What's the definition of "oversquare engine"? - Star Motorcycle Forums: Star Raider, V-Max, V-Star, Road-Star Forum
 
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post #1 of 8 (permalink) Old 11-22-2014, 02:57 PM Thread Starter
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What's the definition of "oversquare engine"?

Really crappy day here and I don't want to light the stove in the garage so I can clean my bike so I'm reading old threads here and came across the following statement:

However the 1100 V-Star engine is an 'oversquare' engine so by nature it does not lend itself to higher torque numbers.

This was in response to a query about doing the single carb conversion. I've never heard the term "oversquare engine" before. What does it mean?
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post #2 of 8 (permalink) Old 11-22-2014, 03:06 PM
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Never heard that phrase before. Curious to know.

87' 1100 Sportster (caffeine runner)
05' 1100 Custom Midnight Edition
07' 1300 V Star Tourer
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post #3 of 8 (permalink) Old 11-22-2014, 03:10 PM
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From Wikipedia
Oversquare or short-stroke engine[edit]
An engine is described as oversquare or short-stroke if its cylinders have a greater bore diameter than its stroke length, giving a bore/stroke ratio greater than 1:1.

An oversquare engine allows for more and larger valves in the head of the cylinder, lower friction losses (due to the reduced distance travelled during each engine rotation) and lower crank stress (due to the lower peak piston speed relative to engine speed). Due to the increased piston- and head surface area, the heat loss increases as the bore/stroke-ratio is increased excessively. Because these characteristics favor higher engine speeds, oversquare engines are often tuned to develop peak torque at a relatively high speed.

The reduced stroke length allows for a shorter cylinder and sometimes a shorter connecting rod, generally making oversquare engines less tall but wider than undersquare engines of similar engine displacement.

87' 1100 Sportster (caffeine runner)
05' 1100 Custom Midnight Edition
07' 1300 V Star Tourer
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post #4 of 8 (permalink) Old 11-22-2014, 05:21 PM
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Exactly....

It's all bore and stroke. That is why the 1100 turns more RPM's and is able to blow by many other carbed V twins that have 50% more cubes at highway speeds.

Dual carbs lend themselves nicely to that set up. The 1100 is set up more like an F1 car....the big displacement bikes (Harley's etc) are more like tractor...low end torque, but run out of steam on the top end.

Sick Mick* 2006 V Star 1100 Custom

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post #5 of 8 (permalink) Old 11-22-2014, 09:17 PM
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Yes indeed, what Mick is saying is so true. (I ride an 1100 Silverado, stock mostly)Just this summer, for example, riding with some Harley boys, going to make a pass, I was last bike in group, traffic coming, had to hurry, the ol boy in front of me was doing all he could do, I blew by him like a freight train passing up a bum to get back in. The 1100 had what I think he wished he had have had

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post #6 of 8 (permalink) Old 11-22-2014, 09:50 PM Thread Starter
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Not really a techy person and my eyes kind of glazed over reading the Wiki definition but it does explain why my bike really pulls so hard once the revs hit 4000 rpm.
Sugar Bear, don't you just love doing that? Now I can throw "oversquare engine" at them too and let them figure it out.
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post #7 of 8 (permalink) Old 11-23-2014, 07:33 AM
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Yeah....it's a term that doesn't get used too much these days. Most just use "long stroke" or "short stroke" to differentiate between between the 2 engine designs.

Obviously there are advantages and disadvantages to each.

Sick Mick* 2006 V Star 1100 Custom

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post #8 of 8 (permalink) Old 11-23-2014, 08:28 PM
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Quote:
Originally Posted by Sick Mick View Post

Obviously there are advantages and disadvantages to each.
Definitely. I had a Shadow 1100 ACE once upon a time, and it felt like it had more grunt power below 2500 rpm's than my 1300 does, but it fell on its face above that point, but the 1300 really shines above 2500.
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