M20 RHD ITB Plenum and filter sizing

[zaq123]

Based on calculations, my 2.9L needs about 82 in.sq. (52864 mm.sq.) air filter surface area (based on about 200 bhp, 6700 rpm peak power and 7000 red line). That's actually pretty big cone filter that barely fits between ITB plenum, top radiator hose and ABS pump. Very tight fit, I'm trying the cone filter that has 152/130mm for the top/bottom outside diameter and 133mm tall. That's about 89 in.sq (57556 mm.sq) of the filter area
Am I approaching this correctly?

I've noticed some folks are using something small like this (pic below) and it makes me question if I'm missing something. What's your take on the subject?

[ForcedFirebird]

To find the actual filter size, you would need to cut it open and open the accordion, then measure. Can't remember if it was here or another site, but someone took the time to cut open a bunch of filters, not only measured them, but flowed them as well. I believe the OEM filter had the most area and was up there in flow.

[It's Soda Not Pop]

You might consider calling RHD or email them. I'm sure they will probable know what you need. You might can rig up a big enclosed filter box to fill up that area. That way you would also get cooler air from outside the engine bay.

[It's Soda Not Pop]

Also this is exactly what I want to do to my E30. What an absolute unit.

[digger]

may need an elbow to point towards the headlight and go above ABS module

https://www.knfilters.com/dimsearch

https://www.knfilters.com/search/universal/round-tapered-universal-air-filter/viewall

i use this one but i use a different plenum so you wont be able to use it but atleast get an idea of area

https://www.knfilters.com/ru-5060-universal-clamp-on-air-filter

[It's Soda Not Pop]

I like this idea

[digger]

Yes, open cone filter is far from optimal.

[zaq123]

To find the actual filter size, you would need to cut it open and open the accordion, then measure. Can't remember if it was here or another site, but someone took the time to cut open a bunch of filters, not only measured them, but flowed them as well. I believe the OEM filter had the most area and was up there in flow.

K&N gives this formula in their FAQs for the area cals. I assume that 20839 number already counts for filter folds/the accordion and their filter material properties . With the cone filter, one just has to average top and bottom diameter and plug the average as D. I'm thinking to use AEM dry cone filter but I'm sure there isn't much difference in that 20839 constant

https://www.knfilters.com/faq/

And also there is this calculator (link below). Although I'm not sure what parameters their are using: https://strikeengine.com/air-filter-...for-power-bhp/

[zaq123]

I like this idea

for 1.8, maybe that box hs a filter big enough for its needs. I don't think one can fit something suitable for 2.9L in that enclosure unless there is no headlight or ABS pump.

[It's Soda Not Pop]

for 1.8, maybe that box hs a filter big enough for its needs. I don't think one can fit something suitable for 2.9L in that enclosure unless there is no headlight or ABS pump.

either way if it could be made larger I think this is a nice OE+ type option.
Also this on a M20 that is a 2.8 I believe. It's from Speedhunter.

[digger]

the s54 panel filter is 75sqin and is not restrictive on 338hp don't over think it too much

[zaq123]

the s54 panel filter is 75sqin and is not restrictive on 338hp don't over think it too much

I used that site calculator, not k&n formula so 82 maybe a little excessive for 2.9.

s54 filter size that you gave is actually spot on if you run it based on k&n formula: A= (198CI x 7900 rpm) /20839 A=75 sq.in. of filter area

So it looks like I would need at least 57 sq. in filter which is still good size filter

[digger]

I used that site calculator, not k&n formula so 82 maybe a little excessive for 2.9.

s54 filter size that you gave is actually spot on if you run it based on k&n formula: A= (198CI x 7900 rpm) /20839 A=75 sq.in. of filter area

So it looks like I would need at least 57 sq. in filter which is still good size filter

Factor the 75 down by ratio of your expected hp vs s54 hp and it’s like 60. So a 5” diameter cylinder 4”long. The equivalent cone should fit.

[_lestat_]

Based on calculations, my 2.9L needs about 82 in.sq. (52864 mm.sq.) air filter surface area (based on about 200 bhp, 6700 rpm peak power and 7000 red line). That's actually pretty big cone filter that barely fits between ITB plenum, top radiator hose and ABS pump. Very tight fit, I'm trying the cone filter that has 152/130mm for the top/bottom outside diameter and 133mm tall. That's about 89 in.sq (57556 mm.sq) of the filter area
Am I approaching this correctly?

I've noticed some folks are using something small like this (pic below) and it makes me question if I'm missing something. What's your take on the subject?

Older post however still interesting. What route did you eventually go?
I ditched the carbon plenum.