968 muffler restriction
04-11-2011, 07:24 PM
#1
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968 muffler restriction
Looking for input on how restrictive the muffler is on our cars. Somehow I think they are not restrictive considering how sensitive a 4 banger is to back pressure and these engines rev pretty good.
04-12-2011, 12:35 PM
#2
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middle muffler quite restrictive ,due to backpressure disk at inlet,and 43 mm oval restrictor
prior to the middle muffler entry,All other parts are fine.
if you chip the car and have KN filter seems it is a must to remove these restrictions,if you need the full
effect of the chip /filter mod.
Perhaps thats why many people are dissapointed with the performance of their new chip/filter addition.
prior to the middle muffler entry,All other parts are fine.
if you chip the car and have KN filter seems it is a must to remove these restrictions,if you need the full
effect of the chip /filter mod.
Perhaps thats why many people are dissapointed with the performance of their new chip/filter addition.
04-12-2011, 01:49 PM
#3
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Thanks.
04-12-2011, 02:27 PM
#4
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quite a can of worms here but im looking at a custom exhaust setup with a less restrictive system mainly for sound quality and lighter weight... performance is a plus but i just hope it at least stays about the same...
04-12-2011, 02:38 PM
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dump the cat, change to 2 1/2 inch pipe, run a resonator and a 20 inch straight through magnaflow.
this setup will be good for about 15~18 hp.
this setup will be good for about 15~18 hp.
04-12-2011, 04:10 PM
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If you just get rid of the mid-muffler, the results are quite loud at WOT. Nice sound at cruse, but a little raspberry when you get into the big pedal. If you put in a cherry bomb in place of the mid-muffler I think you would rid the system of the raspberry and have a good sound.
04-13-2011, 10:18 PM
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i thought i'd post here because this resonator will really help with the building of any free flowing exhaust for the 968, not matter what engine you're running... as it allows for stout sound supression.
in about 90 days i'll be installing my LS3... well, one of the guys here will be doing it, cuz i just don't have the vocabulary on getting the clutch and driveline right... anyway, i've been back and forth about an exhaust that will really help the 'hotcam' make some serious power, but i wish to make good on something Raj had said recently that 'it needs to be quiet or it's crap..." frankly, i happen to agree, but for Raj's philosophy to be preserved, i'm gonna need to do more.... but i'll also try to build one of the best free-flowing exhausts around for the heavy breathing monster....
starting with the engine; LS3 w/ hotcam is rated at 480 hp running the stock exhaust manifolds. up 50 hp over stock.... but w/ upgraded beehive valve springs, and Eric's (TPC) long tube 1 3/4" headers (the first 1 3/4" headers he's done), running into a free flowing exhaust, those numbers should easily climb to about 505 hp.... to keep as close to that number as possible, i'll run the long tubes into a fat Y-pipe and then into 3 1/4" stainless steel pipe.... and then into two trianglular (yes, you heard that right—'triangular') straight through 3" in/out resonators, one right after the other, and tucked up high into the exhaust cubby... finally i'll run this into a very large 24" X 8" X 5" straight-through, 3" in/out Magnaflow.
the goal ? 430~440 hp at the wheels... am i nuts? well we're all nuts, otherwise we wouldn't be here! of course, the resonator will have to be trimmed at one corner to make a smooth curve for a better fitment up into the exhaust cubby... for the rest of you guys. just run the stock headers into 2 1/2" pipe and run this same combination (except only 1 resonator and about an 18~20" Magnaflow) and 2 1/2" or 3" in/out setups.
;
in about 90 days i'll be installing my LS3... well, one of the guys here will be doing it, cuz i just don't have the vocabulary on getting the clutch and driveline right... anyway, i've been back and forth about an exhaust that will really help the 'hotcam' make some serious power, but i wish to make good on something Raj had said recently that 'it needs to be quiet or it's crap..." frankly, i happen to agree, but for Raj's philosophy to be preserved, i'm gonna need to do more.... but i'll also try to build one of the best free-flowing exhausts around for the heavy breathing monster....
starting with the engine; LS3 w/ hotcam is rated at 480 hp running the stock exhaust manifolds. up 50 hp over stock.... but w/ upgraded beehive valve springs, and Eric's (TPC) long tube 1 3/4" headers (the first 1 3/4" headers he's done), running into a free flowing exhaust, those numbers should easily climb to about 505 hp.... to keep as close to that number as possible, i'll run the long tubes into a fat Y-pipe and then into 3 1/4" stainless steel pipe.... and then into two trianglular (yes, you heard that right—'triangular') straight through 3" in/out resonators, one right after the other, and tucked up high into the exhaust cubby... finally i'll run this into a very large 24" X 8" X 5" straight-through, 3" in/out Magnaflow.
the goal ? 430~440 hp at the wheels... am i nuts? well we're all nuts, otherwise we wouldn't be here! of course, the resonator will have to be trimmed at one corner to make a smooth curve for a better fitment up into the exhaust cubby... for the rest of you guys. just run the stock headers into 2 1/2" pipe and run this same combination (except only 1 resonator and about an 18~20" Magnaflow) and 2 1/2" or 3" in/out setups.
;
Last edited by odurandina; 04-13-2011 at 11:11 PM.
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04-14-2011, 08:16 PM
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Odurandina, I hope you will be providing "in process" pictures of the install and before and after dyno runs. Sorry to be off topic...
I know they are two different beasts and that most of the percieved power felt was just quicker turbo spoolup, but on my 951 changing exhaust from factory made a huge different in the butt dyno
I know they are two different beasts and that most of the percieved power felt was just quicker turbo spoolup, but on my 951 changing exhaust from factory made a huge different in the butt dyno
04-14-2011, 09:33 PM
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my exhaust will not make maximum power. reasons;
1. headers with sharp bends right after the heads.
2. impossible to get 8 perfectly spaced exhaust pulses per cycle.
3. 3 1/4" straight pipe with no bends or welds would be ideal after the y-pipe. but, i wanted maximum space outside the pipes for high sound dampening. running two resonators with narrower 3" inlet/outlets right after the y-pipe won't help here.
4. long magnaflow also with narrower inlet/outlet than ideal.
running the hotcam, maybe we'll see a loss of about 10~15 hp over a 'perfect' system = maybe 485~495 hp at the flywheel and 420~430 hp at the wheels, but at least the car won't be unbearably loud.
1. headers with sharp bends right after the heads.
2. impossible to get 8 perfectly spaced exhaust pulses per cycle.
3. 3 1/4" straight pipe with no bends or welds would be ideal after the y-pipe. but, i wanted maximum space outside the pipes for high sound dampening. running two resonators with narrower 3" inlet/outlets right after the y-pipe won't help here.
4. long magnaflow also with narrower inlet/outlet than ideal.
running the hotcam, maybe we'll see a loss of about 10~15 hp over a 'perfect' system = maybe 485~495 hp at the flywheel and 420~430 hp at the wheels, but at least the car won't be unbearably loud.
04-15-2011, 06:53 AM
#10
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If you unbolt the factory catback you can look inside the mid-muffler (aka resonator) and you see a nice wall right at the inlet. Seems pretty restrictive. A glasspack muffler would probably work well (in muffling) in place of that factory resonator and would be less restrictive. I put a cheap glasspack muffler from Summit Racing in my audi (the aftermarket catback only used one muffler and so it was super raspy) and it worked well. I chose a glasspack for the price alone in that case ($30).
What will this do to your performance... I don't want to open that can.
What will this do to your performance... I don't want to open that can.
04-15-2011, 04:42 PM
#11
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I was looking for something unrelated but found these gems.http://vibrantperformance.com/2010_c...logue_pg55.pdf
About $85, retail only.
About $85, retail only.
04-15-2011, 06:46 PM
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I came across these awhile back considering exhaust mods. For those concerned with maintaining some backpressure, they are available custom lengths and number of crimps. Prices seem good. I was planning on running only one of these for the whole cat-back system.
http://classicchambered.com/
http://classicchambered.com/
04-15-2011, 08:16 PM
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of course, many get confused here.... as backpressure doesn't make power.
a free-flowing system with an optimized pipe diameter creates exhaust scavenging. wiki;
"the magnitude of exhaust scavenging is a direct function of the velocity of the high and medium pressure..."
(fore and aft of each pulse as it passes through and exits the system), such that the pulses running behind the preceding pulse are made to flow into a vacuum akin to siphoning gasoline through the correct sized tube. if that tube is too big there isn't enough 'low-pressure' sustained behind each pulse—much the same as you wouldn't want to use a 3 inch wide hose to siphon gasoline.
3" pipe is too small for an LS3 in a single, straight through exhaust making 500 hp.
and 3 1/2" pipe is likely, a little too big.
i pulled a couple of excerps from here;
"THE MYTH OF BACKPRESSURE"
http://www.wheelsjamaicahost.com/whe...pic=846.0;wap2
....The effect of having larger exhaust pipe diameters (in the primary, secondary, collector and cat-back exhaust tubes) has a direct effect on gas velocity and therefore delta P (as well as backpressure levels). The larger the exhaust diameter, the slower the exhaust gasses end up going for a given amount of airflow. Now the ***** of all this tech is that one exhaust size will not work over a large RPM range, so we are left with trying to find the best compromise in sizing for good low RPM velocity without hindering higher RPM flow ability.
It doesn't take a rocket scientist to understand that an engine flows a whole lot more air at 6000 RPM than at 1000 RPM, and so it also makes sense that one single pipe diameter isn't going to acheive optiaml gas velocity and pressure at both these RPM points, given the need to flow such varying volumes.
....Scavenging takes advantage of the momentum of the exiting gasses. In essence, the fast moving exhaust pulse pulls a vacuum behind it. Momentum is mass times velocity. So not only do we need to keep the velocity high to prevent reversion - but it greatly improves the scavenging effect.
Thus we have a balancing act (as others have pointed out). We want to minimize friction to lower the backpressure as much as possible - larger pipes have less friction because they have less surface area per unit volume. But we want to increase the delta P as much as possible to prevent reversion and increase scavenging effects - smaller pipes increase delta P because they increase velocity.....
the rest of the article reads a bit too long but that's basically it....
/
a free-flowing system with an optimized pipe diameter creates exhaust scavenging. wiki;
"the magnitude of exhaust scavenging is a direct function of the velocity of the high and medium pressure..."
(fore and aft of each pulse as it passes through and exits the system), such that the pulses running behind the preceding pulse are made to flow into a vacuum akin to siphoning gasoline through the correct sized tube. if that tube is too big there isn't enough 'low-pressure' sustained behind each pulse—much the same as you wouldn't want to use a 3 inch wide hose to siphon gasoline.
3" pipe is too small for an LS3 in a single, straight through exhaust making 500 hp.
and 3 1/2" pipe is likely, a little too big.
i pulled a couple of excerps from here;
"THE MYTH OF BACKPRESSURE"
http://www.wheelsjamaicahost.com/whe...pic=846.0;wap2
....The effect of having larger exhaust pipe diameters (in the primary, secondary, collector and cat-back exhaust tubes) has a direct effect on gas velocity and therefore delta P (as well as backpressure levels). The larger the exhaust diameter, the slower the exhaust gasses end up going for a given amount of airflow. Now the ***** of all this tech is that one exhaust size will not work over a large RPM range, so we are left with trying to find the best compromise in sizing for good low RPM velocity without hindering higher RPM flow ability.
It doesn't take a rocket scientist to understand that an engine flows a whole lot more air at 6000 RPM than at 1000 RPM, and so it also makes sense that one single pipe diameter isn't going to acheive optiaml gas velocity and pressure at both these RPM points, given the need to flow such varying volumes.
....Scavenging takes advantage of the momentum of the exiting gasses. In essence, the fast moving exhaust pulse pulls a vacuum behind it. Momentum is mass times velocity. So not only do we need to keep the velocity high to prevent reversion - but it greatly improves the scavenging effect.
Thus we have a balancing act (as others have pointed out). We want to minimize friction to lower the backpressure as much as possible - larger pipes have less friction because they have less surface area per unit volume. But we want to increase the delta P as much as possible to prevent reversion and increase scavenging effects - smaller pipes increase delta P because they increase velocity.....
the rest of the article reads a bit too long but that's basically it....
/
Last edited by odurandina; 04-15-2011 at 09:08 PM.
04-15-2011, 09:22 PM
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Seems to be a case of "Do whatever the f*$% makes you happy," as undoubtedly many husbands have heard from their wives a time or two.
What do you all think? If it:
A. Reduces weight,
B. Tickles your auditory senses, and
C. Gives a boost in seat-of-the-pants or dyno proven pull..... It's a win right?
"Success consists of going from failure to failure without loss of enthusiasm."
-Winston Churchill
What do you all think? If it:
A. Reduces weight,
B. Tickles your auditory senses, and
C. Gives a boost in seat-of-the-pants or dyno proven pull..... It's a win right?
"Success consists of going from failure to failure without loss of enthusiasm."
-Winston Churchill