DIY: Nonstop Tuning CR-Lite Pulley

[eTiMaGo]

Originally Posted by Galavoxx

Though I do agree with you that less weight is better for MPG, when were talking rotating mass, this is not true.

A crude explanation: as you start to decrease rotating mass by lightening things like the pulleys and the flywheel, MPG may suffer. The engine revs faster and once spun up it takes more gas to keep things going. Lower mass will take less time to dissapate the energy put into it. Toyota knows this and has designed certain portions of the drivetrain to take advantage of rotating mass for optimal mpg. The pullys are one of these portions. Gains or losses in mpg will be most noticeable on the highway. Around-town should remain the same or maybe get better. Maybe. The main reason for a possible decrease on the highway is that the RPM at which the engine wants to 'cruise' will likely be eliminated. This is due to a less efficient energy storage system. Anyway, wtf do I know. With only the pulley changed out and the flywheel the same, there likely wont be much change.

That's true, at a constant rotational speed, a heavier weight acts as a "buffer" that keeps the rotation steady (think of a spinning top). So, less input is required from the motor to keep the rotation, and gas can be saved. But compared to the frictional forces from air drag, and the fact that the flywheel weighs a lot more than a single small pulley, I don't think it will make such a huge difference.

BUT! In order to get the rotation up to speed, there is more inertia to be overcome (think of how much effort you spend spinning a small, light top vs spinning a larger heavy one), which is where more fuel is required. So, in this kind of stop-and-go traffic situation, less rotational mass can have a good effect on performance and mileage.

Of course, the disadvantage of removing rotational mass in a 4-cylinder daily driver is the idle quality. The engine needs the heavy weight of the flywheel to keep it going during the 3 non-power strokes. So, when you reduce this mass, the engine will slow down between rotations, and at a lower engine speed (idling), this can make things very rough, even stall the engine.

But, as I mentioned before, 80% (if not more) of the rotational mass in our engine/transmission would be from the flywheel, so a ligher crank pulley should not be such a big difference that it can cause problems.

At least that's what my physics education tells me, I can't wait to see the effects for myself