Full Milltek system has Resonance!

I just got the entire Milltek system installed including the new headers. But...<o ></o >[/quote] Well now I discover that this system DOES HAVE RESONANCE !Previously I read that it does not any and was expecting as such.The resonance seems fairly broad in nature and not like other peaky systems, thank goodness. The interior exhaust noise (sound?)starts to notably increase at about 2200 RPM with a medium amount of throttle, peaking at about 2500 RPM and diminishing at around 2800 RPM. My opinion is its too loud just in this range. Above 3000 RPM the noise level seems fine and drops off a fair amount. So this is a definite resonance issue.<o ></o >[/quote] The original OEM exhaust system'snoise levelincreased fairly proportionally to the engine RPM, and that was what I was expecting, but just a slightly louder deeper tone version.<o ></o >[/quote] SoI think itstill has a degree ofresonancehappening in my case. Anybody else observe this? I don’t expect it is related to the install, after all what can go wrong. Not much.<o ></o >[/quote] Apart from that, idle sounds pretty good and the power increase is all thumbs up on the 'Butt dyno'.<o ></o >[/quote] I will persevere for a few weeksbut I’m not expecting any significant change.<o ></o >[/quote] <p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><o ></o >

The exhaust does have a different tone between 2000 and 3000 rpm, and it varies whether you are on the gas or not, for example lugging the engine in 6th gear at 2200 rpm produces a tone different from being at 2200 rpm in the right gear while accelerating. In my opinion it isn't resonance because it isn't an echo sound or a vibration sound such as with a GHL Boxster exhaust, but rather a tone difference based on rpm, throttle, and load that you are hearing. I like that you have control over this tone and can vary its intensity and tone with the throttle and it gives more punch to the sound down low. It is certainly louder than stock but again I don't think it is resonance you are hearing. I'm going to be testing the AWE exhaust on my car here shortly so I'll report how they compare in this area of the rpm range as well as overall sound differences. I guess the operative question isn't whether it is resonance as one person defines it or not as another person defines it but whether or not you are happy with the sound and the performance of the exhaust. Are you? Everyone I've let test my Milltek system has liked it if someone thought there was 'bad resonance' in the exhaust I would have thought someone would have mentioned it because some picky people have listened to it both inside and outside of the car.

Kman, another test I did was to sort of accelerate with a constant amount of throttle from lower RPM to higher RPM with the idea not too force more noise under certain driving conditions but observe the change in volume resulting from the exhaust system subject to increasing RPM. Result being the noise goes up at 2500 RPM and then starts to drop off again.Now the old system is off, I cant go back and compare what it was like before asI dont recall any particular effect. Some technical stuff on Resonance if I may waffle on for a moment... Resonance is the case here, its just a different type than one expects or is accustom to. Resonance also has another parameter, Q factor (Quality), which sounds odd but is a matematical term relating to the the Bandwidth of the Resonance. In this case the Q value is low because the spread of the Resonance is over a wider range. If the Resonance occurs over a very short RPM range it will have a higher Q factor.

so resonance is the sound of the exhaust that went inside the cabin even though the engine is at idle?

When i first fitted mine and for the first week or so it had an anoying rumble/rasp which appears to have gone away now, unless i've just got used to it

Not quite, its the increase of loudness at a specific RPM or small range of RPMs. A good example of resonance is a tuning fork (which has a very high Q) vibrates only at onefrequency. With exhaust system resonance a standing wave can result in the muffler and pipe chambers at a particular vibration freq and the loudness is enhancedunder this condition.So good system designs try to suppress this by absorbtion or reflection or shifting the resonant freq outside the range of use.

Back to my unanswered question then, do you like the way your car sounds/performs now?

KManS, I agree with your comments and findings. It performs better and sounds good, but I feel its a bit too loud only at the 2500 RPM level. Ideally I think the sound should be more linear with RPM. Then again, Im also a fussy person. I think the Milltek design can be improved further.I think I can appreciate more nowthe big effortthat was put into the Cayman OEM system, where Porschehad to contend with meeting all international noise and pollutions limitsas a first piority.

4x4 - A small exhaust leak can cause an increase in noise level. If you haven't already, you might want to have the shop double check that there are no leaks at the various joints in the system and the sensor bungs. Dave

Noise? Resonance? The system is unbelievably quiet, in my opinion. The Porsche metallic rasp is gone, replaced at high rpm's by a 'scalded Toyota' scream. Feels like it makes power at the top, at the expense of some low-end grunt. Will post dyno figures shortly, but my overalll impression is: Someone needs to rip the baffles out of this sucker and maybe cut the muffler cannisters by half. Lee in D.C. Edited by - DCLEE on 10/05/2006 08:12:59 AM Edited by - DCLEE on 10/05/2006 08:15:27 AM

I could not agree more! I have the TUBI as catback, and while it has some resonance, the sound is simply amazing! I get compliments all the time...Anyone else care to share their experiences? Someone said the TUBI might be restrictive, but with the Milltek headers, its just does the job for me. I am soooo happy with the "package". COCOLOCO

I just got my entire Miltek system installed, headers and cat back. I think 4by4's description is exactly what I am experiencing. I have only driven about 40 miles since it was installed. I am also experiencing some vibration at idle, but my car is idling at about 700 RPM. I do not recall at what RPM it was idling before the change over, but it had no vibration. The car fells a little peppier. but I have not had a chance to really say, because there was to much traffic. I find it has a drone/resonance or whatever you want to call it between 2200 and 2800 RPM. It is more noticable while accelerating. If you pass this range of rpms quickly you barely feel it, but if you take your time, it is definetly there. I like everything about it except that drone between 2200 and 2800 rpm. That is my experience. I will know more this weekend since I will be driving it a lot more. I am also supposed to be at my first DE, and looking forward to it.

Jamie, yes I have more vibration at idle too, however that does not seems to bother me. From the outside the idle sounds pretty good. Seems wehave a similar result which is good in a way. Im going to look at the mechanical mounting and think about how to dampen the coupled vibration when I get a bit of time.

4by4 if you find anything to help the resonance let me know, I will do the same. I am also reporting, in a very preliminary fashion, an apparent increase in fuel economy with the system. What torque are people using to attach the headers to the engine? I used 18 to 20, did not want to go any higher for dear of stripping aluminum threads. I have no exhaust gasses leaks. The vibration at idle is more of an observation than a complain.

I can tell you how to eliminate most if not all of the vibration at idle and resonance if you are reasonably mechanically inclined. If you look at the mounting, it's all basically hanging off the end of the tranny, so the ends are unsupported and at the right frequency, start to vibrate up and down. I think Porsche recognized this with the stock exhaust which is why the two rods with the little dampers attached are there. They run from the ends of the bracket to the tranny tail. When I installed mine, I loosened the clamp holding the rod on the exhaust end to slide it out some so it would fit. This takes all the tension off the rod so it can then vibrate. After realizing my error, I loosened everything, jacked the end of the exhaust up an inch or so, then retightened everything so that the rod is now under tension (do this on both sides). The shaking at idle has been eliminated and the resonace is rarely heard. If there is interest, I can post some pictures of how to do this. Alan

Adax I am definetly going to try it. It will be on Monday. the guy that helps me is gone for the weekend. If I can get rid of the resonances I willbe very happy. If you were to post pictures even better. Thanks

you might also want to try re-adapting your throttle body after install...should help with the idle issue. There is thread on how somewhere... dw

Alan,if you could post some pics it would be appreciated thanks. Jaime, I look forward to hearing ypur results later. As Im away on business for a few weeks on Wed so I wont get to look into thisfo some time,so hopefully I may hear some good news later from you guys. Cheers.

I had the GIAC ECU flash done after the Milltek was installed. Before the flash, I noticed a distinct increase in vibration at idle, and also the rumble at 2200-2800 rpm. After the flash, the vibration at idle was gone. After a couple hundred miles, either the rumble lessened, or I got used to it- but at any rate, it is no longer annoying. Edited by - Sleeper on 10/07/2006 6:09:48 PM

Sleeper I find my car is idling about 650 Rpm. Just 50 or 75 Rpm more and it does not vibrate at all. i have not done the ecu flash. What you say makes good sense. You are almost getting me to do the flash. Like I said before if the rumble goes away between 2200 to 2800RPM, I will be a happy camper. If I gain 6hp in the bargain, so be it.

The alternator in my car went Kaput. The car is in the shop. So I will not touch it until next week.

4x4 and jaica I did the full headers and exhaust install and I have the same exact issues that you both describe at both idle and between 2200-2800 rpms. I am not loving the sound or the vibration, I think we are idling about 100rpm too low. once you steep on the gas it goes away. I am going to try moving the exhaust to make it tighter against the rods.

Any news yet on the result?

I have not done a thing, but the resonance appears somewhat milder and now it is from about 2200 to 2700 RPM. Is there a breaking for exhaust systems? I have not done any flash to the ecu. I am wondering how does the GIAC compares to the folks ar Orton?

I've got to add that I never had any issues at idle with the Milltek system, sounds like you've got something loose if you do. ALL, repeat ALL exhaust systems will be loud between ~2200 and ~2800 RPM as this is an artifact of the engine itself and anything but a heavy sound stuffing muffler like the stock system is going to let this engine noise out via the exhaust. The question is how each system handles it. If you think the Milltek is loud in these RPM ranges then you do not want to sit in a car with AWE, Fabspeed, Tubi or 9FF because all of those are louder than the Milltek. ECU tuning has nothing to do with it.

One bad thing with a loud exhaust is it drowns out the sweet sound of the engine!

Sytem has been retentioned now and it is a bit better.