let me write you a story (please bear with me...
)
rod ratio really has nothing to do with stroke length. it might be necessary to change rod ratio due to a long stroke (to get more of the lower, rotating end of the rod out of the bore for clearance) but rod ratio is basically a number dependent on the manufactured deck height and wrist pin height, considering stroke as a constant for a sec.
placing a feature in-game to alter deck height (cylinder deck to crank CL) AND compression height (wrist pin CL to piston crown; general "piston size") would both be effective tools for adjusting rod ratio, which could always just be a stat that gets pumped out by the simulating side of the game. obviously using different pistons would require that the deck height be reset to maintain a previously set stroke length. let me list a few supporting reasons for adjustable deck height/rod ratio:
- the ability to specify a short rod engine would be intensely beneficial in short-stroke, high-RPM engines. this would increase the amount of available peak torque due to a better relationship between rod and crank throw as power is delivered through the "levers" that are these two items.
- being able to adjust this ratio ultimately determines how much mechanical stress the engine sees through each impulse of power, and will logically work for contributing to a reliability factor in the game. generally long rod engines see less stress at the rod journal and experience less eccentric wear on the mains, while sacrificing a bit of peak torque and gaining a heavier internal "hybrid" mass.
- the ability to incorrectly adjust the rod ratio is just one factor* than can contribute to an unsuccessful engine, and since the development is intended to be infinite... this will play a major part in the "difficulty" aspect of the game. if you make a poor engine, i would assume it might not sell as well.
- piston acceleration out of intake-stroke TDC plays a HUGE part in determining how the valve acceleration and port shape/intake work together to create effective inflow. the effect of a minimum-length vs. maximum-length rod in a long-stroke (undersquare) engine will accelerate the piston out of its TDC position earlier and simulate the same effect that increasing RPM will have on witnessed flow, and thus performance. by this same token, a short-stroke engine with longer rods will (dependent on the exhaust system) have a slightly longer hesitation period at BDC before the exhaust stroke, and this will allow expanding gasses a fractionally larger period of time in which to escape through an already-open exhaust valve and reduce pumping losses/increase scavenging effect (up to a point) without altering bore-to-stroke.
if you still believe rod ratio is an unimportant factor, it might be beneficial to spend a few hours researching the topic. it basically amounts to utilizing adaptive-fit cylinder blocks/sleeves, coolant passages, and belts/pushrods that will automatically resize when given the command to increase deck height - and this is obviously independent of stroke length, i.e. the respective positions of the piston must move with the same offset that the deck uses. i am sure a feature to identify clearance issues and prevent adjustments resulting in interference can be included as well.
to anyone saying this relationship isn't realistic, go ahead and compare the rod ratios of many different engines (obviously you need to look outside of one class of engine) and see how they differ. wholly dependent on application, rod ratio can hurt or help the situation. i'm hoping the game isn't JUST cars... but that's all for the future.
it goes without saying that this will also affect packaging of the engine, and allow the user to create a much wider array of performance values for the same given bore, stroke, and number of cylinders. in reality, this is just another dimension that is seriously considered when designing an engine.
i apologize for saying this when one of the developers has already said it flies in the face of their intentions, but i am hoping it is a convincing argument when considering long-term future developments. you said you wanted a "techie" game, well here's how the techies might want it. IMHO.
oh, and since this is my first post.... awesome game! you guys really hit the nail on the head when it comes to gearhead gaming. so thanks for investing so much time and money, i will not forget the title.
- kyle
*also involved in the reliability argument is an addition to adjustable rod ratio: adjustable compression height of the piston, and primarily their overall physical dimensions. some designs do indeed lend themselves to higher out-of-round wear in the thrust direction, and more rocking of the piston perpendicular to thrust. this presents even another factor to use when calculating reliability.
Mon Aug 15, 2011 12:25 pm 
