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Old 03-01-2023, 10:42 PM   #17 (permalink)
Isaac Zachary
High Altitude Hybrid
Join Date: Dec 2020
Location: Gunnison, CO
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Avalon - '13 Toyota Avalon HV
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Originally Posted by Solarpowered View Post
And if you managed to lower the total rotational mass of the engine by 10%, well that's 10% less power needed to start that push, every cycle. So ideally the computer would detect this and spray less fuel.
The rotational mass or inertia is only part of the total inertial mass. So if you lower the rotational inertia by 10%, but rotational inetia is only, say, 20% of total inertia, then you only saved 1%.

The drive shaft also doesn't have a lot of inertia, even if it has a lot of mass. That's because 1. it usually spins slower than the engine, at least when starting out and 2. its mass has a small diameter, not a large one like the flywheel or the wheels.

I could be wrong, but I read somewhere that around 80% of the rotational inertia is in the flywheel. That's why you usually start there before reducing other things.

Aluminum also doesn't fatigue well.

But yes, every little thing adds up. However, there are things that may help only a fraction of a percent, and other things that would be better to put that money towards and get you more percents. Tuning each cylinder for fuel and spark would be one of those things.
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