So the SR20DET is a square bore:stroke ratio - what is the KA and CA?
I'd really like to know, and haven't been able to find or interpret the specs to know.
I know that undersquare is typically a rev-happy engine, like a B16 in the Honda world, square is neutral, and oversquare is torquey but doesn't like to rev.
Can anyone shed light on this?
Undersquare vs Square vs Oversquare
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Daunttless
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When stroke and bore are the same, the engine is square
When the stroke is greater than the bore, the engine is undersquare, generally more torque or low revving engine
When the stroke is less than the bore, the engine is oversquare, generally more hp or revs higher
These rules are general rules, they do not always apply, it depends on quite a lot of factors actually and there are a few notable exceptions to the rule.
The SR is square, because its 86 bore/86 stroke.
The CA is undersquare by a tad weighing in at 83-83.5/84, but because of its design it acts like an oversquare. This is mostly due to its head. : ) Its the same with Honda engines, if I remember correctly the B18 is undersquare as well but is a very high revving engine. : )
Lastly, you have the KA which is also undersquare at 89/92 and it actually fits the rule. : ) Its makes more power on the low end as is expected of an undersquare engine.
A lot of bikes are oversquare and fit the standard oversquare rules. : )
Of course, I may be backwards, let me check. : )
When the stroke is greater than the bore, the engine is undersquare, generally more torque or low revving engine
When the stroke is less than the bore, the engine is oversquare, generally more hp or revs higher
These rules are general rules, they do not always apply, it depends on quite a lot of factors actually and there are a few notable exceptions to the rule.
The SR is square, because its 86 bore/86 stroke.
The CA is undersquare by a tad weighing in at 83-83.5/84, but because of its design it acts like an oversquare. This is mostly due to its head. : ) Its the same with Honda engines, if I remember correctly the B18 is undersquare as well but is a very high revving engine. : )
Lastly, you have the KA which is also undersquare at 89/92 and it actually fits the rule. : ) Its makes more power on the low end as is expected of an undersquare engine.
A lot of bikes are oversquare and fit the standard oversquare rules. : )
Of course, I may be backwards, let me check. : )
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Daunttless
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AkaiRPS13
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Sorry to dig up an old thread but i have a quick Q. if you can make an undersquare engine act like an over' with head design what would happen with an oversquare engine with an under-styled head? does head design difine the engine charicteristics more so than bore-stroke ratios? also where does rod length fit into all of this(determining high or lo end torque and stability at higher RPMs)?
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jmillheiser
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useful RPM range is more a function of Head/Cams/Intake
undersquare engines (like honda engines and the KA and the new QR) and engines with a long stroke in general have more torque potential but of course like on a honda engine that could mean at 6000-8000RPM. undersquare engines tend to rev on the slow side and aren't known for throttle response.
oversquare engines (subaru engines, many V6s and V8s, any boxer engine) tend to rev quickly and are known for fast throttle response. Rod ratio plays a more important part on oversquare engines as piston speed makes up for lack of stroke (especially true on aircooled VW engines which are VERY oversquare and use short rods the 1600 is 85.5 bore x 69 stroke).
undersquare engines tend to be the choice for big turbo motors due to their large exhaust volume which can spool up a large turbo faster.
oversquare engines can make for very responsive and rev happy NA engines(like a hopped up VW) or a fast spooling turobo motor if you use a small turbo (like a WRX)
a square engine (like the SR20 or the honda K20 which has the same bore and stroke as the SR) will behave somewhere in between
undersquare engines (like honda engines and the KA and the new QR) and engines with a long stroke in general have more torque potential but of course like on a honda engine that could mean at 6000-8000RPM. undersquare engines tend to rev on the slow side and aren't known for throttle response.
oversquare engines (subaru engines, many V6s and V8s, any boxer engine) tend to rev quickly and are known for fast throttle response. Rod ratio plays a more important part on oversquare engines as piston speed makes up for lack of stroke (especially true on aircooled VW engines which are VERY oversquare and use short rods the 1600 is 85.5 bore x 69 stroke).
undersquare engines tend to be the choice for big turbo motors due to their large exhaust volume which can spool up a large turbo faster.
oversquare engines can make for very responsive and rev happy NA engines(like a hopped up VW) or a fast spooling turobo motor if you use a small turbo (like a WRX)
a square engine (like the SR20 or the honda K20 which has the same bore and stroke as the SR) will behave somewhere in between
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themadscientist
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Some other things about oversquare vs. undersquare motors; With the longer stroke of the underquare motor the rod has greater movement from side to side as the crank turns. Where the rod connects to the crank is acutally further away from where the rod connects to the pistion, compared to a shorter stroke overquare motor. This causes more side loading in the bore. The pistion in an undersquare motor is traveling at a higher velocity as well. This means that there is less time for the cyl. to fill with the air/fuel mixture during the intake stroke, and expel exaust on the exaust stroke. These two factors go a long way to limit the higher rpm range of a motor. However, as was mentioned above, the head and cams do the most to say where the powerband of a given motor would be. Most of the Honda VTEC motors are undersquare, but are still hi-rpm motors because of the head design.