New Performance Exhaust & Resonating Dreadfulness
Discussion
Three weeks ago I had a new performance exhaust fitted by M.I.J. Performance in Walsall to my Mercedes-Benz SLK350 (R171 2004), all nicely done in stainless-steel.
My aim and desire: Improved performance and a more 'sports' exhaust note, as compared to the mooing of cows that the original equipment pipes produced. I had the engine re-mapped at the same time. The intended outcome was a 'mid-sports exhaust note' and improved performance.
The enhanced performance is indeed superb, more responsive, faster acceleration, pulls better and I'm very pleased with it.
The exhaust note is good too, with the roof down that is; BUT... with the roof up, at around 2000 r.p.m, I get a bloody awful loud droning resonance inside the car, it is actually very, very wearing and very tiring. At one precise sweet spot of pain in the power band; 2100 r.p.m., when the engine is pulling under load, the resonating actually achieves a high pitched vibration that sets any loose bits in the car rattling, including my fillings, my testicles, my eyeballs and brain. SWMBO, on exposure to this penetrating drone sat in the passenger seat for long periods of a 2 x 2hours of drive with her fingers in her ears, taking them out only occasionally to berate me. She didn't actually say "You've ruined a perfectly good car" but she could have and I wouldn't have disagreed.
When I troubled the very helpful man at M.I.J. with this issue he said to leave it for a thousand miles and when the new tubes coke up a bit the sound will mellow. I'm up to over five hundred and it's no better. He also said that should the need arise it'd be no problem to moderate the exhaust.
Now, my quandry is this: It's three hundred mile round trip from home to M.I.J. so I can't keep popping back, I want to get the thing modified in one go and I want it done to my satisfaction. What I want is to keep the extra horses and torques, retain something of an exhaust note at the tail pipe, if I can, but above all, I simply must be rid of this resonating racket in the cabin - anybody have any sensible advice on what's best to do in order to achieve this?
By the way, the new pipes are straight through with silencer boxes at the back - I think the O.E. version has a little boxes half way along the pipe? Is this significant? (I think it might be)
Thank you.
My aim and desire: Improved performance and a more 'sports' exhaust note, as compared to the mooing of cows that the original equipment pipes produced. I had the engine re-mapped at the same time. The intended outcome was a 'mid-sports exhaust note' and improved performance.
The enhanced performance is indeed superb, more responsive, faster acceleration, pulls better and I'm very pleased with it.
The exhaust note is good too, with the roof down that is; BUT... with the roof up, at around 2000 r.p.m, I get a bloody awful loud droning resonance inside the car, it is actually very, very wearing and very tiring. At one precise sweet spot of pain in the power band; 2100 r.p.m., when the engine is pulling under load, the resonating actually achieves a high pitched vibration that sets any loose bits in the car rattling, including my fillings, my testicles, my eyeballs and brain. SWMBO, on exposure to this penetrating drone sat in the passenger seat for long periods of a 2 x 2hours of drive with her fingers in her ears, taking them out only occasionally to berate me. She didn't actually say "You've ruined a perfectly good car" but she could have and I wouldn't have disagreed.
When I troubled the very helpful man at M.I.J. with this issue he said to leave it for a thousand miles and when the new tubes coke up a bit the sound will mellow. I'm up to over five hundred and it's no better. He also said that should the need arise it'd be no problem to moderate the exhaust.
Now, my quandry is this: It's three hundred mile round trip from home to M.I.J. so I can't keep popping back, I want to get the thing modified in one go and I want it done to my satisfaction. What I want is to keep the extra horses and torques, retain something of an exhaust note at the tail pipe, if I can, but above all, I simply must be rid of this resonating racket in the cabin - anybody have any sensible advice on what's best to do in order to achieve this?
By the way, the new pipes are straight through with silencer boxes at the back - I think the O.E. version has a little boxes half way along the pipe? Is this significant? (I think it might be)
Thank you.
Yep, those centre silencer boxes are crucial to drone, and to tone. For a "mid sports note", by which I presume you mean a pretty middle of the road, quiet but sporty tone, they should never have sold you a straight pipe with no silencers, unless the backbox is heavily silenced. Do you have any photos of the backbox?. A professional exhaust place could quite easily fabricate and place a silencer box in the middle. It will dull the edge of the tone and reduce the volume significantly, but it might reduce the drone a bit. If you do a lot of long drives then it probably will be worth getting it done.
It will coke up and become "mellower", that is more woofly at lower revs and they seem to pop and bang more once coked, they don't (in my experience) get any quieter and they certainly don't drone less.
Most sports exhausts drone at constant speed, under-load operation. I have a straight pipe exhaust on my car, no silencing after the car, just a straight pipe all the way to the end of the car, just an aesthetic "backbox" which is actually just a case-end on the straight pipe. It sounds like a swarm of angry hornets, pops and bangs like a howitzer on the gear changes and drones like mad on the motorway. If I had to do a long journey I'd be keeping earplugs in the car, the noise is brilliant but the drone would be headache inducing on motorway slogs - glad I don't have to do any!
It will coke up and become "mellower", that is more woofly at lower revs and they seem to pop and bang more once coked, they don't (in my experience) get any quieter and they certainly don't drone less.
Most sports exhausts drone at constant speed, under-load operation. I have a straight pipe exhaust on my car, no silencing after the car, just a straight pipe all the way to the end of the car, just an aesthetic "backbox" which is actually just a case-end on the straight pipe. It sounds like a swarm of angry hornets, pops and bangs like a howitzer on the gear changes and drones like mad on the motorway. If I had to do a long journey I'd be keeping earplugs in the car, the noise is brilliant but the drone would be headache inducing on motorway slogs - glad I don't have to do any!
I used MIJ for my 944 S2. Much more local to me but I found a similar issue. I went back and they were superb at sorting the problem. Just tell the boss man (helpful bald fella) and he'll get it sorted. They seem to have real pride in their work so I would give them the benefit of the doubt and ask them to sort for free under the warranty provided.
Mastodon2 said:
It will coke up and become "mellower", that is more woofly at lower revs and they seem to pop and bang more once coked, they don't (in my experience) get any quieter and they certainly don't drone less.
This was my understanding too - I certainly thought new exhausts got louder rather than quieter as they wore in?ex vtskid said:
This was my understanding too - I certainly thought new exhausts got louder rather than quieter as they wore in?
They lose some of the treble rasp at low revs, but the bass is just as loud or louder. Your ears don't pick it up much, it's a frequency you feel more than hear. It's just as loud in terms of dbs though. Once they are coked, I think they actually sound even better, and raspier higher up the rev range. The drone is ever-present though!I recently had built a special shape stainless exhaust for my historic rally car. It was about a 3 feet long and had two, two inch perforated tubes running through. It cost a small fortune to build and was welded up (with all the wadding in) by the guys who do Morgan's O.E. work. It sounded great, except at 3000 rpm, there was this hideous resonance, a bit like the sound of a circular saw going though wood.
We did a rally in France and my navigator coughed a lot and the sound got worse. On the ferry back I took the heat shield off and was amazed to see that the vibrations had shattered the outer skin, letting all the gas out. By the time we got home it was a huge hole,
Basically a long unsupported length of stainless will resonate until it breaks due to basic metal fatigue. I replaced with mild steel and the resonance and problem went.
Look at you system for cracks in the outer case. If so it's a badly designed system.
We did a rally in France and my navigator coughed a lot and the sound got worse. On the ferry back I took the heat shield off and was amazed to see that the vibrations had shattered the outer skin, letting all the gas out. By the time we got home it was a huge hole,
Basically a long unsupported length of stainless will resonate until it breaks due to basic metal fatigue. I replaced with mild steel and the resonance and problem went.
Look at you system for cracks in the outer case. If so it's a badly designed system.
I made the 200 mile trip up to MIJ again this morning.
It transpired that the geezer who fabricated/fitted my exhaust didn't comply with his instructions and put on silencer end boxes that were smaller than specified.Hence;too much noise and resonance.
Much genuine apologising for the error ensued, then more apologies when it further transpired that they didn't have the requisite size back end boxes in stock; they'll have to be ordered.
So, I have another 400 mile round trip to look forward to and another Saturday used up to visit MIJ again for remedial work. On the plus side the man who runs the show (Andrew) said they'd reimburse me for petrol money, which I thought was fair enough.
I'll let you know how it all eventually pans out.
It transpired that the geezer who fabricated/fitted my exhaust didn't comply with his instructions and put on silencer end boxes that were smaller than specified.Hence;too much noise and resonance.
Much genuine apologising for the error ensued, then more apologies when it further transpired that they didn't have the requisite size back end boxes in stock; they'll have to be ordered.
So, I have another 400 mile round trip to look forward to and another Saturday used up to visit MIJ again for remedial work. On the plus side the man who runs the show (Andrew) said they'd reimburse me for petrol money, which I thought was fair enough.
I'll let you know how it all eventually pans out.
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