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 Plenum Chambers - What they are, and what they do etc  

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Melvin_in_the_EL
  • Melvin_in_the_EL
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  • Member No.: 7,325
  • Joined: 20-January 04
  • Posts: 109
  • From: Brisbane
Post #1 post 19th June 2005 - 01:47 AM
alright guys, it has never been explained to me why a plenum chamber is used in some applications, and also, where it is fitted, what advantages it gives, what disadvantages if any. So basically, this is a post asking ppl to explain what a plenum chamber is, what it does, where it is fitted and why, and what advantages it has etc.
Cheers

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the red krawler
Post #2

A plenum is a "resovoir" (as such) of air.
A larger plenum gives a larger volume or air to go down the runners.
More volume and more flow = more available air for the engine to use = more power.

Also, a lot of plenums are changed to position the throttle body differently, and have a larger throttle body fitted. Not much point having a 100mm throttle body on a 50mm plenum, its like having a 3" exhaust with a 1 3/4" cat fitted.
70NKY
Post #3

If the red krawler didn't say it, then I may be wrong, but a plenum chamber can also give better flow than a standard intake manifold. I'm thinking of a VL here, and having a plenum in a vl, gives you a shorter intake track, so therefore better throttle response.

Melvin_in_the_EL
Post #4

ok, so now i understand the basic principal, what exactly hooks up to the plenum, like, where does it sit in the bigger picture? where is it placed in regards to the throttle body, what comes off it, ect?

racer by night
Post #5

standard rb25 plenum:
user posted image
custom made rb25 plenum:
user posted image

MoonLight
Post #6

The Plenum chamber is usually directly in line with the throttle body, after the throttle body, I mean. As said, it acts as a resovoir for oxygen on it's way to the engine. Various power and acceleration changes can be made by modifying the length of the 'runners' on the inlet manifold

Melvin_in_the_EL
Post #7

ok, so from what i have gathered from the two pictures posted, it goes from cooler piping, to throttle body, to plenum chamber, to engine? sorry about the neive posts, just trying to work it all out.....

Melvin_in_the_EL
Post #8

also, are they just a hollow chamber? or do they have anything welded inside of them for any particular reason?

prophecy
Post #9

some of them have deflecter plates to avoid the closest cylinders to the intake getting more air than others, ie in the custom one there, the 1st cylinder would gain more air than the others, so they either use a deflector plate, but in that case, they use longer runners (the long pipes going to the motor)

BansheeBuzz
Post #10

the idea behind the plenum chamber is to distribute air to each cylinder more evenly

QuicKSilveR
Post #11

Yeah, The factory cast Manifold have castings inside the plenum that deflect the air and try to get more even flow. Many Custom jobbies are poorl thought out and are just a big chamber....which can cause some cylinders to get more air than others.

QuicKSilveR
Post #12

Here is my plenum that I decided not to go ahead and use.

user posted image

March_Hare
Post #13

the whole purpose of a plenum is to slow down the velocity of the incoming air allowing it to compress slightly increasing the volume in a confined space before flowing on to the engine via the runners. Virtually all vehicles (except those with carbs or in some cases, those with independant throttle bodies) have a plenum of some sort.

Slowing down the velocity of the air entering the plenum allows you to increase the volume of the air, increase in volume = increase in torque. Increasing air velocities allows less air into the engine, but due to the speed of the air travelling it increases throttle response. Thats where physical dimensions play a part.

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