[orphanowner]

While I'm new here, I'm been wrenching on the 944 series Porsches for close to 20 years. I recently got back into personal ownership of one of these great cars when a friend of mine reluctantly decided to take me up on my long standing offer to buy his M030 1994 coupe. The car is setup now for PCA club racing, but has never been on the track due to the owners health issues. Not sure if i'm gonna put it all back to stock or keep it this way as a track car. Car is really too nice for the track.



Anyway, first order of business for me is getting max power out of the stock engine. I"ve attached a pic I took of the stock muffler inlet. Notice the restrictive deverter. Has anyone whacked this out yet? It's in there soley to force the exhaust through the outer chamber of the muffler to keep the EPA noise police happy. This has to go....

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[ds968]

YIKES ! You have an alien in your exhaust. So that's where all " the greys " are hiding pending the inavasion... <img src="/forum/images/smilies/968/tongue.gif" class="smilie" alt="" />



I got rid of the entire catback, saving a ton of weight in the process and getting a hell of a nice tune with my BB system, but for those who wish to keep it stock

( except for that restriction ) this may be a great solution...

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[bob blackwell]

I deleted the rear muffler entirely and ran two straight pipes back to the rear instead. Also saved a lot of weight and improved the sound. No dyno tests to verify additional power but it feels better. Good luck, Bob Blackwell.

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[sayporsha]

Wow. Thanks for posting that pic - I've always wondered what was in that resonator.



Bob, isn't that a little loud with no muffler?

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[RS Barn]

I tried to open the resonator to no avail. There are mutiple restrictor plates in the resonator. It is large enough to handle the volume but is heavy and cannot be modified, therfore other cat back options are required.

Pete

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[Beachboy]

I tried the no rear muffler/resonator that Bob mentions and found it to be too loud. I ended up with a flowmaster in place of the Porsche part (that weighs mucho) for a weight reduction and a nice sound on throttle but quiet when cruising. The shop put the stock tip back on and it looks great for $175.

GO SOX!!!

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[bob blackwell]

Jeff, to me it isn't too loud at all, just has a deeper, more powerful sound as I like to have in a Sport Car. I kept the front resonator and just deleted the rear muffler. Good luck, Bob Blackwell.

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[sayporsha]

Brian, I'd like to see some pics of your Flowmaster system if you get a chance. I'm curious to see how they funneled the 2 pipes into one. Also, which model # is your Flowmaster? They offer so many, it's dizzying.

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[flash]

having now played with a couple of different setups, i can tell you to be very careful about what you do in back pressure reduction - the dyno has shown torque loss by opening it up too far



the first mistake i made was to eliminate the resonator and just run a muffler and i lost almost 20 lb/ft - i've driven 2 other cars that did similar things and they also exhibited similar torque losses - there was a small horsepower increase up top though on mine (don't know about the others, but it makes sense)



adding back in a different resonator helped, but i still have a small turbulence issue givnig me an imperceptable, but visible on the dyno, dip at 3.2k



i am working on new systems that will come with dyno proven increases or not at all



it all really comes down to what you want - just sound or power too

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[Beachboy]

Just to clear this up, I tried removing the rear muffler or whatever you want to call it, not the front one. The pipe was then extended to the srear with the stock tip. It is certainly a matter of opinion but me neighbor, who is not critical on this issue, said he could hear me from miles away and could hear the car idling in my driveway.

Sorry I don't have picture posting ability and my muffler shop just put in the one that fit the best. The two into one is a simple Y connector. I'm sorry I didn't weigh the two units for comparison but the new flowmaster is considerably lighter.

Ha! I just checked the file to see if there was a model # and it was a magna-flow, not flowmaster. But no model # shown.

I think you have to be very careful about who you choose, some of these muffler shops are really hatchet job joints.

I started talking to the owner of this small, non-franchise, shop about how I wanted my car treated, none of his boys were allowed test driving , I know every scratch, etc. when he just took me outside to show me his Viper and reassured me that he knew how I felt about my car and that he would be the only one to drive it.

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[orphanowner]

I'd tend to agree with RS Barn, the stock resonator does have multiple diverters and while I haven't tried to remove them yet, I'll bet it's close to impossible without cutting the muffler open. Porsche spent a lot time and effort on the 968 exhaust, trying to optimize flow without making the car too loud. I've constructed a number of racing exhausts for 944 N.A. cars and anything that showed significant gains in power were all very loud and IMHO, way too loud for a guy that likes to fly under the radar on the street (me). The gains were all over 5000 RPM as well, which worked great for a track car but won't give you any additional grunt for around town driving.



I've attached an image of an exhaust I did on a 968 engined 944 track car. It was barely quiet enough for the loud tracks and wouldn't pass sound at tracks like Laguna Seca, really nothing short of the stock exhaust would work there.

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[orphanowner]

I had some time today and more importantly the motivation to finally dig into the resonator and attempt to remove the diverter plate. Not particulary easy or simple. You know the kind where you practically empty the tool box to complete the job. I will write a DYI if there is enough interest, but this was absolutely a worth while modification and once the diverter is removed, it will be quite obvious that the diverter was an afterthought and added solely for the purpose of sound control. Contrary to popular belief, there is only one diverter in the resonator.



During this project, I learned a lot about what this part is supposed to do and why Porsche had the vendor install it. Basically, it slows the exhaust velocity by forcing it through a pair of slots that equal about 2 square inches and also through the side perforations in the main tube, which then exits behind the diverter. This section of the exhaust is so restrictive that the resonator case is discolored from the additional heat that results from this restriction. I will also comment that the material used in the construction of this part of the exhaust is probably inconel stainless and very resistant to heat. It was very difficult to cut or saw and finally required the flame wrench. The parts I removed required LOTS of tedious sawing, bending, chiseling, and finally torching to cut the pieces up small enough to remove them. The cutting torch went slow, another indication of the durability of this material.



With the "plug" finally removed, the inlet now empties into a 8" deep chamber which feeds the pair of perforated resonator tubes, basically a pair of "glass pack" mufflers, which exit the resonator as the pair of pipes leading to the rear muffler. I’m sure this was the original design as it clearly allows unrestricted flow to the resonator tubes while reducing the resonate frequencies with minimal restriction.



While I’ve only gone for a short test drive, there is a definite difference in the both sound and the engine response. The exhaust note has a little more boom or bass to it and you can actually hear some engine note, which was missing before. Performance wise, the engine seems more responsive and seems to pull stronger on top. I’ve noticed absolutely no decrease in torque or drivability In short time I’ve driven the car. Tomorrow I will do a top end run (or close to it) and report the

results.

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[Greimann]

Great report. I have my torch warming up anticipating your followup!

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[flash]

fun project for sure - sort of supports what i have been thinking and working on in a different direction



any chance you did any low rpm acceleration timing prior to cutting it up, so as to compare with now, to see how the low end torque did?

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[sayporsha]

Thanks for the writeup - great information. Some dyno testing would be great, but a report of day-in/day-out use on the ass dyno would be helpful.



I know the development of the 968 was very costly to Porsche in a time when they were struggling to stay afloat. One wonders if they resorted to quick fixes - afterthoughts - in the end just to get the thing out of development. This design element could have been one of those end runs. Besides, they wouldn't want it to keep up with the Carrera, now would they? <img src="/forum/images/smilies/968/wink.gif" class="smilie" alt="" />

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[orphanowner]

I have some data points from when the car was stock with only a chip. I will compare the performance then to now when I get a chance and post the results.



Eventually I plan some dyno runs, but there is little validation to be gained from that exercise, since I don't have an unmodified dyno run as a baseline.



With that said, there is no question in my mind that a significant flow improvement is gained by removing the diverter from the resonator. No way would Porsche have put forth this much effort into restricting flow unless there was a crisis situation. It's just not logical to start putting restrictor plates in an otherwise sound exhaust design.



I do know of instances where Porsche and VW installed restrictors in the exhaust on certain vehicles and reduced the overall output in others simply to insure that the "pecking order" of various models held integrity. This is such an obvious instance of "intentional" design compromise that I'm certain there is a significant gain to be had with this modification.



UPDATE...ran the car a bunch this morning. Did a measured top end run at my secret testing facility. At least 6 mph increase in my usual GPS validated top speed. Ran the test twice and got the exact same result. While far from scientific, there is definitely a gain. Plus, the butt dyno says the bottom end is stronger as well. Finally, the sound is a large improvement akin to the airbox mod. Anyone local to SoCal is invited to go for ride.

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[flash]

absulutely!!!



drop me an email - let's do it - it's long past time we met anyway

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[Greimann]

Once I get the house done, that is going to be the next mod!

   

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[sayporsha]

Did a measured top end run at my secret testing facility.

Good thing the longitude/latitude weren't displayed on your GPS!



Is there a better way to cut that thing out? I'm reluctant to take a torch to mine. It would be ideal to divide the plate/perforated pipe into thirds, then cut the segments off near the flange & remove them one at a time.

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[Mark]

[quote name='Greimann' date='Nov 24 2005, 02:13 PM']Once I get the house done, that is going to be the next mod!



[right][post="12762"]<{POST_SNAPBACK}>[/post][/right][/quote]





Wonder how many people clicked on the picture. <img src="/forum/images/smilies/968/biggrin.gif" class="smilie" alt="" />

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