Bore x Stroke

[avgas]

I was reconciling/writing the Goldwing.

What you need to study is momentum by the sounds of things lol

[Big Dave]

What you need to study is momentum by the sounds of things lol

The next paragraph mentions inertia. 405kg wet.

edit - I just re-read it - momentum is a better angle. ;-)

[Mikkel]

It's hip to be square.

[nudemetalz]

A lot of the 2-stroke performance road-bikes have square bore and stroke.
eg RG-250 54mm x 54mm and RGV-250 56mm x 50.6mm (which is barely oversquare).
These engines don't really rev high (10-12,000 rpm) compared to the performance multis but have the peak hp and torque relatively close together and are peaky.
So it's a whole different kettle of fish when doing the 2-stroke vs 4-stroke bore and stroke talk.

Just thought I'd throw that meaningless bit of info in.

[merv]

Just to add a light bit of further comment to this thread is I think its funny we refer to square when a piston is normally round, so even though many of the good old 2 strokes had a 54x54 engine and we called them square, how square is it anyway?

Now we know Dave is talking about the Gold Wing which is slightly short stroked and doesn't rev that high we know he is talking about an engine built for its task - stacks of torque and the ability to cruise forever at reasonably low revs with multi-cylinders and horizontally opposed to keep it smooth.

[avgas]

The next paragraph mentions inertia. 405kg wet.

edit - I just re-read it - momentum is a better angle. ;-)

like an anchor to water

[Ixion]

Cool - I had a pretty good handle on it - that Ixion is on another planet - not actually a planet - that is.

I was reconciling/writing the Goldwing.

-----------------------

More impressive is how it goes.

Its Liquid-cooled 4-stroke, 12-valve, SOHC flat – 6 cylinder engine has a
Displacement of 1,832cc with a rather square 74 x 71 Bore and Stroke and a compression ratio of 9.8:1.

It’s got some ‘schtonk’. It puts out 87kw (117hp) at 5,500rpm, but that isn’t the important figure. The 167nm of torque at 4,000rpm, is.

--------------------------

'Rather square' is too subjective?

One's enough. Two's plenty. Three's luxury. Four's a car. Six is a truck.

[JMemonic]

Think you've got your squares mixed up.

Short Stoke = over square
Long Stoke = under square

http://en.wikipedia.org/wiki/Stroke_ratio

Thanks for that was thinking I was wrong but that section of the brain had already fallen asleep. Edited my original post.

[nadroj]

While we are on this subject what is the accepted maximum piston speed now days?
As previously mentioned around 4,000fpm used to be max and the first Honda 750 fours were 4,100fpm at redline if memory serves me correct.
I did calculations on a Ford Flathead V8 powered Bonneville roadster a few years ago & came up with 5,200fpm so it obviously had a rather strong girdle to stop it farting south!

[Big Dave]

like an anchor to water

Quite remarkably and I admit - surprisingly - not so.

It's testament to the importance of the height of the centre of gravity as much as the mass.

They skids along.

[Forest]

While we are on this subject what is the accepted maximum piston speed now days?
As previously mentioned around 4,000fpm used to be max and the first Honda 750 fours were 4,100fpm at redline if memory serves me correct.
I did calculations on a Ford Flathead V8 powered Bonneville roadster a few years ago & came up with 5,200fpm so it obviously had a rather strong girdle to stop it farting south!

As a datapoint, the Ducati superbike engines max out at around 5,400 fpm.

[Motu]

[QUOTE=JMemonic;
Long stroke, or under square is generally (in automotive terms) an older design now and rarely used, it will be low revving with high torque, .[/QUOTE]

I suggest you check out bore/stroke specifications of modern car engines,they are most often long stroke.More to do with emissions really,a short stroke engine is prone to producing Co and HC because of the large combustion chamber.

Some preconcieved assumptions about short/long stroke....and Dave is right to be puzzled.A short stroke engine produces more low speed torque than a long stroke - think hydraulics....the large surface area of the piston applying a lot of pressure,a short sharp shock giving more torque.Trials bikes have the highest low speed torque of all motorcycle engines....and are short stroke.

It was something I noticed over 35 years ago when riding British bikes - why did the short stroke BSA A65 (and Yamaha XS1 with the same 75x74mm) have more bottom end grunt than the revvy long stroke Triumph engine .... it should have been the other way around.

[Big Dave]

>>More to do with emissions really,a short stroke engine is prone to producing Co and HC because of the large combustion chamber.<<<

Because it is less efficient?

[Motu]

Too much surface area....and quench areas that force the fuel back into a liquid state.

[popelli]

- why did the short stroke BSA A65 have more bottom end grunt than the revvy long stroke Triumph engine .... it should have been the other way around.

and the bsa had more power on the top end as well

nothing to do with bore / stroke but everything to do with head design and the amount of air you can flow through it