Just want to start off by saying this: lets put the "X pipes don't make power" thread behind us for a minute here. I have a tiptronic coupe, and I'd like to put an exhaust on it, but the tip loves to lug around town in the drone zone of the 996tt.

There are three basic layouts that are on the market currently, from what I can tell:
- conventional/twin can (no crossover)
- X pipes
- butt-jointed U pipes

Again, putting any power rumors/speculation aside: when the exhaust has a crossover, it sounds a lot better than the conventional twin can designs, and from what I can gather from this forum, there is less drone in the cabin as well. Other random caveats I've read: reducing the diameter back down to accept the factory tips seems to reduce drone as well https://www.6speedonline.com/forums/...4&postcount=20


Something that I have not seen on 996tt exhausts is the use of side branched resonators to cancel out the resonant frequencies. Here is a post on 6SO that the user had made a custom exhaust and ended up resolving the drone with side branched resonators. There are a few calculations that need to be taken into account to move the drone into a different RPM range or eliminate the majority of it: https://www.6speedonline.com/forums/...esonators.html

Here is a picture of an HKS exhaust for a 370z that has a side branch resonator in it


Here is a video of a company that explains their product of this

The other idea I had, mostly because of the X pipe thread, was to use a MAC prochamber where an X would be. I don't know how long these units are, so I don't even know if this is a possibility because of the bend angle you'd need to make the pipes. But assuming it is feasible, this should eliminate the reduced volume for gasses to flow through at the X, but still keep a lot of the crossover features of the X, and hopefully keeping the sweet sound of the X pipe.

Cutaway of the prochamber:

Seems like the length of the box could be the limiting factor, as I don't know if we have the vertical height to work with on our cars.


Just trying to think outside the box and get some feedback before I have an exhaust fabricated this summer. I don't mind the exhaust being (reasonably) loud outside of the car, but it's the cabin resonance that I could do without. With the recent exhaust pissing match going on earlier this week, it made me try to think of some other ways to get a good sound of of the exhaust.

You guys have any thoughts on ways to cut down on exhaust drone and still keep a crossover design?

 

Subscribed.

 

With the cost of Porsche's exhaust and being very small amount of piping compared to a front engine car, I would figure that they would know about this technology and implemented it on these big dollar exhausts systems.

I wonder if there is a power loss with this set up?

If this works for our Porsche's I would order the straight x pipe from Speetech ASAP and replace my muffler x pipe!

I am hoping one of the exhaust companies can chime in with there thoughts........Speedtech?

Thanks

Bobby

ba

 

Interesting idea/theory. I don't think anyone ever said the X pipe DOESN'T make power. It just doesn't make EFFICIENT power. How efficient can an exhaust be if the exhaust gases are crashing into each other trying to get out? It sounds awesome, but as you can see, anyone trying to make huge power is doing something else.

 

Most after market exhaust drone on a TIP.
gut out the OEm one and your issue is solved...
We have a used RUF which is a a OEM redone by them.. I drove the car which is also a TIP... less drone then most Ive heard... IDK about the performance but Im guessing your not into big HP...

 

Actually there are twin cans that are joined by a connector/crossover,,like my Milltek,Cargraphics,to name a few..
Also there is another type,,A criss cross type from Protomotive which I think is a great set-up for power ,as his customers make big power with it..
EB Werks has a different X-merge then all of the rest..
I believe a 2.5 '' pipe will keep the velocity up at lower RPMs to put a hamper on drone but a 3'' will not have the velocity to keep it from droning.
It is going to be hard for us to have our cake and eat it too..

 

I'm not sure if there is a power loss or not, but I think that if designed right it will be negligible - If the exhaust were to be angled so that air would want to go into the dead-end resonator, I imagine it would cause turbulence, but not restriction.
Thanks! Will be interested to possibly try some of these ideas out, depending on what my fabricator is comfortable with. And I agree with you, that the angle that the gasses are coming together (as well as the loss of cross-sectional volume) at the X isn't as efficient as it *could* be if comparing it to straight pipes, but then again... what is?

I'm not ready to take my car to get the exhaust built yet, so I put some thought towards it and these were some alternatives I haven't seen come about yet and was wondering if it were for engineering reasons or just because nobody had thought of implementing them into the cramped 996tt exhaust piping.

Here is an FVD exhaust on a 996 GT3 rally car, and I think with some anterior/posterior angulation like this (rather than perfectly vertical), there is a slight chance that a prochamber could fit in there where the crossover is.



Another idea I had came from looking at Tim's center exhaust - just having a very narrow aperture between the two 180* U bends on the exhaust, allowing for the resonant properties to combine (if that's actually what they'd do), but minimal 'crashing' of the exhaust gasses. Going a step further one could build the exhaust as if the U bends were to touch but not join each other in a butt-joint, take a very thin (2"?) section out of the proximal area and replace it with some sort of a figure 8 or oval pipe so that the exhaust is truly open from one side to the other, but would have no congestion with it.

Tim's exhaust

^I think that is a more ideal way to get each side to communicate without causing much more backpressure. If one could make that a little bit wider, like the following photoshop, it would be even better since there would be no volume loss:

Granted, that would be a big PITA for a fabricator I'd imagine


Just thinking out loud here with you guys. If I'm way off my rocker... save me the wasted thoughts haha

 

Believe it or not ,,when I went from the stock tips and Milltek 2.5'' tail pipes out from the muffler to a true 2.75'' set-up from there it did start to drone then,,but it did only get a little louder all the way around.

 

Exactly, just a tune on my car so nothing really power wise. And you're right again on why I'm trying to think outside the box here - tips just flat out drone more. I love the sound your X (as well as others) makes, which is why I'm scratching my head over a merged design. I think you're right that the gutted OEM would be the most reasonable set up (financially too) but X pipe exhausts just sound night and day better...
I've seen the protomotive referenced a couple times as being great for power, but in looking at it with now flow analysis... I don't know how.

With the joined twin cans, are you talking something like an H pipe? Where there is a pipe that joins at 90* to either exhaust bank that connects the two sides?

 

re-reading this.... maybe this is why the X pipes tend to drone less?? Little bit of constriction causes an increase in velocity as well as letting each side's resonance hit each other. If that's part of the cause of drone, then it would make sense... drone at part throttle where the exhaust gasses will not need the additional volume, but the additional velocity will keep the part throttle drone at bay

You're not the only one, I believe it! https://www.6speedonline.com/forums/...4&postcount=20

 

I have a had a few conversations with Kevin from UMW,,he is a sharp guy and does try things out, he has tryed a few custom x-pipes close to whats out against his favorite 100 cellEuro Pipe and the 100 cell Milltek..He gave me the info that the X-pipe design will loose low and lower mid over those traditional set-ups on up to 650 HP cars?..He is not a fan of them,,,but others are not a fan of him?..He was great with talking shop and info, he knows my build history and I never spent a penny with him..

 

The AWE tuning exhaust is known for having less drone than most exhausts. It's a 2.5" system which accounts for a lot of it I'm sure, but they don't use a X-over type system either AFAIK

 

I can not believe no one makes some type of stepped pipe to keep the velocity up and drone minimal but I would guess because you have the biggest size ID coming out of the turbo first?
The criss cross type system seems to be the one with the least bends and no collector, almost all straight except for at first turn to run with bumper and the last turn to the exhaust tips which all have that but the straight pipes, which should flow very good.You can even put a window in them were they criss cross individually and it still wouldnt be smashing the two sides together.
I hate to bring that system up again but I get no input on why no one else goes with it?

 

I have also always wondered why the exhaust manufacturers don't use hemholtz chambers to reduce drone. I was thinking of trying it myself. I have several ideas I want to try and my Physics degreed engineer friend and I were going to try our hand at exhaust design. Maybe I'll finally get some use out of my welder.

 

helmholtz in the sense of a branched resonator, or hemholtz in the sense like some of the corsa mufflers have built into them internally?

I've thought about using corsa mufflers with whatever system I build for that reason, but that's a pretty expensive mistake if it doesn't work lol.

If it's the slowing/cooling/contraction of the exhaust gasses that cause drone (is it?? ), that would shine some light on why the narrower stock tip exits drone less than slash cuts.

Would muffler/resonator placement have any consideration when it comes to drone? Say you only used one muffler per side, would it be better to place them closer or farther from the turbos? I'm guessing farther, but only because that's where mufflers traditionally go in front motor cars, right after the rear axle.