E30 318i: Noisy exhaust gets a bung / silencer

My E30 has a 4" straight-through Japanese tuner style exhaust back-box fitted, which to the say least is LOUD. In fact, it's one of the loudest I've heard on any car, including a Subaru turbo I had with a de-cat pipe. I figured the centre-box had also been removed from the E30, given the noise level, but find it is still there under the car and looks to have been replaced not too long ago, so I guess the only reason for the volume from this 1.8 litre 4-banger is because it never had a catalytic converter from the factory and is subject to no emission controls that bind (and quieten) modern cars. This E30 is 1988, so must have been right at the end of this phenomena.

While the loud pipe might be fun on a jaunt, working on the engine at home I find myself needing to start and idle the car constantly for testing and this is where the noise causes a problem, mainly with my neighbours and passers-by. They tolerated it for a couple of weeks, but with a few running problems that are still being ironed out and the car unable to move to another location I decided to try and mute it a bit. 

I had two options. Buy a more sociable back-box or get a silencing 'bung' for the current one. I'm not best pleased with look of the Jap-style straight-cut end pipe, I mean I like them but don't feel it suits the boxy E30 and though I'm down with car style juxtapositions all DAY, this isn't the one I would have chosen, so first looked for a replacement. New stock items are not expensive, but too much for this project, so second hand was the way, with twin 'sports' style spurious back boxes and used OEM items going for between £50 and £100. I was tempted by a nice twin square pipe from a German tuner, but the seller had no idea how loud it was and at £55, I still deemed it too pricey at this uncertain stage in the project. People at work fit ‘bungs’ to their motorbikes so I thought this was budget way to reduce the burble by a few dB.

DOES IT WORK?

Yes and no. It certainly takes the edge off the noise level, that ‘crack’ has gone, but it’s still one loud exhaust. The info says it reduces sound levels by up to 15 decibels and I have adjusted to the quietest, most restrictive setting, but without a dB meter I can’t really say if it is that much. In my opinion it’s not to that great an extent but it is somewhat quieter. 

Don’t expect the exhaust to sound as quiet as a stock back box with baffle plates. I suppose you’re never going to get a quiet exhaust tone and still enjoy the slight increase in power a straight-through pipe gives, so as ever there is a compromise, but it has certainly done the trick for me of making the car less anti-social when tuning it in my driveway! Who knows, when I get the E30 out and about over the summer the bung may well be coming back out.