| Without going vastly indepth on this, you have to take into consideration what backpressure really is. Just because you have a bigger exhaust does not mean you are going to flow more air through it. There is a scavaging effect that happens when exhaust is expelled through the exhaust valves. When the valve opens it pulses spent gas out at a certain rate. If the exhaust size is too large it will SLOW down the rate of gas expulsion creating a negative effect in gas exiting the cylinder. An optimal sized exhaust will flow faster (even though it is smaller) increasing the scavaging effect by creating a vacuum to pull the gases out of the cylinder creating more room for fresh air to come into the cylinder for it's next stroke. If your exhaust is too large it will IMPEDE the exit of gases because they will not have the mass to fill the exhaust up at the rate they would if the diameter (volume) was smaller, actually slowing down exhaust gas speed and negating the scavaging effect. Mike
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21:11:03 01/17/05
