🛠️ Heavier Rotating Mass in TBI Engines: What Changed?
🔩 1. Heavier Crankshaft & Flywheel Mass
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The 2023–2024 TBI 2-stroke engines (especially the 250/300 EXC/XC and their Husqvarna/GasGas equivalents) have been given increased crankshaft and flywheel inertia.
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This was done to improve traction, especially at low RPM — which is a huge advantage in technical enduro and slippery terrain.
👉 Result: More stable power delivery and less stalling. The bike “chugs” better at low revs.
⚖️ 2. Why the TPI Was Lighter
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The TPI engines (2018–2023) had lighter rotating assemblies, making them:
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Snappier
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Quicker to rev
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But also more prone to stalling in slow, technical riding
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⚡ How This Affects the Riding Feel
| Feature | TPI Engine | TBI Engine |
|---|---|---|
| Rotational Inertia | Lighter | Heavier |
| Low-RPM Chugging | Can stall more easily | Very stable & tractable |
| Throttle Response | Quick & snappy | Smoother, more linear |
| Technical Terrain | Less forgiving | Easier to control, more grip |
🔁 Combined with Other Changes
The heavier engine internals in the TBI are part of a complete redesign, including:
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New counter-balancer shafts to reduce vibration
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A redesigned throttle body for smoother fueling
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Refined ignition timing and fuel mapping
So while the engine is technically heavier, it’s much more refined and rider-friendly, especially for enduro.
🧠 TL;DR:
Yes — the TBI engine has heavier rotating mass (crankshaft, flywheel) than the TPI. This makes it less twitchy, better in technical terrain, and smoother to ride — even if it revs a bit slower.
