Here is a nifty little graph I found online, measuring muffler backpressure on turboed cars. Thought you guys would like to see it, if you are turboed or not:

 

where do the inches of water come into play in back-pressure? just trying to understand the graph a bit better...the bigger the bar, the more back pressure right

 

Inches of water is the amount of water the backpressure will consistently suspend above the exhaust. It's the same as inches of vacuum pulled by your engine. A higher absolute value of vacuum is better. Same here, the more inches of water that can be supported in a column, the more backpressure there is.

 

Inches would be far more accurate measure than say PSI because of how low it is.

 

If this graph teaches us anything, it's that mufflers are for little girls.
On a more serious note, where did you find this? Any notes on how it's being calculated?

 

arent some of those straight through? that doesnt seem like it would be able to cause any backpressure..

 

You'd be surprised. They still cause a lot of turbulence.

 

I was just looking randomly at turboed cars. Found out about a 5th injector trick for 4 cylinders as well:

http://thedodgegarage.com/turbo_exhaust.html

 

cool beans. I live in Ontario, so any cars older than 20years no longer need to pass emissions. Straight pipes to glass packs for me