Crankshaft¶
The rotating backbone. Its inertia governs throttle response and idle stability; its specs set a ceiling on RPM.
What it is¶
The crankshaft converts the pistons' up-and-down motion into rotation. For tuning, its key properties are rotational inertia (how much it resists changes in speed), its bearing specs, and its maximum safe RPM.
Why it matters¶
Crank inertia is a balancing act:
- High inertia (a heavy crank) makes the engine stable at idle and smooths out power delivery, but it makes the engine slow to rev — lazy throttle response.
- Low inertia (a light crank) gives snappy throttle response but a less stable idle that's more prone to hunting and stalling.
Its maximum RPM also feeds the rev limiter: the engine's redline is the lowest max-RPM among all components, so a weak crank can cap the whole engine.
How to tune it¶
Match crank inertia to the engine's purpose. A street engine values the stable idle and smooth delivery of more inertia; a race engine wants the response of a lighter crank and accepts a busier idle (which idle control then has to manage).
Rule of thumb
Lighter crank = faster revs but twitchier idle. If a light build hunts at idle, that's the trade-off you bought — tune idle control to suit, or add inertia.
In the game¶
Crank selection is on the Setup page. Its inertia visibly affects how fast RPM rises on a throttle blip and how steady the idle sits.