Thought so. I have used that analogy with most of my friends and only a few of them seem to get it... And they claim to be mechanically inclined car people...

 

exhaust myths are as big as octane myths, and other myths.

 

so if a 3" is bad for dd n/a would an open header be just as bad?

 

Generally not as bad but it would still not be as good as a good set of pipes, even if it is just going out the side behind the drivers wheel. It needs a little more than the collecter to join the gasses.

 

A long tube header is ideal, but if it is not practical shorties with the correct exhaust tube size for scavaging. Two things are key to tube size selection, low turbulence(back pressure)/high velocity(scavaging). Too big you lose velocity, too small you create turbulence.

 

Magnaflow 2.5 inch exhaust worked GREAT on my car. As stated before its probably 2.25 internal. 3" is just too big for naturally aspirated 4 cylinders.

I may be wrong but in personal experience I've learned you want as little back pressure as possible. However the answer to this isn't throwing on an exhaust thats 4" bigger than stock.

So my understanding would be, you want as small pipe size as possible while still avoiding backpressure?

 

Yup, thats the balance: High exhaust velocity, low backpressure.

 

Word, we all know 5" piping is out of the question unless you are running quad digit h.p.

I saw a 1300 hp Lexus sc300 running 4.5 and he needed it.

 

Your stock 2.25" is just fine! just replace the muffler and d/p!