[parptarf]

I'm gonna start with saying I know(And noticed) the stock exhaust get's great down low tourque compared to a cat-back one which gives a little top end and much richer sound.



What will I need to do to my cat back to get back my low end(I realize I'd have to give up my 5-ish top end HP)? Smaller tubes? Change my muffler?

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[Cloud9...68]

Best thing to do would be to wait for Flash to complete his work on the NA package (see thread on the subject), as it will include optimization of the exhaust.

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[parptarf]

Let's change this up a bit. How do I easily get more sound from the stock exhaust?

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[flash]

more sound is easy. unfortunately it almost always means less torque.



i have a setup that all initial testing shows to work, but i have not yet put it on the dyno, which is why i have not released it. it is a few db louder than stock, a nice deep warm note, and no discernible resonance. it loses a few pounds of weight. the parts are lifetime warranty. it retains the OEM cat.



just waiting on the test car to be ready

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[parptarf]

Sounds good!



But about the cat-back exhausts. I'm guessing it's more complicated than just jamming a resistor of some kind to create more back pressure?

And any hints in the right direction on what's most likely the lose the least amount of torque for the most amount of sound. As you've said before, the sound note of this car isn't the issue, the problem is that there's not enough of it.

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[flash]

you never ever ever want back pressure. that term gets tossed around a lot and used incorrectly.



gas velocity is everything. speed it up too much by means of things like free flow mufflers and such, and you get a big torque dip. slow it down too much and it costs you upper end horsepower.



our OEM system was really quite a feat of engineering. not only did they have to deal with gas velocity, but they also had to deal with pulse timing and cam overlap. these things can dramatically affect scavenging.



i have spent now about $13k working on cat-back systems and testing of them, and i'm not the only one. i think i finally have the optimal setup, but as i've said, i still have to put it on the dyno to be sure. i'll be doing sound recordings as well. when i'm done, i'll post the list of components, and what needs to be done. i'm not going to be selling systems. this way, anybody can go get the stuff themselves, take it to their local muffler guy, and put it in.



i anticipate doing this in october. i'm just waiting on the test car to have its wiring harness reinstalled.

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[parptarf]

I'm guessing what I really thinking of its gas velocity. But would decreasing the internal diameter of the pipe do anything to slow it down?

It's not like it's gonna be a perfect solution, but anything to get my torque back, or at least some of it without sacrificing that great sound my Janspeed makes.

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[flash]

no. in fact, that will speed it up, but reduce the volume, and could increase back pressure. it's like squeezing off your garden hose.



this is the problem with all of the existing cat-backs out there. there has not yet been a system that does not compromise something somewhere. you just get to pick where you want the compromise.



i am hoping that the system i am working on will not have such compromises, and if they do, it would only be at the very top end, where it doesn't really matter much anyway.



film at 11.



i wish i had flow data and design specs on the janspeed, but i don't, so i can't really recommend what to do to modify it.

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[parptarf]

Obviously that would speed it up. My "anything-science-related" is a little rusty these days. <img src="/forum/images/smilies/968/wink.png" class="smilie" alt="" />

So what I need is to slow town the gasses without reducing volume? I have a resonator looking thing before the rear muffler that is detachable. Maybe there's something in there creating pressure or reducing the volume?

I could always try and just straight pipe it to my rear muffler, all I'd really need is a 2,5" pipe.

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[flash]

if you are losing torque, then things are probably moving too fast already. a straight pipe would make it worse. what you likely need is a different resonator or muffler, and one that does not flow as freely.



if it's a straight through the muffler, you're screwed. i can tell you that one for sure.



unfortunately, anything you do to slow things down a bit will also lower the volume.



based on what you are saying, i don't think you are going to be happy using the components you currently have. welcome to the club. we're having jackets made next week. like i said, $13k and 14 systems before i got to something that looks like it worked.

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[parptarf]

If I'm gonna have the exhaust off anyweay to put the stock one back in, I'll check the resonator to see if there's something to be done there. Maybe it's just a straight up box.



Another thing, about the stock exhaust. I read on R.L. that if you remove the plate on the engine side of the OEM resonator, you'd get a more responsive car(meaning low end) and gain some sound.

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[flash]

nope. i actually got to drive the car that first did this. he's 20 minutes from me. what you get is more upper end response, not lower end. you lost low end, just like anything else that opens up the flow. you did get some throttle response though, as long as the revs were over 4k, because that's the overlap point on the intake manifold. it did get a bit louder though.



this is one where a lack of ability to describe things, and a natural tendency to let adrenaline dictate how you drive, gets in the way of development. what one guy says is "more responsive" is not that the next guys says it is. some guys are focused on bottom end, and some on top. neither ever seems to pay attention to the other.



basically, if you want more bottom end, you'll need to cork it up. however, that will also quiet it down. it will also cost you top end.



send me what you can on the system so i can try to figure something out.

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[parptarf]

The Janspeed is basically a pretty simple design. It's a 2.5" pipe that goes from the OEM cat and into a resonator. Looks to be about the same size as the OEM one but a lot shorter. Out of that there's a 2.5" pipe that goes into a muffler, from eye sight it might me 60% in size to the OEM one. From there out it looks like 2.5" or 3" to the tailpipe.



And then back to the OEM exhaust. So from what I understand removing the plate in the resonator can work as a middle ground to the cat-back and stock?







And here's a somewhat unrelated question. I cleaned the OEM exhaust a little today since I have it off the car. And I pulled parts of my catalysator out of the resonator, and you can hear it's full of smaller pieces. If I remember correctly my cat didn't look too good when I chaned the exhaust either. Basically I'm pretty sure I need a new one. Will any cat work on this car?

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[flash]

yes, but the key to knowing what to do with the janspeed is to know if they units are a "straight through" design, or if they have baffles, or a turnaround.



removing the plate was a ghetto way of getting some more noise, a bit of throttle response, and a little bit of upper end, at the expense of some bottom end.



the OEM cat is a far better flow design than any aftermarket cat. further, if you have emissions testing, you may very well have a problem getting it to pass. i tried a couple of the aftermarket cats out there, and even with the biggest one available, i had to get it really hot to pass right at the limits. the aftermarket cats are ceramic, and the OEM one is precious metal. very different results.



it is very rare for the cat to disintegrate. it normally just clogs up. if you drop the system down, you can look straight into the cat, and you should see the honeycomb inside. if it is not missing any pieces, then the things you found were from the resonator.

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[parptarf]

The resonator is a straight though, but the muffler has an "S" bend internally if I recall correctly.



The middle of the honeycomb is missing, unless my memory is completely going bad. I also pulled off a honeycomb piece that was stuck in one of the holes of the resonator plate.

It passed the last EU certefication without any issues and they always do an emission test. I'm guessing the OEM cats are hard to come by and expensive when you do come by one.

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[flash]

depending on the severity of the "S" that muffler may or may not be the issue. the straight through resonator is almost certainly not doing as much as you appear to want to give you back low end.



if the honeycomb is broken, then it needs to be replaced for sure. OEM is NLA. the best you can do there is a used one. other than that, you are hunting for something that would cross-apply to this car. the way it works over here, is that even though the catalogs may list the 968 for an application, it was not tested on the 968. once a cat manufacturer gets approval on one engine in the class, it is then added to the other engines int that class without any further testing required. not sure if there are other cats available RoW.

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[parptarf]

I went out and had a look at my rear muffler ,looks like it might be a stragiht though that one too. Though all I can see is that it's coming out on the same side as it's coming in, it can still have a bend in there.

But anything can do to my resonator to try and fix it? I'll at least start there if anything.





I'll send an email to a deailer about a cat. They can usually get a lot of parts that are not longer made.

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[flash]

just having a bend really does nothing, unless it reverses direction.



you'll have to change resonators, but the only one that really does anything to restore torque will take out a lot of sound level.



i'm old and don't really want to hear the exhaust unless i am stepping on it. i want it in the background so i know it's there, but not really present in the cabin. if you're looking for a loud exhaust, then you need to get used to bottom end loss.



this is all incredibly subjective, and there is no perfect answer. i think i have gotten as close as can be, but i still need to test it on the dyno to be sure.

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[parptarf]

The one I have now isn't really loud. All I hear in the cabin is a low growl. It's much, much quieter than the RSbarn or B&B ones.



I'll see what I'll do and wait for your exhaust detailes to be done. <img src="/forum/images/smilies/968/smile.png" class="smilie" alt="" />

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[kzem1]

I would like a bit louder and deeper sound from my exhaust. The BB seems a bit deeper than the RSBarn catback I heard with my ears. At least I think it seemed that way. Will this exhaust set up work and/or be recommended for an SC car or just normally aspirated Flash? A friend of mine just bought a brand new M6 and it sounds really good to me.

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