I've always been fascinated with active exhaust systems and how you could cruise with little exhaust noise, but open it up and have an awesome throaty roar. I was wondering if it is possible to fabricate one or if there is such thing as an aftermarket active exhaust system.

 

look up exhaust cutouts or "e-cutouts" see here

you could conceivably set up an RPM switch that would trigger it to open at a pre-set RPM or a reed switch at the throttle body to open it at a certain throttle angle. the later is probably easiest.

 

I imagine the the actually process of getting the baffles to open would be easy. If it were an electronic tach it probably uses variable voltages to display the rpms, so you could just set it to open at a certain voltage, which should be pretty easy. I'm more inquisitive about the actual process of opening the baffles. How would you go about actually creating an electronically controlled baffles system?

 

you don't. you buy it.

 

Oh. Totally my bad. I glanced at link and thought it was a throttle body and it confused me. Those are awesome though. Thanks!

 

My system wasn't active, but maybe I can share it anyway. I used this kind cut-off setup when I had a 2.5" exhaust. Direct replacement for catalytic converter and butterfly valve (QTP) is operated by switch.


It's starting 2.5" header flange and expand to the 3" diameter, cat-back connection is 2.5" like rest off the exhaust system.





View from the header flange:





I have to scratch my head when I fabricate it, but after all everything fits nice.





Ground clearance was also good, as you can see. Compare to the swaybar.





Here is overlayed graph how it performed. Cut-off versus 2.5" full exhaust with Vibrant resonator (8" or 10" long, can't remember) and Hytech 2.5" twinloop. Obviously 2.5" exhaust system wasn't optimal but at least it was quieter, lol.





This way also have a deficiency, when you tune your engine for that cut-off, it's not optimal when you run with restricted exhaust. Because engine doesn't breath as well, afr is richer.

 

How badly does it effect low end torque if you leave it tuned for the restricted exhaust? Does it still have enough back pressure to be beneficial, or is it purely for sound at that point?

 

Active Tail Silencer - Silencers - Exhaust

Vs

Control Valves - Exhaust

 

Dynomax has a pretty cool muffler, will do exactly what you want it to do.

DynoMax® VT® Mufflers - DynoMax® Performance Exhaust

 

Low cam torque/power curves are identical, as you can see, so there wasn't almost any effects. In other words, no need for tuning. High cam was a whole different story. This cut-off flowed even slightly better than 3" full-exhaust. Piping, mufflers etc. always resist flowing, but it is all about how much.
Back pressure isn't needed any situation.