A while back there was a discussion about vacum pumps and evac tbes. I had my car in the shop the other day and removed a hose from my valve cover breather and connected my Snap-on vacum gauge. While I could feel a little at idle it didn't show on the gauge but from 2,000 to 3,000 it was a steady 2in of vacum. My tubes are homemade black iron pipe nipples that I welded in the header collectors. I did cut a slot in the pipe and it is in the stream to help create a draw just like you would with a piece of hose using compressed air to start a siphon.

Did some testing on that setup a few years back 355 in. motor single 4 pulled 7 inches at about 6500 down track i/8th mile

^^^^^^^ That’s Amazing evac results imho. I have evac and think they work, but don’t own a gauge to verify.

quote:

Originally posted by vetman:
Did some testing on that setup a few years back 355 in. motor single 4 pulled 7 inches at about 6500 down track i/8th mile

Is that measuring in the hose like I did or in the motor like others do with a pump and a sensor?

Vacunm outlet in valve cover to gauge duct taped to cowl nothing fancy but good data

So I think a killer EVAC system is totally overlooked for classes or guys that simply don't want a vacuum pump. It's something I plan on trying. I have a few different ideas. It's worth the effort. A basic 5" was worth noticeable HP on the dyno with thin rings and totally sealed up.

Chris, what are you using for a vacuum source?

I had an SBC on the dyno that had evac tubes, well we capped them off, and left the breather to atmosphere, because my O2 sensors are located after the collectors. So after we were done, we hooked them up for the final pull of the day. I was shocked that the engine made 8hp more. This wasn't a maxed out engine, made somewhere around 450 -500hp

quote:

Originally posted by FastLane:
Chris, what are you using for a vacuum source?

The tank is hooked to the manifold and one header collector and the other side of the tank to the breather. Then on the other header, breather to collector.

quote:

Originally posted by vetman:
Did some testing on that setup a few years back 355 in. motor single 4 pulled 7 inches at about 6500 down track i/8th mile

I would have never thought you could get any where near 7 inches of vacuum with evac system. That is pretty good for sure.

I’m confused. But that’s easy!
Did I read You have a vac pump and breather to header tubes?