Axiom Home Page Forums General Discussion Technical Questions In wall speaker wire

OK, I'll give you that. Eats, shoots, and leaves.

But your room's still square.

Ha, ha! "Plenum" is kind of a weird word, as in . . ."How's it going? Oh, not bad, but I'm having trouble with my plenum. ."

Alan

I actually came across the word plenum in my automotive world first. There's a spacer between the intake funnel, and the throttle body. That's referred to as a plenum.

Not long after I got a job installing networking cable in a school. They told me I needed plenum wire. That didn't make any sense at all, because I knew, from context, that a plenum had something to do with the intake on a car.

So to have the two worlds meet up on my head I had to find the root of the meaning. After that I've always insisted on the correct usage.

Why not just call it "Wire in the hole".

Yep. I blew up the plenum (known as upper intake in the Mustang world) with nitrous about 8 or so years back... Was fun times :D. I actually had it on video at one point but I don't know where it is now.

Plenum is a word for all the 'tubes' within the manifolds, rough definition would be a an area for air movement, which is what an intake manifold does.

Chris, the spacer you are talking about is in fact just a spacer for the throttlebody. You would be using it to elongate the length of the runners of the intake for more airflow at some specific RPM the designer of the system decided on, also known as 'port tuning'. Toyotas and a few, well many now, other manufacturers run dual intake runners with butterfly valves that open at different times to increase either high RPM or Low RPM performance. (I hope I got that right, it has been awhile since I had to think about design specifics)

I own Mazda RX-7s (three of them at this point in time). It was the FSM (Factory Service Manual) which referred to the plastic spacer as the plenum. I only bring it up, because the RX-7, starting in 1989 did indeed have a VDI (Variable Dynamic Intake), or two paths through the intake manifold. A longer path for the lower RPM range, where the inertia of the air mass would help charge the combustion chamber. Actually to the point where it could reach slightly higher than atmospheric pressure. Then at higher RPMs, 5500+, it would switch to the shorter path, because at this point the engine is gulping down so much air the longer path is a restriction.

Mazda did the same for the exhaust ports starting with the GSL-SE (a Special Edition) of the 1985 RX-7. A rotary engine behaves more like a 2-stroke than a 4-stoke. Changing the position of a port changes the engine's timing. At higher RPMs, 3600+, auxiliary exhaust ports open, extending the port timing slightly to help purge the chamber which is only open for a very short period of time. This extended time causes over-lap between the exhaust and intake, while adding power, allows some unburned mixture to exit the tail pipe. The aux ports were not used on the turbo models (no sense in having the pressurized intake blowing straight out the exhaust), nor the RX-8, which had to meet stricter smog specs.

But with enough overlap you can get that cool flame out the tail pipe

Oh, the RX-7s are known for that. Even the turbos without overlap will go momentarily rich on deceleration (especially when using a open-air blow off valve, with the stock air meter). The rotary engine's exhaust is so hot it has no trouble igniting when it reaches the oxygen-rich atmosphere.

My sister had an RX-3 that would do it