Inline 4s

Originally Posted by -Ralph-

Torque gets you moving when you open the throttle, and give you the forward shove, but whether or not power builds and gives you blistering acceleration and speed as you get revs towards the red line, or whether it "tails off" is all about how many horses the bike produces. You can't look at either in isolation, the nature of the engine's power delivery is a combination of the two.

Of course, but by looking at torque, you're looking at a function of HP and rpm already, so it's by definition not looking at it in isolation...? Unless I am misunderstanding what you are saying, of course. Acceleration is provided by the torque so I can't see saying it is "all about the horses" is accurate....sorry. Again it might be me misunderstanding or misinterpreting what you're saying.

Originally Posted by -Ralph-

BTW, whether something "tail's away" on a dyno graph all depends on the vertical axis scale on the graph.

The SV produces 28 ftlb from 2500 revs, peaks at 47, and "tails off" to about 35.

Most of the IL4's produce 15ftlb at 3000 revs. Peak at about the same, and "tail off" at about 35 as well, albeit both at much higher revs

By comparison if you put the two on the same vertical axis scale, the SV would have a relatively flat torque curve, which is what makes it pull like a bigger bike lower down the rev range

I would agree the SV, on the same vertical scale, would have a flatter torque curve, yes. At a given (low) rpm I have no argument with the statement that an SV can accelerate better (precisely for the reasons you mention, it has more torque there).

However, you can still look at an SV dyno graph in isolation and see it does tail away - what you could mean is "how much" it tails away is dependent on the vertical scale (obviously).

To be honest I'm not quite sure what I'm arguing about here - whether the SV tails away (acceleration wise) after 8k? Is that in question - I don't think you're disagreeing with the dyno chart figures, so given that, the torque is falling away after ~8k...the HP isn't rising enough to match the RPM, so the torque formula shows it will reduce the torque (which the graph then shows)?

Looking at and comparing the SV chart with a GSX-R600 chart (http://www.areapnolimits.com/images/..._dyno_1005.gif) my personal view is that the torque is what I'm feeling as the difference. It's falling from ~8k on the SV and ~13k on the GSX-R. I would agree with that from my experience of these bikes. If we want to give some figures, then we can say that the SV is falling in the last ~27% of it's rev range, whereas the GSX-R is falling in the last ~18% of it's rev range. Perhaps because of this smaller percentage of the rev range spent "tailing away" it's not so noticeable on an IL4.

Originally Posted by monkey

Someone was telling me just that the other day...

I think it's all swings and roundabouts. Until recently I had a twin, a triple and a four all of which I love/d in their own special way.

Cylinder snobbery is pants.

Also, I agree with this/hold this view the most - I only want people to stop trying to say one is better than the other!

[Mej]

Originally Posted by Tim in Belgium

I've liked 1s, twins and IL4s so far, all are good but different.

second this.

Love the noise of twins, but my 750 was anything but bland. Loves singles and did like the noise of the tripple i rode (d675).

[yorkie_chris]

Originally Posted by muffles

torque hp yadda yadda

Horsepower is a function of torque and rpm, not the other way around.

Torque... applied through gears and on moment arm of tyre contact patch to spindle produces a tractive effort.

Call that tractive effort F... F = ma a = F/m


Past peak torque, rate of acceleration is reducing.

[SoulKiss]

Originally Posted by Sid Squid

You need to ride more Kawasakis - they definately have it, lots of it, that's not in question, what 'it' is is the question

Like my lovely 08 Z750

[G]

I love all bikes. Each serve a purpose.

I'll be switching to a twin next, but I still love IL4. It just depends what you want out of riding at any particular time in your life.

[yorkie_chris]

Originally Posted by Sid Squid

I don't prefer either, but technically speaking fours are better then twins. Technically twins don't make better power at the low end, they just run out of the necessary piston/valve area and thus their volumetric efficiency falls significantly when the revs rise, add to this that for a given capacity a twin's relatively heavy reciprocating parts reach their practical limits at a lower rotational speed and the piston speed limit, (which I understand is about 90m/s for a road engine about now), of the relatively longer stroke limits the max safe revs - racing twins spin much faster as their much reduced engine life is not important.
The suggestion that you need to rev the round things off a four to make it go is just plain wrong, they often make good power at the bottom and keep going when twins run out of puff. And even if they didn't it's just numbers on a dial, who cares where the needle is pointing? Pit your SV650 against a Panther and it would seem revvy, would this be a reasonable criticism of your SV?.

You could apply same arguments against fours and for sixes, and look how well they lasted

Twins making better power at low end can be lots of things, geometry of intake tracts, cam profiles and timing, carburetion, allsorts of things most of which could be applied to a four.

Redlines and such, if you have a twin of similar ratio to a four and similar peak piston speed it will probably rev about the same.
Compare the 'busa to the SV...


One thing worth mentioning with twins is crankcase pumping loss, they have 2 fluctuations offset by 90 deg... where a four has two pairs of them offset by 180 degrees so they cancel out. Means less losses shipping gas in and out of crank breathers and hence more power/economy.

Originally Posted by yorkie_chris

Horsepower is a function of torque and rpm, not the other way around.

Actually...both ways round, unless there is a special definition in engineering (I can only tell you for mathematics, not engineering, but you can refactor a function so that it is a function of any of it's variables)

Other than that, you said the important bit which I was trying to say - the rate of acceleration is reducing, which is the tailing off effect...

[yorkie_chris]

Well yeah obviously you can switch the sum around, but when you have a dyno trace the directly measured result is the torque.

From right back in ye olde times when it was measured by force on a torque arm from a brake drum... thus brake horse power.

Originally Posted by yorkie_chris

Well yeah obviously you can switch the sum around, but when you have a dyno trace the directly measured result is the torque.

From right back in ye olde times when it was measured by force on a torque arm from a brake drum... thus brake horse power.

Can't argue with that...I was just being picky