The Technical Questions Thread

[NSXType-R]

Why is there a disparity in MotoGP between the teams themselves between which format they use for engines - inline-4 or V4? Why do none of the Japanese 4 make a V4 litrebike while Aprillia does? What are the advantages and disadvantages of each configuration?

Vibration, size issues, maybe? An inline 4 isn't very balanced, I think and is comparatively long.

A V4 is slightly shorter, and slightly more balanced.

I'm surprised they don't use flat engines- lower center of gravity, much better balance.

On a side note, what's wrong with using a V4 for a car? We use I4s all the time.

[LeonOfTheDead]

Why is there a disparity in MotoGP between the teams themselves between which format they use for engines - inline-4 or V4? Why do none of the Japanese 4 make a V4 litrebike while Aprillia does? What are the advantages and disadvantages of each configuration?

Vibration, size issues, maybe? An inline 4 isn't very balanced, I think and is comparatively long.

A V4 is slightly shorter, and slightly more balanced.

I'm surprised they don't use flat engines- lower center of gravity, much better balance.

On a side note, what's wrong with using a V4 for a car? We use I4s all the time.

An I4 is simpler, you have a single head, two camshafts and so on.
A V4 is shorter, and on a bike it allows to reduce the frontal section of the bike, hence more speed and even a bit of agility.
I don't think a V4 is better balanced than an I4, should do some calculation and I DON'T WANT TO DO THAT.
A flat engine would be simply too large, and if you noticed how much the bike is inclined during corners, it simply wouldn't be possible.

We put a bit too much attention on the balanced- or not aspect.
I4 aren't balanced, but with counter rotating and rotating additional shafts that's pretty much solved, since...ever. Also these shafts aren't selfish as they could be used for moving other stuff.
In a bike, specifically, having a smaller or narrower engine is much mroe important. The minor speed you could gain in the straight would be inferior to the speed you can gain in corners with a smaller and more "dense" bike.
Both V4s and I4s can be considered small engines, each in its own way.
BTW, Honda uses a V4.

On road bike a balanced engine would be more important, but:
-if it's a sportsbike, it isn't comfortable or silent, so a bit of additional vibrations wouldn't make such a difference
-on a cruiser like those huge BMWs, you can use their boxer engines, or perfectly design the additional shafts to balance the engine, since you have a lot of space and the bike is already heavy.

On cars, a V4 is simply pointless. Since there is no space-issue, having two heads is worst than having a smaller engine.

[Matra et Alpine]

With the reductino to 800cc it swung the design benefits in favour of a V4 design.
Especially coming from a V5 of 1000cc

With the smaller size most stopped seeking ultimate power from the desing and instead went for drivability. AND yet still they ahve more power than last year

ON other comments ... you want an engine low enough so that it doesn't effect the lean-ability of the bike/rider AND not so low that teh rider can't get the bike leant over

[hightower99]

So why not a flat 4 placed latitudinally? Thats about as low as you can go, and it is no wider than a V4 positioned latitudinally... That there would be much less inertial torque required to lean the bike over???

[LeonOfTheDead]

So why not a flat 4 placed latitudinally? Thats about as low as you can go, and it is no wider than a V4 positioned latitudinally... That there would be much less inertial torque required to lean the bike over???

the V shape allow you to have only one area in which the bike in the lower part would be larger, while with a flat engine the whole bottom part would be large along side the whole length of the bike.
It isn't a very compact engine.

[fpv_gtho]

Together with the gearbox, surely that would be too long.

[hightower99]

the V shape allow you to have only one area in which the bike in the lower part would be larger, while with a flat engine the whole bottom part would be large along side the whole length of the bike.
It isn't a very compact engine.

So what? It wouldn't cause an increase in drag and I doubt that the short stroke engine would reach the whole length of the bottom of the body...

Together with the gearbox, surely that would be too long.

Depends entirely on how you make the gearbox. I bet a solution could be found that could keep the whole package more than short enough to stay in the bike.

[LeonOfTheDead]

So what? It wouldn't cause an increase in drag and I doubt that the short stroke engine would reach the whole length of the bottom of the body...

yes it would cause a major drag, but mainly it wouldn't fit or allow for a decent handling

Depends entirely on how you make the gearbox. I bet a solution could be found that could keep the whole package more than short enough to stay in the bike.

if it was so easily possible to "found a solution", then they would have at least tried it.
Even BMW which has quite an experience in flat engines for bikes doesn't use them int heir sportsbikes.

[fpv_gtho]

You think it could be done to fit in a current chassis, given the extra space needed between the crank and gearbox over I4/V4 designs, and also given the necessary clearance to the front wheel and radiator?

I cant see it getting done without lengthening the chassis, which would surely affect other aspects of the handling negatively.

[LeonOfTheDead]

You think it could be done to fit in a current chassis, given the extra space needed between the crank and gearbox over I4/V4 designs, and also given the necessary clearance to the front wheel and radiator?

I cant see it getting done without lengthening the chassis, which would surely affect other aspects of the handling negatively.

pretty much,
A longer and wider (in the lower part) bike. What's the point?
Surely the CG would be lower, but it would even weight more.
having a low CG when the bike is larger it's a bit of a contradiction though.

[Matra et Alpine]

Couple of points unique to bikes.
The swinging arm mounts the rear wheel and you want to hang it off the rear of the gearbox.
So you cant' use all the space to the rear wheel for engine Gets used for electronics and fuel though !
By "latitudanl" do you mean the crank runing the length of the bike ?
Sadly as an engine only spins in one diuretion this is a nightmare fora compeition bike.
As you rev, increase the rotational momentum in the engin it then either pulls the bike up or pushes it down when leant over. So whilst it CAN be a useful to lift a bike on the exit of a corner, the downside of it wanting to slam you into the tarmac makes it bad. So riders have to hold off the throttle longer than a cross-frame crank engine does.
MotoGP bikes are TINY.
The wheelbase is as short as it can be so the bike turns and changes direction more quickly.
Lengtheneing the wheelbase woudl lead to everyone overtaking on the way into corners and leaving behind on the way out. Watch a H-D turn versus a sportsbike

[hightower99]

yes it would cause a major drag, but mainly it wouldn't fit or allow for a decent handling

How so? You certainly wouldn't increase frontal area and you could probably decrease it a fair bit...

if it was so easily possible to "found a solution", then they would have at least tried it.
Even BMW which has quite an experience in flat engines for bikes doesn't use them int heir sportsbikes.

Actually BMW does make sports bikes with flat twin engines... Please understand that I am only playing devils advocate and that I don't reallt think that all super bikes should be running flat 4s.

You think it could be done to fit in a current chassis, given the extra space needed between the crank and gearbox over I4/V4 designs, and also given the necessary clearance to the front wheel and radiator?

I cant see it getting done without lengthening the chassis, which would surely affect other aspects of the handling negatively.

Well as I said I am just playing devil advocate but I am sure that if someone wanted to they could come up with a solution that would not require lengthening the bike and a smart soution as to where the transmission should be.

By "latitudanl" do you mean the crank runing the length of the bike ?

No I don't. You know how the engine is in say a BMW HP2... turn the engine around 90 degrees so that the pistons face towards the front tire and rear tire.

[LeonOfTheDead]

How so? You certainly wouldn't increase frontal area and you could probably decrease it a fair bit...

If you don't have technical reasons to say that it could even be reduced, then don't say it, no matter who you are advocating.
Perhaps the frontal area wouldn't be larger, but certainly the same section would maintain itself for a longer part of the bike, increasing drag.

Oh, I just remembered when you said that it could be quite a short engine using a short stroke...perhaps you should know that the stroke isn't taking the larger part of the length of the cylinder, so it would be that much shorter, and a V4 or I4 would be way shorter.

Actually BMW does make sports bikes with flat twin engines... Please understand that I am only playing devils advocate and that I don't reallt think that all super bikes should be running flat 4s.

Yeah, like their new SBK ride...

Well as I said I am just playing devil advocate but I am sure that if someone wanted to they could come up with a solution that would not require lengthening the bike and a smart soution as to where the transmission should be.

ok so Bugatti didn't want to do the Veyron quickly, they wanted to spend 4 years trying to make it stick to the ground, because if someone want to do something, well, it would be surely possible.

[fpv_gtho]

I cant see any logical position to put the gearbox though other than at the end of the swingarm which seems to be the current norm. Having the chain drive and the necessary tension through the suspension travel would be a pretty big restriction on gearbox placement.

[hightower99]

If you don't have technical reasons to say that it could even be reduced, then don't say it, no matter who you are advocating.
Perhaps the frontal area wouldn't be larger, but certainly the same section would maintain itself for a longer part of the bike, increasing drag.

The technical reasons are relatively simple. Normally a V4 be relatively tall, stretching from the bottom of the main frame rail down to just past halfway. This means that the body will need to be a certain width down that far. With a flat 4, the engine itself produces a smaller frontal area which allows the body to be made smaller where the engine no longer occupies space. Current bikes need to maintain a section big enough to fit the engine and gearbox, the whole package stretches from the front of the body (just behind the main radiator) back to the rear suspension arm mount. With a flat 4 the bottom will have a slightly larger section but the upper parts of the body can be narrowed and there will be more room for more advanced air control over the rider.

Oh, I just remembered when you said that it could be quite a short engine using a short stroke...perhaps you should know that the stroke isn't taking the larger part of the length of the cylinder, so it would be that much shorter, and a V4 or I4 would be way shorter.

The question was about whether or not a flat 4 would have room under the bike... since the capacity is set at 990cc the stroke can be very short and therefore the engine will not be very long. AFAICS there shouldn't be a problem with space.