The petrolhead obsession with exhaust pipes probably has deeply Freudian associations and ones we'll neatly gloss over here, thank you very much.
Fatness and/or quantity should relate to power
There's no escaping, however, that the visible extremity of your car's exhaust system is a very powerful statement of power, performance and status and one clearly understood by all. Even the non car savvy can understand the basics - the fatter and/or more numerous the exhaust pipes the faster (and by extension flasher) the car in question.
Back in the day when displays of wealth and status were more subtle and coded than they are now it was a more discreet badge of honour. Two pipes on your BMW's silencer meant the chap in the 318i knew you were rocking with a straight-six and were therefore his social superior. Hot hatches made do with meagre pea-shooter exhausts and only true exotica with V8s or V12s were permitted the extravagance of quad exhaust pipes.
Which is why this modern trend for out and out exhaust fakery needs to be stamped on. It's getting out of control; when even a Ford Focus ST runs a back box a quarter of the width of the rear bumper and OTT enough to make a Lamborghini Aventador blush you know things are getting out of hand. Likewise when the number of exhaust exits equals the number of cylinders. One could, for example, argue that the Subaru Impreza's downfall began when it adopted quad pipes rather than a single designer label backbox. Similarly, since when did a straight-six M3 need the same?
Lambo style pipe for a Focus? Bit tragic really
It's doubly ironic that as legislators go further and further to strangle what comes out of our exhausts in terms of emissions and noise the visual excess has gone the other way, to the point that it's almost beyond parody.
The Audi R8 V10 is but one of many examples. Big bore circular exhaust exits play a significant part of the visual differentiation from 'base' V8 models and are an essential element of the rear end aesthetics. Yes, we just used 'big bore' and 'rear end aesthetics' in the same sentence. Sorry.
Anyway. What's particularly upsetting about this arrangement is that you don't have to look too closely to see that the impressive chromed 'exhaust' is nothing of the sort and, in fact, the real thing is about a third of the diameter and entirely separate from this mere bumper trim. Audi's far from the only culprit in this far too obvious fakery and, frankly, it's insulting even if it still sounds spectacular. Likewise the pointless extra weight some of these poor cars must be lumping around in the name of questionable aesthetics.
Aural enhancement shouldn't come from speakers
As is the trend for fake exhaust notes, most (in)famously
audio-enhanced V8. Again, we can blame the legislators for this one. But when your car bristles with a Countach-like array of exhausts but sounds like a 1.3 L you're within your rights to feel put out.
Inspired in part by the highly amusing Velominati stylistic 'rules' for road cyclists PH has, as a consequence, decided on an entirely unilateral etiquette guide to exhaust pipe configurations with regard to engine type and location. We hope you agree. You know where to find us if you don't...
Exhausts - The Rules
A good, honest exhaust placement - bravo
Single pipe only, sided to reflect the location of the exhaust manifold where appropriate.
is the most extreme example of this rule but the same applies whether the exhaust is inside or outside of the bodywork. Double barrel exhaust tips are only acceptable for engines of more than four cylinders. Centre exits acceptable for transverse engines where the exhaust is routed thus for the line of least resistance, eg, old Minis.
Unless using a shared turbo V6s are permitted a single-exit pipe per cylinder bank, paired centrally like the Jaguar F-Type or at any distance apart as required by aesthetic demands. Quad pipes are ONLY acceptable for engines of eight cylinders or more, spacing again at manufacturer's discretion so grouped together (eg. Corvette Stingray, Pagani Zonda) or in pairs. Any more than four pipes looks daft. If even Ferrari at the height of 70s excess thought so (ref. 365 GT4 BB and subsequent 512BB).
Even Ferrari realised six pipes just look daft
Normally aspirated horizontally opposed engines may, in extreme examples (ie, VW Beetle) be permitted more than one pipe. Single turbo boxer engines should only use a single exit pipe, location as appropriate. Twin turbo flat-sixes may be permitted two single-exit pipes but only if individual turbo and manifold assemblies are used on each cylinder bank. Porsche 911s ALWAYS look cooler with a single corner-exit pipe.
Trims, diameters and other details
The diameter of the pipe exit should reflect that of the exhaust system as a whole; artificially flared pipes are to be avoided at all costs. Likewise, the exhaust tip should be part of the system as a whole - 'free floating' trim details with 'hidden' exits contained within are unacceptable. Straight-cut, plain gauge tubing (stainless steel or titanium) will always look cooler than 'rolled' or chromed trims. Chamfering is acceptable, especially if it matches the angle of the bumper or diffuser.
Signature off centre Alfa exhausts always cool
Quirks and traditions
Triple-exit pipes are as thorny an issue as three-spoke alloys and to be treated with extreme caution. Where dictated by the exhaust system - eg, Ferrari F40 and Porsche 911 RS 3.0, with its capped straight through track exits and corner 'road' system - it can be sub-zero cool. The 458's F40 homage triple-exit system treads a fine line but is acceptable.
Only Italian cars, specifically Alfa Romeos, can get away with the off-centre, angled single pipe that looks like a wizened old gent nonchalantly smoking a fag out of the corner of his mouth.
Should be consistent across the rev range and not artificially augmented; contrived start-up blips with the system fully open before closing the valves and settling down to a quiet idle are especially objectionable (see Porsche, Ferrari, etc). If you need to temporarily quieten your exhaust slip-on cans are acceptable.
Pops, bangs and crackles should only occur 'naturally' and not due to contrived ECU controlled 'misfires'. Ditto flames.
Always cool, subject to abiding by regulations with regard to engine configuration, aspiration and location. End of.
Just don't scrutinise too closely or truth is revealed
Exhausts hall of fame:
Jaguar F-Type V6
Caterham Seven (K-Series, so it's the passenger that burns their leg, not you)
Mercedes-Benz SLR McLaren
Audi R8 V10
Renaultsport Megane 265
Any 911 with chrome exhaust tips
Subaru Impreza STI (hatch)
Ford Focus ST
Vauxhall VXR8 (current)
[Sources: Ferrari 365 GT4 BB pic RM Auctions]