i have recentally rebuilt my engin and i want to supercharge it. with my compression ratio i dont want to boost more than 8 psi. with 8 psi how much horse power would that give me. some people say 100 some say 50, i was wondering would any one know. also if i was to get a computer flash should i wait untill its supercharged or would it mater?

Thanx peepz

 

every pound of boost is good for a 8-9% increase in hp and every 10degrees the temp of the incoming air drops is good for a 2% increase.

 

so on a 300hp engin i would be well over 100 hp increase with 8 psi?
with the math u saying it would be up near 200 hp increase that dosent sound right.

 

One of the supercharger websites says that it will increase an average of 35-40% on your maximum hp and tq. That is figuring 7.5% boost and under 9:1 compression. So 100 hp gain sounds about right because no engine is 100% efficient.

 

The pressure of the atmosphere
when using psi is about 14.7
so with 8 psi of boost
it would be like 22.7 psi

{22.7/14.7} raised to exponent 1.2
= 1.68

so in theory
a supercharged engine with 8 psi of boost
would give about 68% more hp
and a 220 hp Magnum 5.2
would go to a bit less than 370 hp
but you need to subtract about 2 to 4 hp per psi of boost.

But my guess is that you can't use 8 psi of boost
unless you can use 100 octane gasoline somehow...or perhaps e85
Maybe 4 psi of boost in summer on 93 octane
and 5-6 psi of boost in winter cold
....but it depends on how willing you are to risk losing a cylinder
and having the engine rebuilt.
Intercooler makes a big difference.

Old post below explains how pressure and temperature affect hp levels
====

Page 415 of the Bosch Automotive Handbook, 5th edition

http://tinyurl.com/yplr3d

has the two equations you need
to see how horsepower and torque change
when either temperature or pressure change.

For temperature the offical equation
used by Americans (SAE) Europeans (ISO) and Japanese (JIN)
is:

{ Temperature Before + 460/Temperature After +460} raised to 0.6 power

you need a scientific calculator to do this
but there is one built into every Windows computer
under Start...All Programs....Accessories

As an example,
say that your re-locate your air inlet to a spot where the air temperature
drops to 80 degrees
when before the air coming in had been 100 degrees.

{100 +460 divided by 80 + 460} raised to exponent 0.6

={560/540} raised to exponent 0.6

= {1.037} raised to exponent 0.6

= 1.022

You mulitply this number times your horsepower or torque
so if your engine.
If your engine makes 230 hp at peak
1.022 times 230 = 235 horsepower with the 20 degree lower air temperature.

You may have heard the 'Rule of Thumb' that each 10 degree F reduction in air temperature improves horsepower by 'about' 1% and the equation above is where that comes from, but is more accurate. The rule of thumb gives inaccurate estimates when the temperature changes a lot.

For corrections when the pressure changes
the following equation is used:

{absolute pressure after/absolute pressure before} raised to exponent 1.2

As an example
say that the weather is changing where you live
and one day the weatherman says the pressure is
29.5 inches of Mercury as a stormy "Low" passes over
then the next day a clear sky "High Pressure Area" passes over
and the pressure rises to 30 inches of Mercury

{30/29.5} raised to exponent 1.2
{1.0169} raised to exponent 1.2
= 1.0204

It is important to realize
that built right into your engine
are IAT (intake air temperature)
and MAP (manifold air pressure)
sensors.

Your IAT and MAP sensor outputs can tell you whether an aftermarket air intake has helped or hurt your power output. You can read these sensors
yourself by using an OBD-II scanner, or a cheap electrical multimeter.

 

A intercooled ATI Procharger running 8lbs of boost on a lightly modified 5.9 had an increase of 100+ hp at the crank.