Custom Plenum

[boostinhard]

Hey,
Im making a custom plenum my for n12 and Im after a bit of adcise... I have the basic shape figured out - very similiar to the BIG plenums used on GTR's but on its side. Im having bellmouthed inlet runner sit off the floor of the plenum and am making it out of alloy. I just wanted to know what formula I should be using to calculate the approximate size this plenum shold be??? I was thinking around 2-2.5 litres should be heaps? Its a 1.5 turbo running 20psi...
Sam

[Blood]

err... i am kinda slow..
what is a plenum ???

I know others dont know, but are too scared to admit it on here ... :hitwall:

[boostinhard]

Hey,
ok.... the plenum is the box type thing after the throttle body on a blown engine. Custom/aftermarket units can reap signifigant benefits and surprisingly HKS dont make units for 1983 N12 Exa's!!! lol - custom is the only way to go.
Sam

[exa18]

You're an idiot......
No chris, everyone knew what a plenum was, it's just you that doesn't know.

[boostinhard]

Hey,
haha.... Na man, a lot of NA guys wont know what a plenum chamber is...
Sam

[chris2]

We used to call it the plymouth chamber!!!!

my understanding is the runner should be a cyclinders worth( 340 cc) plenum (plymoth!)shuld be at least 4 cylinders worth (1.5ltr)

[boostinhard]

Hey,
yeah - that sounds pretty fair... the runners should end up being that lenght and the plenum I planned was going to be around the 2-2.5 litre area so that dhould be fine too...
Sam

[KAMELEON]

working around a rule like this works very well and most custom manifolds are made like this
double the engine in litres and u have the volume in litres
eg in ure instance sam 1.5lt motor=3litres of inlet plenum volume

[boostinhard]

Hey,
Hmmm okay - might have to get the measuring tape out again then... lol
sam :hitwall:

[Lonx]

boostin, its not just about having a larger or more open plenum design. By calculating the correct volume for u're engine at a given RPM & the right size intake runners - you can get up to about 15 - 20% more power.... We'll have a chat about it if u like, been researching these for the past year until about 3 months ago when I decided to go for my quad throttles. ICQ or MSN is fine with me if u're interested.

[boostinhard]

Hey,
yeah - I know... Which also makes me wonder why you went for quad throttle bodies... No good unless your allways pulling very high rpm... Dont have ICQ nad just had my hotmail hijaked by some dork recently!!! So post your thoughts here!
sam

[Lonx]

Would rather not post everything I learnt publicly, sorry, but its nothing personal. The plenum is still a fair idea for me, but the quads interested me for a number of reasons, and the sound would be amazing. I'm building my car up to my tastes, not so its the fastest or the most powerful hehe.... tho the plenum might end up being designed, who knows at this stage. The head and exhaust has to come first (yes my exa is pretty basic still).... then I'll worry about that. Look on the net for plenum theory info, u may find the resource I learnt some very interesting things from.

[boostinhard]

Hey,
okay - thats fair enough. If you have any inside ideas that may be of use in this project - please email me at slpa@eakin.edu.au your help/theories would be greatlky appreciated. I too have done some research - but not to that extent. Just a good 5-10 hours on the net...
Sam