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know that the vacuum pumps are capable of producing more vacuum- but how much more is really necessary or beneficial? Do the header evac tubes even provide enough vacuum to see any benefit or HP gain?

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Here's my worth.
I run an evac tube system. It's been on for well over ten years. I also have a full exhaust system that runs all the way to the back bumper. Through trial and error, I found out that you can not use a "mouse trap" type muffler with a tube type evac system. These mufflers create too much back pressure. You need a "straight thru" type muffler. I use Dynamax but any "straight thru" muffler should work. As far as horsepower gains...I don't know of any gains in this area. I do know that engine oil leaks have stopped. Maybe it's a coincidence, but I have also noticed that my oil stays cleaner longer.
As far as how much vacuum is created... It really doesn't matter. Any vacuum is better than pressure. With that, a vacuum pump will use up some horsepower. A tube type evac system doesn't.

Again, my