98 legacy induction hum issue

[jonnywombat]

I have a 98 legacy 2.0 gls (uk spec). (Normally aspirated)

 

I fitted a universal induction kit, made up of an adaptor plate, gaskets, and a cone filter

 

I fitted it and removed the standard air box, and also fabricated a bracket to stop the filter flopping about.

 

When I started the engine the was a loud whistle/hum/howl from the induction system (in the region of the MAF sensor). The car ran fine, but had this hum which died off under load.

 

All the plumbing from the throttle body up to and including the MAF is standard.

 

This howl was so loud I have refitted the original airbox (and this stopped the hum).

 

Is this a known issue, and if so is there a work around, coz it made quite a difference having the hi flow filter fitted.

 

Thanks in advance

 

Jonny

[nipper]

This is not a known issue, its just physics. We have gotten spoiled by new cars. Older cars with 4 bbls when the secondarys would open, it would sind like a jet plane taking off. A hell of a lot of air moves through an intake manifold, its going to make a lot of noise. $ cylinders also have a "roar" to them at specific rpm ranges, its a unavoidable charecteristic of a 4 cylinder engine. Subarus do a good job of muffling this noise, but as you found out it does exist.

 

Factory intakes are engineered about as good as its going to get. They are a compromise due to noise standards, customers desires, and performance. They breathe very well.

 

Cone filters may breathe better, but at a price. They allow more dirt into the engine. They are usually have some sort of oil impregnation, which will annoy the electronics (or damage them). For the few HP gain you get they really arent worth the trouble.

 

nipper

[86BRATMAN]

That sounds normal, my mom's 98 2.2 Legacy has done that from day one of the intake mod.

[Hotshot]

Subaru engines really don't see much gain from changing the air filter, but if you do want it sounds a little better, you could always just pull out the intake silencer and run a piece of hose from the airbox into the fender. I am quite pleased with the results of doing only this to mine.

[jonnywombat]

HI there,

 

Thanks for your replies.

 

I appreciate what induction noise is, I have years of experience preparing and modifying vehicles on two and four wheels, this noise in not normal induction "roar" which i would find desirable.

 

This noise is the same as the noise you get when blowing across a bottle top, (except much louder) and I guess it is being caused by resonance in the plastic air box/pipes, or something within the MAF sensor housing vibrating.

 

As I found a noticeable gain in performance with increased low down torque, and a little more top end power, I propose the replace the air box/ducting system from the throttle bodies back and fabricate my own out of 3 inch silicone hoses.

 

Thanks for your help, and if anyone has any pointers for construction then I would appreciate them.

 

Jonny

[Hotshot]

Just make sure you take lots of pictures, and let us know how it turns out.