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?
[quote=“Bourinov”]+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)[/quote]
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=(3002200)/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)
[quote=“darkjedi”]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?[/quote]
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:rri.se/popup/performancegraphs.php?ChartsID=47 The same ford 1.6
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.
[quote=“darkjedi”]
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.[/quote]
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?
[quote=“darkjedi”]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?[/quote]
It looks like they increased the stroke (and consequently, lowered the max RPM,) to make a bit more low end torque probably to better comply with emissions standards. The more low end torque makes up for the loss of max RPM (engines are typically much more responsive at higher RPM’s, especially the type used in the s2000,) so they can meet tightening emissions and not lose too much of the feel of the engine.
That may be the case. I saw that alot of people prefer the 2.0 version.
To me it seems the torque came from the higher capacity, but milder cams were used to lower the power band and increase low end torque further
[quote=“darkjedi”]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.[/quote]
diesels also operate at a much higher compression level than petrol engines and because of the slower burn they need the longer stroke to help take advantage of all the engergy.
that’s exactly what i said.
[quote=“darkjedi”]That may be the case. I saw that alot of people prefer the 2.0 version.
To me it seems the torque came from the higher capacity, but milder cams were used to lower the power band and increase low end torque further[/quote]
Peak torque is where the engine is basically at it’s most efficient. The reason it drops off is that the amount of air going into and out of the engine starts to be too much for the intake runners/valves/exhaust manifold and they can’t keep up. Think of it like trying to run a marathon breathing through a snorkel. At first, you are not tired and can breath pretty easily through it, but once you start getting tired and start huffing and puffing, you have a hard time sucking more air through the snorkel.
The air in intake runners moves through in waves, when the intake valve is open the piston moving down on the intake stroke sucks air in through the intake valve. This pulls air through the intake runners, when the valve closes the air is still moving through the intake runner due to lots of physics things, and hits the closed valve and creates a small pressurized area. The more air behind it, the longer it will hold that pressure in that area (think of it like waiting in a line, if someone moves forwards and stops, the person behind them runs into the back of them, and this lasts longer if you have more people in line). If you have long runners, there is lots of air behind it and the pressurized area sits there for a while and continues to build due to the air further down the runners continuing to push it’s way in because of momentum until the valve opens again and makes a charging effect. If you’re runners are too short, or engine running too slowly, this wave springs back and starts moving back out of the runners and into the intake plenum/intake piping/atmosphere. This means the intake runners are tuned to charge best above a certain rpm (the longer or thinner the runners, the lower the RPM,). The charging effect is great at low RPM’s, but once you’re speeding up the valve is opening much faster now and that pressure wave doesn’t have enough time to build up as much, until the effect is gone at high engine speeds, and will dramatically decrease performance if you continue to increase engine speed. Make the runners shorter and bigger in diameter, and then it needs a lot more sucking to get that pressure built up. Once you’re at high RPM’s, you have the pistons sucking in enough air that the air is moving with enough velocity through the intake runners to start building up a charge.
Example:
Two identical engines, same length intake runners, one with 1" diameter runners, one with 2" diameter runners.
The 1" diameter engine is pulling the same amount of air through the intake runners at 2000rpm as the 2" diameter engine, but the air being pulled through the 1" diameter runners is a higher pressure as it has to rush through much faster. This creates that charging effect at low speeds where the size of the runner can keep up with the demands of the engine and increases power at low RPM’s. Now at 5000rpm, the 1" diameter runners can’t keep up and a vacuum starts to form at certain areas and the charging effect is gone. The engines computer will now inject less fuel to keep the air to fuel ratio the same and as you can imagine it falls on it’s face performance wise (if you have a carb, it starts to run rich). If we look at the 2" diameter engine, the vastly larger runners have more potential to allow a lot more air to pass through, which is now moving though enough air at 5000rpm to start to get that charging effect. Now take that longer, 2" diameter runners engine and shorten them, now the charging effect doesn’t happen until even higher RPM’s. Excellent for racing conditions, not so much for drivability, fuel economy, emissions.
That is how intake runners effect how an engine breaths. Also, turbo/superchargers basically multiply this effect. Cam profiles change when, how long, and how big valves open. Increase the amount of time a valve is open and suck more air in, this means it will take longer for that charge to build up in the intake runners, but will increase HP/torque at top end. To increase your peak torque and lower the RPM it occurs at to a lower RPM using the same intake runners and head, you need to increase your stroke. That is where I was going with that, but it kind of went off in a tangent.
Sorry if this seems to be going off on a tangent, I really love talking about the physics (and once you get me started…) and such of how engines work and hope to one day design engines as a job. I mean no disrespect and am not trying to deliberately confuse anyone or anything like that.
Edit: Grammar, some physics that clears some stuff up
Edit2: Added some more things about pressure waves in the intake runners