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Following a previous thread on here about my boxter s making a raspy noise at certain revs I took it to the garage and it's not blowing, however they thought it may be a baffle that has gone, which is what folks on here suggested.
I know nothing about cat exhausts but assume baffles are in the back box so this is the part that needs replacing. Having a quick Google they look to cost anything between 300 quid and 3 grand. It's an old boxter 986s and rarely gets used, I certainly don't need/want a performance exhaust. Just something that doesn't make it sound like a race car at 2000 rpm.
What's wrong with something like this, which is obviously at cheaper end of scale..
https://www.ebay.co.uk/itm/TOYOSPORTS-STAINLESS-STEEL-EXHAUST-FROM-CAT-PORSCHE-BOXSTER-986-2-5L-2-7L-3-2L/190734822833?_trksid=p2504926.m5232.l9681
Ta
In my (non Porsche) experience Toyo sports or similar exhausts are just loud with no tone/quality to the sound...
Was horrible on my car and changed for a cobra exhaust instead which was also loud but no raspy/droning noises and complemented the cars sound.
Probably nothing mechanically. But there's more to turning an exhaust than just de restricting the airflow and making it louder, so cheap might sound a bit crap, not add any power at the high revs and actually reduce it lower down as back pressure helps he exhaust draw the the exhaust fumes from the cylinder.
The OH's fiesta needed a new exhaust a couple of years ago, I bought the absolute cheapest one I could find on ebay. It was in three pieces and painted with zink paint. It was so bad* that when it went back to kwickfit for its mot they tried to tell me it was a 2nd hand one that had been painted!
Still there two and a bit years later.
Have you found the source of the rattle or just guessing at the back box? Catalysts rattle when the honeycomb breaks up.
*I don't think it was that bad, although the paint did fall of the flexible section the first time it got hot.
It's not rattling as such, just a deep roaring sound at around 2500 rvs which goes away when you pass 3000. Sound like a hole in the exhaust, but there isn't one.
But yes, I'm guessing it's the baffles based on what folks said on here, plus the garage.
It's only done 65000 miles so I doubt the cat has gone.
back pressure helps he exhaust draw the the exhaust fumes from the cylinder
That seems counter-intuitive at best. How does pressure in the opposite direction to the gas flow manage to "draw out" exhaust fumes?
A well designed exhaust can gain you power over an open pipe. There are shock waves related to valve closing so sound waves traveling along the pipe and being partially reflected at pipe junctions. If the exhaust is designed such that the resulting standing wave is reflected back off the valve as it opens there is a reduced presure which helps initial cyclinder clearing. That is frequency dependant and usually results in a sharp power curve peak because if the standing wave has a high pressure point at the valve, clearing is hindered. If the standing waves in the pipe can be absorbed with a muffler that doesn't restrict gas flow the power curver can be smoothed and the total power under the curve increased.
Google something like "standing waves exhaust systems".
I was one of the first users of the classic RC 40 exhaust ststem for Minis. I was also the quietest Mini competing, safe in the knowledge that it was also worth a couple of BHP.
Backpressure doesn't help draw out exhaust fumes...however some back pressure is beneficial for performance and fuel economy as it prevents air and fuel being sucked out of the cylinder when the inlet and exhaust valves overlap and are both open momentarily...a bit of exhaust back pressure helps to prevent the induction air/fuel mixture from just getting sucked out into the exhaust reducing what gets into the cylinder.
That is why aftermarket 'performance' exhausts that basically reduce back pressure to make a fruity 'sporty' noise are anything but performance...the OEM tends to build the exhaust to have the right amount of back pressure...especially in the higher end performance cars.
Best to go OEM if you can on something like a Porsche....or else what's the point in having a Porsche? have you tried a Porsche breakers? OEM Porsche exhausts are stainless steel so last for may years, and the sort of thing you should be able to buy second hand from a crashed Boxster. Try PH Sporstcars in Derbyshire. They're a Porsche breakers and specialist. I used to get a lot of the parts from them back when I had an old 944. If they can't help you with an actual backbox they should be able to advise you on where to source one and what's good and what's not.
Best to go OEM if you can on something like a Porsche….or else what’s the point in having a Porsche
In principle I agree, however I've just been stung with a 15k bill to fix my house so not exactly flush with cash at the moment, hence looking at budget options. In reality the car gets driven to about 50% of it's potential at most so it's not as if I'll miss a few bhp. I'll check out the place you recommend though and see of they have any at a comparable price.
Get a second hand OEM, far quieter, and nicer.
Plenty of used ones on eBay for £70 - £300 ish (not sure if I've searched for the exact one).
I'd go for a genuine used one, especially as you're not 100% sure it's the issue.
The thing that worries me about a second hand one is whats to say its in any better Nick than the one I currently have..ie..by the time I fit it and try it out it's a bit late then if it's also goosed.
Apart from an annoying noise, is it actually broken? That's the sort of thing I'd just fling in the "to-do" pile if it came down to cash flow.
Toyosports are cheap, I would not expect it to be quiet, fit can also require tweaking (I had to use Oxy Acetylene to heat and bend the last one I fitted to get it to line up (different car))
back pressure helps he exhaust draw the the exhaust fumes from the cylinder
Bollocks, thats just people repeating shit they read on the internet that they dont understand.
However exhaust velocity is important, and primary, secondary and exhaust size are crucial if you want to tune performance for a certain RPM/flow. Hence why fitting a 3" pipe to a stock car can reduce performance due to the drop in exaust velocity and the loss of scavenging.
Turbo exhausts are different, you want to maximise pressure differential across the exhaust turbine to increase efficiency (max power and spool).
I've got a 206 gti 180 for a cheap toy for the track. Came with a toyosports. I couldn't drive it. It was just too loud. Drone. Made a nice pop and chatter though. Just not for me.
Bollocks, thats just people repeating shit they read on the internet that they dont understand.
Mehhhh, 4 years of fluid dynamics lectures and research published in a scientific journal on a (tenuously) related subject, what would I know..............
Second hand parts are usually in pretty good nick...from breakers they're usually salvaged from crashed cars so they can tell you the age and what car it's come off. the challenge with an exhaust of course, is that they usually corrode form inside out, but there are usually tell-tale signs and typical areas of corrosion and the specialists will know where they are, but with a stainless exhaust you know its going to last for years, a decade or more, and it's milage related, so if off a lower mileage car then the chances are you'll get some half decent life from it.
Also the Porsche parts scene in the states is huge with more specialists out there than you can throw a stick at, and sourcing parts from the states was useful too...though the exchange rate is not so favourable now, but you might be able to get an aftermarket copy of an OEM backbox from the states, shipped and imported for less than you think.
Anyway, worth a try. Not saying running a Porsche will ever be cheap...though not necessarily as expensive as you might think, but utilising specialist breakers is always a good option and if its an older car, say ten years old or more, then if you buy a few cheaper parts from the dealership, get to know the staff and the manager, join the Porsche club GB, they'll often they'll give you decent discount. I often bought parts from the dealer in Nottingham for my 944, like brake parts for example where I wasn't comfortable buying from the breakers, and always got a decent 15% to 20% off. Probably varies from dealer to dealer, but they always seemed to treat owners of older cars quite well at the Nottingham Porsche dealership and sorted me out a few times when I was struggling to source parts and sorted me out with discounts. Sometimes parts were priced quiet cheaply...or cheaper than you might imagine, sometimes I just had to swallow a big bill. But Porsches are not unique in that regard. Plenty of run of the mill cars out there are as expensive or moreso to run than a Porsche.
back pressure helps he exhaust draw the the exhaust fumes from the cylinder
Bollocks, thats just people repeating shit they read on the internet that they dont understand.
Mehhhh, 4 years of fluid dynamics lectures and research published in a scientific journal on a (tenuously) related subject, what would I know…………..
Ok, why does back pressure help draw the exhaust fumes from the cylinder?
A smaller (but correctly sized) pipe will have a higher exhaust gas velocity which will help draw the exhaust gas from they cylinder compared to a pipe which is too large (which will have less back pressure, but a lower exhaust velocity). The smaller pipe will have a higher back pressure than the larger pipe, however that is a side effect and not the cause of the increased scavenging.
Fellow 986S owner here.
First - have you had a poke around underneath yourself? The Cat heatshields (one each side) are notorious for rotting around the mounts and coming loose which will give you exactly the kind of rattle you talk about. Think they're about £30 from Porsche and not a difficult job to replace. Also check the "quilted" ally heat shield that lines the underneath of the boot floor that can also rot through around the mountings.
As far as replacement back boxes go. OE is the way forward - I'd get a secondhand one from a specialist breaker (there's one in Leeds if that's handy for you). If you're feeling a bit naughty - google "Boxster exhaust bypass mod" and get that done before you fit it. Sounds normal (slightly throatier) at below 4k rpm, no droning when cruising and perfectly domestically acceptable, but howls more like a GT series car at high revs. Best (and only) mod I've made to mine.
(mine is on nigh on 100k and the original silencer looks a bit scabby, but is in mechanically good nick, so I'd be surprised if yours has died at 2/3 that.)
When I fitted an SS system to my Landy I discovered that different steels resonate differently and give a different sound to the exhaust. The original mild steel system was definitely more effective in absorbing the sound. The second problem was that the SS bracket holding the middle silencer box to the chassis kept snapping because it couldn't cope with vibration. I kept sending the broken ones back under warranty and they kept coming back with a redesigned bracket and kept breaking after a few months. If the bracket didn't snap it tore away from the welds along the seam of the box.
Speak to Lee at Cotswold Porsche Specialists - he'll point you in the right direction, might even have something to hand that will work for you.
You are on the wrong forum! But yes genuine exhausts are very expensive. Aftermarket you risk ruining the car with a boomy noise.
Try http://www.boxa.net/forum/
When the exhausts rotted out on my 996 I replaced with used "take offs" where someone had upgraded early in the cars left and kept them on the shelf.
"Top Gear" exhausts have a good rep on the 911 forum.