Interesting. I thought they were cutouts that you could un-cap and bypass the second mufflers. Backpressure tubes makes some sense though.

wow. What the hell is that. Stick to the basics haha.

Looks interesting...

back pressure tubes? I would imagine those are more to achieve the right "exhaust note" rather then effect the overall velocity of the exhaust gases.
Correct me if im wrong here, but wouldn't narrowing the piping to increase exhaust velocity be more effective than adding "backpressure" tubes.

No. The whole point of backpressure tubes is that, past a certain exhaust velocity, they're bypassed. In other words, they're variable -- they give you backpressure at low rpm (which is where you want it), but don't restrict flow at higher rpms. If you just narrow the piping, you lose that variability. These tubes are really no different than what HKS did on their exhaust for the 350, so I'm not sure why everyone is so puzzled by these secondary tubes. (Well, maybe people haven't ever seen the HKS 350 exhaust or something.)

http://www.modacar.com/Merchant2/gra...reddy%20ti.gif

sounds mean. i would like to hear it at wot.

Semtex,

Thanks for the pic post as I wonder whether the 5Zigen does not have a similar setup when viewed underneath with the extra cans atop the actual mufflers? Can you please fly your private jet to Japan and find the answer for me? Inquisitive minds want to know. (Now watch AK smoke me on finding this out first.)

Active autowerke uses the HKS style for all of their high end exhausts too.

A side note on HKS. I believe in the most recent Grassroots Motorsports Magazine they tested several exhausts for the 335i and the HKS exhaust was their pick.

I believe those extra canisters on the HKS are for sound reduction and avoidance of drone.

"Backpressure tubes"? Forget what you've heard, but backpressure is a bad thing and kills power. Initialgemini had it right, as exhaust velocity is key. The key is to match pipe diameter to give the greatest exhaust velocity with the least amount of backpressure and of course matching to your power band. A narrow pipe will have greater velocity at low RPMs while a wider pipe will flow better at high RPMs so a well-designed exhaust will take this into account and should have a correct balance.

There's no need for separate piping if all you're looking to do is reduce sound -- that's what in-line resonators are for. Now, I want to be clear here. I am not vouching for the effectiveness of using separate piping for backpressure, I'm just explaining what the intent behind the design is. Personally, I think they're gimmicky. But believe what you want to believe. It doesn't make an ounce of difference to me.

My understanding of fluid dynamics is fairly basic, thanks for explaining.

From the marketing of the HKS hi-power exhaust, these extra canisters are for sound reduction and tuning. In this regard, they are similar to resonators. Search for "dead chambers" for more info on this.

Hmm...well that makes the design even worse, IMO. Extra piping = extra weight. If the right sound can't be achieved with the normal in-line resonators and mufflers, that's just not good. Just my 2 cents.

With regards to the SACLAM unit, it looks to me as though the HUGE resonators up front are what cures the drone, and the extra piping out back prevents the loss of backpressure.

Now, the HKS unit shown above looks like it serves both purposes by incorporating a "dead-end" with a resonator attached to it.

Also, backpressure isn't bad if its used correctly. For N/A applications, you need backpressure to prevent the loss of torque in free flowing exhausts. If you have too much though, then you will lose power. Think of it as a glass of red wine a day. In moderation, its actually good for you, but in excess its not. Horsepower and torque are both important IMO, and not just horsepower.

Hard data is what really would convince one way or the other...............where's the comparitive dyno chart, that and the weight numbers?