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hi i designed engines a few years ago, and now tried your engine demo, I think the program is really cool, but it seems that there are missing a connection between bore and stroke, example if you increase the length of stroke and keep the cylinder bore dia the revolution for the max torque be falling and vice versa if you increase the bore according to the stroke, it does not seem like it has any effect in the demo.
looking forward to try the complete game.

Regards Jasp.

The reason that doesn't occur is that it doesn't happen in real life either (or at least not documented in any of the engineering textbooks we reference)

What really defines the where in the RPM range peak torque is at, is how volumetrically efficient the engine is (how much air it sucks in) and that's mostly a function of intake/port/head/exhaust manifold design, and cam profile.

Hope that answers your questions

I agree. The stroke/bore ratio is of no consequence on where the peak torque is delivered, that is only a result of tuning. but it has an effect on the general size of the engine: large bore engines are wider, but shorter and long stroke engines are taller ,but thinner. A large bore engine has more surface available for valves and generates less friction on the block and also less stress on the crank. on the other hand it suffers higher accelerations and requires stronger rods and pins.

Hi Thanks for the quick reply. the experience I have had, if you want an engine with high torque at low revs, you need a long stroke compared to the bore, which also provides an engine that is not as rotation willing as a motor with big bore and short stroke.
keep up the good work.

Regards

Jasp

+1 with Jasp (Stroke is lever, long = more torque at low RPM)

this is what I learned during my studies theoretical mechanics (Harley Davidson is an excellent example)

a bmw 1.6 with 84mm X 72mm produces 150 nm @ 4000 rpm
a for focus 1.6 with 79mm X 81.2mm produces 150 nm @ 4000 rpm
a honda 1.6 with 25 hp more than the others has a 75x90 engine and produces 142 nm @ 5500 rpm

Are you starting to see the picture?

Diesel truck engines (just using diesel engines as an example, not talking about diesel engines in particular, in fact not at all) and tractor engines show this too (think Dodge 3.7 slant-six). Long stroke, smaller bore makes for lots of torque. This is because with the long stroke the individual strokes are longer, i.e. on the power stroke the expanding gasses push on the piston for longer, creating more torque. These engines don't like high rpm's due to the relatively small sized valves for how large the cylinder is, the greater mass of the connecting rods, and the greater forces exerted on the crankshaft due to the larger throw. This means you can get engines that only make double digits HP ratings, but 200-300+ ft-lbs of torque, this is especially true with tractor engines (a farmall model M from the 50's makes something like 30 hp with a 4.1L inline 4, but somewhere around 200ft-lbs of torque with a bore/stroke of 98/133 and 4.75:1 comp) A lot of these engines are capable of making much more torque, but what happens is the manufacturers lengthen intake runners/exhaust manifolds, square ports, use smaller valves, etc... to move the point at which you make peak torque down in the rev range and make more torque in total at lower RPM's. This is great for agricultural, commercial, and industrial vehicles as it means the engine can work it's hardest at a lower RPM where it is sipping fuel and saving wear and tear. This is an element that is missing from the game, but would add soooo much work and time in developing and adding that I think most would agree would not be really worth it.

EDIT: also forgot about cams, the LSA (Lobe separation angle, or angle of separation between the intake and exhaust valves) has a lot to do with the torque an engine makes. A higher value LSA (112-115 degrees) will net lower torque, but make a broader range, while a lower LSA value (108-111 degrees) will give higher torque but will make the torque in more of a peak. Manufacturers have found LSA values typically in the 108-115 degree area are best, any out of that range and you start to loose power with no apparent gain elsewhere.

Remember, HP = (torque(ft-lbs)*RPM)/5252, so if you have an engine that makes a peak torque of 300ft-lbs at 2200rpm, HP=(300*2200)/5252, (660000)/5252 = 125hp. That means at 2200rpm, that engine is making 125hp and 300lb-ft of torque (of course that isn't peak HP)

See my post above, there is more to hp/torque graphs than just bore and stroke. A lot has to do with the head design, intake/exhaust runners, etc...

The BMW probably has a smaller LSA value, short intake runners, large circular intake ports and runners with large valves and ditto for the exhaust. The ford probably has longer, smaller intake runners with likely nears as makes no difference the same size valves. The BMW is probably very well tuned as BMW's typically are, but I assure you below 4000RPM's the ford engine makes more torque than the BMW engine.

diesel engines operate differently. they can only function well with long strokes.

LE:http://www.rri.se/popup/performancegraphs.php?ChartsID=47 The same ford 1.6
http://www.rri.se/popup/performancegraphs.php?ChartsID=403 A similar bmw engine (seems this one has a better curve)

I have driven all of these and they seem the same to me. the bmw feels a little more responsive, but they don't seem to pull differently.

I changed that post to make it seem like I wasn't just talking about diesel engines. I was just using them as an example, but diesel engines don't necessarily need a long stroke to run properly. The 7.3L ford Powerstroke has a 104mm bore by 106mm stroke. I mean, those are big numbers, but the bore/stroke ratio is pretty conservative.

assuming everything in the heads are exactly the same, the engine with larger stroke than bore will make more toque but not rev as high, torque is force at an angle over a certain length. This does not mean the engine wont rev as high, as mentioned hondas with a 75x90 bore/stroke still rev to 8k pretty easily, 9k with some valvetrain work.

mm for mm, boring an engine will produce more horsepower than you will get out of stroking it.

you have to think of an engine as a pump, the bottom of the engine is only rotating and reciprocating, most of the power and torque are gained through work to the head, intake, and exhaust

I think it has to do more with size than anything. diesels can operate oversquare, but will not work efficiently. diesel burns slow so it needs a long stroke to generate the necessary torque. also the pistons are much longer and needspace.
I used to belive the same about stroke on petrols, but after more studies i came to the conclussion that they are not related. maybe with carbureted engines, but newer ones seem to be unaffected.

It is very hard to compare two engines to each other. This sounds weasly, I know, but it is simply because of a lot of information about specifics of design that is not available from the manufacturer but play a key part in engine performance. Things that you have to cut a section of the head to see like port geometry, shape of the piston crown, cam lift/duration/LSA. You would have to take the same engine, but modify one to only have a longer stroke to actually see the difference bore/stroke ratios have.

i don't know, thetruth seems to be somwhere in the middle.

I know that what you say is logical, but the results seem to tell a different story. I know the heads differ quite alot. Also the BMW has 8v and the ford has 16v.
i have chosen engines with equivalent power to be as close as possible. other 1.6 engine seem to have similar stats. It's difficult to obtain clear results since we do not have engine production plants.

A stroked engine with identical heads are the 2.0l and 2.2l engines in the honda S2000. the 2.2 produces a little more torque, but is detuned to reduce max power rpm and that also increases torque. what's your opinion?