Calculating required Exhaust pipe diameter

[Tasmaniak]

So with that being said, where does back pressure come into the equation? If my understanding is correct, on a standard run of the mill street car, you don't want to eliminate back pressure altogether... especially in the front half of the exhaust near the engine itself. Perhaps NAAF you can explain that one to me? It was explained years ago in a vehicle emissions course I was required to take in the US but I don't remember it now.

 

[Immortality]

The key word I see in your question is "emissions".

Modern engines use an EGR system to assist with emissions. See http://en.wikipedia.org/wiki/Exhaust_gas_recirculation


Basically back pressure sort of acts like an EGR system because back pressure means a certain amount of exhaust gas is left in the combustion chamber. The way I see it, if performance is your primary goal than back pressure isn't wanted or required.

 

[Not_An_Abba_Fan]

Spot on immortality.

 

[Tasmaniak]

So on the stock standard street car coming for a replacement exhaust, would you attempt to eliminate the back pressure, or just don't care and put a standard replacement back in?

 

[Immortality]

Depends what you want and how much you want to spend. You could fit a run of the mill cat back exhaust and unleash a couple of killer wasps or just fit a standard system and have a standard car.

 

[Not_An_Abba_Fan]

You will never eliminate back pressure, but you can reduce it. With everything, the more you spend, the more you get.

 

[Tasmaniak]

It makes sense now. Thanks guys.