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alistairolsen
Token Scot
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1998 Vauxhall Corsa
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 Posted: Tue Feb 23, 2010 9:47 am Post subject: Inlet plenum design |
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On a broad level.......
The sort of plenum Rob runs on his LET, there is normally a guide for volume within the plenum I believe, anyone know a formula or rule of thumb?
The plenum cover can be tapered like a swedish plenum, any guidance in the loss of cross sectional area along the length? common sense would say the area aver the fourth port should be a quarter of that over the first one but they taper isnt normally anywhere near that big?
Trumpets - I know a round edge on the ports aids flow if you dont have trumpets (like a pulsar backplate) but I remember reading somewhere a complete trumpet with the return edge is better, standing pround of the backplate? a lot better or very little?
What sort of distance should one have between the open fact of the trumpets and the plenum cover?
cheers! |
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Stefan
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alistairolsen
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| Posted: Tue Feb 23, 2010 2:23 pm Post subject: |
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Stefan, I signed up but it still wont let me view it:
alistairolsen, you do not have permission to access this page. This could be due to one of several reasons:
1. Your user account may not have sufficient privileges to access this page. Are you trying to edit someone else's post, access administrative features or some other privileged system?
2. If you are trying to post, the administrator may have disabled your account, or it may be awaiting activation.
can you copy and past the post by any chance?
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stt
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| Posted: Tue Feb 23, 2010 2:29 pm Post subject: |
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volume of plenum = 1.5 x capacity of engine
as a rough rule |
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stt
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| Posted: Tue Feb 23, 2010 2:30 pm Post subject: |
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| actually - its volume of air between throttle body and valves = 1.5 x capacity |
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alistairolsen
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1998 Vauxhall Corsa
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| Posted: Tue Feb 23, 2010 2:45 pm Post subject: |
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That wont be far away then!
Taking 30mm diameter runners a foot long gives me 850cc leaving 1550cc for the plenum. on the basis of the plenum being 350mm long (likely longer in practice) that gives an average cross section are of 44.3 cm^2 which is a 3 inch tube. removing the volume of trumpets and the flat plate on one side of the tube will allow me to make it a fraction longer. |
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Stefan
Guru of 8v engines
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| Posted: Tue Feb 23, 2010 6:15 pm Post subject: |
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From part of the thread.
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Plenum Sizing
Although it is possible to calculate a particular plenum volume to suit a target rpm range, it's rather tedious to do properly on a calculator. Instead are some "rules of thumb" to help chose an initial volume. The volume should be selected with the previous points on plenum volume in mind.
Naturally Aspirated
Production/near stock engines - 0.3 to 1.0 times total engine capacity
Race production type engines - 1.0 to 2.0 times total engine capacity
Race engines with one-throttle-per-cylinder - up to 10.0 times total engine capacity (as big as you can package is the general rule here)
Turbocharged
Production/near stock engines - 0.5 to 1.0 times total engine capacity
Race engines (all types) - 1.0 to 2.0 times total engine capacity
Of course the volume is not the only thing to consider in plenum design. The design details which include the requirements of equal flow distribution, throttle response and effects on the primary runner etc. need to be considered. These details will be covered later on.
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Previous points.
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Plenum
Larger plenum (also larger total manifold volume) - moves the lower torque peak to a lower rpm. Over a certain volume there will be no lower torque peak. Larger plenums also enhance the tuning of the primary runners and can even out runner-to-runner air distribution. This generally increases peak hp.
Smaller plenum (also smaller total manifold volume) - moves the lower torque peak to a higher rpm. Smaller volumes will have the opposite effect on the tuning ability of the primary runners.
Plenum and total manifold volume will also effect throttle response which may be important in some applications. Generally the smaller the volume the faster the throttle response. This does of course depend on the engines rotating inertia etc.
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chip
Vaux TOTB Mgr
Joined: 11 Oct 2006
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Location: Somerset
1990 Vauxhall Nova
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| Posted: Mon Mar 01, 2010 11:47 am Post subject: |
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| alistairolsen wrote: | That wont be far away then!
Taking 30mm diameter runners a foot long gives me 850cc leaving 1550cc for the plenum. on the basis of the plenum being 350mm long (likely longer in practice) that gives an average cross section are of 44.3 cm^2 which is a 3 inch tube. removing the volume of trumpets and the flat plate on one side of the tube will allow me to make it a fraction longer. |
dont forget the volume inside the head too between the inlet mating face and the back of the valves
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Stefan
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| Posted: Mon Mar 01, 2010 6:15 pm Post subject: |
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Note. In the rules of thumb I listed above, the factors are for plenum volume only.
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dewismotorsport
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Location: Coventry & Barnstaple
1994 Vauxhall Corsa
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| Posted: Mon Mar 01, 2010 11:33 pm Post subject: |
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I use this to work mine out: helmholtz resonance.
Just google it, it should come up 
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Benc
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| Posted: Tue Mar 02, 2010 10:40 pm Post subject: |
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| hey stef, we should all meet up and put your flow bench to use |
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