Exhaust Pressure and Dimensions

[samoz3]

Hey guys, I been reading and increasing my knowledge about car stuff, and I been reading about exhaust stuff lately.

People always say that bigger exhaust piping is better than small. Now, I want to know why this is. In school, they've talked about Bernoulli's principle(those who dont know what that is, look at the bottom). Now, based on that principle, wouldnt it mean that smaller exhaust would get rid of everything faster due to the larger pressure?

Bernoulli's Principle: less pressure = faster flow and vice versa. Example: Blowing through a straw makes the air move very fast to the end of the straw. Blowing through a cardboard tube is much slower. A venturi's tube works as well.

http://www.mste.uiuc.edu/davea/aviation/bernoulliPrinciple.html explains it well.

 

[00 Agent]

It comes down to the amount of air that can flow through the exhaust, not how fast it can flow. It's a little different for NA cars, but pretty much the bigger the better on turbo cars. That's as deep as I'm going to get, you can find more technical stuff on this subject by searching. There's lots of discussions on it out there.

 

[samoz3]

but wouldn't being able to move all the exhaust out quicker be better than just letting it snail out?

 

[00 Agent]

You've mentioned the straw thing...take a deep breath and blow it all out as fast as you can through a coffee stirrer straw. Then get your big cardboard tube and do the same thing. Note how much longer it takes you to "flow" all your air through the small "pipe" verses the big one.

 

[DSMeclipse4G63]

that and you realize that a turbocharger creates alot of exhaust back pressure. With that pressure being created you need room for it to release, and our cars produce enough exhaust/pressure to utilize a 2.5" or 3" exhaust.
Andrew

 

[samoz3]

Couldnt I just not have an exhaust pipe and just let it blow out? Although, itmight gas the driver and passengers

 

[igs]

Think of it as "bandwidth". A single straw can't flow as much as a larger pipe that's equivalent to 20 straws.

 

[samoz3]

oh wow, i hate bandwidth. DIE AOL!

 

[got_no_sol]

Think of it like weather - Wind is created by area's of low and high pressure. The air flows from the area of high to the area of low. The more space you have for the high pressure to move into the low pressure (ie the exhaust) the faster and freer (is that a real word? ) it will flow...

 

[00 Agent]

oh wow, i hate bandwidth. DIE AOL!

Bandwidth is a good thing. You probably mean you hate the lack of [available] bandwidth.