Intake whistle through K&N filters

[Ralph Morgan]

Can anyone offer a solution,or at least a suggested cause, for the annoying inlet "whistle" I get on wide throttle openings? Engine is a newly installed 1.8 Zetec, with 40 DCOEs and new K&N filters. I've tracked it to the air filters, and checked everything for tightness, thinking it could be due to air being drawn past the backplates. I've also checked clearance between the inlet trumpets and the filter end plates, but this seems OK at about 35mm. Any other ideas? It's an annoyance, at least, especially as the engine is generally so smooth after the Crossflow it replaced.

[Julian Thompson]

Very interesting. Remove the filters very briefly and see if the noise goes.

 

Read some of the stuff on the "longer trumpets, colder air" thread; I wonder if your filter plate is creating some kind of resonance?

 

Of course it could just be a simple pipe off somewhere or other misc. item but I'd be interested.

[stevefoster]

Have you got the new style moulded one piece carb to inlet manifold 'O' rings?

There are really for 45 size carbs and can cause a reed effect on the air passing them, expanding and contracting to enter the manifold.

It was so bad on my previous car I put the old ali plated 'O' ring solution back on. Problem solved.

 

This could be you problem.

 

/Steve

 

My racing pics, 7 DIY, race prep. Updated often here

Hants (North) and Berkshire area club site

here

 

[stevefoster]

Have you got the new style moulded one piece carb to inlet manifold 'O' rings?

There are really for 45 size carbs and can cause a reed effect on the air passing them, expanding and contracting to enter the manifold.

It was so bad on my previous car I put the old ali plated 'O' ring solution back on. Problem solved.

 

This could be you problem.

 

/Steve

 

My racing pics, 7 DIY, race prep. Updated often here

Hants (North) and Berkshire area club site

here

 

[Ralph Morgan]

The carbs are new, and have the alloy sheet/rubber ring spacers between carb and manifold (I think they've got a trade name that I can't recall at the moment) The old carbs on the Crossflow that I replaced had cast alloy spacers with O-rings fitting in grooves. Trouble is I got rid of those with the manifold when I sold all the bits from the X-Flow so can't try them! Seems possible that the problem is in this area, though. Must affect mixture strength/consistency too, if air is being drawn in here? I'll try tightening the fixing nuts a bit as a start (although I'm aware that they mustn't be too tight otherwise there are problems of float vibration and fuel foaming). The thread on "longer trumpets, colder air" actually prompted me to post this query, but I'll re-read it to see if there are any pointers there.

[stevefoster]

The ones you describe are the whistling ones! They are really for DCOE 45's!

I have a set of 2nd hand DCOE 40 ones if you are near you can try them...

Whereabouts are you Ralph?

 

Tightening them won't help. Air is not leaking the rings are sealing ok. It's the air expansion into the

larger gap and then contraction to go into the inlet manifold that makes the noise!!

 

/Steve

 

My racing pics, 7 DIY, race prep. Updated often here

Hants (North) and Berkshire area club site

here

 

 

Edited by - stevefoster on 14 Nov 2002 20:39:27

[simonstevens]

my nephew had a new corsa and in true boy racer style fitted a k&n induction kit which sounded lovely at full chat but when the engine was warm the filter made a quiet farting noise!!!! he changed it for a pipercross and all was good it also sounded much better on song!!!

[Noel Mclaughlin]

For what its worth , I once fitted a Holley 4 barrell carb onto a V8 that I once owned and had a high pitched whistle develope after I did it. after taking weeks to work through all the usual "vaccuum leak" type causes in desperation I put the car on a chassis dyno and ran it whilst crawling all through the engine bay with a piece of hose in my ear trying to trace the source. It turned out to be a slight sharp edged step between the carb adaptor and the throat of the inlet manifold. It may be that the Oring plates referred to by others are giving a similar effect to my situation. It sounded like Tweety bird and his extended family all shouting at once, this in spite of 5 litres of V8 barking away producing in this case about 300 hp, noisy enough in its own right .

[Ralph Morgan]

Steve,

 

I'm in Swindon (well, someone has to live there!). I would be happy to buy them from you (or "borrow" them and buy some new ones if they work) - contact me offline on: morganr4@bp.com or 01793 762937 (home number) if you get a moment and lets see if we can sort out something. I'm kicking myself for letting the old items go with the crossflow inlet manifold when I sold it!

 

(As a thought - we've got some friends coming over on Sunday and they live in Little Sandhurst - is this anywhere near you in North Hants? I'm sure they would pick them up and bring them over if it was not too far out of their way)

 

Cheers,

 

Ralph