Bob Tunnell offers a custom FlowMaster exhaust. The fact that Bob uses something other than the factory piece strongly suggests that it brings something to the table. I've previously had good experiences with FlowMasters on American iron. Bob provided various relevant information in the course of responding to some questions I posed:

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I produce two different models: one with a regular 2-chamber FlowMaster for $300 and one with a DeltaFlow 2-chamber FlowMaster (quieter) for $340. Both feature a 2-into-1 collector immediately behind the cats with a 3" pipe leading to the muffler in the OEM location and using OEM mounting hardware. The muffler exit has a 3" round tip in the center of the OEM location. The entire construction is galvanized steel and weighs about 26# (about half the stock M3 system).

It is designed to flow at virtually the same rate as the OEM exhaust. The reason I didn't open up the flow is to preserve low-end torque which is critical in autocrossing and essential for smooth street driving. Most aftermarket units reduce back pressure to the point that peak horsepower might be increased, but at the expense of low end power.

I occasionally drive my M3 cross country to events and the exhaust note of the standard FlowMaster muffler is a bit more noticeable than I'd like for long distance driving, but it's perfect for racing. The loudness is completely rpm related so unless you're driving around town at WOT it's not really loud enough to attract the police. I drive in front of the police station for our area frequently and they never give me a second look. I have set off a car alarm or two driving through parking garages, but I think it has far more to do with harmonics than loudness.

But if your car is primarily for street use, I'd suggest using the DeltaFlow model of muffler which is considerably quieter inside and outside the car. FlowMaster charges $40 more for those mufflers so I have to pass it along.

I want to emphasize that this is a performance exhaust and I make to representation about it being OEM-quality. It is not designed to be pretty and I'd characterize its appearance as "industrial" and "functional." [Didn't look too bad to me from the accompanying JPG -- not to be mistaken polished stainless steel though). I've used them on many race cars and a couple street cars, and have yet to have one fail, however, I sell them without warranty of any kind.

The OEM exhaust system is very, very good power-wise. In fact, of all the aftermarket systems TC Kline has dyno'd *none* put out better torque than the OEM unit."

"My goal in talking to the engineers at Flowmaster was to merely *match* the power of the OEM unit, but try to save some weight. My cat-back unit weighs about 26 pounds and the OEM unit weighs a little over 50 so I met my goal big
time."

Did you ever dyno the Flowmaster? No, not yet. But I have done before and after acceleration runs using a g.analyst and the FlowMaster is *slightly* faster than the stock unit. Again, all I cared about was not *losing* any power, so a "slightly" faster unit was a big and pleasant surprise."

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I am not in any way affiliated with Bob Tunnell, Flowmaster, etc. However, I continue to strongly consider getting one of these units. Anyone on the List with any direct experience with this FlowMaster exhaust?

Lew Becker

• Original Message ----- > Date: Thu, 30 Nov 2000 20:53:26 -0700

  > From: "Rob" <motor_at_cadvision.com>
  > Subject: Honest power gains with perf. muffler?
  >
  > I know most people on the list have aftermarket exhaust systems on
  their

  > M3's but I suspect many did it for looks, sound and or weight savings. Who
  > has personally dyno'd their cars pre and post exhaust install to check for
  > power gains?.
  > I know what all the mfg's claim for power gains (5-8hp) but I'd like to
  hear

  > it from individual owners. I'm not looking for anything but power and need
  > to decide if its worth spending ~$600.
  >
  > TIA,
  > Rob