[bob blackwell]

I removed the front resonator and rear muffler completely on my first 968 and used a straight pipe all the way back where I used a Supertrapp mufler with the ability to "tune" the exhaust by adding or removing discs from the supertrapp. It was loud, and had a sound that was unpleasant to some when you really accellerated hard. (I thought it sounded great). The back pressure could be regained by removing discs (quieter too) and the performance felt fine (no dyno tests). The complete stock exhaust was available for resale (which I did) or replacement later, good luck, Bob Blackwell..

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[orphanowner]

[quote name='flash' date='Dec 4 2005, 05:03 PM']steve - in looking at the above post (nice job by the way) am i correct in understanding that the 2 tubes are not present in the center section of the resonator, and are only present in the last section?

[right][post="13085"]<{POST_SNAPBACK}>[/post][/right][/quote]





Yes, the two tubes are only in the last section of the resonator. These tubes are the same tubes that lead to the rear muffler, however they are perforated in the resonator and surrounded by fiberglass packing to reduce noise.

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[flash]

yeah - saw the perfs - having velocity thoughts - interesting - may have to break out the manometer again

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[RS Barn]

OK so I'm going to add some more input even if I have to mention alternative options. The stock system was designed with a very specific hp and noise cap. It is very effective in that range. As we add mods to the 968 , the exhaust becomes another area to consider modifying. Compression, air and exhaust need to work together. There have been some cool cheap mods and chips that have really added to the potential of the 968. I am looking outside the box into some serious HP and TQ for this motor. Therefore all three areas need to be addressed. The stock exhaust is limited and I have proved that from my testing. others that have tested feel the same way. I moved on to a system that can handle much more power.

The mods to the stock resonator are viable and seem to work well within the basic stock upgrade parameters although not tested . I think they will fall short of my goals for much more power.

Thanks to anyone who takes the time to try something new.

Pete

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[Greimann]

Update to this thread! I had a chance to instrument this little modification now that I took time to do it. I read the back pressure of the stock exhaust system at that convenient but mysterious little bung that is just in front of the cat. Drilled and tapped for a 1/8" pipe fitting and some copper tubing.

   

Stock back pressure at a full power run to 7000 RPM is 5.5 PSI. Not bad really for a stock system.



Enter the torch. I actually tried the hole saw method first and while that worked to remove the "alien face" disk, the rest of the structure needs to be flamed out. If I was to recommend an efficient approach, I would torch out the perforated tube first, then torch out the center disk second. If you get your nose in there, you will see what I mean. It is hard to photograph.



       



After the torch treatment, the backpressure to 7000 RPM was 4 psi. 27% reduction. Not bad either. The sound is barely noticeable to be more growly than stock. Certainly quieter than aftermarket. Maybe a bit livelier on the throttle. Regardless, it is fun to get the torch out!



Anyone out there care to instrument up a B&B or similar for comparison?

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[S_Cal968]

Dave,

I'm assuming that your muffler and muffler bearings are stock? <img src="/forum/images/smilies/968/biggrin.gif" class="smilie" alt="" />



In my case since I'm torchless, I may just install the straight pipe instead. That should reduce weight and get the flow benefit.

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[flash]

i have 2 systems that can be tested - mine and pete's

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[tsj9197]

i did this mod over the weekend.

seems to add a little sound and help throttle response.

not quite as much as drilling the pipes on my harley though <img src="/forum/images/smilies/968/smile.gif" class="smilie" alt="" />



any long term updates to this mod??

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[baz]

I undertook this mod in Sept `07 and combined with the air box modification, Promax ROW chip and 98 octane fuel it seemed to provide a noticeable "seat of the pants" overall improvement to the driveably and sound of the car.

Interested in comments from anyone else who carried out mod.

As an aside it cost $50 and one hour in the local muffler shop to complete the removal.

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[unknown4u]

Has this modification also effect on making a tiptronic a bit faster?

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[baz]

"After the torch treatment, the backpressure to 7000 RPM was 4 psi. 27% reduction. Not bad either. The sound is barely noticeable to be more growly than stock. Certainly quieter than aftermarket. Maybe a bit livelier on the throttle."

Dave`s test above would suggest that there is a "benefit" but never quantified by dyno testing.

If there is a HP gain I would assume it would be relatively minor but consistent across the 6spd/tip.

Those that had done it so far seem to have reported a consistent belief that there is a benefit to be had and as the end result is based upon the sum of the parts as long as it is postive modification it is probably worth doing.

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[flash]

i've been in a car that had this done - it seemed to rev a bit more freely up top, but seemed to lose a bit down low - this would be in line with all of the lower restriction straight through systems out there - the tone was a bit better though, which may be enough to make it more fun

it is important to understand that while back pressure is bad, low velocity is worse - the latter is frequently misnomered as back pressure

what we have found that removing back pressure almost always results in lower velocity - the result is a low mid range torque loss (sometimes very dramatic) - the benefits are sometimes a couple of horsepower up top

it all comes down to what is important to you

one of these days i'll spend more time and money on a new system that gets it all, but after spending well over $10k on these things already, i think it will be a while

to date the only thing proven not to lose torque is the rs barn cat-back

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