How to silence your exhaust without silencing your power

By Andre - dre99gsx

QTEC (Quick Time Electric Cutout) - By Quick Time
Contact: Barry or Ken at QuickTime Performance

There comes a time when us performance enthusiasts require more power. For us turbo gurus, that power increase requires good exhaust flow, but we are faced with a dilemma. Good exhaust flow = big exhaust. How big? Well, some of us guys run 3" exhausts (turbo-back). Some of us run 4". I, personally, run a 3.5" turbo-back custom exhaust system, which has proven itself over and over at the dyno and street. But, with the exhaust size, comes exhaust noise, and the inevitable exhaust noise TICKETS from your friendly police, as well as annoying the neighbors.

There are a few ways around the system, but it's a given that whichever way you go about silencing your exhaust, you will lose power. For example, take into consideration my 3.5" turbo-back system. This system has one mandrel bend (downpipe) followed by a "sewer-like" long tube to the rear, ending with a 4" Dynomax Bullet muffler. This thing is LOUD! At idle, it rumbles the house, shakes the mirrors, messages your back. At cruise, it drones at every RPM and loosens every damn bolt you thought was seized. At WOT, it sounds massive.

A few attempts were had at silencing the system. These included a 2nd muffler midway, a resonator, and a catalytic converter. All three plus the 4" muffler I currently run. How well did it muffle? I thought it muffled well, but the police didn't. I have since received 2 tickets for exhaust noise, and mind you on daily commute with this car, I barely take it over 4000rpm or 50% throttle. I'm a conservative driver 98% of the time.

Then I stumbled onto Quick Time. I was introduced to Barry who believed in this product, an electrically controlled cut out.

This cut-out has been used by quite a few, including the NASIOC (Subaru WRX) community. I immediately thought this would be the answer to my problem. WRONG ANSWER. For the cut out to work, I would have to open up the exhaust to air, bypassing all my mufflers. This is great for power, but I have an issue with going fast and making noise. The quieter you can be, the higher the chances you can slip under the radar, literally. Add to this an external gate "blatttting" out to air, and the noise becomes unbearable.

2nd solution: Create a catalytic bypass system, where upon opening the valve, exhaust would be directed to a second path, most likely a 3" pipe, around the cat, and back into the exhaust. This would bypass the catalytic converter (which is a restrictor), allowing full exhaust flow and power, yet allow me to close the valve and reduce my exhaust tone across the rev range. But, after some convincing, this posed two issues. The obvious is the complication with the law. One look under the car, and you definitely know something illegal is going on. The second is exhaust tone. Even with the valve closed diverting the exhaust around the cat, I would still get quite a bit of exhaust tone as is! Wrong answer #2.

3rd solution: After being introduced to Barry at QTP, I was informed of an idea that was in the wood works. The idea was simple: Use one of these valves INLINE with the exhaust system, cut a few small holes in the butterfly plate to allow some exhaust flow at cruise and idle, and allow the user to flip the switch, open the valve, and get full exhaust flow while maintaining some level of muffling using their current muffler system. Sounds great, but does it work?

TESTING PHASE 1 - 12/15/04

Being that I run a 3.5" exhaust, I had to choose a valve that would allow a full 3.5" surface area. This would require their 4" valve. Yes, a 3.85" butterfly valve that is meant to fit inside a 4" O.D. exhaust pipe. For this to work properly, I would have to flare some 3.5" pipe out to 4" or so I.D.

This required 4" 3-bolt flanges for both sides of the cutout valve. From the 4" flanges, a 4"-to-3.5" reducer on each side was hand built (these are available from other manufactures, and will most likely be included in the complete package offered by QTP). This allowed clearance for the valve to fully open.

The entire unit was installed after the catalytic converter, but I begun testing without the catalytic converter to get a worst-case scenario with respect to noise levels.

* Looks like rust, but its mud :) AWD is too much fun!

* Clearance from AWD driveshaft.

* Clearance from AWD Driveshaft center hoop.

Testing had been done earlier with one 9/16" hole cut into the plate. This provided a considerable reduction in exhaust tone, with one drawback. NO POWER. Being a guy that drives his car 100 miles a day through long highways and winding hills, I sometimes need just a little boost to keep up with traffic. With a 9/16" hole for exhaust flow, I could barely get to 1psi. I would be that guy on the slow lane going uphill at 40mph because I was just "giving it all she's got Captain." Some might argue that I could have just opened the valve a bit, and keep it slightly open the entire trip. This then becomes a hassle. I like to have the best of both worlds: Insane power and daily driveability/comfort/sanity. I do not embrace the job of opening and closing a switch every 5 minutes when I see a hill or not. When I am cruising, I like to watch the road, listen to music, and relax. Forget my gauges, forget my switches, forget it all.

I then decided to double the surface area allowed for exhaust flow. Two 9/16" holes were drilled on the plate.

With the plate closed, the exhaust tone did not increase much from the single 9/16" hole. But, I had power. I could now drive up-hills at 80mph in 5th gear, and see some boost, although not as much as I would like, it's respectable. You also hear a funny "hissss" from the restriction.

More testing is underway, including some video footage with sound of different exhaust tones, and dB readings at idle and cruise.

Holes would best be drilled next to each other on butterfly side that exhaust may pressurize causing the valve to prematurely open. The valve motor is strong, but this would be the logical way to go about it.

Every exhaust size/motor size will require different hole sizes. This would have to be determined by further testing by the QTP team, or give the user a blank plate and let them drill to their specifications.

This system could be used in two ways:

1) Normally open for driving, one tiny hole in plate. When pulled over by the police, or on your way home late at night, close the valve. You get almost NO power, but you won't hear the car at all.

Or, 2) A few more holes in the plate for normal driving, opening it up when you want full power (as I have it now).

Contact Barry or Ken at QTP for more information/availability on this product. These modified units should be available as a complete package soon.