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engine charactistics

Discussion in 'New Riders and Riding Tips' started by Zaphod, Apr 27, 2007.

  1. Hi all,

    Can anyone explain the differences in engines - v-twin vs parallel, 2 cylinder vs 4 cylinder.

    I've riden 2-strokes on farms etc. I like the reviews I've read about the Kawasaki's - especially the ZX6-R but what is the real difference as far as general motoring with the different engines?

    The local bike shop says "go v-twin" - usually this is a cruiser - which I don't particularly want. Another said "avoid 4 cylinders - to revvy" (huh?)

    My biking requirements - commute to work, weekend's away and would love to do a weeks cruise on holidays.

  2. Generally:

    Twins and V-twins: Easy, smooth delivery of power, with most of the fun down lower in the rev range. Don't need to be revved as hard as inline-4s, good for commuting. V-twins are not limited to cruisers, look at the VTR250/VTR1000, SV650, Ducatis etc.

    4-cylinders: Quite a bit more revvy, need to give it more throttle to set off but they keep on going after the twins run out of puff. Not as easy to commute on (also depends on the bike) but are definitely suited to highways more than the twins are.

    That is just two types of engine configuration (you also have your singles, triples etc etc). Both will do the job as good as each other, if in a different way, I suggest you try a few.

  3. Ok.

    It is easy to make a gutless, revless four cylinder. Drive a 2.7 litre hilux and you'll know all about it. :p

    Ignoring agricultural dinosaurs, basic rules of thumb for motorcycle engines:

    Two strokes work as roughly a vehicle of twice the effective capacity of a 4 stroke. eg a 250cc two stroke will put out about the same power as a 500cc four stroke.

    How the power is "lumped" together depends on whether a bike is easy to use or a vicious beast.

    Hence an RGV 250cc 2 stroke puts out more power than GS 500 and is basically useless until it switches on - the price of the 65hp top end is not much anywhere else - while the 50 hp GS500 is grunty but no real whoosh at the top.

    But, ignoring a race tuned two stroke versus a 30 year old designed commuter, there are some more visible examples with 250cc bikes.

    In the end, a motor cannot be "magically way more powerful" than something with a similar construction and capacity.

    What it can do is be designed so that it trades off performance at one part of it's rev range for another.

    So, if you want an insane top end, expect to have no bottom end. If you want grunty low end like trailbikes need, then dont expect it to whizz up to 18,000 rpm.

    When you're talking same capacity and same type of engine, "rules" about numbers of cylinders make more sense. Part of it is true, part of it is due to tuning.

    A 4 cylinder has the smallest pistons and smallest valves, rods etc. Everything is much lighter and can move much faster, with the intent of higher rpm. As such carbs, cam and ignition timing are all set for highest peak power at the highest rpm the engine can safely deal with.

    More rpm = more power, but only at those high rpm, and means far less down low.

    So yeah, they are more revvy and more gutless down low.

    Twins will have bigger pistons and valves with more weight and momentum than a 4 cylinder. This gives them a reduced rev range relative to a 4 cylinder, so the designers will ensure that cams, valves, carbs etc all match to that available power and use it to it's best advantage. The end trade off is more low end and mid range, and less top end at lower rpm.

    A single is this same compromise, but even more so. great low end power, solid midrange, but not really any top end at all.

    there is no best engine or magical number of cylinders. Choose what you want to ride based on how you think you'll want to ride it.

    And find another bike shop. if they dont want to listen to the customer, stuff them.
  4. Not entirely true. A water cooled engine for example can run a higher compression ratio, and therefore produce more power and torque, than an air-cooled engine of the same constructiuon/configuration/capacity. Of course an air cooled engine (generally) is cheaper, simpler, and more reliable. This also applies to number of cylinders, the more you have the higher the compression ratio you can run - so you end up with an engine that it smoother (less vibration), but with a greater number of moving parts (which can affect reliability).

  5. Except it's a watercooled engine versus an aircooled engine and thus a completely different construction.....

    Agree with your comment, but it doesnt really disprove my point.
  6. Not always that different as a lot of engines are converted from air to water cooling but I get your point. I assumed by similar construction you meant build tolerance, since that can make a massive difference to power output (ie compare a mass-produced engine to one that has been hand built).
  7. For what you said you do i would avoid the 250cc 4pot screamers.

    How about the best of both worlds, inline 3's (yum, trumpy daytona, damn it for not being learner legal) and V4's (rvf400):D