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PolarStar "Kythera" HPA Engine for Airsoft Rifles (Model: SA - Ver2 M4)

ID: 19157 (HPA-PS-10000774)
PolarStar Kythera HPA Engine for Airsoft Rifles (Model: SA - Ver2 M4)
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  • Designed from the ground up as a high performance mechanical HPA system, not a modification of a solenoid operated design
  • Patent pending valve mechanism provides excellent efficiency and consistent velocity combined with a realistic trigger pull and reset
  • Completes a full shot cycle on the trigger pull alone which translates into consistent nozzle movement and rapid follow up shots
  • Adjustable trigger. Adjustments include: Weight, length of pull and over travel
  • Adjustable nozzle dwell/return speed
  • Wide operating pressure range of 60 to 180psi
The Kythera has been the most eagerly anticipated products from PolarStar in the past decade. This HPA system is a radical departure from all previous systems that PolarStar has produced since the Kythera does not use a battery, an FCU or any type of electronics. The Kythera is completely mechanical. This means you never have to worry about charging batteries or work with delicate electronics. It also means that the system is completely waterproof.

The name "Kythera" (ky-the-ra) was derived from the Antikythera Mechanism which is a mysterious device that was discovered by sponge divers off the coast of the Greek island Antikyther. The mechanism was so advanced in design that scientists have been studying it for decades to discover its purpose. The machine dates from around the end of the 2nd century B.C. and is the most sophisticated mechanism known from the ancient world. Nothing as complex is known for the next thousand years. The Antikythera Mechanism is now understood to be dedicated to astronomical phenomena and operates as a complex mechanical "computer" which tracks the cycles of the Solar System.

For this reason we used the name Kythera for the valve mechanism at the core of a new line of PolarStar mechanical HPA systems. Although it contains very few parts and is easy to install and maintain, the system incorporates a very intelligent design and is unlike anything else on the market. The system was designed as a mechanical system from the ground up and uses a realistic trigger mechanism which can be applied to single-shot, semi-automatic and fully-automatic systems.

Realistic Trigger: What sets this system apart from other mechanical systems is the design of its trigger. The trigger mechanism is designed to replicate the function, weight and feel of a real single-action firearm trigger. It feels real because it is real. The hardened alloy steel sears catch and release the stainless steel spool valve in the same way the sears of a real firearm catch and release the hammer or striker. This gives the Kythera trigger the distinct break and reset you would expect to feel when firing a real single action firearm. The trigger mechanism in the Kythera SA is also adjustable, allowing the user to fine tune the weight and over travel. Additionally, the internal firing valve is balanced and the only force applied during firing is the main spring. This means the function and feel of the trigger is independent of input pressure and velocity.

Complete Shot Cycle: The design of the Kythera SA completes a shot cycle on the trigger pull. This gives you the proven closed bolt performance of the Fusion Engine and F2 in a completely mechanical, waterproof system with a realistic trigger. It does not require the trigger to be released before the nozzle chambers the next round and the firing volume is refilled. This occurs automatically and consistently every shot, with adjustable nozzle dwell and return speed.
As the system resets and recharges immediately after firing, it is ready to fire again before the trigger has been released. This means the system can cycle very quickly for faster follow up shots and a lower potential for double feeding.

Extremely Efficient and Consistent: The valve design of the Kythera operates without the need for air to control the opening or closing of the valve. Without a pilot valve, 100% of the air going into the system is fired through the nozzle allowing it to operate very efficiently. In addition to being extremely efficient, the system is also extremely consistent. The valve is released at the same point every shot with the same force applied, regardless of trigger input.

Universal Charging Cord: The steel cord visible at the back of the system is attached to a cocking mechanism for the internal spool valve. Although the system automatically cocks the spool valve when the system is pressurized, since the Kythera uses a balanced valve, it is possible in certain situations that the valve could stall and needs to be manually cocked. This typically only happens if the system is run completely out of air so that the pressure drops below the operating range of the system. The cord is designed to be either routed through the grip of the rifle for easy access or even possibly attached in some fashion to the charging handle.

Easy Installation: The Kythera SA system installs into a standard gearbox as a single assembly and typically does not require any modification to the gearbox. There are no separate parts to install and the only parts needing to be retained from the gearbox is the trigger, spring guide, selector and safety components.

Wide Velocity Adjustment Range: The Kythera has a wide operating pressure range of 60psi to 180psi which allows you to fine tune the velocity of the system and tailor for different requirements and applications. Within this pressure range we observed a muzzle velocity of 270 - 500fps w/ .20g using a 6.05x380mm barrel. This lets a single Kythera be used in any role ranging from CQB to Sniper by mainly just adjusting the input pressure from your air rig.

Manufacturer: PolarStar Airsoft


Operating Pressure: 60psi - 180psi
Velocity Ranges: 270fps - 500fps (measured using .20g 6mm BBs & 6.05 ID x 380mm L barrel)
Fire Modes: Semi-Automatic

About PolarStar

PolarStar Precision Airsoft was formed in January 2009 to fill a need for high quality, precision manufactured airsoft components designed for performance and longevity.The 2011 release of the patented Fusion Engine HPA system marked a change in direction for PolarStar. The focus shifted from developing upgrade components within the constraints of existing systems to developing innovative HPA systems and accessories which replace the aging AEG technology.PolarStar Airsoft is a division of PolarStar Engineering & Machine (PSE&M), a unique blend of tenured American toolmakers and a full service CAE/CAD/CAM (Computer Aided Engineering, Design, and Manufacturing), special crafts machine shop keeping alive our proud manufacturing heritage of Made in the USA. Founded in 1997, PSE&M began by servicing the automotive racing industry through the design and producing systems and components from art to part. Operating under the auspices of the Delaware Association of Professional Engineers, we retain a Professional Engineer (P.E.) on staff to ensure and certify all design and engineering standards are met. In addition to our own product line, PolarStar also offers engineering and manufacturing services tailored to the airsoft industry.

10 Customer Reviews

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by Jack G. on 01/25/2024
"I got this from a friend who was getting out of the sport and he had only run it through one game. I've installed about a dozen of these as well so I'm fairly familiar with the system and I am always impressed with the rugged reliability that the Kythera shows. I would recommend it to anyone who wants a fairly simplistic engine that is low maintenance and a fantastic results achiever.

by Michael O. on 10/25/2023
"I run it in a VFC MCX, had to cut the spring guide short with a pipe cutter to get it to fit. Was easy work (sit & spin lol). I threw in the 'Polarstar Gearbox Shim Set for Cylinder Conversion Kits (Size: 0.157")' shims and fit is perfect. You can empty an EPM pretty quick on semi the perks outweigh loss of auto for sure. It does exactly what a well tuned F2 does in semi when you follow P*s directions. Nice having something in airsoft that isn't constantly letting me down. Things a tank.

Use techT lube internally, the P* vids on youtube (watch em) explain even if you overdo it it'll just get cycled into the dump chamber. The vids explain how to set up the trigger pull, just follow the directions and use a tiny bit of blue loktite. It's really simple, all the people who say they don't work well didn't watch the vid. I haven't cleaned internals in a Millsim and dozens of games. I'd say plan to clean/lube every 4-6 months of heavy play, maybe yearly-more if you don't play much. No biggie.

Was told it's a temperamental system but I think they got greedy with the trigger pull. I run mine really short with near immediate reset just fine by following the directions in the vid. You have to go back the minimum amount of turns when they tell you, it costs you no pull & you won't have any problems with this unit at all. Like ever, things a tank. If you get greedy it won't work at all. If you run into issues start from scratch, once it's done right and loktit'd you'll never fk with it again.

All I have to do is throw my stuff in the truck and drive out to a game without waiting for batteries to charge if I forgot. Just came in clinch at a Milsim as a backup. Now I'm here replacing the AEG that went down with another Kythera. Things run like Gump once they get going.

Did Maxhop, Maple leaf autobot, 6.03 PDI & a G&P steel trigger. Right at field limits of 1.85j it's a laser. Feels like it want's to be a DMR, just runs better and better with more pressure.
by brandon g. on 09/09/2023
"I bought the Sr25 version and put it in a cyma platinum sr25, it works just the same as the m4 version but be aware, the trigger will not reset properly unless you put all the spacers under the reset spring, the trigger will be harder to pull but it will work. overall, I feel bad using it because it's just unfair in some cases, the consistency and range/power increase is very VERY noticeable, I can hit 75 ~ 100-yard shots with this thing. if you hate money then I couldn't recommend any more.

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