Bourinov wrote:+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)
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)
Mon Nov 05, 2012 9:29 pm 
