Sound
OK, I’ll admit it: I was after a nice exhaust note. I wanted to balance out the sound of the M42 intake with some exhaust rumble. And that was precisely the problem. How do you get a 4-banger to rumble? It isn’t exactly a 427 cubic inch Ford we’re starting with. We’ve all heard the buzzy, “mosquito on amphetamines” sound that results from sticking a “fart can” on the back of a Japanese econo-box. Yuck! That definitely would not do. I was looking for a low-pitched burble and something not too loud. After all, I didn’t want to completely drown out the intake whine I love so much. Also, I do a lot of road trips with this car, so I was hoping to avoid a droning exhaust note at highway speeds.
The Search
I started my search by posting on the several internet discussion forums I frequent. The consensus seemed to be that I would find the Ansa, B&B Tri-Flow, and Borla systems unsatisfying because they are all rather loud and have a raspy, metallic edge to their sounds. The Supersprint cat-back system looked like a good candidate, but at $470 USD it struck me as overpriced for a non-stainless unit.
I considered using a simple SuperTrapp muffler ($120-$200 USD). This is an old design that is well known in the motorcycle racing world. It basically consists of a long tube 4 inches in diameter with a steel core and some fibreglass packing material in between. You can adjust the flow through the muffler by adding or removing metal spacer discs. The more discs you add, the more air flows out between them, and the louder the exhaust note. The fewer the number of discs, the more backpressure, and the quieter the exhaust note. This looked promising: I could remove discs on the street to keep noise levels down, and then add discs when heading out on the track to maximize flow.
The problem with the SuperTrapp system is that it is very prone to rust. People who have used this system have reported significant corrosion after a single season! In theory you can tune the muffler by swapping discs in and out, but in practice this becomes impossible since the whole thing rusts solid. So you’re forced to make a compromise between good flow with an obnoxiously loud, buzzy sound vs. reduced power with a reasonably quiet sound. As I said earlier, I didn’t expect major horsepower gains from adding an aftermarket exhaust, but I certainly didn’t plan to lose any! It seemed the SuperTrapp would not suit my needs.
Rice, Anyone?
I finally came across a good candidate: the Dynomax “Super Turbo.” I can practically hear your jaws dropping! You’re probably thinking (as I was) that the Dynomax brand is closely associated with the Orange Julep riceboy scene. Didn’t I just get through saying I didn’t want that fart-can sound? Relax. I was assured by a fellow E30 318is fanatic and regular contributor to the old bmwe30.net internet forum that the Super Turbo was exactly what I was looking for. He promised it would yield a deep, throaty burble. I was skeptical, but the price was only $34.95 USD. I figured it was worth a try. After all, I could always throw it out and pick up a Supersprint cat-back system if I was dissatisfied.
When I went on-line to order the Super Turbo, I was surprised at the variety of options available. The one recommended to me was a 2.5 inch diameter model with offset inlet and offset outlet, so that’s what I ordered. It turns out the diameter I actually needed was 2.25 inch, but I wasn’t concerned since any muffler shop should be able to make it fit without any difficulty. The muffler arrived in the mail a few days later. The first thing I noticed was that it was two-thirds the size of the factory unit and only half the weight. So far so good.
I brought the unit to a local muffler shop and we discussed various options for mounting. They felt they would be able to bolt the Super Turbo to the factory mounting points and even use the stock muffler straps. Because of its small size, the Super Turbo sat pretty far from the rear valence when we tried this. So, our options were either to drill new mounting holes into the chassis to bring the body of the muffler closer to the rear valence or keep the muffler where it was and fabricate a custom tailpipe. I didn’t like the idea of drilling new holes, so I opted for a custom tailpipe. I was impressed: they used galvanized steel and mandrel bent it to fit the factory cut-out. Mandrel bending is preferable to simple crimping since it conserves the inner diameter of the tube, thus does preserving flow through the pipe. The new tailpipe fit perfectly and looks nice enough that it doesn’t need a tip (that’s a relief …aftermarket tips practically scream “rice”).
The Moment of Truth
So how does it sound? Great! The sound is remarkably subdued: it’s only marginally louder than stock, and there’s a very slight “burble” to the idle. Under acceleration there is a nice, deep growl as opposed to the raspy sound of some systems. There is no trace of the harsh buzz or highway drone that I’ve heard on so many aftermarket systems. This is exactly the sound I was hoping for. I was afraid the exhaust note would be too loud and overpowering, but it turns out I needn’t have worried. If anything, it could stand to be slightly louder.
My “butt-dyno” does not register any horsepower difference between this set-up and stock, but I wasn’t expecting any performance gains. I just wanted to balance out the sound of the car a bit. Now there’s enough exhaust growl to balance the intake whine up front. The first time I drove through a short tunnel, I just had to smile. This is one sweet exhaust for 35 bucks! Finally, a low-cost mod that actually does what it’s supposed to do! Maybe we can learn something from the riceboys after all.
Grand Master
Originally Posted by Dr. evil
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