I've just had a 2nd hand Hayward & Scott backbox fitted to my JDM Forester S/tb.

When the box is cold the sound is great, but once it heats up and you're driving at motorway speeds (70 to 90 ish) there is a low, boomy resonance which is really taking the edge off my enjoyment of the car... to the point I'm seriously thinking of refitting the original backbox. But I don't really want to do this, if it can be avoided.

At the moment I've got a Subaru centre section without catalyst or silencer. If this was replaced by a resonated centre would it help to resolve the problem? Or are there any other "cures" (partial or total) that anyone can suggest?

I realise that the resonance probably isn't as much of a problem in an ordinary scoob, but presumably wagon owners will have had similar issues.

 

Any ideas from peeps on the day shift?

 

I get some resonanse in my Impreza Wagon.. check the connections between centre and backbox is not leaking and tighten the connection bolts further.. I have found it tends to relax and come lose..

Resonator might help but cannot really be sure until you try it, would hate to say it would solve it and you spend the money to find it didn't.

I have H&S downpipe, centre and backbox.. I have put exhaust wrap on the downpipe to try and keep in cabin noise down slightly which I think helps but cannot be sure as I never ran it without it.
Refitting the centre section with the cat in if anything made it louder inside the car.. as the noise seemed to hang around in the cat and get transmitted through into the cabin.

Worth also checking the mounts are not touching the body work ewtc do you have a towbar? I do and mine will slowly move around until the exhaust mount it resting on the towbar and will the resonate louder.. I have moved the mounts and stiffened the rubber with cable ties.

You could exhaust wrap the backbox I guess that might help.

JGM

 

I tried everything I could think of including 4 different back boxes to get rid of the resonance on my MY98 which has a H&S downpipe (wrapped), Magnex "resonated" centre and H&S back box. The noise betwen 2500/3000 rpm drove me daft until I removed the resonator for another reason and noticed how tinny it was - tap it with a metallic object and it rings like a bell. Anyway, I wrapped it with some ladder tape that I had access to (it's used for lagging boilers etc) and covered that with thin aluminium sheeting to protect it (held on with jubilee clips) and refitted it to the car. The difference is unbelieveable with a nice deep note and 95% of the resonance gone . I daresay that exhaust wrap will have the same effect. Hope this helps.

 

PS: Very disappointed in Magnex...

 

Have you insulated the floor of the boot ? I used underlay to see if it made any difference, and it's still there

Steve

 

I fitted a full Noise Killer kit and it made no noticeable difference

 

I spent an hour last night putting Dynamat on the boot floor and particularly in the spare wheel well, that helped quite a bit (MY'97 Impreza Wagon)