Saw this on the Dynomax web site and thought it might be usefull to those wondering what size exhaust system to use.

 

Ive also read that you need to have 2.2 CFM of exhaust flow, per HP the engine makes, after the port.

 

I KNEW IT...a 400 horse 350 needs a single 3.5"...i'm glad i didn't get my exhaust yet, i was gonna listen to everybody and get a single 3"....i think i'm gonna do dual 2.5's tho instead cuz no way am i forkin over the bills for a mufflex.....that chart is awesome, that thing would really come in handy for all the exhaust pipe size questions on this board...somebody should just put that in there sig for how many times that question is asked around here...

 

Right 2.2CFM per HP that the engine makes. So if your engine puts out 400HP that equals 880CFM. That means you need a muffler(S) and pipe(s) that will flow that much.

Question is does this also apply to the intake. If 880CFM is going out the tailpipe does that not mean that 880CFM is comming in on the intake side. If so then then the modified MAF and 52MM throttle body are becomming restrictive above the 350HP level. Basing this on 750CFM for the MAF and 52MM throttle body.

 

I may not know a whole lot about exhaust, but chemisty thats I know!

About of the same amount comes out as comes in (from a chemist in training):

What happens in an engine is-
2(C8 H18) + 25(02) = 18(C 02) + 16(H2 0)

C8H18 is gas, O2 is air, CO2 is carbon dioxide, H20 is water (in case I don't make any sense)

The coeffieciants before everything are the moles, a measure of the number of atoms. So, for every 25 moles of O2 your carb takes in, it puts out 18 moles of CO2 and 16 moles of H2O. At the temperature it comes in, it needs about 0.84 cubic feet of O2 for every mole. So there needs to be 21 cubic feet of intake to complete the equation. At 90 degress Celsius (about what exhaust is when it comes out), the 18 moles of CO2 and 16 moles of H2O will be 36 cubic feet.

So, in recap, for every 1 cubic foot that comes in, 1.71 cubic feet goes out. This is all if everything goes perfectly according to chemisty, which it won't always, what with half-reactions to CO and what not...Mostly what I was getting at was that you have more exhaust than you have intake

Hopefully at least one person found this interesting. If anyone wants to see the math, let me know. And thanks for listening!

 

Actually that does make some sense. One of the things I was overlooking was that gasoline is being injected into the engine after the above mentioned items and then of course combustion. So then the exhaust is made up of different gases than what was taken in plus the heat. I will take your word on the 1.71:1 ratio. Hehehehe. Allen