backpressure and exhaust info

[TonkaTom]

I found this on the internet and thought it was interesting, plus it cleared up some things for me, so I thought I'd share it. I had no part in making it, just spotted it on digg. So enjoy.

http://www.automotiveforums.com/vbulletin/t943495.html

[SCT]

Very interesting...

However, of course water would exit at a faster rate when you block the end off with your finger. It's being compressed by the pressure and is building up within the hose. And then something has to give that being your finger. Same deal goes with engines. The piston is forcing the exhaust gases out. If something restricts the flow, the the faster flow is just compensating for the amount of compression that is being built up within the exhaust system.

That's why I never understood backpressure shit. Basically saying if I swallowed a half golfball and lodge it in my airway, I'll breathe better... yea right.

As long as your piston is not being dragged by trying to force exhaust gases out the chamber, you're running good IMO. Unless you have a turbo which requires a faster flow/ velocity.

[eage8]

Originally Posted by SCT

Very interesting...

However, of course water would exit at a faster rate when you block the end off with your finger. It's being compressed by the pressure and is building up within the hose. And then something has to give that being your finger. Same deal goes with engines. The piston is forcing the exhaust gases out. If something restricts the flow, the the faster flow is just compensating for the amount of compression that is being built up within the exhaust system.

That's why I never understood backpressure shit. Basically saying if I swallowed a half golfball and lodge it in my airway, I'll breathe better... yea right.

As long as your piston is not being dragged by trying to force exhaust gases out the chamber, you're running good IMO. Unless you have a turbo which requires a faster flow/ velocity.

if you have a bigger exhaust, it'll decrease the strength of the exhaust pulses leading to having more exhaust in the exhaust pipe...

turbo exhausts can be however big you want, because the gain of the turbo spooling faster is better than the loss of the slower velocity exhaust...

take this with a grain of salt through, I don't really understand it all that well either lol.

[World of Noise]

Originally Posted by eage8

turbo exhausts can be however big you want, because the gain of the turbo spooling faster is better than the loss of the slower velocity exhaust...

I was curious about that, thanks for clearing it up!

[jmaz87]

i would agree, i tried several exhaust setups on my 4afte at several boost levels before i was happy.

the small turbo spools low enough to compensate for any loss i would have had with my 2.5" DP

i ended up sweeping the DP forward, down, then back and gave it a few bends over the front Cross Member then a straight shot to the gas tank where i change to 2.25 just before the 90

the idea being absolutely no restriction straight of the turbo all the way to the rear tires where the 2.25/magnaflow would just barely constrict increasing overall velocity without compromising actual CFM.

CFM (ft^3/min) is really what all of this comes down to. especially with a turbo setup, i still think there is a limit especially when matching intercooler piping to exhaust piping.
i used 2.5" IC piping because i have a very large inter cooler and so i'm essentially maximizing my relatively small GT17 which maintains efficiency off boost (low turbine resistance)