i want something stiff...

Mr Quoter-vator Joined: 16 Feb 2004 Posts: 7405

gotcha....

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

vauxhalls are better to see the taper on, will try and find a pic.

Mr Quoter-vator Joined: 16 Feb 2004 Posts: 7405

so would a fabricated plenum like te thing in jimbos sig , with the correct taper, be worth makin to replace the renault one?

Forum Moderator Joined: 16 Feb 2004 Posts: 1356

You would maybe see better velocity I suppose if the innards were worked correctly

Mr Quoter-vator Joined: 16 Feb 2004 Posts: 7405

what would be the ideal plenum setup? shapes, sizes etc?

Gay Rights Activist Joined: 07 Apr 2004 Posts: 1268

ideal size(volume) is 14 times engine size. cant remember why tho, just that its 14x!!
ideal set-up would be throttle bodies!!

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

erm its not 14x, try 1.5 x.

Forum Moderator Joined: 16 Feb 2004 Posts: 1356

Haha that would make the 2.0 ltr inlet plenum 28 ltrs! I'd like to see you fit something that big in your AX! Very Happy

Gay Rights Activist Joined: 07 Apr 2004 Posts: 1268

why is it 1.5?

for for an engine speed of say 8000 rpm there are going to be 133.3 revs/sec. this means there is going to be 66.6,say 67, induction strokes per/sec. each induction stroke=450cc (for F7P), so in one second, 30150cc,s of air is induced.

if its 1.5 times, that would make it 2700 cc's--not big enough.

14x1800=25200 cc's--still smaller, bit this is compensated by fresh air entering plenum

Gay Rights Activist Joined: 07 Apr 2004 Posts: 1268

wot (I mean what really)?? the AX is a 1.4!! so i wouldnt have to fit a 28l plenum in.
this is for flat out performane, when a restrictor is often used, its a way around the restrictor--having enough air available to cope with a few seconds of snap acceleration.
thats before u start saying a standard one isnt even that big.......

Forum Moderator Joined: 16 Feb 2004 Posts: 1356

I am quite aware that the AX is a 1.4... its a joke. Don't get so uptight wee man. Wink

Forum Moderator Joined: 16 Feb 2004 Posts: 1356

And the induction stroke for the F7P is not 450cc if the Displacement is 1764 is it?

Gay Rights Activist Joined: 07 Apr 2004 Posts: 1268

aahhh jesus!!

it was a quick calculation....i used 1.8!!

Forum Moderator Joined: 16 Feb 2004 Posts: 1356

I do not agree with your understanding. Just because the engine can engulf x amount of air per minute at full revolutions, does not mean that if that whole amount is not available constantly that you will get a an airflow restriction.

Gay Rights Activist Joined: 07 Apr 2004 Posts: 1268

"that whole amount is not available constantly that you will get a an airflow restriction."

if it isnt there, it cant have it, hence cylinders arnt filled as much

Forum Moderator Joined: 16 Feb 2004 Posts: 1356

Yes but your calculations are for max airflow over a period of time (60 seconds). By whole amount I mean the 14x the engine capacity that you say. The car can only use 441cc of air uncompressed per intake stroke, so the other 26019cc that is sat in the plenum is unused until the next inlet.... there is no way in my mind that you need 14 times the engine disp sat in the plenum. So whether or not you have a lot of air in the plenum of not, the engine is still going to compress the same amount, and that 441cc is still going to get drawn in by vacum regardless of inlet manifold litreage.

Forum Moderator Joined: 16 Feb 2004 Posts: 1356

Sorry if that don't make sense to you folks, I don't have the Auto vocabulary that you lot do

Gay Rights Activist Joined: 07 Apr 2004 Posts: 1268

"The car can only use 441cc of air uncompressed per intake stroke"

this is per induction stroke, there are 2 every revolution, and so there are 67 induction revs in a second (at 8000RPM) so in total its around 30150cc.

so for every second the engine is running at 8000Rpm, it needs 30150cc of air. this is however assuming 100%V.E. so in reallity its going to be a bit less, 85% perhaps, so around 25627cc's is required (cos this is how much the engine physically takes in).
this makes 14x1800=25200 far more realistic than 1.5 x

Forum Moderator Joined: 16 Feb 2004 Posts: 1356

By two per revolution do you mean two at the same time?

Gay Rights Activist Joined: 07 Apr 2004 Posts: 1268

no.
it takes 2 revolutions for a 4stroke engine to complete its cycle. this means on a single cylinder there is an induction stroke every other revolution. however, with four cylinders, on one revolution, there are 2 induction strokes.

Forum Moderator Joined: 16 Feb 2004 Posts: 1356

So if thats the case why don't you see perfomance cars on the road and in sport with huge tanks sticking out the side with a tiny nose cone on the end? It would be like having a small fuel tank stuck on the front of the lump