 hp) or a boost referenced mechanical fuel pump in conjunction with a low pressure electric pump (i.e. Holley blue, Comp 140 or similar
Although some manufacturers claim a specific horsepower increase, superchargers actually add horsepower as a percentage gain (percentage of an atmosphere). Assuming an engine with a compression ratio of around 9:1 running pump gas,if a supercharger gives your engine 14.7 psi of boost (another atmosphere) that will essentially double the output of your engine, everything else being equal. After adjusting for thermal and mechanical energy transfer, if an efficient centrifugal supercharger is generating 7.5 psi (approx. 1/2 an atmosphere), you will see around a 35-40% gain in horsepower and torque at your non-supercharged maximum horsepower rpm. If detonation forces you to use an ignition/timing retard system, you will of course see less of a gain because backing off several degrees of timing will greatly reduce an engine's power output. At higher boost levels, the heat generated by compressing air will produce diminishing returns as the boost is increased, although the use of intercooling or racing fuel can avoid this scenario of diminishing returns. Assuming the use of intercooling to run higher boost levels while maintaining reliability, a 100% increase can generally be achieved at around 17 psi on an engine with 9:1 compression running pump gas.
Basic Building
Engine Specifications
The following specifications are general guidelines offered to aide in
building an engine for street use. For more detailed specifications regarding your specific application or for "strip only" use, please consult a professional engine builder.
Pistons:
Forged pistons recommended for all applications. Cast and hypereutectic pistons can be used but should be limited to lower horsepower (approx 450-500 hp) applications.
Compression ratio:
For pump gas (91-93 octane) applications, a compression ratio of 8.5:1
to 9:1 is recommended for boost levels of 8-10 psi. Higher octane fuel
will allow you to run higher boost levels, approximately 1 psi for every
2 points of octane. To determine the maximum boost level for your
compression ratio (using pump gas), refer to the enclosed compression
ratio chart.
Heads:
The same rules for normally aspirated engines apply to supercharged
motors. Higher flowing heads will help generate more horsepower than
stock heads. Supercharging produces a percentage gain in horsepower; by starting
with more base horsepower a modified motor will receive a larger total hp gain
(from the same percentage gain).Porting, especially on the exhaust side is recommended. Aluminum heads will allow you to run approximately 1 psi more boost than cast iron
heads due to their ability to dissipate heat.
Cam:
Lobe separation: 112 to 116 degrees
Split pattern: Exhaust duration and lift approximately 10 degrees and .010, respectively, greater than intake. Install cam straight up. Contact a cam manufacturer for lifts and durations that best suit your application.
Crankshaft and rods:
Cast up to 450 horsepower, forged for higher horsepower or for rpm
levels above 6,000 rpm.
Exhaust:
Headers are recommended. The size of headers are dependent on whether you are wanting to create more low end torque or high rpm horsepower.
Intake manifold:
Dual planes are recommended to improve low end torque, however may
require staggered jetting for good fuel distribution with carbureted applications.
Carburetor:
Holley double pumper w/ mechanical secondaries.
cfm 600 (#4776) for up to 500 hp
cfm 650(#4777) for up to 650 hp
cfm 700 (#4778) for up to 750 hp
cfm 750 (#4779) for up to 900 hp
All carburetor’s will require removal of the choke assembly and choke
horn, replacement of the floats with the solid nitrophyl floats and jetted to suit your motor.
Fuel pump (carbureted applications):
Your fuel pump must be capable of supplying the proper amount of fuel
flow at the maximum operating pressure. To determine maximum operating fuel pressure requirement, add your maximum boost pressure to your initial idle fuel pressure.
Example:
psi 8 idle fuel press.) + (10 psi boost press.) = 18 psi max. fuel press.
multiplying this figure by 1.2 (20% safety factor) gives us 21.6 psi
To determine required fuel flow, multiply your total expected horsepower
by a bsfc (brake specific fuel consumption) of .65. This will give your
fuel flow requirement in 1bs/hr. To convert to gallons per hour, divide
this figure by 5.87.
Example:
(boosted hp500 ) x (.65 lbs/hr/hp bsfc) = 325 lbs/hr fuel flow
lbs/hr325/ 5.87 lbs/gal = 55.4 gals/hr fuel flow
Therefore, a fuel pump capable of providing a minimum fuel flow of 55.4
gals/hr at a pressure of 21.6 psi is required.
This can be accomplished by an all electric high pressure-high flow fuel
pump (i.e. SX #18201, B.G. 400, Magna-Flow 250 or similar type fuel
pump) and a return style, boost sensitive fuel pressure regulator
Mallory #4309 or similar). Or by using a boost referenced mechanical fuel pump only (up to 500 hp) or a boost referenced mechanical fuel pump in conjunction with a low pressure electric pump (i.e. Holley blue, Comp 140 or similar