air fillters

[jerseyvixen]

any one used webcons low profile air filters the ones that go onto the trumpets
have you had any problems thinking of fitting to race tuned 1760 xflow
thanks

[rev-erend]

These ones ?



http://www.webcon.co.uk/

They look useful..

[stevieturbo]

Useful perhaps. But any filter that sits so close to the trumpet mouth, massively reduces airflow.

Ideally you'd want at least the bore of the trumpet space available above the trumpet. I think ideal is at least twice that figure though.

[Mr2Mike]

My friend has the equivalent Pipercross filter on his Pug 205 rally car and that is (or rather was) producing nearly 280bhp from a 2.0L engine. As long as there is at least a couple of cm between the trumpet and the inside of the filter you should be fine.

[Simon Says]

If your on twin 45;S 0R 48'S you will need more than 20mm of clearance between trumpet and filter i can tell you that much 40mm would be nearer the mark try http://www.pipercross.net/competition/products_px6...

[Pumaracing]

stevieturbo said:

Useful perhaps. But any filter that sits so close to the trumpet mouth, massively reduces airflow.

Ideally you'd want at least the bore of the trumpet space available above the trumpet. I think ideal is at least twice that figure though.

Actually no, this is a common misconception but maths comes to the rescue. Assume a straight pipe rather than a flared bellmouth and the area of the pipe is Pi D^2/4. The area of the annulus around that pipe between it and a filter wall is Pi D H where H is the clearance.

If D^2/4 = DxH we get D x D /4 = D x H so D/4=H in other words the area of the annulus equals the area of the pipe when H = D/4.

So a 40mm rampipe would only need a 10mm gap to the nearest wall to have an equivalent flow area. With a flared bellmouth H can be even less because the area of the annulus is proportional to the o/d of the bellmouth not the i/d.

In practice if the clearance is even half the bore i/d then the flow area of the annulus is way bigger than the flow area of the pipe so no restriction occurs. It's not uncommon for rampipes to be situated very close to filter walls for resonance purposes without creating a flow restriction.

What does create a massive flow retriction is filter socks that sit adjacent to the bellmouth end so only the area of the bellmouth is filtering air. As long as the filter sits a good bit off the end of the bellmouth it all works out ok.

[Pumaracing]

There's a very interesting tech article on induction system mods here.

http://autospeed.com/cms/A_0629/article.html

Go to part 4 and you see a rampipe inside an air filter box which is near as dammit touching the airbox wall. The author presumed this would cause a flow restriction and made a new shorter rampipe that sat a good inch or more from the filter box wall. He ended up worsening the induction system flow.

Food for thought.

[spend]

Pumaracing said:

There's a very interesting tech article on induction system mods here.

http://autospeed.com/cms/A_0629/article.html

Go to part 4 and you see a rampipe inside an air filter box which is near as dammit touching the airbox wall. The author presumed this would cause a flow restriction and made a new shorter rampipe that sat a good inch or more from the filter box wall. He ended up worsening the induction system flow.

Food for thought.

I thought that was only relevant to the length of the runner behind the bell mouth. Other articles have proved that a length of consistent smooth dia into AFM's (etc..) is quite critical. sting the airbox wall away from the trumpet would have given totally different results IMHO.

[Mr2Mike]

spend said:

I thought that was only relevant to the length of the runner behind the bell mouth. Other articles have proved that a length of consistent smooth dia into AFM's (etc..) is quite critical.

That's only because hot wire AFMs are sensitive to turbulent flow, and too much turbulence can really mess up the fuelling. I know someone on who tried putting the AFM directly on his turbo inlet (probably about the worst place possible) with predictably poor results; the car would barely run past idle.

What most people don't realise is that the bulk of the airflow going into an open pipe, especially one with a bell mouth, enters at an angle from the side of the inlet rather than a straight shot from right in front of it. This is why you can get such an inlet so close to a flat surface with negligible change in flow.