Installed TS catback, have drone, anything I can do?
 

Hello all. I installed the Top Speed Pro 1 cat back exhaust. All my stock cats are still in place.

I have a loud drone between 2,500 and 3,100 rpm. Car is a '01S.

Anything I can do about it? Any hints to improve the drone? Everything else sounds good but the drone is quite loud and annoying, if I can get rid of it all is good.

I wonder - I used some steel about 1.5" long to lower the mounting bracket as it seemed high to me. I did not want to tilt it down with spacers. Wonder if the slightly less support from bracket contributes to drone?

Thanks!

If the muffler is a 2-can design, there's not much you can do. My car came with a Brullen catback muffler (no longer in business) installed by the PO. Made me nuts for a while. I love the sound and the volume and have adjusted my driving style to stay over 3k as much as possible.
You'll learn to love the drone, or keep the revs out of the drone zone. I did, however, find a factory muffler (free)and all the incidentals (pipes & clamps for $30) to install it if I decide to break down and go back to stock.

I've heard tails that using these EasySeal Exhaust Clamps will take away the drone.

EasySeal Exhaust Clamps: Torca EasySeal Clamps in Stainless Steel for Lap Joint Connections

Kram is dead on with the clamps. Guys that are using those clamps have eliminated the drone problem. Stay out of the drone zone. Not good for the car anyway. Just my opinion.

Not gonna work... Clamps don't fix resonance. ;)

[The exhaust pipes in automobile exhaust systems are designed as acoustic resonators that work with the muffler to reduce noise, by making sound waves "cancel each other out"[1]. The "exhaust note" is an important feature for many vehicle owners, so both the original manufacturers and the after-market suppliers use the resonator to enhance the sound. In 'tuned exhaust' systems designed for performance, the resonance of the exhaust pipes can also be used to 'suck' the combustion products out of the combustion chamber at a particular engine speed or range of speeds.]

http://en.wikipedia.org/wiki/Resonator

I also installed the top speed cat back mufflers on my 01 S and got the drone.

The solution was to get the 2nd cat delete pipes from Top Speed and no more drone and awesome sound.

You will very happy if you do this and its an easier job than the mufflers.

Thanks everyone.

I replaced my muffler because stock had something loose inside that rattled. Getting better sound was a benefit I looked forward to, however this drone is excessive.

Appears as though the 2 can setup is prone to drone (rhyme every time) but can be minimized.

I am going to recheck my set-up for possible leaks, put on the recommended clamps, and if that does not work will consider installing test pipes.

Concern I have with test pipes will be that the exhaust will become loud. Any input here is appreciated as well - how much louder without the secondary cats? And does the 2nd cat delete eliminate all the drone, or just make it better?

I would put the stock exhaust back on but the rattle is annoying.

Thanks!

Gary

I put on my GHL exhaust a few weeks ago and thought the drone was obnoxious. BUT - now that I ahve had it a few weeks, first off I dont notice it too much but it is very easy to feather the throttle when need be to lessen drone. I am now in love with the sound and drive the car just to hear it. It can rattle my brain all it wants, I cant get enough.

I got the TS. Same resonance at those rpms. Helps remind me to keep the revs up when cruising around. I like a loud sports car, so it's fine.

Someone who installed the test pipes recently mentioned basically the opposite, that it was too noisy at higher rpms, but they didn't seem to complain of the brain-shaking resonance at low rpms, so I was confused. I guess you need the test pipes, as others mentioned.

I had fitment issues with mine that caused minor drone. After getting a welder to tighten everything and fix the exhaust leaks for $50, there were less vibrations and no drone. The car and exhaust feel very solid and well put together now. The car is quiet when I am cruising and only gets loud when I accelerate.

My tips were high hitting the rear bumper. Once I put spacers(50 washers) in and longer bolts from Home Depot, the tips lowered and now they look great.
One thing to mention. I installed Test pipes a month before the cat-back exhaust.

It looks like this now.
http://farm4.staticflickr.com/3736/9...49df954f39.jpg

I installed the Cat delete pipes at the same time that I installed the exhaust. At first, I thought what have I done? The drone was unbearable. Once I put the clamps on, sealing a major leak, and then fiddling with the u-pipes to make sure they weren't leaking, the drone was eliminated. The key seems to be eliminating any leaks and making sure everything is solid. Once you get it sorted, the sound is great! Good luck:cheers:

Topless - wonder what would happen if a pipe is welded between the 2 cans, connecting them? Would resonance go away?

Just had a muffler shop look at it, said there are no leaks and all looks well assembled.

I am going to next step, trying out the clamps. Is 2" the right size?

By the way, the car does feel more responsive...

Yes, 2" is the right size.

Lets all be clear on this. You never want any exhaust leaks in the system. Make sure it is absolutely tight. The sound from an exhaust leak is different from 2-3k acoustic resonance drone caused by exhaust tuning. Apples and oranges. The goal is a tight exhaust AND no 2-3k acoustic resonance.

To solve the resonance problem you need wave cancellation in the 2-3K drone zone. Sort of the same technology as the Bose headphones that cancel outside noise. A perfectly placed connector pipe that is the right length and right diameter might work. It will require math or a lot of trial and error. A noticeable drone or nasty exhaust note is an indication that resonance and acoustic standing waves are interfering with the free flow of exhaust gases. I have not yet seen a drone-free 2-can exhaust but it is possible with precise acoustic tuning.

Essentially Porsche engineers carefully tune the stock exhaust to cancel frequencies in the 2-3K drone range, reduce overall loudness from 110db to about 90db, and let the sweetness of the motor come through under full throttle. They spend a ton of R&D time and money to get the sound right because it is a big part of Porsche DNA. The stock exhaust is big and heavy but it works well. The best solution I have seen is to do the Pedro sport exhaust mod which retains the 2-3k wave cancellation while letting more sound out.

I hope this helps.

Topless, excellent post, thanks! Fascinating stuff.

I am going to give the clamps a shot because it is easy and simple, if that does not work I will rethink what to do - TS or return to stock?

from another thread:
You could try this, though the fabrication may not be cheap:
http://www.planet-9.com/987-cayman-boxster-modifications/50861-exhaust-drone-resonator-fix-design-construction.html

Stephen,

Interesting read. People say deleting 2nd cats takes away the drone, which seems counterintuitive to me as it increases flow, and I would think also increases noise.

However after reading the Planet-9 thread my conclusion is that taking away the cats changes length of exhaust path, which changes shape of sound wave, and in this case apparently reducing resonance.

Still scratching my head - test pipes, or go back to stock with Pedro mod.

Gary

This guy definitely understands the problem. The devil is in the details and it looks like he did a lot of R&D to get the results he wanted. Good link! :cheers:

I would still consider the cat delete pipes. They aren't needed, reduces weight, less restrictive air flow, and probably helps with the drone. The clamps will help as well.

Clamps and pipes on the way!

Should I be able to remove the bolts from the flange end, or will I need to have them torched for removal? The DIY video on TS site recommends taking it to a shop to have bolts heated with torch for removal.

Thanks!

All of my bolts came off easily, except for, you guessed it, the last one. Try some penetrating lubricant first and then give it a try.

I have a fitment question with the bypass pipes.

I have a PedroBar - it is a rear brace bar - that takes up some space over the rear wheel support bracket about 1/2". The stock pipe (with cat) runs over the PedroBar, and there is very little clearance space.

I wonder if the TopSpeed bypass pipes have a bend that allows for clearance over the PedroBar.

Does anyone have the TopSpeed bypass pipes and PedroBar installed?

Or, can anyone recall if there is more or less clearance with the TopSpeed pipes vs stock?

Appreciate it!

Did you ever get rid of the drone?

I have the Pedro bar also. I bought a set of old Stebro bypass pipes that contacted the Pedro bar on the pass side. I now have the old Fabspeed design that fits fine with the Pedro bar. Maybe someone with the Topspeed pipes can measure the clearance for you.

Drone comes from cheaply built pipes with thin steel and no insulation. Leaks don't help but it's inherent with all the mass produced exhaust parts that most people can and want to afford. As one who used to build 993 sport cat and delete pipes, we got lucky In having no drone with our parts. We got poo poo'd by the die hards that said what we did shouldn't work but it did with no drone and hp/tq gains. Wish we were still in it sometimes :(
But you guys won't get zero drone with the common mass market stuff. It's not made well enough.

Just my .00002 cents ( inflation adjusted)

I moved one of the clamps towards the flange a bit today on my TS and tightened it well. Heard a creeping exhaust leak getting worse. Noise went considerably down at low rpms. I've tightened the clamps a couple of times in the past but saw how I thought one could be more effectively placed this time and think it sounds better than it ever has before. I can see how people have more predictable results with welding. Probably doesn't "fix" the drone, but man, it can get loud if there's the slightest leak.

Mine took a few washers on one side, and just one on the other mounting bracket point, and it sits only a few mms away from the heat shield. No melting, and I've run it hard in 105+ temps this august. The heat shield is some sort of metal (?) Some people might be going to unnecessary lengths (no pun intended) to get the exhaust away from the bumper, which then makes it stick out more, and not as nice looking. My .02 anyways.

Tommy,

I have the pipes and clamps recommended by Bruce, but no time install yet.

It is killing me, I cannot wait to get those pipes on! My impression is the exhaust and pipes are designed to work together.

Will give report as soon as they are installed.

BTW, I agree with Hayden, moving clamps around to improve seal improves the drone. I removed my 1.5" extension and used a couple of spacers to add some space between tips and lower bumper.

Gary

Gary,

Thanks for the response, I was thinking about getting this exhaust for my car. I have a 98, so i only have the one pair of cats. I like the thought of a little better sounding exhaust note, but i could do without the drone.

Tommy

Just wrap your headers very thigh along with the curved parts of the exhaust system. No need to wrap it all 100% to the tail. Just so the vibration is managed at some area is sufficient. You'll get rid off of 50% if not all drone

oh and with headers wrapped it makes your motor run cooler. Wraps are about the same price as the famous aftermarket thermostat... forgot the name of it. 160 or something ;)