Importance of CFM flow in exhaust
Importance of CFM flow in exhaust I was just wondering how important is cfm flow in the exhaust system. How much power can be added? I have read that you wan't 2.2 cfm for every horsepower. So lets say you have 330hp which would require 660cfm, now lets you have cats and they are restricting your flow to 200 cfm per bank resulting in 400 overall cfm. What kind of power would be had by removing the cats and having the exhaust flow the extra 200 cfm or more? I was also reading that on top of restriction inside cats there is turbulance created which has a negative affect on scavenging
can anyone give more insight?
can anyone give more insight?
The 2.2 CFM per HP is a guideline for minimizing the restriction of the exhaust. Basically, open header versus full exhausts that flow 2.2 CFM per HP at 20" of water have shown little impact on power; some full exhaust systems gained power, but by such a small amount that probably falls with in the accuracy of the dyno. The flow is turbulant in the entire exhaust which can't be avoided unless you went to an unrealistic exhaust pipe size (think on the order of 6" exhaust) and then you have lost power for other reasons besides adding a lot of weight from the pipes.
The thing to understand is that the CFM for cats floating around the net is at a curtain pressure given in inches of water. If you go to a higher pressure it will flow more CFM, but then you can't get all of the exhaust gases out of the cylinders, so you can't take in as much fuel and air on the next engine cycle (less power). If you get less restrictive cats you can get more exhaust gas out of the cylinders. I'll let someelse chime in for a rule of thumb on HP increase.
The thing to understand is that the CFM for cats floating around the net is at a curtain pressure given in inches of water. If you go to a higher pressure it will flow more CFM, but then you can't get all of the exhaust gases out of the cylinders, so you can't take in as much fuel and air on the next engine cycle (less power). If you get less restrictive cats you can get more exhaust gas out of the cylinders. I'll let someelse chime in for a rule of thumb on HP increase.
