STILLEN 370Z Supercharger System - Announcement!!!

racerxj17 · 08-17-2010, 05:03 PM

Quote:

Originally Posted by Phimosis

About spreading false information: Headers don't cause supercharged cars to lose boost.

From a physics standpoint, increasing exhaust backpressure makes it harder to get exahust gas out, which makes it harder to get fresh air in. If you apply resistance to the outlet side of a compressor, the pressure goes up. Reducing the resistance increases volume of airflow and decreases pressure. Think of the tire compressor at a gas station. When the valve is shut, it is flowing zero cubic feet per minute and making 150 psi. When you open the valve and it's flowing air into your tire, it's flowing, say 10 cfm and making 35 psi because of the resistance in your tire. When you open the valve and let it blow into the atmosphere, it's flowing, say 20 cfm, but making 0 psi of pressure.

Now, cars make hp by burning gasoline with air at a fixed ratio. Having air under pressure doesn't let you burn more gas and make more power. Having more AIR let's you burn more gas and make more power. Boost helps you get more air in, but like in the analogy above, if there is less resistance, like blowing the tire filler into the atmoshpere, there will be less boost, but more total air moved, which will give more power.

So, long tube headers are NOT decreasing boost (with the implication being that if you have less boost, you are making less power). Headers simply decrease the outflow resistance so the boost level is whatever your compressor can make against the closed intake valves.

In the case of the GTM supercharger, they are using a smaller unit that reaches max boost and flow characteristics at a lower RPM, but then at higher rpm, the unit does not increase airflow in the linear fashion that engine consumes air. This leads to a drop off in boost. It gives a nice fat torque curve that falls off at high rpm, similar to what you see on most turbo cars. Then, when you couple that with a free flowing exhaust, the boost numbers are lower than predicted in the higher rpm range, but will likely be same as predicted in the lower and mid range.

GTM's higher stages of their supercharger kit use a larger compressor and you probably won't see the fall off in boost at high rpm (even with headers), but the torque curve will probably look more like the unit that Stillen has developed.

this+++

i have used the same blower used in the GTM kit on my old tacoma 4.0. when i installed headers, i did drop about 1.5 psi, but i also gained 15+ rwhp from 2500 rpm and up.

i generally stay out of these types of arguments, because in general people are to ill informed on how a supercharger actually works.......the people that DO know the above, already know it

OKC370Z · 08-18-2010, 06:10 AM

Quote:

Originally Posted by racerxj17

this+++

i have used the same blower used in the GTM kit on my old tacoma 4.0. when i installed headers, i did drop about 1.5 psi, but i also gained 15+ rwhp from 2500 rpm and up.

i generally stay out of these types of arguments, because in general people are to ill informed on how a supercharger actually works.......the people that DO know the above, already know it

A lot of people are just ignorant in understanding the process and to the terms used. Boost is loosly used in conversations about turbos and supercharges in large part because boost is the only parameter that can be measured and used to "compare" peformance in like applications. Unfortuanately we can't measure the actual air volume entering into the intake.

As mentioned above boost refers to the amount of resistance to the air flow produced by FI systems. Boost is relative to the amount of air that can be "forced" (hence the term "Forced Inductions") into the engines cyclinder while the intake valve is open. There is only a small duration that the intake vavle is open on any given cylinder while all the others are closed. This is going to provide resistance to the air being forced into the intake by the FI system.

Just remember that boost can only be used to compare peformance of like engines with like FI sytems. All Z's for instance will make the same horsepower (provided all peformance accessories are the same, i.e. headers, cats, etc.) at the same boost levels provided from different FI systems, PROVIDED that the the FI sytems are delivering the same amount of air at the same rpm. Since different FI sysytems spin faster or have larger impellers they will move more air than smaller ones and will produce more "Boost" at lower rpms and produce more power. The reason for the increase in boost is due to the larger systems trying to "Force" more air into the cylinder when the intake valves are open.

"More air being forced against the same resistance will increase pressure (boost)". Example: a fan moving 100 cfm through a 4" diameter pipe may produce .5 psi at the discharge of the fan. When you replace the 4" pipe with a 2" the air flow decreases and the pressue at the discharge of the fan increases. Now install a larger fan that can overcome said resistance and make it large enough to produce 100 cfm throug the 2" pipe than you will see 100 cfm at a much greater pressure at the discarge of the fan.

P2/P1=(cfm2/cfm1)squared

Where P=pressure and CFM=cubic feet per minute of air volume

The equation above is a statement that states: that an increase in air volume through the same area (say a motors intake) will increase the pressure in the intake by the "square" of the cfm or air volume increase.

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