The Perfect Exhaust System

[mppickett]

Ok, sports fans. Here's a problem that many of us face: we want our cars to be quiet enough around town that we don't incur the wrath of our neighbors or appear as larger blips on the local constabulary's radar than we already do. BUT, when we want to uncork it, we want all of the growl and roar that our engines can produce (and as little of the backpressure as possible). For those of us with 930 engines, backpressure can be a particular downer as it causes the turbo to spool up more slowly.

Being the old turbo porsche driving environmentalist that I am, I bought a metal substrate 6" catalytic converter, (very little backpressure) and paired it with a straight thru 3" flowmaster muffler. The system is finished off with two 4" polished stainless tail pipes (one from the turbo and the other from the wastegate).

My muffler guy finished the welding and handed me the keys. When I cranked it up, I thought that someone had started playing that scene from Apocalypse Now where the choppers are flying in playing Wagner's "Flight of the Valkyries." After offering to pay for the cracked glass in the windows of the stores in the block, I decided I needed to make it a little quieter. Of course that was after taking it out on the highway just to make sure that the car performed as I suspected it would (turbos like to breathe!).

I came up with a hairbrained scheme that I'm sure is wrong-headed in a dozen different ways and will probably cause cancer and the appearance of weapons of mass destruction in several sketchy third world countries. For those of you who have absolutely nothing better to do and want to follow my decidedly poor example (of course holding me harmless from whatever mischief you incur), I have documented a way to have your thunder and happy neighbors too.

The basic idea is a cross between a hot rod exhaust cutout (not much room to add one of these to the exhaust system) and the old stovepipe flue controls. I decided to put a cutoff plate that could control how open the tailpipe was to the muffler. This has a dramatic effect on the noise level of the exhaust and also adds a lot of backpressure. I wanted the plate's angle to be adjustable with a wrench in the first phase and eventually from inside the car (later phase).

My experiment:
1. I went to the hardware store and bought a steel bolt (4.5" long for my particular application), jam nuts and washers. This will be my pivot rod. I also bought a front plate for a standard electrical box (around 5-6" square) from which I would cut the cutoff plate.

2. I put the bolt into a vice and used an angle grinder to cut a slot from the head to about 1/2 inch from the end of the threads. I drilled to holes through the bolt to insert screws to hold the plate in place.

3. Using the angle grinder I cut out a disk (cutoff plate) from the electrical cover plate that would just fit inside the tailpipe.

4. I drilled holes through my tailpipe and inserted the pivot bolt into the holes. I slipped the cutoff plate into the tailpipe and into the slot in the pivot bolt. Using a wrench to turn the pivot bolt I moved the plate around until it was centered in the bolt and would turn freely in the tailpipe. I then marked the plate through the screw holes in the bolt.

5. I removed the plate, drilled the two screw holes and two large (approximately 15mm in my case) holes on either side of where the plate passed through the bolt). These larger holes prevent the plate from ever totally blocking off the exhaust system.

6. I reassembled the bolt and plate using screws and anti-seize compound.

7. I closed the cutoff plate and started the engine - nirvana! I could actually hear the great busy sound of the engine and not just the scary rumble that used to loosen the filings in my teeth. I drove it for a half an hour with no problems. Full throttle in 1st and 2nd were reasonable but it lacked the head snapping rush of boost. 3rd gear was decidedly boring but it was quiet enough that I could hear the radio while I was driving on the highway. Hmmm, this might be a reasonable setting for long trips.

8. Of course I stopped at a rest area and used a wrench to turn the cutoff plate to the fully open position. My baby was back. I have dreams of spring return to the closed position and a throttle cable-like hand opener for full performance (or even cooler, a solenoid that snaps the cutoff plate open at full throttle).

Anyway, like I said you should never do what I have done. It is a really bad idea and probably bad for your health and your car. If you're crazy enough to want to anyway, here are some pictures:

[TRE Cup]

sorry to rain on your clever idea, but you can buy electrically operated exhaust gate valves all the time. The hot rodders use these, and one of our regular posters here, had us install a pair on his GT2 style race/street car. A push of the dash mounted switch and it is the glorious wail of an untamed 6

Other car "disciplines" (low riders, hot rodders, road racers, etc) all have cool stuff that can be gleaned from for use on our toys

have fun- your car must sound like a 935 on boost !

[84_Carrera]

TRE Cup - I looked into those when I had my 500hp supercharged Taurus SHO, I wanted exhaust butterflies to open (to correspond with the electrically activated / vacuum actuated intake secondary butterflies, but the time needed to open them being all-electric was useless - by the time they opened I'd already be at redline, and shifting again. IIRC it took 2-3 seconds for them to open, best case.

[mppickett]

TRE Cup,
You're right about the cutouts. JEGs has as good a selection as I've seen. The problem I was solving was inexpensively adding quietness when I needed it.

84_Carrera,
I didn't know how fast the electric cutouts were but from your experience, they could be too slow for automatic engagement. One thing that I've thought about from the solenoid engagement point of view is that the engagement should be as fast as possible but the disengagement should have a couple of seconds delay. This would allow my turbo to continue to spin at full speed between shifts. Easy enough with a 555 integrated circuit timer, but at this point I'm still in phase I.

[RarlyL8]

I wondered how long it would be before someone posted on this subject.

Back in October of last year I applied for a patent on an active exhaust system for the 930 and SC/Carrera. The patent was accepted for review and I am now in longevity testing.

This is much more difficult that it appears. Part of the difficulty lies in keeping the system light weight while having instant valve response and longevity. There are many systems on the market and I have found none that satisfy my criteria, which is why I decided to make my own. I have spent a small fortune purchasing and testing many of the valves and activators on the market so the system can be mass produced. The last detail left is to find a machinist to economically produce the parts I could not source.

Another part of the difficulty is space. My patent design fits in the normal space occupied by the stock muffler. The only mod needed is a valance cutout for the bypass or dump pipe.

It is great that you see a need and took on the task. You will have the best chance for success by using a valve that is already on the market and proven.

[mppickett]

That's funny, Brian. I thought of you when I was fooling around with this thing and suspected you had already put on your thinking cap. Good luck with the patent application (and let me know if I owe you anything)!
Mike

Originally Posted by RarlyL8

I wondered how long it would be before someone posted on this subject.

Back in October of last year I applied for a patent on an active exhaust system for the 930 and SC/Carrera. The patent was accepted for review and I am now in longevity testing.

This is much more difficult that it appears. Part of the difficulty lies in keeping the system light weight while having instant valve response and longevity. There are many systems on the market and I have found none that satisfy my criteria, which is why I decided to make my own. I have spent a small fortune purchasing and testing many of the valves and activators on the market so the system can be mass produced. The last detail left is to find a machinist to economically produce the parts I could not source.

Another part of the difficulty is space. My patent design fits in the normal space occupied by the stock muffler. The only mod needed is a valance cutout for the bypass or dump pipe.

It is great that you see a need and took on the task. You will have the best chance for success by using a valve that is already on the market and proven.

[JayG]

LOL

A cutout?! Wow good thing you made this post before you went to the patent office!

[TRE Cup]

go look at close up pics of the mex blue turbo on e bay (or on auto kennel's site) . it has a pierburg made boost actuated valve that goes wide open under boost (don't ask me, the first owner had it installed)

the ferrari F 50 has a similar unit

there are other mfg that have the same thing

[JayG]

Originally Posted by TRE Cup

go look at close up pics of the mex blue turbo on e bay (or on auto kennel's site) . it has a pierburg made boost actuated valve that goes wide open under boost (don't ask me, the first owner had it installed)

the ferrari F 50 has a similar unit

there are other mfg that have the same thing

Stock 3kgt VR4's have it. Its called active exhaust and is controlled by actuators. That particular system came out in 91. The new Z06 has it too.

[911pcars]

Some Nissans (and other manufacturers I'm sure) have a valve inside the muffler, controlled purely by exhaust flow/pressure, not manually controlled. However, at the manufacturing level, there's usually an army of engineers who know the flow characteristics to actuate the mechanical gate, then close it per determined specs. A similar approach would have to be custom-configured for your particular engine which brings us to a more realistic and easier to install manual control. The simplest would be a flow or flow-diversion valve controlled by a Bowden cable. A more sophisticated approach uses a valve-controlled servo motor which is throttle and/or RPM-activated via any number of electronic boxes on the market.

Longevity would be an issue in any valve operating in a harsh exhaust environment.

Sherwood

[RarlyL8]

No Mike, you won't owe me anything, Ha!

Obviously active exhausts exist in many vehicles and have for decades. This is way more than a simple stove valve.
What makes this go-round unique is the application. There was no patented system design for the 911 and 930 application. What I submitted is a system that is activated using engine parameters as well as a manual bypass for both on and off. So if ricer-boy rolls up you hit a switch and open it up and when smokie comes looking you can quickly shut it off. Default is automatic and is controlled by boost pressure.
I had planned to debut the system months ago but have run into many issues mainly having to do with mass production. One-off prototypes are a lot easier to make than an executable design for the masses.

Is there a link to the mex blue car?

[175K911]

Interesting topic. I've seen the ones JEGS and Summit sell. Much more common application is in boating. Most common brand is Captains Choice. My last two boats had this system... through the props to be quiet to get out of the marina, then opening up into the through hull 4" stainless unmuffled tips for out on the water.

[Joeaksa]

Remember that this might work fine on some 911 engines but there are others that are so sensitive to mixture changes that doing a change like this without adjusting the mixture could result in internal damage.

[Kroggers]

Is this a 930 focus design, or will it work on a car that does not have any turbo boost? Will it be for use with two in mufflers as well as one in, or just one version. Do you need an SC to do some testing on

Originally Posted by RarlyL8

No Mike, you won't owe me anything, Ha!

Obviously active exhausts exist in many vehicles and have for decades. This is way more than a simple stove valve.
What makes this go-round unique is the application. There was no patented system design for the 911 and 930 application. What I submitted is a system that is activated using engine parameters as well as a manual bypass for both on and off. So if ricer-boy rolls up you hit a switch and open it up and when smokie comes looking you can quickly shut it off. Default is automatic and is controlled by boost pressure.
I had planned to debut the system months ago but have run into many issues mainly having to do with mass production. One-off prototypes are a lot easier to make than an executable design for the masses.

Is there a link to the mex blue car?

[RarlyL8]

Mike - have you considered a MagnaFlow dual out with a valve on the passenger's side outlet? The design of the Magnaflow is a straight shot out the passenger's side and a switch-back on the driver's side, which would work well for what you are trying to do.

Remember that this might work fine on some 911 engines but there are others that are so sensitive to mixture changes that doing a change like this without adjusting the mixture could result in internal damage.

That is a consideration and one of the parameters I am working with. I have found that in the 930 there is a detectable change in the fine tune A/F ratios that is dependant on back pressure. I have tried a couple of different muffler designs to lessen the change while still greatly reducing sound level. With that being said, The A/F change never falls out of the acceptable range when set correctly. As with anything else the fuel delivery system needs to be in spec before any mods are made. Same goes for a Carrera or SC or any other car.

The system will work for both 930s and 911s. The 930 uses boost signal to open the valve while the 911 uses back pressure.

[mppickett]

Brian - I had that particular MagnaFlow dual out on the supercharged miata I used to race and had to set up a way to block the passenger side when I wasn't on the track. It had a nice tone and little backpressure in the blocked mode and was very aggressive with both sides open. The reason I didn't try it out on the Porsche was I was trying to squeeze the catalytic converter in line after the turbo. You are right about there not being very much space back there. I'm not doing much of my own welding yet and have been hesitant (read too cheap) to play around with the configuration very much.

Originally Posted by RarlyL8

Mike - have you considered a MagnaFlow dual out with a valve on the passenger's side outlet? The design of the Magnaflow is a straight shot out the passenger's side and a switch-back on the driver's side, which would work well for what you are trying to do.

[911 tweaks]

Brian... what can you tell and or show us about your apploication??
When will prototypes be avail or tested?
Prices? Performance gains if any... or is this for sound?
How will the SC fuel dist adj to more air flow with your device?
Look fwd to what you offer and how it performs!!
Best of luck!!
Bob

[RarlyL8]

Mike - with the turbo you can use a short aftermarket cat/muffler combo but space gets real tight. The valved tailpipe can come off the cat on the passenger's side and a 180 bend will take the muffler outlet to the driver's side as seen in the stock configuration. The trouble with that is the muffler and DS tailpipe will protrude under the valance. Space is really a problem for the 930.

Bob - I am about 6 months behind right now but progress is being made. The prototype is fugly, many changes and multiple weldings have turned it into a Frankenstein. I have all the parts to build the Beta unit which will look very nice.
It is still "iffy" as to weather this project is viable for the masses. Costs are very high due to the design constraints placed on a valve assembly that must function in a hellish environment. I had hoped for a price point about $300 over the cost of one of my dual outlet mufflers. So far I can't get near that. I can post a picture of the initial prototype but it bears little resemblance to the final product.

[sammyg2]

Loud exhaust on the street sucks.

You wanna uncork it? Take it to the track.

[911 tweaks]

Thanks Brian for the info... I would love to see a pic of what you are working with...
a tip (,aybe), if this starts getting costly and or to time consuming, maybe, (I have no affiliation or if he would be interested) maybe give Ben a call or email to see if his awesome welding, fab and obvious muffler talants can help you out or be a partner ~ help to some degree.... just an idea...

Best of luck with this and I would be in for one as prior to seeing your post I was planning on buying one of thos elect jobs w/ the sliding round door... after more thought, if I was to do ~ use one of these, I would "think", but what do I know, that a "spring" type of door inside the muffler that is exhaust pressure controlled. Different "spring values" for different engine configurations of which some sophisticated calculations of exhaust gas flow would need to be determined to find the correct spring rate...
just another of my ideas...inputs...
Best of luck and keep me informed as to how this goes and if I can be of any help... I live for the 911 tweaks!!!!!!!!!!!!!
Bob