Planet-9 Porsche Forum banner

1 - 20 of 53 Posts

·
Senior Porsche Financier
Joined
·
732 Posts
Discussion Starter #1
I had intended to append my latest / final attempt at drone reduction to the first (whale) thread:
http://www.planet-9.com/987-cayman-boxster-modifications/50861-exhaust-drone-resonator-fix-design-construction.html

... as it was going to simply be a better 2 --> 1 tip assembly for the gen-1 borla exhaust. My prior attempt, documented near the end of that older thread, eliminated the true-dual nature of the borla exhaust, combining the two sides thru an X-pipe.

It reduced the drone somewhat and there were some concerns expressed about the path the exhaust took - each side crossing the other - in terms of possible performance loss. I never felt anything but solid performance, however.

The 'better' 2 --> 1 tip assembly consists of a 2-->1 merge collector, 2.25" inlets & 3" outlet -- which is only 5" long and so the entire assembly will fit in the same footprint as the Borla tip assembly.

A picture of that collector is below.

one last stab in the dark and I was going to call it quits, for better or worse. If I got an improvement w/ this latest tip then that's what I'd run, else, I'd use the prior attempt. All good.

But I found mention of exhaust 'inserts' used to quiet an existing system. I poked around, finding a cone -based design and, Car Chemistry's (CC) disc -based inserts. The CC insert is pictured below.

I was going to try the CC insert on the "inexpensive and probably couldn't hurt" basis. The web had the usual stew of 'merican V8 muscle comments but nothing which applied to opposed flat-6 engines.

And then I found the following post on pelicanpart's bulletin board - use of one of CC's inserts per side quieted an otherwise unlivable setup and, posted later in the thread, took a significant bite out of the drone.

the good stuff starts:
How to remove exhaust resonance/drone? - Page 2 - Pelican Parts Technical BBS

... the drone mention is the last on this page. Actual experience on a dual exhaust w/ a 3.6 flat-6.

I've ordered 2 of the 3-disc inserts, one/side. They will go into the tip assembly or into the Borla exhaust itself, just downstream of the header flange. The inserts seem to work best the closer to the headers they're placed.

If I can't fit them near the header w/o cutting then they should *just* fit into the tip assembly.

So, New thread because this could really show some results. More pictures when I actually have something in-hand to show.

I may try the inserts first w/ the borla tip assembly (keeping the true dual exhaust) and then w/ my joined tip. I prefer the sound of the latter and think I may be getting some side-side exhaust scavenging benefits w/ the two sides joined.

stay tuned!

-PM.
 

·
Senior Porsche Financier
Joined
·
732 Posts
Discussion Starter #2
Borla exhaust drone fix, part 2, the steel has landed

Three pictures after receiving the steel from Columbia River Mandrel Bends - as always the order and their work were spot-on.

first - the pieces. For a nominal fee CRMB cut 1/2" off one leg of each of the 90-degree bends and expanded that end for slip fit. The merge collector is shown below the two 90s and the 3" tube to the left will be used for the exhaust tip.

Some or all of the bend in the 3" piece will be used to straighten out the downward slant of the installed tip assembly - it drops ~ 1-1/2". The angled 3" piece will exit the rear of the car dead horizontal, I hope.

Second picture - the cut pieces ready to weld. I cut down the slip-fit inlets on the merge collector and 5-1/2" off the legs of the 90s so that the completed assembly, tip and all, will fit in the 12" - 13" available. The stock borla tip assembly is shown for comparison.

Third - welded! My welds are still **** (can you say '****' here? last time I tried I couldn't). I've dressed the welds some and will touch them up more but it's close.

Tomorrow it goes on the car and I'll finish assembly of the tip on the car - at least enough to tack it into the right orientation. Then I'll go for a test drive.

ALSO - the Car Chemistry inserts will arrive tomorrow so they'll be installed also.

Great things are afoot.

mmmv,
-PM.
 

Attachments

·
Senior Porsche Financier
Joined
·
732 Posts
Discussion Starter #3 (Edited)
Borla exhaust drone fix, painted, on the car and on the road

Alrightthen! one more picture below - the tip assembly painted.

I ended up installing the car chemistry inserts into the legs of the tip assembly I built -- and didn't get any pictures. I had to trim about 1.25" from the inlet end of the center tube. the 3-disc assembly was placed so that the first was in the expanded section of the 90 bend -- the coupling to attach to the borla muffler assembly on each side of the car.

This was the tricky bit - that first disc would nest *inside* the snouts of the borla muffler assembly which would in turn nest inside the expanded bit on the ends of the assembly I built -- each end of the 'T'.

The CC insert was placed inside the new tip assembly so the first disc was inside the expanded bit and the 2'nd and 3'rd were just behind where the tube restricted back down to 2-1/4". The inserts were pop riveted in place w/ steel rivets. I'll try to follow up w/ a picture detail of the inserts inside each end of the 'T' that is the new tip assembly. see the picture below. the cut end of the left insert's inner tube just extends from the left side of the tip assembly.

I put it on the car and went for a drive. I *think* the drone level is near to that of the stock exhaust ... slight between 2000 and 2400 rpm but very livable. Maybe a touch worse than stock but it's an improvement over the prior X-pipe design.

Since my original plan was to ceramic coat the X-pipe version, I'd installed a prior attempt (a true-dual) which droned a lot, so that's what my last 2 weeks' experience was. Pretty grating and what I have now is much better - and much better than unmodified borla drone levels.

I actually found myself turning the radio down some - because I didn't need it all that loud to drown out the exhaust.

The one thing I'd do differently is to keep about 3" more of the 90-degree bends' length on the legs which connected to the Y merge collector -- instead of butt welding a diagonal cut piece of 3" I'd just use the 3" end of the collector as my exhaust 'tip'. A pretty minimalist look and very purpose built but that's what I like.

Columbia River will also weld at $10/per and so I could buy the 3 pieces and have them cut, expand and weld and have a finished piece. I'm going to create an entry here for safekeeping so that I have the exact lengths every piece ended up at. I did minor cutting on top of the original specs to CRMB.

very satisfied! If anyone wants the picky details I'll post assembly instructions. w/ the CC inserts inside the ends of the tip assembly it's a tighter build - not as much room for error.
 

Attachments

·
Senior Porsche Financier
Joined
·
732 Posts
Discussion Starter #5
sorry, but no - I'm very pleased to put this one to bed. Car Chemistry had some dyno (non) results for their inserts; no significant difference.

If anything I'll come down on the side of a small gain in performance due to the side/side exhaust scavenging allowed by the Y-collector.

and for that matter I'd give up a couple of HP just for the noise reduction - my butt dyno has no changes at all to report.

thanks for the interest!

-PM.
 

·
Senior Porsche Financier
Joined
·
732 Posts
Discussion Starter #6
I'm headed up to Kansas Speedway today (8/16) and tomorrow to watch the grand-am and continental tire race practice, qualifying and the races themselves.

If anyone in the area wants to hear the new exhaust, please drop me a message!

-PM.
 

·
Senior Porsche Financier
Joined
·
732 Posts
Discussion Starter #7
Just a quick comment after 500 miles w/ the Borla and its new tip assembly - this eagle has landed!

The drone is down to stock levels -- there's still intake & road noises at the frequencies necessary to cause the body to resonate (drone). But it's considerably more age appropriate -- for good or ill -- and really easy to live with.

Gone is the deep-deep idle and low exhaust note; the exhaust is not a true dual any more and one side does not reinforce the other to create a low fundamental note. Obviously this is a basic change to the sound of the car but I wanted the borla's performance w/o all the noise.

The power is all there and reminds me of the shriek of 911 race cars as they wind up and out - but obviously a lot quieter.

I attribute most of the improvement to the car chemistry inserts -- even after installing them near the very end of the exhaust passage. I'd hoped to attach them just downstream of the header flange but there's a slight bend in the borla's tube which doesn't allow the inserts entrance.

I'm in the middle of One Last Thing -- I've gutted the stock exhaust tip (the pig's snout) and am using it to fill out the space occupied by the lone 3" slant cut tip. (the 3" tip will exit the center of said snout).

It will all be painted matte black and then I'm done. Really.
 

·
Registered
Joined
·
251 Posts
Please tell us some additional details: You used the 3 disc insert (2" diameter?) - did you use the disc or washer type plug shown in the picture or neither? As I understand it you could have done any of those three possibilities. If you used the disc or the washer like plug did they go on the insert closer to the header (upstream) or closer to exhaust tip (downstream)?
 

·
Senior Porsche Financier
Joined
·
732 Posts
Discussion Starter #9 (Edited)
Please tell us some additional details: You used the 3 disc insert (2" diameter?) - did you use the disc or washer type plug shown in the picture or neither? As I understand it you could have done any of those three possibilities. If you used the disc or the washer like plug did they go on the insert closer to the header (upstream) or closer to exhaust tip (downstream)?
Thanks for the questions!

I used two 2-1/4" 3-disc inserts - one for each side.

[edit:] regarding fit -- the fit inside the leg of the 16 gauge mandrel bent 90s is snug but acceptable. As noted the upstream-most disc actually nests inside the outlet of the muffler assembly which in-turn fits inside the expanded 90-degree bend.

The only thing dodgy about this attempt is the distance between the expansions on the new tip: too narrow and you won't leave enough to clamp the borla muffler assemblies to. Too wide and you won't have any lateral shift with which to center the tip. I'm fighting that now.

I intend soon to post my final build dimensions so that I don't suffer this issue again when/if I have a stainless version built.

....

Neither washer/plug was used - I cut about 1-1/2" of the inner tube on the inlet side of each insert -- cut smack in the middle of the last set of indentations.

Which may have been a small mistake -- the directions w/ the inserts show where to cut as a bit closer to the first disc on the inlet side. cutting as I did I kept the last set of indentations in the inner tube which may pose a very slight restriction of the inner tube.

When I pull the tip assembly (soon!) I'll trim it back as shown but it's more for my (obsessive) peace of mind than any perceived problem.

The whole setup sounds pretty tame unless I'm winding it out - then in has a pleasing wail.

To be clear - I wanted to retain the structure and power of the borla exhaust but w/o the actual drone and sound. What I have now is much easier to live with but it is a fundamentally different sound.

thanks again,

Mark
 

·
Senior Porsche Financier
Joined
·
732 Posts
Discussion Starter #10 (Edited)
Oven Roaster Porcine Rhinoplasty

putting it another way - adding the gutted stock CS pig-snout exhaust tip to the new exhaust assembly.

But before we can dine we have a couple of pictures of the car chemistry inserts installed in the new tip -- the first is as initially installed. The second was after trimming the flash resulting from the original cut.
 

·
Senior Porsche Financier
Joined
·
732 Posts
Discussion Starter #11 (Edited)
and for your dining pleasure ...

1) Ugly welds, unpainted and unpolished.
2) Everything looks better w/ a coat of paint.
3) The finish was oven-baked for added flavor.

Bon appetit! It goes on the car tomorrow morning.
 

·
Senior Porsche Financier
Joined
·
732 Posts
Discussion Starter #12 (Edited)
steel pieces dimenstions and cuts, & drone and air-fuel ratio

Back again! the painted exhaust tip is on the car and still works.

Tucked away in Car Chemistry's web site is a note on air-fuel ratio and exhaust noise. It mentions that a too-rich mix causes a much louder exhaust note, all other things being equal.

And that came to mind on a test drive after installing the painted tip -- in the driveway the car had idled back down from its startup rpm and so I thought it was finished w/ its warm-up sequence, richer mix and all.

On the road I was displeased to find an increase in drone under the driving conditions which droned. some 10 minutes / miles later that drone was gone again and I recalled car chemistry's note on AFR.

I put the episode down to warmup of engine, oil and water to taking a lot longer than I'd imagined.

------

Build notes:

2-1/4" 16 gauge 90 degree bends, 3" center line radius, 6" legs:

  • To get the total length of this piece from end of one leg to the outside of the other leg -- 10-1/8": leg length + center line radius + tube radius == 6" + 3" + 1-1/8"
  • Cut 1" from one leg of both bends and expand that cut end for slip fit. This is each side's connection w/ the rest of the borla muffler assemblies.
  • The other leg connects w/ the Y merge collector and is trimmed depending on where you want the end of the collector located on the finished tip, front to back. Cutting 5-1/2" from these legs left just enough to weld to, and required a 2-3/4" piece of 3" welded to the outlet of the collector to act as an exhaust "tip". only cut 2-1/2" (or so, ymmv) from this leg if you want to omit the tip-let piece and place the outlet of the Y rearmost. I may try this next as I like the minimalist race-built look.
Y merge collector:

  • As purchased the collector w/ slip-fit inlets is 6" long, not the 5" of the butt weld version.
  • As noted, I cut as much as I could from the leg of the 90s connecting to the collector. I also cut 1" from the slip fit collector inlets so to leave room for a "tip" piece at the collector outlet.
  • If building w/ the collector outlet as the tip, this trim isn't necessary.

A photo of the installed assembly is attached - not the best as I couldn't see the display on my fone to properly frame the shot.

If anyone has a tip "heat shield" (catalog description) to fit that trapezoidal space around the exhaust tip to sell let me know - I can't justify buying a new one but I lost mine some time ago and want to finish the look.



-PM.
 

·
Senior Porsche Financier
Joined
·
732 Posts
Discussion Starter #13 (Edited)
Ceramic coated porcine rhinoplasty

Still working with the borla tip assembly w/ the outer shield taken from the stock exhaust tip. still looks like a pig snout to me, hence the references to 'porcine'. Now really (reallyreally) entering its final phase -- I'm liking the result so much I had the whole exhaust ceramic coated.

And I half expect another change to the drone characteristics of this exhaust: The ceramic coating will keep much more of the exhaust charge's heat in the charge and so significantly raise the speed of sound inside the exhaust. Won't affect the *frequency* of the sound produced at any given rpm but will increase its *wavelength*.

So I may be cutting the drone issue/search in half by this move -- if the drone rpm point drops significantly then what has been observed is due to resonance inside the exhaust, acting a bit like an organ pipe.

And if it doesn't then it's an effect of the exhaust note as it travels in normal temp air. stay tuned on that.

a couple of pictures and they don't do it justice. It looks good enough to lick but I'd never do that. and post about it. Ceramic coating by Springfield (MO) Powder Coating -- an excellent job and very reasonably priced.

And yes, it's sitting on my living room rug but that's OK as it's really clean. I do the dirty car jobs on the kitchen counter and in the bathtub.
 

·
Senior Porsche Financier
Joined
·
732 Posts
Discussion Starter #15
Yogi Berra edition

an update, and a reason why drone is hard to beat.

The update is I'm still happy w/ the above work. I had my borla ceramic coated as well as the tip assembly shown here. still loving the results.

There's one distinct drone-ish note which isn't going away and I think it's intake resonance. If you look at many modern intakes, between the air filter and manifold there are often one or more heimholtz resonators ... done in plastic and looking like side plumbing which don't go anywhere. My 0.0002 is they're explicitly tuned to eliminate specific resonances.

I *may* play w/ one such, but the air intake, and the left side of the cayman's engine, is packaged very tightly. maybe later.

And the interesting bit is I'm preparing to replace my rusted exhaust manifold (the ones w/ the dead cats) w/ some ceramic coated used ones.

That's not the interesting bit though. The interesting bit is the replacement manifold-engine gaskets I bought to accompany the header swap. like so:

2014-05-14 20.46.10.jpg

pressed / embossed between the exhaust ports is a continuous channel linking all three ports. Remember that the stock header's runners are 3 different lengths.

With every exhaust pulse, the header is resonating at 3 different frequencies, not counting harmonics, cancellations, acolytes, followers, honkers, lispers, trolls and dimwit random noise ... it's never going to be one frequency to cancel!

I stand a much greater chance of dealing w/ the intake resonance, because there's only one length of runner involved.

Be well,
-PM.

"You can see a lot just by looking." - Y. Berra
 

·
Registered
Joined
·
15 Posts
Thank you Plainsman!. I followed your work with reducing the drone from the Borla exhaust. I was a little concern about exhaust flow restriction with the use of car chemistry exhaust inserts. Therefore, instead of using a 2.25 inch CC inserts I used a 3inch. These things are awesome,..they do work. The buzzing and ear pressurizing drone between 2000 - 3000rpm is now reduced to a tolerable level. In fact, the exhaust sound within 2k-3k rpm is now pleasurable. The signature borla howling and wailing sound from 3500 rpm and beyond is still there it's just slightly tuned down. As for exhaust flow, I'm confident to report that there's zero sign of restriction.
 

Attachments

·
Registered
Joined
·
15 Posts
I'm very satisfied with the result that I just had to post again. I'm back in my office after over an hour of spirited driving with the "Car Chemistry" Borla exhaust,..Holy crap! The power and the sound, it's intoxicating. Acceleration is crisp. The exhaust sound is sensual. The car emits a mild burble at idle through 2200 rpm. If you have a Borla exhaust and love the sound but hate the drone? Add a 3 inch 3 disk Car Chemistry inserts. BTW I did not use any of the included plugs for the inserts.
 

·
Registered
Joined
·
1,726 Posts
Good that people exist that attempt to improve things because borla exhaust on a Porsche is just wrong...goes well on on a chevy though.
 

·
Senior Porsche Financier
Joined
·
732 Posts
Discussion Starter #20 (Edited)
I'm very satisfied with the result that I just had to post again. I'm back in my office after over an hour of spirited driving with the "Car Chemistry" Borla exhaust,..Holy crap! The power and the sound, it's intoxicating. Acceleration is crisp. The exhaust sound is sensual. The car emits a mild burble at idle through 2200 rpm. If you have a Borla exhaust and love the sound but hate the drone? Add a 3 inch 3 disk Car Chemistry inserts. BTW I did not use any of the included plugs for the inserts.
Dumb question -- I'm assuming you went with 3" diameter inserts ... Where did you find 3" plumbing on the borla to insert them? Mine is 2-1/4" tube from the header flange until the tips.

Edit - it was a dumb question - I looked at your photos -- really inventive!
 
1 - 20 of 53 Posts
Top