Under vs Oversquare

[Law_]

As we know, our engine has 75 mm Bore and 79 mm Stroke.
This, based on wikipedia is known as undersquare or long-stroke engine (still, almost square). This is what is said about undersquare engines and i'm quoting:

"This can be a negative trait, since a longer stroke usually results in greater friction, more stress on the crankshaft, and a smaller bore requires smaller valves which restrict gaseous exchange. An undersquare engine usually has a lower redline than an oversquare one, but it generates more low-end torque.

Undersquare engines typically are, proportionally, shorter in length, heavier, and taller than equivalent oversquare ones, which is one of the reasons why this type of engine is not generally used.."

So, based on this i'm saying that our engines are not so high rev oriented but more torque oriented... Am i wrong?
Here talks about an undersquare Chrysler engine that was limited by his connecting rods as ours.

Just to remember, in this block, the connecting rods tend to fail near 220 hp, but the crankshaft is still going at 500.

http://en.wikipedia.org/wiki/Stroke_ratio

[Law_]

Consulting several sources i could see that Honda D16's were much more undersquare engines (75 x 90), D15's also (75 x 85), but D13 were just marginally undersquare... other series like the new L series have already slightly oversquare engines... On that series, the 1.2L ivtec oversquare (minor stroke) doing almost the same power as the 1.3L ivtec wich is undersquare (major stroke).

So, and concluding, our engine can be one of the bests in the D-Series to rev but have not the best design to do that...

Still, im very impressed by the Honda capability of high revving so much...This logic seems not to work here.
Type R's and Mugen RR engines are sligthly undersquare too...
i would love to discuss with an Honda engineer about this

[saxophonias]

Good points, but this is general theory of engine building. Undersquare or oversquare engines show a tendency, that is just a factor that you have to combine with numerous others in order to conclude about engine performance. D16 75x90 is worse than d13 75x76. Still D16 revs higher, has more low mid and high end power to d12/d13/d14/d15. So is it just dimensions? Of course not. I think that you could see these differences come into play if you had 2 engines with exactly the same specs but only different in these numbers (different bore different stroke but same capacity).
But this is not just theory among honda d-engines. D16 lets say being 75x90 in combination with its worse rode to stroke ratio can't rev let's say 8000rpms with long reliability. And this is because the power exerted in the block and the speed of pistons and rods are multiplied greatly with revving with the given engine design and size. The majority of engine tuners in the USA verify that, by saying that the safe rev limit for stock d16 rods are +200-300 rpms.
On the contrary, lower capacity d-series engines are more confident revving, as their design doesn'tt apply so much strength in the rods with extra revving. There are numerous examples of d14s that rev almost 8000rpms d13 with carb with out rev limiter that rev to the sky without braking a rod and more d12 that do the same.

[Raimundo]

Saxophonias, rod x stroke can only give us shortblock performance. D16 have VTEC, and high profile cams are great for high revs, with custom exhaust/intake you can easily take a D16 engine to 7500/7800 (real) rpm, so, almost 8000rpm in the dash. It is possible that this will harm the rods.

D16Z9 revs higher than D16Z6, don't know if there is a difference between the engines

[Law_]

Understood perfectly. Thank you for reading the hole text Just to complete rod to stroke ratio of D14 is 1.75. Consider ideal in a street motor

[saxophonias]

Understood perfectly. Thank you for reading the hole text Just to complete rod to stroke ratio of D14 is 1.75. Consider ideal in a street motor

And this is why we are lucky for N/A at least tuning!! It gives potential

[mynameisowen]

Also if you notice our engine and most honda engines although they may be techinically undersquare have a lot shorter strokes than other engines. For exmaple old v8 engines tend to have massively long strokes, and thats one of the reasons they make lots of torque like you said.

Both these engines are undersquare but the d14 is marginally undersquare whilst the muscle v8s are largely undersquare. You have to compare the numbers aswell.

[Law_]

Also if you notice our engine and most honda engines although they may be techinically undersquare have a lot shorter strokes than other engines. For exmaple old v8 engines tend to have massively long strokes, and thats one of the reasons they make lots of torque like you said.

Both these engines are undersquare but the d14 is marginally undersquare whilst the muscle v8s are largely undersquare. You have to compare the numbers aswell.

Yes, that and the fact that bore to stroke ratio alone does not allow to conclude much about the engine behaviour is the most important. Thanks !

[hondaNickx]

Guys D13 & D14 are the engines that are the best not the worst!The D16 engines have the worst R/S ratio and extremely high pistons speeds .
They mechanicly have a handicap making higher rpm's.The high stroke and the low r/s ratio put's tremendous pressure on the cylinders walls after the power stroke .

That's why they tend to wear faster ,they have more stress inside the engine .
That's why all of them don't make power after 8000rpm.
That's why D14 rods can handle More horsepower in comparison with D16 rods .They have far less stress so they can handly more horsepower in comparison.Offcourse D14 rods can't handle as much as D16 rods ,because the d16 rods are thicker.But if they were both the same size the D14 could handle more Hp .
D14's have a real good R/S ratio of 1.75 :1 and they are lightly undersquare .They tend to have the powerband in higher rpm's .D16 have their powerband in the lower rpm's.
Oversquare is better imo cause the engine has better potential.A great example is a B16 Oversquare and 1.74 R/S ratio
Engines with High R/s ratio generally need high velocity (intake ports ,head ports ...) the downside is they don't make much torque .The ideal R/s ratio according to Larry from Endyn would 1.74 :1 .Which would be the perfect balance between torque and Hp.

[saxophonias]

Very true!