Hi Gary,

The bore/stroke ratio is mathematical formula of bore diameter divided by the length of the stroke.

A 1:1 ratio would be a "square" engine (4 inch bore/4 inch stroke; 87mm bore /87mm stroke; etc).

A 0.5:1 ratio would be under square (2 inch bore/4 inch stroke)

A 2:1 ratio would be over square (8 inch bore/4 inch stroke)

Another figure you'll see in conjunction with the "bore/stroke ratio" is the "rod/stroke ratio" which concerns the connecting rod length to stroke length. This takes into consideration the angle of the connecting rod to the wall of the bore.

Where swept area comes into effect is the determining of the compression ratio:

Swept bore volume + unswept bore volume, divided by unswept bore volume (9 cubic inches + 1 cubic inch) / 1 cubic inch = 10/1 = ten to one (10:1) compression ratio.

There are some excellent books out there that give good descriptions of the different terms and how they baffect the design of an engine. I'm on the rig right now so don't have access to my library at home and even then I might not find the books...too much is still in boxes and the bookcases are packed in the garage.

I got into all this back in my Norton racing and Pontiac GTO and Tans Am hotrodding days. get some books and read...really fascinating. With a little thought, I might remember some of the authors and books but the mind is a blank right now...OK, I'm 64..Ihave an excuse! <LOL>

The Internal Combustion Engine in Theory and Practice, Volume 1: Thermodynamics, Fluid Flow, Performance

by Charles Fayette Taylor Volunes I & II

Four Stroke Tuning by A. Graham Bell

Two Stroke Tuning by A. Graham Bell

...a few off the top of my head and a quicky search...

Hopper

--- On Wed, 10/12/11, Gary L. Smith <lgranch@laughing-gargoyle.com> wrote:

From: Gary L. Smith <lgranch@laughing-gargoyle.com>
Subject: Re: [DucatiST] The New Ducati Engine!
To: st2_owners@yahoogroups.com
Date: Wednesday, October 12, 2011, 12:51 PM

OK Hopper et all,
My understanding of "over square" is that the swept area of the
piston is longer than the bore of the cylinder. An "under square"
engine is one that has a bore larger than the swept area of the piston.
Please correct me if I'm wrong and explain please.

Thanks,
Gary '01 ST4 Gaston, OR

On 10/12/2011 7:07 AM, HOPPER ELDRIDGE wrote:
>
> Nick, go back to the information page and search through it. There are
> a lot of tech pages in there. The engine is rotated a bit back for
> more clearance to the front wheel but not as much as I figured it
> would be from earlier information I had read...6 dgrees if I remember
> correctly.
> I agree with you too in that the bike is getting too complicated and
> tech oriented. You'll shudder every time it rains or you give it a
> bath. The newer bikes have too many problems as it is...now this one.
> Love the HP readings but as you go to higher over square numbers, the
> HP is shifted further up the RPM range. The power curves were nicely
> linear though, not curvilinear. The basic design of a 90 degree V twin
> will give better torque than other designs but the over square figures
> will null that out to a point.
> On my olde racing Norman White Norton Commando, we used a drag race
> cam with the idea that a heavy flywheeled long stroke vertical twin
> had enough torque in basic design but needed more HP. The bike did
> well enough in BOTT that Tony Rutter approached Norm about racing it
> in the '84 IOM pre-72 production class until that class was
> eliminated...bummer!
> Cheers...Hopper
> --- On *Wed, 10/12/11, Nick Woods /<nickw@cooptel.net>/* wrote:
>
>
> From: Nick Woods <nickw@cooptel.net>
> Subject: Re: [DucatiST] The New Ducati Engine!
> To: st2_owners@yahoogroups.com
> Date: Wednesday, October 12, 2011, 1:46 AM
>
>
>
> --- In st2_owners@yahoogroups.com
> <http://us.mc807.mail.yahoo.com/mc/compose?to=st2_owners%40yahoogroups.com>,
> Jan Wysocki <st@...> wrote:
> >
> > I'm not entirely sure it's _my_ future.
> >
> > Ok, it's a desmo L-twin
>
> Yes, still a 90-degree motor, but did anyone else notice that the
> engine on the stand seemed to be rotated backwards to give a
> more-conventional vee configuration? I couldn't be sure of the
> angle of the datum line provided by the script on the clutch case,
> 'cos there were just too many atmospheric soft-focus close-ups....
>
> It's obvious that the only thrust of Ducati is top-end bhp, with
> masses of high-tech gizmos to make the thing rideable at more
> modest speeds, but I guess that's what sells bikes these days.
> Probably it was always that way, and only the technology has changed.
>
> NickW, UK
>
>