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MG MGB Technical - Hissing K&N's?

i've just fitted a pair of K & N air filters, the alloy type, as reported by most the intake noise is much louder. I also have a hissing as the i put peddle to the metal, and the carbs pull in air, is this just the K & N's letting more air in & working normally?
Scott Ralph

Sounds normal.

The hissing isn't coming from air being pulled through the filter element - it's coming from the
carburettor throat itself. If you drove around without any air filters at all (not recommended), the
hissing will get louder still.

The stock Cooper air filters are fully enshrouded in a metal housing, and this not only help keep
ambient dirt off of the element, it also dampens sound.

Most aftermarket units have the filter element exposed and have little sound dampening.

If the hissing is bothersome, K&N makes filter elements that fit inside the stock Cooper cans.
Daniel Wong

One thing you have to watch out for when installing K&Ns is that there is more than one type of installation.

There are pancake style filters with chrome plated stamped sheet metal plates front and rear (in relation to the mouth of the carb). The others generally use the same filter element as fit the stock air cans, but use some sort of outer end plate(s) and re-use the cast aluminum back plate used with the OE air cans.

The latter type make use of the cast back plate because it is an easy swap, AND because it has an integrated velocity (stub) stack designed for efficiency and smoothing of the air flow into the carbs, producing a bit more horses and torque and, coincidentally, less noise.

The pancake style does not come with any sort of velocity/stub stack and as the air enters the throat of the carb, the air entering from the sides does not do so smoothly and, just like some whistles, will shriek as it has to negotiate that rather sharp turn into the carb at higher speeds. Obviously, this will create a bit more noise than if a velocity/stub stack had been used.

If you absoulutely, positively have to use the pancake style K&N units, then get the stub stacks from outfits like 7 Enterprises or APT or modify the chromed sheet metal back plate provided by K&N to accomodate the OE cast back plate. A nibbling tool will allow your to carve a hole the same size as the hole in the OE air can back plate.

Good luck!
Bob Muenchausen

This thread was discussed on 12/02/2002

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