sydr Posted 8April, 2013 Report Share Posted 8April, 2013 When I had my engine rebuilt, I sold the SSI's and the attached exhaust system because I was advised that the SSI's were too narrow. That old exhaust was the best sounding zorst anyone ever put on one of our cars. Noisy at idle, and downright loud at full throttle, but always lovely to listen to. So, the new engine is magnificent. 3.4 litres with lots of candy making very good power and loads of torque. But the new exhaust is doing my head in. At idle, it is crisp and nice. Between 2000 rpm and until just over 3000, it drones in a manner I can best describe as 'unpleasant' and annoying. At full chat, it howls merrily and is lovely. Loud, real loud, but it doesn't matter 'cos I never light the fuse fully unless I'm on the track. Now, I want to know that I'm driving my Porsche. I don't want a sterile sewing machine sound. But by the time I'd driven from Sydney to Wakefield Park on Saturday, my head was throbbing because the drone is just at cruising speed. I'm told that the droning may come from the crossover - the pipes from each bank of cylinders are siamesed into each other before they continue into 2 discrete silencers. It is suggested that the siamesing of the pipes adds some horsepower, which I don't wish to lose. So far, I've had the twin outlets moved so that they point away from each other, and put filter 'tips' onto them. These has improved matters but not solved them. If your zorst droned and you've solved the problem without losing power I'd love to hear what you did. Link to comment Share on other sites More sharing options...
GC9911 Posted 8April, 2013 Report Share Posted 8April, 2013 Back in the bad old per Porsche days I had a 300zx & changed the exhausts. Sounded great at low & high speed but in the middle it had the worst drone ever, totally unbearable to the point I had the old system put back on. It turned out they had butchered the crossover between the exhausts. I ended up getting a Remus exhaust put on which ended up costing a bomb but no drone. Link to comment Share on other sites More sharing options...
clutch-monkey Posted 10April, 2013 Report Share Posted 10April, 2013 might have to switch to a single muffler - a dual exit one, you can simply block off one exhaust tip when driving long distances. Link to comment Share on other sites More sharing options...
sydr Posted 10April, 2013 Author Report Share Posted 10April, 2013 Seems I'm in good company, lots of info here Link to comment Share on other sites More sharing options...
wasserkuhl Posted 10April, 2013 Report Share Posted 10April, 2013 I have hand made Butler Exhaust manifold into a Dansk Sport 2 in 2 out. It doesn't drone much but is still quite loud. Well Loud enough for er indoors to tell me to change gears sometimes!! Do you have a std intake filter? Link to comment Share on other sites More sharing options...
sydr Posted 11April, 2013 Author Report Share Posted 11April, 2013 I have hand made Butler Exhaust manifold into a Dansk Sport 2 in 2 out. It doesn't drone much but is still quite loud. Well Loud enough for er indoors to tell me to change gears sometimes!! Do you have a std intake filter? No, not at all standard; - I have a very nice GT3 induction set up with a free flow filter and variable plenum lengths feeding direct to head individual throttle bodies. Now, don't go getting plenum envy, but here's what it looks like: and from there, it goes into this: which in turns meets for a short while, here: and then proceeds to individual mufflers and then two outlets. I'm told it sounds good at full noise on the track. The engine/Gearbox etc was all built by AutoHaus Hamilton. They've built a lot of trick engines as well as standard ones and are very dependable; however it seems that most of their trick engines with this kind of zorst are track only so if they get the drone it does not matter, whereas I still drive to the track and use the car for other things too. This is not a bleat about AutoHaus Hamilton's work, because they have built me the most awe inspiring engine and then gone over the entire car and replaced anything that was suspect. So after nearly 30 years' my car feels like new again but it goes a whole lot better. In fact, apart from the zorst drone, the engine is smoother, more tractable, easier to drive, has much more power and torque. Much much nicer to drive than the old standard engine and very exciting when I light the fuse. It is just that the drone kicks in from 2000-3000 rpm which is the cruising speed in top on the highway, and I want to sort it out. Link to comment Share on other sites More sharing options...
clutch-monkey Posted 11April, 2013 Report Share Posted 11April, 2013 goddamn, i want your manifold! haha giving me ideas for when i rebuild the 3.6 .. in your situation i would leave the headers as is and get a fabspeed style muffler (or something smaller) and bolt that into place instead. that way can block an outlet for driving to the track, take the plug off for track. Link to comment Share on other sites More sharing options...
Uncle Posted 12April, 2013 Report Share Posted 12April, 2013 GT35 or KKK27 active muffler will fix it! Link to comment Share on other sites More sharing options...
sydr Posted 12April, 2013 Author Report Share Posted 12April, 2013 is this what you mean? this is what I turn up on GT35, didn't find much on kkk27 Link to comment Share on other sites More sharing options...
sydr Posted 12April, 2013 Author Report Share Posted 12April, 2013 btw, other 911 owners have tried this: and this: Some of these seem to work, some of the time Link to comment Share on other sites More sharing options...
Glom1098 Posted 15May, 2013 Report Share Posted 15May, 2013 Hi mate I have ssi headers and a monty two in one out that had a similar terrible drone-it seems as if the drone zone for the flat six is unfortunately right in the cruising rev range of 2-3k. Not noticeable at the track but a bore in traffic or the highway. Ive solved it satisfactorily with a two disc car chemistry insert in the tailpipe. It does have a restrictive effect and a small but definite effect on top end power but is removable at the track. Exhaust sound is quite different but you can tune the amount of restriction to a degree-it's more of a blow than a roar except at full chat. For me it's an acceptable compromise for the street. Cheers Link to comment Share on other sites More sharing options...
OZ930 Posted 15May, 2013 Report Share Posted 15May, 2013 GT35 or KKK27 active muffler will fix it! LOL ! Have to agree Uncle ! Link to comment Share on other sites More sharing options...
sladey Posted 15May, 2013 Report Share Posted 15May, 2013 My understanding is most aftermarket mufflers drone. I've got 993 H/Es on my 3.2 with an M&K backbox (triple-out - cap the two rear ones or cap the side one) Droning used to be quite bad until I realised that I'd cut the side out too close and it was causing resonance on the bodywork, I had a longer piece welded on to make sure it properly clears the bodywork Not too bad now but it's still noisy. For daily drive to and from work this isn't an issue, - same for track driving, but a 200 mile motorway drive isn't much fun So I now use these for long journeys http://www.bose.co.uk/GB/en/home-and-personal-audio/headphones-and-headsets/acoustic-noise-cancelling-headphones/ They work a treat. You just have to remember to switch the engine off before you take them off or you crap yourself at the noise. Link to comment Share on other sites More sharing options...
OZ930 Posted 15May, 2013 Report Share Posted 15May, 2013 What you are are experiencing is harmonic resonance http://www.physicsforums.com/showthread.php?t=475510 There are are also articles on the "planet 9" website too If you look up exhaust resonant harmonics there are quite a few articles on the subject. Cheers BTW: the GT35 and KKK27 are turbo chargers Link to comment Share on other sites More sharing options...
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