For pure performance, taking noise and emissions out the equation, what's the best design? Is it a straight short pipe? Also, why do bikes have exhausts out the front of the engine? (Obvs V twins have 1 at front and 1 at back, mainly thinking IL4) If they came out the back then the pipes would be shorter therefore lighter wouldn't they?
Practically never. It depends. - there are literally hundreds of factors to consider. Even this: depends on your aim - Torque or horsepower, fastest round a track, fastest accelerating, highest top speed? sorry for what might seem a non-answer.
For pure performance you want just an equal length exhaust manifold. Everybody claiming differently just doesn’t know and adheres to urban legends The reason engines are mounted as they are is extremely simple: The intake side takes much more room and isn’t as flexible as the exhaus side of an engine. There isn’t enough room before you hit the front wheel. And you and your shock might get roasted by the exhaus pipes. So really very simple answer Raoul
Equal to what? You are wrong. Motorcycle engines are traditionally mounted exhaust front due to 1. Latent heat of evaporation causing jet freezing 2. The need for relatively long exhausts and silencers to make motorcycles a viable form of transport.
Not necessarily correct, there is a whole raft of factors used in exhaust design, it is a complicated science, but differing lengths can be utilized and compensated for by using different sizes and bends, there is some quite good books on the subject if you can be bothered looking for them, but in the end it comes down to an effort/reward ratio, do you really need to spend time and money chasing that last couple of HP or just be happy with what you have.
Isnt it the gas that needs to be equal from each pipe? Which is why longer headers from front cylinder on a twin is matched with a shorter, wider one for the rear cylinder on many Ducati’s? And what about those spaghetti systems, that process the gas in particular way so as to move the performance characteristics? Buy a Harley @Cream_Revenge : you don’t have these worries with those
HI NZDave, I know about this stuff (I mean not as an exhaust engineer of course) but I am quite into engines. What you are talking about is putting an emphasis, in collaboration with the cam profile, on a certain rev range. And yes, there are millions of self influencing factors in engine and combustion chamber design, I totally agree. But breaking down the thread opener's question to a simple answer, for pure performance there is not more than "let the gasses flow as freely as possible) To clear the combustion chamber more efficiently you make a nice and expensive manifold where all exhaust pipes are of equal length before they join together In fact there is no single answer to cylinder head design (and surrounding parts) at all as each part depends on the other Raoul
It is about pulsations of the exhaust gas which can help suck the burned gasses out of the combustion chamber. Very roughly described. "spaghetti" systems is what I am referring to as equal length exhaust manifolds. What Ducati does is save money and space on complicated spaghetti systems by reducing the diameter of the one port to come to a similar result. It works rather ok but not as good as a real "spaghetti" Raoul
Reverse heads was quite popular for custom bikes years ago, Not very practical though, as mentioned the package used today gives cooling to the exhausts and compact and practical location of the carburetors or throttle bodies away from the elements. Length of exhaust can make differences to back pressure and power particularly on two strokes, different exhausts can alter where peak power comes in the rev range, even different exhaust materials can make a difference, the hotter the exhaust the quicker the fumes are removed hence wrapping, inconel is particularly good for this, it is very thin and light yet retains more heat than more conventional materials. This might be complete rubbish but it my understanding. Steve
This is rather correct, there hadn't not only been custombikes with reversed heads but always experiments with race bikes as well. The thing is that you won't get enough weight on the front wheel of you move the engine back sufficiently to have the intake at the front. 2 strokes is a very different story as nearly everything is different there. Raoul
No need to be sorry and no interest in discussing. Everybody can believe what he wants, if it makes you feel better understand my postings just as my “opinion”
Hi CreamR This idea is very easy to check and find to be untrue. The straightest, shortest pipe that lets the gases flow as freely as possible is just the exhaust port in the head. Anything more would be adding a restriction. The big holes in the power curve and low peak power on any dyno / test ride will show you there is a good bit of science and engineering going on in the design of any exhaust.
It used to be said that four equal length headers joined to one silencer (4 into 1) used to make most power, but joining two pairs of headers, then joining those again (4 to 2 to 1) was nearly as good on power but had better torque characteristics. That was on Range Rover V8s with a manifold for each bank of four cylinders.
Thinking the s4rs I am buying, and going short Termi which is single outlet. Really not a fan of the big shotgun exhausts, and my old 620 worked well with a 2:1 custom system
