Caterham R300D K&N Air Filter

[rotorwings]

I recently bought a K&N air filter (model 33-2036), which is listed on the Caterham parts site as "AIR FILTER R300 RACE CAR 33-2036", for my R300D.
Link: http://caterhamparts.co.uk/product.php?id_product=...

The problem is that the width of the filter is perhaps 2-3mm to narrow and this would allow air to bypass the filter in a couple of places. .

Are there multiple sizes of air-boxes out there? Or is there some trick I am missing?

[David Rowe]

You have a sharp eye, not many have spotted this.

You need a k&n filter part number 33-2409 which is correct for the air box and provides a perfect seal. The other part number is incorrect.

Regards
David

[rotorwings]

David Rowe said:

You have a sharp eye, not many have spotted this.

You need a k&n filter part number 33-2409 which is correct for the air box and provides a perfect seal. The other part number is incorrect.

Thanks David.

One other part of the fit that didn't seem to work was the thickness of the rubber surround. This seemed to this on the filter I had, so the airbag didn't really clamp down on the filter seal.

Does this one have a thicker (higher) rubber surround?

[David Rowe]

Yep, the seal height is higher. This is the correct air filter for the airbox now, it's standard fiitment.

Regards
David

[rotorwings]

David Rowe said:

Yep, the seal height is higher. This is the correct air filter for the airbox now, it's standard fiitment.

I got one of those filters and fitted it tonight. The outside dimensions are perfect for the air-box, but the seal height is not. It is actually thinner than the seal on the paper Ford filter that was fitted originally.

I ended up adding 3mm of sticky-back neoprene rubber to the filter to just to get it to touch the top part of the air-box and then another 3mm to the air-box to create a snug fit. But after 6mm (total) extra rubber to pad it out, it now fits perfectly.

People should take a careful look at their filter fitment, there may be more than a few without a proper seal.
I wouldn't be surprised if every air-box is somehow unique either. To Caterham, QC is just a fancy lawyer.

[David Rowe]

Glad I could be of help.

I have fitted a few of these filters to include 6 new R300 builds and each one didn't need any kind of packing around the filter. I would suggest you have a problem elsewhere if you need foam packing to achieve a good seal. It's not required.

[rotorwings]

David Rowe said:

Glad I could be of help.

I have fitted a few of these filters to include 6 new R300 builds and each one didn't need any kind of packing around the filter. I would suggest you have a problem elsewhere if you need foam packing to achieve a good seal. It's not required.

The gap between the upper and lower part of the air-box when all screws are tightened and the surfaces are hard up against each other is 10mm.
The height of the filter rubber that sits between the two surfaces is 7mm.
That's why I needed 3mm of neoprene added to the underside of the filter to make it even touch the top, then I added another 3mm the the lower air-box case to give a snug fit.

Unless my air-box is different, these filters are not providing a proper seal. Even the Ford filter that comes std. is 10mm high around the seal. Really, even the ford filters are probably not mating perfectly.

Has the air-box design changed since 2012?

[rotorwings]

rotorwings said:

The gap between the upper and lower part of the air-box when all screws are tightened and the surfaces are hard up against each other is 10mm.
The height of the filter rubber that sits between the two surfaces is 7mm.
That's why I needed 3mm of neoprene added to the underside of the filter to make it even touch the top, then I added another 3mm the the lower air-box case to give a snug fit.

Unless my air-box is different, these filters are not providing a proper seal. Even the Ford filter that comes std. is 10mm high around the seal. Really, even the ford filters are probably not mating perfectly.

Anyway, with my modifications it will work fine.

Has the air-box design changed since 2012?