View Full Version : Car OEM Exhaust Systems

23rd Aug 2013, 10:52
Why do car manufacturers fit such poor exhaust systems to cars as standard. Even in the upper end, the Mercedes SLS is an example I have found. An aftermarket systems seems to liberate a large number of hp, better sound with no apparent drawbacks.

Just 2 examples I have found. They have good comparison photos.

NEW: G55 AMG Long Tube Headers - Supersprint LabsSupersprint Labs (http://supersprintlabs.com/portfolio/new-g55-amg-long-tube-headers/)

Mercedes-Benz SLS AMG R&D Notes | Supersprint LabsSupersprint Labs (http://supersprintlabs.com/portfolio/mercedes-benz-sls-amg-rd-notes/)

I can understand cheapo systems in the cheapest cars. If these aftermarket exhausts do such a good job, why wouldn't a manufacturer adopt them as standard fitment in the half million dollar cars.

Or....is there something I have missed.

23rd Aug 2013, 11:31
Good bits cost more,simple ! Most cars are built to a price.

23rd Aug 2013, 11:37
I fitted an after-market exhaust to my Merc E300. When I took it in for the service at the Merc garage, the fitter showed me the similar Merc exhaust I should have had fitted. It was twice the size. He informed me that the after-market one I'd had fitted would have a considerable affect on the car's performance.

23rd Aug 2013, 11:37
I understand that in a $20,000 car, but a car approaching $500,000?? Heck, a few ticks on the options pages can add a hundred grand.

23rd Aug 2013, 12:12
Why do car manufacturers fit such poor exhaust systems to cars as standard.

Since changing over to diesel cars in the 1980's I have never had to replace an exhaust system. No idea in what way "poor" is meant but they certainly last.

23rd Aug 2013, 13:18
Manufacturers exhausts are designed to meet pretty stringent emissions regulations. You'd probably find that when fitted with the aftermarket ones that give more power there would a corresponding increase in emissions. I bought a 2nd hand Lotus Exige once and wondered why it failed its MOT abysmally on emissions until I opened up the undertray and found a straight through pipe where the cat should have been!

Same goes for ECU remaps and the like that give more power (and sometimes better economy!).

blue up
23rd Aug 2013, 16:33
Make your own for under 300 and double the horsepower. :}


23rd Aug 2013, 17:47
Exactly so. The manufacturers' exhausts are calibrated to the engine, to produce the optimum back-pressure for efficiency and emissions compliance. An after-market one may produce more power (or not) or be cheaper, but it may not meet the emissions requirements and may end up with an on-the-spot fine in some places where roadside testing is done.

cockney steve
23rd Aug 2013, 21:09
Let's be clear, there are aftermarket "performance" exhausts and aftermarket "reolacement" exhausts.

As already discussed, Performance enhancing products may well make the car noisier than the manufacturer intended or r make it unable to meet the new-car noise regulations...sometimes , the "performance " is nothing to do with power, for instance,stainless-steel, guaranteed for life systems. (Invariably, the sound-absorbent glass-wool packing becomes choked with soot and other products of combustion, so theybecome progressively noisier.
Replacements are usually of identical size and form to the O.E. fitment and, indeed, the same manufacturer usually supplies both the car-factory and the aftermarket.
The construction can vary enormously in quality,- the "Top Ten" current biggest-sellers will have a really shoddy, dirt-cheap, lasts 13 months availability, as well as a top-quality, heavy gauge system made from aluminium-coated steel,often with a 2 -or-3-year warranty.

each individual part should be fully compatible, fitting-wise with the rest of the system....typically, front-pipe, cat, centre-box and pipe, tail-box and pipe.
OE fitment has certainly improved in the last 10 years and a system can be expected to do at least 4 years....back in the day, the likes of the morris Marina and Mark 4 ford Cortina would rust in a particular area and the rest would be so bad that dismantling and replacing a section was not viable...12-18 months life was normal.

23rd Aug 2013, 22:19
Exhausts lasting 3 years....holy crap, you guys in blighty do it tough. Here in Oz its normal to have exhausts last 10 years or more, I have had 4 cars still have original exhausts after 20 years. Caveat, you only get that if you always make sure the exhaust is properly warm before you shut it down.

We don't have roadside emissions testing down here and the manufacturers are coy as to what their systems do to the numbers. They all have catalytic converters fitted and I wouldn't dream of fitting a straight through pipe in place of the cat.

Some of these systems are works of art, the Fabspeed system for the Porsche 911 991 make the sound total hornbag. There does seem to be a lot of people down here fitting aftermarkets on the Ferrari F458 as the original systems tends to split and cause the car to catch fire.

unstable load
24th Aug 2013, 07:06
Back pressure in automotive (four-stroke engine) exhaust Back pressure caused by the exhaust system (http://en.wikipedia.org/wiki/Exhaust_system) (consisting of the exhaust manifold (http://en.wikipedia.org/wiki/Exhaust_manifold), catalytic converter (http://en.wikipedia.org/wiki/Catalytic_converter), muffler (http://en.wikipedia.org/wiki/Muffler) and connecting pipes (http://en.wikipedia.org/wiki/Pipe_%28fluid_conveyance%29)) of an automotive four-stroke engine (http://en.wikipedia.org/wiki/Four-stroke_engine) has a negative effect on engine efficiency (http://en.wikipedia.org/wiki/Engine_efficiency) resulting in a decrease of power (http://en.wikipedia.org/wiki/Power_%28physics%29) output that must be compensated by increasing fuel consumption (http://en.wikipedia.org/wiki/Fuel_economy_in_automobiles).
Frm Wiki, but a Googoo or other search will turn up enough info to rubbish
back pressure as a benefit in an exhaust system.

The optimum back pressure is NONE, but that gets noisy or expensive to silence.

Takan Inchovit
24th Aug 2013, 07:14
Exhausts lasting 3 years....holy crap, Would that be partly due to salt being put on the roads in winter?

Each engine has its optimum exhaust size/dia for performance; too big on a turbo eng and it can overboost.

24th Aug 2013, 07:45
Fantastic, blue up. What is that thing - a side valve Ford Ten?

Metro man
24th Aug 2013, 08:42
Ideally the exhaust system should suck the incoming mixture into the cylinder as the exhaust valve is closing and the inlet valve is opening. Careful tuning is required to ensure a low pressure in the exhaust system occurs at this point as the exhaust gas is a series of pops rather than a smooth stream.

When I was growing up, car manufacturers would fit cheap, mild steel exhausts to new cars to keep costs down. The combination of salt on the roads during winter and short journeys which allowed condensation to collect in the silencer, ensured a relatively short lifespan.

Stainless steel was a good aftermarket alternative if you intended to keep the car for a long time.

blue up
24th Aug 2013, 08:43
Thanks, RJM. Sidevavle 8hp Morris Minor, circa 1932. Slightly better than the original in terms of performance (and weight!) Mild steel since it is easier to fix but I polish the steel before it gets welded. The insides get a wash down with thinners, get heated with a blowtorch and then aluminised paint gets swilled round the inside. Once it has cooked off it will last for years.


24th Aug 2013, 08:47
Someone has made the comment that came to my mind - since changing over to diesel cars about 12 years ago I have never replaced an exhaust on any car. With petrol cars it seemed to happen quite frequently. Is there less corrosive aciditiy in diesel fumes?

Lon More
24th Aug 2013, 08:49
as stated, price. Plus the fact hat the average Merc driver couldn't tell the difference, If you upgrade the exhaust, don't forget he air intake. Simply fitting a K&N filter should make a difference.

cockney steve
24th Aug 2013, 11:57
If you upgrade the exhaust, don't forget he air intake. Simply fitting a K&N filter should make a difference.
been there, done that, along with the Norton spark booster, the Michelin low rolling resistance tyres, the Peco extractor exhaust, the gerferator inlet-atomiser Nearly forgot, the Slick 50 in the engine oil and the Molyslip in the gearbox and axle.....
Well, I have to tell you, fitting them and a few other economy devices left my wallet a bit depleted, but all was not lost,- all those 5% to 10% savings add up, you know....so every couple of hundred miles the fuel tank would overflow and need draining....a right nuisance , with a length of hosepipe and an ex-WD jerrycan, I felt like a criminal and I couldn't sell the surplus , as it would only work in a car equipped with all the economy devices. :p

Re- tuned exhausts..As MM and Unstable have suggested, the resonant tuning of a system can have a dramatic effect....Many old British motorbikesused on the track, had a "Megaphone" exhaust "silencer"
as engine revs came up, the exhaust note changed and a sudden surge of power appeared....at the critical speed, the sound waves would reflect back and forth, sucking out the burnt charge and pulling the incoming charge right through the cylinder . The reflected pressure-wave from the "Mega" would push the charge back into the cylinder....meanwhile, the tuned induction-tract was ramming a bit more in....that's why many high performance engines have such odd valve-timing...effectively, you have "free" supercharging, but only over a narrow rev-range

I remember the early Jap bikes in the 60's contesting the 50CC class in the Isle of Man...it was reported the engines produced massive power in a rev-band of about 200 RPM..outside of that, rough and gutless!
They had gearboxes with around 20 speeds and stunned the traditional folk.....the authorities , of course, banned a lot of these innovative ideas.

Formula 1 and rally cars still rely on resonant-tuned inlets and exhausts
flexibility is traded for a narrow, but large powerband .

there's a lot more to inlets and exhausts than just filtering and quietening :8

24th Aug 2013, 12:06
Frm Wiki, but a Googoo or other search will turn up enough info to rubbish
back pressure as a benefit in an exhaust system.

The optimum back pressure is NONE, but that gets noisy or expensive to silence.

If emissions, noise and calibration are irrelevant, that would be correct. However, to comply with EU regulations (and others, elsewhere) accurate calibration and in-operation monitoring is required. Back pressure (properly calibrated) is part of that. Hence, no.

I suspect the folks who wrote that Wiki article weren't engine engineers or calibrators. It sounds like racing enthusiasts to me.

24th Aug 2013, 12:10
No STP then Steve?

Lon More
24th Aug 2013, 13:38
You forgot to fill the tyres with nitrogen Steve, and what grease did you use in the wheel bearings?

24th Aug 2013, 14:33
After thinking about my glorious youth spent doing horrible, amateurish things to cars to make them go faster or at least sound louder, not to mention towing them with bits of rope, welding up wheels (and worse), I've come to the conclusion that I should be grateful - not only that I'm still breathing but that I was able to have such fun. A lot of it had to do with isolation - our farm wasn't too far from our state's capital city, but from there it was 600 miles to the nearest city eastwards and 1600 miles to the same west. So we were in a quiet part of a backwater, with all the freedom that entails.

And it's a hard habit to give up once acquired. Even as a mature adult, it was hard to beat the pleasure of the resonating boom from a 2.7 litre, 4 cylinder Healey with a 1 3/4 in extractor and exhaust system setting off car alarms throughout a multilevel car park. There was a particular point in second gear at which the exhaust note seemed to be the at the resonant frequency of reinforced concrete. Wonderful. I don't think there was much back pressure though.

29th Aug 2013, 01:33
I've got a 16 yr old Nissan with the original exhaust and battery. The exhaust has no discernible corrosion on it whatsoever. I've had to replace a suspension strut (30 quid) and 5 light bulbs. No rust. Most boring car I've ever had, but it's disturbingly reliable. I've got to remember to change the timing chain (yes) at 240,000 miles ... mrsr1 doesn't want a new(er) car as this one still has a cassette player. Fair enough, I said.

29th Aug 2013, 04:05
My new Nissan rusted out it's first exhaust system in just 2 years, replaced under warranty. 5 years later the bottom of the tail pipe rusted out but I just so happened to be changing the old toilet cistern and the chromed down pipe cut to size fitted perfectly giving me a sporty chrome tipped exhaust. Still sounded like crap though.

My new Commodore came fitted with an all stainless steel long life exhaust as OEM. It's 13 years old now and I reckon the exhaust manifolds will hole out before its exhaust system. Good excuse to fit a new high flow manifold and extractors :E.

Lightning Mate
29th Aug 2013, 09:56
Well, I changed my last Mercedes when it was ten years old.

It still had its' original system and CAT, and an inspection showed hardly any rust at all.

I have little reason to doubt that my new one will be any different.

Effluent Man
27th Sep 2013, 19:39
The latest scandal is road springs.I swear they make them out of spaghetti.Never used to hear of them breaking but these days if you park a car up for a couple of weeks then move it....boing its gone.A customer of mine took his car for MOT all four were broken.

27th Sep 2013, 19:48
I agree with road springs being susceptible to breakage - especially, it seems Peugeots (and reasonably recent models, too). I know of several owners who have experienced failures - in one case the broken spring ripped open the tyre sidewall (fortunately when parking, so not at speed).

I also find pieces of roadspings scattered along the edge of roads in the village.

Bradley Hardacre
27th Sep 2013, 19:57
might be to do with the state of the roads in the UK

27th Sep 2013, 21:07
Coil spring failures | AA (http://www.theaa.com/motoring_advice/car-servicing-repair/coil-springs-breaking.html)

Lighter weight construction and salt corrosion seem to be the main factors

Cornish Jack
27th Sep 2013, 21:21
For Cockney Steve et al - the real indicator of what exhaust tuning can do is shown in model aircraft engines - particularly C/L racing. The noise change when one of these beasts gets 'on the pipe' has to be heard to be believed!! VERY narrow rev band but they do go a bit!!
Re diesel exhausts, I ran a Citroen BX turbo diesel on the original exhaust for its life up to scrapping at 328,000 miles - no repairs needed.

Effluent Man
28th Sep 2013, 07:09
Just think about this logically.If this was happening on a component on a jet airliner would it be tolerated? It's quite simple really the car manufacturers make their way to Spring City Seuchuan Province and weigh out some factory owner about three quid a throw for these springs.Then,surprise,surprise they snap in twain at the drop of a hat.It's cheapskateism full stop.then the customer stumps up a hundred quid a spring to replace them.I must have fitted a dozen this year.

Paraffin Budgie
28th Sep 2013, 09:33
And don't forget the Mangoletsi Manifold Modifier.....

That did nothing at all on my Mk 1 Cortina.

28th Sep 2013, 12:35
I agree with road springs being susceptible to breakage - especially, it seems Peugeots (and reasonably recent models, too). I know of several owners who have experienced failures - in one case the broken spring ripped open the tyre sidewall (fortunately when parking, so not at speed).

Some "Pugs" have front coil springs with narrower coils at the bottom, rather than the parallel sided ones that most cars have. If the spring snaps at one of the narrower coils (and I've heard of a few cases) the wider coils above can drop down over the spring seat on the suspension strut, allowing the suspension to drop right down. The broken end of the coil still attached to the car then digs into the inside wall of the tyre. I know of one case where the wheel was locked when this happened. Not a safe design imho. :ooh:

cockney steve
28th Sep 2013, 21:06
@ Cornish Jack my first "hands-on " experience was with a Mills .75, followed by an ED Bee , then an AM10 all 2-stroke diesels....AHHH the smell of Ether and castor Oil!
I currently have a 30-size heli that i'm steeling myself to crash...again! that's a Glow-engine....apparently, the filament in the glowplug ignites the fuel through catalytic reaction with it..... I do believe an impressive rocket-motor can be made with some platinum and hydrogen-peroxide. I digress, as usual.

@ Vulcanised, Lon More et al No room for STP once the Wynns Friction-Proofing, Bardahl, and Molyspeed had been added....then there was the Molyslip grease for the wheel bearings no nitrogen back then, but an extra 10 PSI in the tyres gave a hard , but "interesting" ride on cross-ply tyres and the rolling resistance was reduced in proportion to the loss of grip!

Of course there are thousands of these paragons of engineering expertise , still performing as reliable transport (for baked beans?) somewhere, as the Cavity-sealing Dinitrol,Waxoyl,and the like, ensured they'd never rust -out, didn't they? :E

28th Sep 2013, 21:24
My abiding memory of the ED Bee is the nylon prop attached to it which resulted in a heavily scarred forefinger and much loss of blood and the pain.

cockney steve
28th Sep 2013, 22:13
^^^^^ You too?!:O Never could get the thing to run reliably!

28th Sep 2013, 22:24
My abiding memory of the ED Bee is the nylon prop attached to it which resulted in a heavily scarred forefinger and much loss of blood and the pain.

Me too! :ok:

28th Sep 2013, 23:19
I'm fed up with modern wheel bearings. In all the cars I ever drove with greasable bearings I didn't ever replace one. In the last ten years I have replaced five VW Golf front bearings, one rear, one front on the old Suburban, three front on the Yukon and the other day Mrs VJ had BOTH the rear bearings on her 3 year old Honda Civic replaced (under warranty, thank goodness.)

Sealed bearings are a curse.

29th Sep 2013, 10:08
Model aeroplanes can be great examples of resonant exhausts. Here's a video...you can't miss the point where the 2.5cc motor gets "on the pipe"!

F2A World Record - Control-line model aircraft speed. - YouTube (http://youtu.be/4vAw1CC4A3g)