Athena expands its off-road catalogue with Big Bore Extreme, a new range of cylinder kits designed to squeeze more out of the most popular 250 4T models on the market and bring them closer to 300cc capacity, combining a larger bore cylinder, dedicated piston, reinforced components and GET Boost electronic management.

Beefier engine, more pull and a stronger response, but without ruining the balance and lightness that make 250 four-strokes so attractive. To achieve that, Athena offers a complete technical package developed to deliver a stronger riding experience across off-road disciplines.

The new Big Bore Extreme kits are aimed at both amateur riders and more experienced users looking for a livelier response from low revs, more traction when opening the throttle and more effective acceleration out of corners, says Athena. In other words, that extra bit of torque and drive that is often missing from a 250 4T when the going gets heavy or when you need to fire out of a corner.

Athena also presents these kits as an interesting option for riders thinking about moving from a 250 to a 450, but wanting to do it progressively, with an intermediate step close to 300cc. The bike gains more substance in the power delivery without reaching the more physical and demanding character of a 450.

85mm cylinder and no crankcase machining

At the heart of the kit is an 85mm bore cylinder, developed to increase capacity to around 300cc. One of the key points is that it does not require machining of the engine crankcases, an important detail for anyone looking for a serious performance upgrade without making the installation more complicated than necessary.

The cylinder combines a steel liner co-cast inside an aluminium body, a solution designed to better handle the thermal and mechanical demands of off-road use. With this, Athena is aiming for dimensional stability, wear resistance and consistent performance even when the bike is working in tough conditions.

Dedicated piston and reinforced components

As you would expect, the increase in capacity comes with a dedicated piston. It is made from aluminium alloy and designed to withstand the higher loads generated by this configuration.

The package includes some high-level technical details: a skirt with molybdenum disulphide coating, a DLC-treated piston pin and special steel piston rings with chromium nitride coating. Translated into paddock language: less friction, better wear resistance and more consistent performance over time.

The kit is completed with a gasket set developed for each application, with the aim of ensuring precise assembly, good compatibility and resistance to the temperatures typical of motocross and off-road riding.

GET Boost: matching electronic management

One of the key points of the Big Bore Extreme project is that Athena has not simply produced an oversized cylinder. The brand has developed the package as a complete system, where the mechanical and electronic sides work together.

That is why the kits are paired with GET Boost, a preconfigured hardware module developed together with GET, the electronics brand within the Athena group. This system allows the bike’s original ECU to be retained while optimising combustion and fuelling management to make better use of the increased displacement.

In other words, the engine not only breathes with greater capacity, it also receives adapted management to get the most out of the new setup.

Fitting models

The Athena Big Bore Extreme range is currently available for the following 250 4T motocross platforms:

• Honda CRF 250R, from 2018 to 2026
• Yamaha YZ250F, from 2019 to 2024
• Kawasaki KX250, from 2023 to 2026
• KTM 250 SX-F and Husqvarna FC 250, from 2016 to 2022
• GASGAS MC 250F, from 2021 to 2023

A serious alternative for those who want more engine

With the Big Bore Extreme kits, Athena strengthens its presence in the off-road aftermarket with a technically advanced solution that makes a lot of sense for many riders: keeping the light and manageable base of a 250 4T, but gaining that extra punch that can make the difference in acceleration, corner exits and demanding terrain.

Athena offers a kind of halfway point: a 250 with more substance, more torque and a fuller power delivery, but without losing the ease of use that makes these quarter-litre bikes so popular.

More information: www.athena.eu