A small increase in engine size seems to have made a large increase in output. Looks like it was a good change for sure.

 

The interesting part is that they simply shortened the connecting rods a few millimeters to increase the displacement.

 

You lost me there.
How does shortening the connecting rods change displacement?
Maybe shorter rods because of a longer stroke?

To answer my own questions:

Shorter rods won't change displacement.

The 300s increased displacement is a result of increasing the stroke from 41.2mm on the 250 to 49mm on the 300.

 

From Ultimate Motorcycling:

Further highlighting changes for this model, it features new, lighter piston pins to further reduce reciprocating weight and help preserve a high redline, new shorter connecting rods to offset new longer crank throws, and new sleeveless 'open-deck' die-cast aluminum cylinders that are 800 grams lighter and feature a friction-reducing 'T-treatment' plating.

 

From Ultimate Motorcycling:

Quote:
Further highlighting changes for this model, it features new, lighter piston pins to further reduce reciprocating weight and help preserve a high redline, new shorter connecting rods to offset new longer crank throws, and new sleeveless 'open-deck' die-cast aluminum cylinders that are 800 grams lighter and feature a friction-reducing 'T-treatment' plating.

The longer crank throws are responsible for the increase in displacement.
Shorter rods were necessary but had nothing to do with displacement.

Do some research.

 

Good stuff, admin.

 

It's a combination of the two that determine stroke. Changing connecting rod length, which changes the length of travel to TDC along with the length of the crank, will determine displacement.

With all other things being equal, if you lengthen the connecting rod, you will shrink the displacement and vice-versa.

 

You win.
You are wrong, but someone else can try to explain it to you.

 

I made a quick diagram how con rod length can effect displacement. (not to scale and exaggerated for clarity)

Lets' assume that both cylinders diagrammed below are at TDC. With all other things being equal, a shorter rod (B) will result in a larger displacement (A) and a longer rod (D) will result in a smaller displacement (C).

Saying that rod length has no effect on displacement is actually incorrect.

 

You're right that it would, all buy itself, increase the volume in the cylinder, but it isn't going to move any more air, or compress it enough to take advantage.

So, simply shortening the con rod is going to cause a power loss.

 

I was going to just drop this, but you guys are putting out information that is totally wrong and may cause some problems for anyone that believes it.
Here's a link to the Powroll website and I think they probably know.

Powroll

Pay particular attention to the 4th segment.

It states:

Rod length has nothing to do with displacement. Really. Trust us on this one.

Here's the best way to figure out why this is true. You've probably got a glass of your favorite beverage sitting in front of you right now, don't you? Okay, lets say that glass is 1/2 full and has 10 oz of liquid inside. Now, pick up the glass and hold it up in the air.

Is there more liquid in the glass? Nope. Same amount, it's just in a different location.

Now, put the glass back down. Same amount of liquid? Of course -- unless you cheated and took a swig on the way down.

The rod does the same thing that your arm just did. It only changes the location, but not the displacement.

Changing rod length can change the way an engine produces power, but it will never change the actual displacement.

Okay, take a drink of the stuff in the glass, you deserve it!

Why is this so difficult to understand?

 

You guys?

Where did I say it increased displacement? I said it would NOT move any more air (psstt...another way of saying displacement).

 

[Cycle World]

I want to talk about the torque curve. Seems to me that it would be very hard to stall out when taking off in first. Seems an experienced rider could take off in second with little time in the friction zone.

 

What has changed with the gearing? With my 250, I found myself shifting very quickly.

 

I would like to state for the record that:

1. Charles was correct. Rod length does NOT change displacement.

2. Rob and Charles said the same thing.

3. Please read below.

 

Dodsfall:
Do not confuse volume with displacement. Re-read what Rob Moore has stated. He speaketh the truth.

 

Some of the good got deleted with the bad, so I'll repost the good.

Displacement isn't changed by a shorter con rod because displacement is the difference in volume between top dead center and bottom dead center ( divided by 4 for a 4 cycle engine because only 1 of the 4 trips the piston makes moves in air/fuel....disregard cam overlap for our purposes here)

Stroke is a function of the distance between the center of the crankshaft and the crankpin where the con rod is connected. A larger throw yields more stroke.

A shorter con rod by itself would actually lower compression ratio and lower the engine's power.

 

I almost forgot (remembered on the ride in to work this morning), that is per cylinder.

 

The link I posted earlier covered displacement quite well, but......
The problem with it was I screwed up that link when I posted it.
Here's the Powroll link posted correctly. (I hope)
powroll
Their web-site basically explains what Powroll does, but it has a lot of good, and to me, interesting information.
One thing that impresses me is the fact that they have been doing this since 1964 and this was pretty radical stuff in those days.
The "heat shrunk rod" in particular was a pretty simple solution to a problem that would have cost a lot of money to resolve with high priced tooling.