l.chadburn

Hi all

Question - Is a DECAT, CUP and G_PIPE combination too loud for built up areas?

Lee

crg53

Yes, most definitely, if you take both the mufflers and the cat off, all you have left is a straight through exhaust, doesn't even sound good.

mr pg

YEEESSS! Have heard one such set up, and could be heard a long, long way off. Sounds fantastic (from a distance), but way too loud. Plod would not be happy.
The owner used to be on here, so I'm sure others will chip in. Cup, or G pipe, but not both.

jaguarman

I would imagine that it would be very, VERY loud.

I have a G pipe and my wife thinks that is too loud. I think it's fine, nice burble and slight popping on the overun.

Why not try one step at a time and see what you think.

freedman

Too loud for anywhere IMO

I tried it after my secondary box split at Spa. I soon took the G pipe off and put a repaired box back in its place!

Bypass and Cup, or Bypass and G pipe, dependant on your tatse, as they both sound different

But all 3 sounds just sounds ridiculous

l.chadburn

Cheers guys.

I have Decat and G pipe at the minute, which I love the sound of.

When I bought the near side bumper with the exhaust cut out, the guy was also selling a dual pipe which replaces the tail pipe and splits into 2. However it doesn't fit when the silencer under the bumper is on.
So looks like I will be refitting the final silencer and running this with decat and cup.

Lee

PorscheZen

Beware - you may not get the performance that you expect with such a free flowing exhaust (aka - no back pressure). This can cause a number of conditions such as running too rich and creating crusty deposits on your pistons . Also, I found that without specific engine mapping/chip, running w/out all the exhaust restrictions also reduced engine performance.
Like this:

August West

Some numbers to kick around...

Max Flow CFMs:

Cat 442cfm
Primary 396 cfm
Secondary 462 cfm

I can't remember where I saw these numbers but I took note of them for future regurgitation. The numbers show that the Primary muffler is the most restrictive of the three components.

My understanding is that some back pressure is required to attain streetable low- to mid-range torque. Full flow exhaust is strictly for high rpm horsepower as in full-on racing engines.

Having said all that, I love my sport cat/stock primary/G-pipe exhaust. With a cup airbox cover, the noise above 4000 rpm is nothing short of glorious. I chose the sport cat because there's only a 2 horsepower difference between it and a full-on cat bypass and it makes me feel slightly less guilty of my emissions footprint.

RW964

Good numbers I have seen them before.I have the two pipes cup and J pipe what I have put a eye on if you change the pri pipe you wil get better top end and lose a bit of lower tourque. If you leave the primary on and change out the sec aka G or J pipe you gain lower end tourque and not top end speed.
I like the sound of the cup pipe as it sounds like a true Poursche.. Really nice. The G pipe sounds like a muscle car a bit . The two are about the same level of sound... Just my two cents worth .......

Some numbers to kick around...

Max Flow CFMs:

Cat 442cfm
Primary 396 cfm
Secondary 462 cfm

I can't remember where I saw these numbers but I took note of them for future regurgitation. The numbers show that the Primary muffler is the most restrictive of the three components.

My understanding is that some back pressure is required to attain streetable low- to mid-range torque. Full flow exhaust is strictly for high rpm horsepower as in full-on racing engines.

Having said all that, I love my sport cat/stock primary/G-pipe exhaust. With a cup airbox cover, the noise above 4000 rpm is nothing short of glorious. I chose the sport cat because there's only a 2 horsepower difference between it and a full-on cat bypass and it makes me feel slightly less guilty of my emissions footprint.

Steve Weiner-Rennsport Systems

These cars are rather sensitive to exhaust tuning and one can easily ruin factory performance.

Removing the cat, primary & secondary mufflers destroys low & mid-range performance without any return at high RPM. Its a large net loss.

Removing the secondary muffler and replacing it with a bypass aids low & mid-range power and just the ticket for cars with stock gear ratios.

Removing the primary muffler for the Cup pipe reduces low & mid-range and adds a little on top. Good choice for cars with close-ratio gears used at the track.

Removing the cat and replacing it with a "test pipe" gives a slight reduction in low end power and trades that for a nice boost in the mid-range and on top.

The most popular one we do for street cars is the seconday bypass and "test pipe". Together with a proper chip thats programmed for these changes, its a very noticeable improvement in power.

Steve Weiner-Rennsport Systems

Those deposits are from excessive oil consumption, not rich fuel mixtures.

crg53

I have been running a test pipe / primary bypass for quit some time now, wouldn't mind trying the test pipe / secondary bypass. Is there any difference in performance between the short G pipe and the long one (goose neck) other than the size of cause.

napaul

if i may i would like to ask steve a question would the test pipe(drilled out cat) and secondary bypass(gpipe) affect idle in any way from the reduction in backpressure? and would a chip that is tuned to these changes as you mentioned to be beneficial to those of us who make these exhaust changes?

RW964

Steve I hope I can use your lines of wisdom kinda what I was talking about .. I changed out the two pipes at diff times and could note the differance in the while my butt dyno 'not calibrated" could tell a change between the two pipes. Slight but a change. The J pipe made the car better to drive not alot of clutch peddle to get going and shift. The cup pipe may be not as loud. Bettter sound. BUT the G pipe is better in every day driving as Steve may have stated. I would go with lower end grunt for street than top end on the street as that is where we drive em at .... Now added a chip and all came together.. Made for the setup.... Next may be a cat bypass Steve you do a great job here keeping us a in a straight line ---------------------------------------------------------------------------->


these cars are rather sensitive to exhaust tuning and one can easily ruin factory performance.

Removing the cat, primary & secondary mufflers destroys low & mid-range performance without any return at high RPM. Its a large net loss.

Removing the secondary muffler and replacing it with a bypass aids low & mid-range power and just the ticket for cars with stock gear ratios.

Removing the primary muffler for the Cup pipe reduces low & mid-range and adds a little on top. Good choice for cars with close-ratio gears used at the track.

Removing the cat and replacing it with a "test pipe" gives a slight reduction in low end power and trades that for a nice boost in the mid-range and on top.

The most popular one we do for street cars is the seconday bypass and "test pipe". Together with a proper chip thats programmed for these changes, its a very noticeable improvement in power.
__________________
Steve Weiner
Rennsport Systems
Portland Oregon
503.244.0990

AFKC

I have tried every combo, and most will not agree but I like stock cat and both mufflers bypassed. It is loud, but I only put about 1k miles a year on my car. If I drove it every day I would do g pipe and cat bypass. My car pulls very hard at all rpm's with the two mufflers bypassed. All bypassed is fun for a little bit, but very loud and I did notice a loss in power.