[rufushusky]

It is the pressure that the exhaust gas is forcing back on the engine. Too much of it and very bad things can happen.

 

[rufushusky]

So a person can set up a gauge off the exh. manifold to get the reading?? Same as boost gauge?? I've seen someone use some type of filter to keep soot from messing up the gauge, I think....

I would run copper tubing for the first 7-10ft of boost tubing and then plastic tubing. I have seen a few things about a filter but I am not sure on that one....