Plenum size vs intake size
Discussion
Logic tells me that as I have a 72mm plenum (with no AFM); the inlet pipe from the air cleaner to the plenum must also be at least 72mm: however is there any point going any bigger. Assuming the air filter is 100% efficient and has no pressure drop at WOT, is a matched intake diameter to the butterfly size ideal?
I am aware of a range of modified intakes/plenums to maximise air flow.. and reported increases in bhp.. however is it correct to assume the butterfly diameter in the plenum (as the narrowest point) is the point of most air flow restriction.
Reason for asking is I am working on putting a pod air filter in the LHS guard.. and have found suitable air intake ducting that has an inside diamter of 72mm.
A larger diameter pipe means a larger air reservoir is available .. however I am unsure if a 72mm inlet pipe is too small in diameter.
I am aware of a range of modified intakes/plenums to maximise air flow.. and reported increases in bhp.. however is it correct to assume the butterfly diameter in the plenum (as the narrowest point) is the point of most air flow restriction.
Reason for asking is I am working on putting a pod air filter in the LHS guard.. and have found suitable air intake ducting that has an inside diamter of 72mm.
A larger diameter pipe means a larger air reservoir is available .. however I am unsure if a 72mm inlet pipe is too small in diameter.
From what I've seen there are typically 10-2xbhp losses in the filter - plenum pipework. How you claw some of that back is open to interpretation, words like big, straight, short, smooth, cool are all you can keep in mind IMHO, as all the solutions will to some extent be some kind of compromise.
Go up in size if you can fit it in.
Std pipe in 3" diameter will give you approx 10% in area but you won't be restricting things too much with 72mm pipe, make some pressure measurements over the pipe length when you're done ( at full revs and throttle) that will tell you if the pipes big enough
Std pipe in 3" diameter will give you approx 10% in area but you won't be restricting things too much with 72mm pipe, make some pressure measurements over the pipe length when you're done ( at full revs and throttle) that will tell you if the pipes big enough
)Here's an update:
At WOT (5800 rpm) with just my ACT elbow fitted to my 72mm plenum, I see at pressure drop of abt 1 kpa.. (100kpa barometric vs 99 WOT)..
So I am getting 5-6kpa drop at WOT in my air intake. I currently have 75mm (3") Silicon pipe from elbow to the standard air clean box.
Plan is to dump the std air box by putting a pod filter in the wing, then use the 75mm silicon pipe to connect filter to elbow.
At WOT (5800 rpm) with just my ACT elbow fitted to my 72mm plenum, I see at pressure drop of abt 1 kpa.. (100kpa barometric vs 99 WOT)..
So I am getting 5-6kpa drop at WOT in my air intake. I currently have 75mm (3") Silicon pipe from elbow to the standard air clean box.
Plan is to dump the std air box by putting a pod filter in the wing, then use the 75mm silicon pipe to connect filter to elbow.
cinquecento said:
Here's an update:
At WOT (5800 rpm) with just my ACT elbow fitted to my 72mm plenum, I see at pressure drop of abt 1 kpa.. (100kpa barometric vs 99 WOT)..
So I am getting 5-6kpa drop at WOT in my air intake. I currently have 75mm (3") Silicon pipe from elbow to the standard air clean box.
Plan is to dump the std air box by putting a pod filter in the wing, then use the 75mm silicon pipe to connect filter to elbow.
Could you explain where the figures come from again? You seem to be measuring a 1kPa drop, where does the 5-6kPa you mention come from?At WOT (5800 rpm) with just my ACT elbow fitted to my 72mm plenum, I see at pressure drop of abt 1 kpa.. (100kpa barometric vs 99 WOT)..
So I am getting 5-6kpa drop at WOT in my air intake. I currently have 75mm (3") Silicon pipe from elbow to the standard air clean box.
Plan is to dump the std air box by putting a pod filter in the wing, then use the 75mm silicon pipe to connect filter to elbow.
Do you still have an air filter attached? You can easily lose several kPa just across the filter. The dynamic pressure drop across a 72mm choke would probably be around 1.5 kPa and if you still had an AFM the pressure drop across that would be a lot higher (haven't measured it but back-of-the-beermat calcs suggest around 6 kPa total for a 50mm choke).
Edited by GreenV8S on Saturday 5th September 17:51
Pete: Yes.. I could have been clearer...
The background to this is: with air filter and inlet ducting in place, I am dropping 5-6 kpa on ambient above 4800 rpm at WOT. I have no AFM (running MS)
When I just have the 90deg elbow connected (so no ducting and air filter), I only drop abt 1kpa on ambient above 4800 rpm at WOT.
Interstingly with no ducting/air filter I see a 2kpa difference at idle: 39kpa at 800rpm (I'm at see level) vs 41 with filter attached.
Eliot: Thanks for the tip.. I'll stick the IAT sensor in the wing and see how it goes..
Thanks for all the feedback..
The background to this is: with air filter and inlet ducting in place, I am dropping 5-6 kpa on ambient above 4800 rpm at WOT. I have no AFM (running MS)
When I just have the 90deg elbow connected (so no ducting and air filter), I only drop abt 1kpa on ambient above 4800 rpm at WOT.
Interstingly with no ducting/air filter I see a 2kpa difference at idle: 39kpa at 800rpm (I'm at see level) vs 41 with filter attached.
Eliot: Thanks for the tip.. I'll stick the IAT sensor in the wing and see how it goes..
Thanks for all the feedback..
Gassing Station | Griffith | Top of Page | What's New | My Stuff