Max Power

ok, this is all theoretical, i just thought this might have the possibility of having some usefulness to it.

what if you were to hook up a boost gague to a n/a motor. of course im guessing it would show a vaccuum all the time, but this way, you could maybe test different types of intakes and designs and see if they really speed up airflow or not?

just wondering. let me know what you guys think?

dubcac

They wouldn't read enough to notice any changes. Remember boost gauges read pressurized air; this is done via the compressor, not an air intake.

The Bum

If you could find a guage that reads the opposite of pressure, that should be able to read what your looking for.

dubcac

You'd just need an airflow meter.

Max Power

oo thats smart, do those things work on the fly? like when your car is driving on the road? because you could test ram air kits if it could . .

1stGenCRXer

It's called a vacuum guage guys, and not that hard to read...

If you're pulling high vacuum at high RPM, you have a higher flow speed. If you change manifolds and pull less vacuum at the same RPM, then your intake velocity has slowed down. Of course, the best time to take these readings is at WOT starting from a fairly low RPM, and then wait for the reading to stabilize. If you read zero in/hg at WOT, then you're either at your optimum throttle body/runner size for your engine, or actually too large. If you're running more than zero [or actually less since we're dealing with vacuum] then you still have some restriction on the intake side. Also, at cruise speed you can use a vacuum guage to determine your most efficient throttle angle/cruise RPM [which I use on the tow vehicle].

Vacuum guages are available all over the place, and most boost guages have a vacuum reading on the low side of the scale, but of course people are only interested in the positive manifold pressure readings it can give.

rev

What would be really beneficial is to hook up vacuum gauges in various location in the intake tract - say in the air intake before the throttle body, in the plenum, just before the injector and in the head runner. That way you could get a really good look at the more and less efficient parts of your intake tract. If you have a high vacuum reading where the intake bolts to the head but a lower reading in the plenum then that would tell you that there is an obstruction between the two that needs attention. I have done similar research on my flowbench using a small probe to determine lazy and active areas of the ports. It's a good way to learn how air moves.

If you do the simplest thing - hook up a vacuum gauge to the intake plenum - and follow the vacuum readings at WOT as you go up in RPM, it should stay at zero. If you start getting vacuum more than 1 inHg or so in the plenum then there is a restriction, generally at the throttle body and you need a bigger throttle body if you plan on driving at that rpm.

You can also hook up a vacuum/boost gauge to your crankcase if you run on the ragged edge of detonation. If you notice a sudden fluctuation decreasing vacuum or increasing boost in the readings then the rings are most likely fluttering from detonation and it is time to lay off. Some people even have a warning light set to go off or a nitrous kill switch if the reading gets to a certain level to save the engine.