[unevrkno]

Can anyone tell me where to find a cheap test pipe for the 968?

Can anyone tell me whether it's even worth the time and money to install a test pipe? Performance improvements?

Thanks
John

Partial Post: Please Login or Register to read the full post.

[Ryan]

Do you have a performance exhaust as well? Others have tried high-flow cats with a loss in power over the good old factory unit, so I would doubt you would see a gain from a test pipe. Engine needs the back-pressure.

Partial Post: Please Login or Register to read the full post.

[unevrkno]

<!--quoteo(post=72158:date=May 19 2009, 08:36 AM:name=Ryan)-->QUOTE (Ryan @ May 19 2009, 08:36 AM) <{POST_SNAPBACK}><!--quotec-->Do you have a performance exhaust as well? Others have tried high-flow cats with a loss in power over the good old factory unit, so I would doubt you would see a gain from a test pipe. Engine needs the back-pressure.<!--QuoteEnd--><!--QuoteEEnd-->


Yes, I do have a B&B cat back system which did seem to help the engine breath better. I was hoping the elimination of the cat could add a bit more as well as some more growl. Sounds like you've had some experience with the lack of back pressure. How did your car respond to it?

Partial Post: Please Login or Register to read the full post.

[flash]

nope - just torque loss with restriction reduction - open flow systems may give you a couple of horsepower up top, but at the expense of torque in the mids and lows - typically we see a big dip at about 3400 in those systems

the B&B is no exception to this - a couple of ponies up top, but a dip in the middle - depending on how you drive this could be a problem

to date the only system with dyno charts to back it up that shows no losses is the RS Barn system - no other system has published charts to support their claims

unlike most cars, we have a problem with the dual resonance intake manifold - the pulse timing gets messed up when you open up the exhaust too much

the problem is not "back pressure" though it is commonly referred to as that - the problem is gas velocity - the larger the tube, the slower the velocity - bad - most mufflers have the same problem - they slow down the gasses - again, bad

a couple of us have spent thousands of dollars working this out and trying different stuff - do a search here and you will find a lot of info and experiences on these different systems, what they did, and how people liked them or didn't

Partial Post: Please Login or Register to read the full post.

[dporschey]

Would an intake manifold custom made like the one on rsbarn's website help to solve some of these "back pressure" issues and allow for a free flowing exhaust

Partial Post: Please Login or Register to read the full post.

[flash]

theoretically it could, but the problem is that the dual resonance manifold makes 4psi boost which is responsible for over 10 hp - it would be tough for any exhaust to make that up, let alone make more

Partial Post: Please Login or Register to read the full post.

[Fox944]

<!--quoteo(post=72176:date=May 19 2009, 12:16 PM:name=unevrkno)-->QUOTE (unevrkno @ May 19 2009, 12:16 PM) <{POST_SNAPBACK}><!--quotec-->Yes, I do have a B&B cat back system which did seem to help the engine breath better. I was hoping the elimination of the cat could add a bit more as well as some more growl. Sounds like you've had some experience with the lack of back pressure. How did your car respond to it?<!--QuoteEnd--><!--QuoteEEnd-->


does your B&B have a resonator? if it does, you will get the extra growl you are looking for by removing it and still leaving your cat intact.

Partial Post: Please Login or Register to read the full post.

[unevrkno]

<!--quoteo(post=72214:date=May 19 2009, 05:17 PM:name=Fox944)-->QUOTE (Fox944 @ May 19 2009, 05:17 PM) <{POST_SNAPBACK}><!--quotec-->does your B&B have a resonator? if it does, you will get the extra growl you are looking for by removing it and still leaving your cat intact.<!--QuoteEnd--><!--QuoteEEnd-->


Yes, it does have a resonator. It would be worth the time to swap it out and see what happens. As discussed in another reply, I did in fact notice a loss in torque and chalked it up to "breathing better". No simple solutions....

<!--quoteo(post=72179:date=May 19 2009, 11:40 AM:name=flash)-->QUOTE (flash @ May 19 2009, 11:40 AM) <{POST_SNAPBACK}><!--quotec-->nope - just torque loss with restriction reduction - open flow systems may give you a couple of horsepower up top, but at the expense of torque in the mids and lows - typically we see a big dip at about 3400 in those systems

the B&B is no exception to this - a couple of ponies up top, but a dip in the middle - depending on how you drive this could be a problem

to date the only system with dyno charts to back it up that shows no losses is the RS Barn system - no other system has published charts to support their claims

unlike most cars, we have a problem with the dual resonance intake manifold - the pulse timing gets messed up when you open up the exhaust too much

the problem is not "back pressure" though it is commonly referred to as that - the problem is gas velocity - the larger the tube, the slower the velocity - bad - most mufflers have the same problem - they slow down the gasses - again, bad

a couple of us have spent thousands of dollars working this out and trying different stuff - do a search here and you will find a lot of info and experiences on these different systems, what they did, and how people liked them or didn't<!--QuoteEnd--><!--QuoteEEnd-->


Thanks for your sage advice. Without a dyno it's hard to really tell what's going on. I did notice the torque drop-off and simply misread it as breathing better. Do you have the RS Barn system in your vehicle? Did it deliver its claims?

Partial Post: Please Login or Register to read the full post.

[flash]

while you are certainly free to do what you like, if you didn't like the torque loss when you added the B&B, you won't like it any better when you stick in the test pipe

Partial Post: Please Login or Register to read the full post.

[ds968]

First of all, from a practical standpoint that torque dip lasts for less than a fraction of a second and furthemore, you can feel it only if you're keeping the car steady at 3400rpm then step on the gas at that very point. If you drive these cars the way they're meant to be driven that blink-of-an-eye dip is so insignificant in the overall scheme of things that to my mind it's a totally irrelevant point of consideration. Since I generally go trough the rpm range quite quiclky, even in normal driving while shifting trough the gears the revvs climb at a rate that makes that dip nothing more than a dyno read but of no consequence in any typical ( well, ok, what I call typical [img]style_emoticons/<#EMO_DIR#>/rolleyes.gif[/img] ) driving scenario. So if you're crusing in 4th or 5th at 3400rpm and decide to floor it, yes you'll notice it ...for a moment..

The hp and torque gain at the top and everywhere else in the rpm range, except for the 3400 -3600 spot trough which, I repeat, you blast by in a half blink of an eye, that you otherwise get with the BB, and above all that sweet growl sound ( mine is the no resonator option ) which to my ears is so much deeper and perfectly tuned than anything else I've heard on these cars is well worth the "sacrifice"..

just my .02 ..

Partial Post: Please Login or Register to read the full post.

[flash]

driving around town, i find myself at that point often enough that i have to make a conscious effort to keep it above 4k as it is, and i don't have that torque dip - it's pretty annoying - the engine lacks torque there to begin with - i'd hate to lose any more

lol - of course this could also me trying to rationalize the $11k i spent working on systems trying to get rid of it

Partial Post: Please Login or Register to read the full post.

[Kunz]

My experiance with removing the cat and driving a Cargraphic catback vs stock were like that:
BIG gain of torque from 2000-3000rpm, quite a dip at 3400rpm, a bit of a gain from 4200 - 5000rpm and loss of some hp over that. With the RSBarn header added we were able to get back some hp at high rev while keeping the gain at low revs and a slightly better situation at 3400rpm.
I personally found the dip at 3400rpm EXTREMLY boring! If you were driving around at let's say 2500rpm, dicided to pull away and floor it the engine would kick in really nice, made you alway looking for what's coming now... and then the dip! I was like a broken promise every time. You can also hear the breafing of the engine is very inefficient at that point. Sure, after that the car would pull nice again and you felt like being even faster than you really were due to the well increasing torque after the dip...
I experianced that keeping the stock cat in place and add a 2 1/2 Catback straight through adds some torque over the whole range and even some hp up the revs without provocing a real dip. It is this very setup I also drive with the SC right now...

Partial Post: Please Login or Register to read the full post.

[flash]

yup - the factory cat gave me back some torque too, after having tried a half dozen high flow units and failed miserably

lol - sometimes they just get it right

Partial Post: Please Login or Register to read the full post.

[ds968]

<!--quoteo(post=72287:date=May 20 2009, 01:22 PM:name=Kunz)-->QUOTE (Kunz @ May 20 2009, 01:22 PM) <{POST_SNAPBACK}><!--quotec-->I experianced that keeping the stock cat in place and add a 2 1/2 Catback straight through adds some torque over the whole range and even some hp up the revs without provocing a real dip.<!--QuoteEnd--><!--QuoteEEnd-->

Exactly my experience as well. Careful though, that's only the case with the 2.5" , nothing bigger !
BB as well as a few others out there also make a 3" catback pipe system for the 968 which is really designed for serioulsy modified engines, otherwise the loss of torque will be very pronounced and at a lot more than at just the 3400-3600 spot..

Had to smile when I read Bob's note on spending $ 11k to search for a solution to this glitch; that's the problem with perfectionists dammit, sometimes that attribute turns into OCD [img]style_emoticons/<#EMO_DIR#>/wink.gif[/img] Then again, the results are often stuff that benefits the entire community, so who's complaining ?! [img]style_emoticons/<#EMO_DIR#>/tongue.gif[/img]

Partial Post: Please Login or Register to read the full post.

[Kunz]

Here the GTech runs with

• </li>

Black: stock system

• </li>

Green: RSBarn header, 100-Cell cat, Carpraphic Catback

• </li>

Red: RSBarn header, 100-Cell cat, Carpraphic Catback and tuned / running on E85... actually not a bad curve and gain...

Partial Post: Please Login or Register to read the full post.

[unregular_joe]

I kind of like the idea of putting in a test pipe with a 2.5 aftermarket cat back

I actually have a several of different questions.

In regards to the gas velocity, if one was to use header/manifold wrap all the way back to the muffler would the increased in-pipe temperature create more velocity thereby eliminating the need for Dynamat and the Resonator?

In regards to the dip in the rev-range @ 3400, would any of the E-PROMs help eliminate that?

Oh and what manufacturer has a test pipe for a 968?

Partial Post: Please Login or Register to read the full post.

[flash]

this car is weird when it comes to exhaust

test pipes lose low end torque - this is true on just about any car, but it is even more so on ours - they can gain a bit of top end hp, and if you are on the track, that can help - on the street, it hurts - on some tracks where you need the low end torque coming out of a corner, it hurts - they also lean out the mixture, so be careful on that

wrapping can help scavenging, but it can also create cracks - thermotec is very clear about not overlapping too much, or covering the collector

thusfar no tuning has been able to eliminate the 3400 dip - the rs barn chip does about the best at minimizing it

Partial Post: Please Login or Register to read the full post.

[unregular_joe]

So if done properly wrapping the exhaust is helpful. Next question is how far back?

I've done a little research on the scavenging effect ,but they don't really specify on how what is the optimum set-up - especially for our cars. if we can manipulate the high and medium pressures in the manifold and the mid-pipe (cat or no cat?) , how much of the cat-back should we cover?

Do we want a long Medium pressure zone and a short Low? Or vice-versa?

Partial Post: Please Login or Register to read the full post.

[flash]

i wrapped my header, and it quieted it down, and did control the heat - not sure if it did better in scavenging or performance

i have never wrapped an entire pipe, as i always use thick tubing, and therefore have never needed it

remember that this car does not behave like any other - the dual resonant intake manifold creates a pulse timing complication that gets upset when you start messing with the exhaust - the typical result with anything free-flow is an exacerbation of the torque dip at 3.4k or so

even the stock system installed things to slow down and realign the gasses - there are 2 very specific items in the system that are specifically designed to correct pulse timing and slow things down - then they ran it into 2 pipes to speed it back up, then choked it back down again at the end

after 11 systems here, and about as many at pete's, i think we've come to some very real conclusions on this stuff - there is no perfect system - the one he has now is the best performing over the widest range of all of the aftermarket systems out there - there are others that have different sounds, others that make more top end at the expense of low end, and still others that have different appearances - you have to decide what you want out of a system

if you want to try to find more, you will have to do some trial and error - welcome to the club - we are having jackets made next week

Partial Post: Please Login or Register to read the full post.

[unregular_joe]

i think i'll wrap the header, the area directly after the cat (on the mid-pipe) and again on the cat-back just before the first bend.

The reasoning behind my theory is that, like you said, Porsche intended to speed up the gasses by splitting them up into two smaller pipes. Due to the fact that i've got free flow muffler i'll leave that area alone.

That said now i need a to the chip to match. I'm not too sure if i need the ProMax/Racer X top end. I need a power upgrade but without the dip in the mid-range.

Partial Post: Please Login or Register to read the full post.