zero compression yes Zero lol !
Ok I get what your saying now . I was figuring the flowing exhaust through the collector would create a suction pulling from the dead hole the way we used to use a running faucet to create a vacuum source in science class .
It can and does, when the pipe is active. With a dead cylinder, nothing is coming down the pipe. It is the slug of hot air moving down the pipe, entering the merge, that creates the suction. No slug, no suction. Of course the other 3 cylinders are firing into the merge as well, but their suction is moving up their pipes. And the result of those other 3 slugs of hot air piling up in the merge is pressure there that is higher than atmospheric.
A good single exhaust system will run at 4 psi or less. A very good dual might run 2psi or less. In the plenum at idle, the vacuum is about 11 inches say. This is a minus psi. As in less than zero psi. As the rpm goes up, so does the vacuum (to a point around 2200 rpm), and so the minus pressure goes still further from zero.
To compare apples to apples, you have to convert psi-gauge to psi absolute, and unfortunately I have forgotten the methodology. But even not-knowing it you can clearly see that the pressure in the exhaust is probably 2 or more times what it is in the plenum. Two times is 200% more, Guess which gases, when given a chance,are going where.
Air always moves from an area of high pressure to an area of low pressure.
EDIT; The following belongs in a different thread; I think my computer screwed up....
If you want proof of this, it is in your vacuum gauge.
Your vacuum prior to this event was 11.5,right.
During the event, it was 5,right?
And now it is 10 to 11 and drifting,right.
Well why do you think the vacuum changed from 11.5 to 5.0? Do you think it was cuz one cylinder wasn't working? Well, now that the vacuum is back, put the gauge on it and disconnect one plug wire. I guarantee you, running on 7 cylinders with no other changes from the pre-event, your vacuum will not drop from 11.5 to 5. I believe that loss of vacuum was actually a gain of pressure from the exhaust system!, coupled with the loss of rpm it caused.
And I believe that may have been the pressure which was blowing your metering rod pistons up off their seats, and causing the surging. Well,lucky guess on that, I suppose, cuz I never actually saw the pistons dancing.
