Air filter size

[The AJP Griff]

Hi all,can somone tell me how you calculate air filter size for a known BHP please?

[stevieturbo]

I dont think there is any simple way. Some filters flow and perform better than others, so no one equation would suffice.

K&N and Green to give indications on their website for their own filters though.

[K13 WJD]

you can calculate it. but why.

You'd have to know the exact intake volume at max RPM. then you'd have to know the capacity for airflow from the filter.

Fairly simple calculation.

However, in reality, a great big whacking filter might not make any more power than a smaller version. my bitch likes something to suck on.....if you know what i mean

[GreenV8S]

I think you can get a rough idea of the maximum power you can get from a filter before the restriction starts to become a problem, but you will probably size the filter way above that anyway. The main difference from changing the size (as long as you keep it above that minimum) is how long the filter lasts before the extra restriction from clogging becomes a problem.

[knighty]

I remember sizing an ITG triple layer foam filter for a 270bhp 4 pot a few years back........I think they said something like for every 4bhp, use 1 square inch of filter area......but I would phone ITG and clarify that figure as I'm well rusty on the subject......they are a very helpful mob with such questions

[K13 WJD]

here here......itg are, i also remember getting a 1 off filter made by them........For a straight 6 MX-5. a while ago now right enough !

[The AJP Griff]

Cheers for the replies all.The 1 inch/4hp type of calculation is the sort of thing what i was looking for,so i'll call ITG to confirm.

[CRE]

Hi Mike,
Yes the 1" Sq per 4bhp is a good rule of thumb, I too got this figure from ITG.
Very helpful blokes (but then I did used to work for their boss playing with blown rangies!)

Jamie

[HarryW]

Not a bad formula in here http://www.rpmoutlet.com/formula.htm it assumes the engine is a pump and the unrestricted volume of filtered air required by that pump, as opposed to a specific power output.

[rev-erend]

Don't know if any of you follow motorbike developments .. but for the last 10 years or so the after filter air chamber volume has been about the same as the fuel capacity.

No link intended or implied .. but what is important is that a one litre bike is having an air supply of 25 litres.. all available the other side if the butterfly but it's available filtered air.

Now - it's not easy to create a vaccum - so if you remove a lot of air - it gets replaced..sufficent filter area needed.

Imagine Linford christie without the big lungs .. not so fast.. but with big lungs..