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MG MGF Technical - Resonance and the K&N


Just thinking about the induction properties of the K&N.

When you open the throttle from low revs, you sometimes get the whole assembly to resonate, in a way that the standard filter, with it's more compliant hose to the throttle body, does not do.

If it resonates, presumably the air flow is going to be less smooth through the assembly.

If you swapped the rubber mounting pipe with a more compliant material, and mounted the cone filter to a hardpoint in the engine bay, would you lose the air induction properties?

Raj Jena
Raj Jena


But would it sound as good!!!!!!!!!!!!!!!!!!!

Ted Newman

The vibration is secondary to the harmonics of both the engine itself on its engine mounts, and of the air travelling through it. Attempting to externally steady the filter will have no effect upon these route causes of the reasonance you describe, and in fact, the flexi-tube has appalling air flow characteristics because of those soft rubber involutions...

Perhaps the vibrations associated with a low engine speed would be better utilised by having a longer intake tract?
Rob Bell

Good point Ted 8-)

Rob - How does it compare with the ITG? I seem to remember someone saying that the ITG bolts directly onto the throttle body assembly.

Raj Jena P58 NVF
Raj Jena

The ITG should NOT bolt directly to the throttle body. Certainly, those installed by either Techspeed or PTP aren't- but have a 6 inch spacer tube- rather like the 57i.

How do they compare? Good question! The rolling road data is not so different- perhaps 1 or 2 bhp in ITG's favour. On the real road, then there probably is more advantage to the ITG installation. Being isolated from the engine's heat, the air intake is cooler and therefore denser = more power. Probably more than 5 bhp more power, and even more noticably, more mid range torque.

All this has nothing to do with the filters themselves. It is all to do with cold air, and an ITG filter enclosure with a K&N filter will perform just as well as an ITG filter. Moral of the story? At least shield the air filter- and better still, put it inside an air box.

Rob Bell

Or flowerpot, eh Rob?

Nice idea that, I'll have to get around to trying it.

Steve Childs

Exactly Steve. 1.19 from Homebase- plus I got a lid...

MGFlowerpot ;o)
Rob Bell

Next year:-

Baby K&Ns as grown by Rob in his greenhouse! Hardy perennials prefer part shade but will thrive in heat, water & feed occasionally with a mixture of 50% Alcohol and 50% Rainwater.

Ted Newman


Well, the owner/ gardener would thrive on the alcohol anyway!
Rob Bell

This thread was discussed on 20/06/2001

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