AT Power’s patented Shaftless technology, explained and backed by CFD simulation.
In 2005, AT Power revolutionised butterfly throttle design with our patented Shaftless technology, eliminating the butterfly throttle’s one significant weakness: the shaft in the airway. Butterfly throttles remain unbeatable for idle stability, part-throttle control and mechanical simplicity — which is why they’re used from grassroots racing to Formula One, WEC and WRC. But a conventional butterfly pays a permanent price for its simplicity, and it pays it at every throttle opening.
The problem with a conventional butterfly
A traditional butterfly carries its blade on a metal shaft that runs straight across the centre of the bore, held by exposed screw heads — and it sits there whether the throttle is closed, cruising or wide open. Air cannot pass through it, so it must squeeze around it, accelerate, and then collapse back together on the other side. That collapse is turbulence: energy your engine spent accelerating the air, thrown away as churn instead of delivered to the cylinders.
The result, at every throttle position:
- Less total airflow through the same bore size
- A turbulent, slow-moving wake trailing several bore-diameters downstream of the shaft, degrading the quality of the air delivered to the manifold
- Wasted pressure — dynamic pressure lost in the wake that is never recovered
What the CFD shows
We simulated our production 50 mm throttle body geometry — ram-pipe, housing and blade, sliced directly from the manufacturing CAD — with a computational flow solver, running the shafted and shaftless valves under identical conditions. The only difference between the two cases is the shaft.
With the throttle wide open and conditions matched:
- The shaft adds +29% pressure loss across the valve region itself
- At the same airflow, the shafted valve needs ≈15% more pressure drop
- As a device, the Shaftless throttle has ≈7% higher flow conductance — and the advantage holds at every opening angle, not just wide open
The effect grows as throttles get smaller. A shaft’s diameter is set by stiffness, not bore size, so it consumes a proportionally larger share of a small bore — exactly where high-performance ITB setups live. On a 40 mm body the shaft’s valve-region penalty rises above +40%.
The Shaftless solution
Our award-winning design supports the blade from its rim, removing the shaft and screws from the airway entirely.
- Ultra-thin blade — knife-edged leading and trailing edges minimise separation from the plate itself
- No shaft or screws in the bore — nothing left in the airway but the blade’s edge
- Near open-bore flow — verified on the flow bench at 99.5% of the airflow of an open bore
What this means for your engine
- Up to 10% more airflow than a conventional shafted throttle of the same size — the largest gains on smaller bores, where the shaft hurts most
- More usable power: at wide-open throttle, ~1% more airflow supports ~1% more torque
- Downsize without penalty: a Shaftless throttle flows like a conventional throttle a size or two larger, so you can specify a smaller bore for higher intake velocity and sharper part-throttle response — with no flow cost
- Cleaner air delivery: no shaft wake means a more uniform velocity profile into the manifold — better cylinder-to-cylinder distribution and cleaner airflow-sensor signals
Proven where it matters
Combined with our in-house R&D on inlet geometry and precision CNC manufacturing, Shaftless technology lets a compact, lightweight AT Power throttle outperform larger conventional systems — from road-going builds to the highest levels of motorsport.
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Simulation figures from a 2-D lattice-Boltzmann study of the 50 mm body mid-plane, shafted vs shaftless run like-for-like with the shaft as the only variable — the figures isolate the shaft alone and are conservative of the complete design. Flow-bench figures (99.5% open-bore, up to 10% more airflow) from AT Power product testing.
