Quote:
Originally posted by Prelewd
As taken from madh0 at nwhonda.com:
H22 rods are longer, and produce a lower rod/stroke ratio in the engine. The angle to the piston wall is greater, which puts more strain on the engine. The added strain will give you a broader torque range however. The piston speed will be higher with a longer rod as well.
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that statement is backwards. a longer rod will decrease sidewall forces during crank rotation. it also slows piston speeds.
if you were to take a single crank, two differing rod lengths, and two differing block deck heights, the degree of angle acting on the rod when the crank is at 90 degrees BTDC will be less with a longer rod.
this means less sidewall force compared to a shorter rod on the same crank.
a shorter rod also means the piston speeds are increased as the rods base has to travel a longer distance around the circumference of the crank's rotation, in comparison with a longer rod on the same crank.
1.75:1 rod/stroke ratio is considered "square". it's a comprimise to give a decent amount of torque while preventing the loss of power due to friction from sidewall loading.
with a rod/stroke ratio of 1.49:1 on the H23 compared to the 1.59:1 of the H22, it shows the H22's rods being longer. this produces less bearing stress, less side force, and slower piston speeds. these are all the things you need to do to increase high-rpm capability and reliability at those higher speeds. slower piston speeds also allow for more efficent breathing, especially at higher rpm, as the piston doesnt drop too quickly to get an efficent fuel charge. the closer to 1.75:1 you get, the better your results. over that, you give up torque for higher rpm capability... this condition is called "oversquare".
the B16A features a 1.749:1 rod/stroke ratio. this is why it revs higher and produces power easily, as there's less bearing stress and side load friction. it can essentially breathe more efficiently... well enough to support high-rpm performance.
the F20C in the S2000 is a prime example. it's rod/stroke ratio is also 1.75:1.
so in closing, being undersquare (short rod, long stroke) will decrease performance by creating more side force and increasing piston speeds. this results in reduced efficiency at high rpm due to friction, breathability, and increased bearing stress.
being oversquare (long rod, short stroke) will decrease piston speeds, reduce side force, and reduce bearing stress... but at the sacrifice of torque due to the slow piston speeds at low rpm.
being in the middle at 1.75:1 rod/stroke ratio will provide a happy medium of both.