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• MaxFlow has built 40 years of trust, with tens of thousands of kits sold.
• Two U.S. patents establish MaxFlow as the original inventor of the cage supported  foam chainsaw filter with sealed endwalls.
• MaxFlow sells a purpose‑built filtration system, not a repurposed pre‑filter or sleeve.
• Our product is demonstrably superior in oil capacity, particle retention, and engine protection, with tests to back up these claims.
• MaxFlow is the ONLY filter supplier that designs and builds all of the components incorporated into their filter kits. All their filter element are manufactured in OREGON, USA, not imported, assuring exceptional durability and quality control.
• Decades of experience performing flow bench bench testing goes into each new design. No other chainsaw filter beats the airflow numbers of a MaxFlow filter, or is tested to our standards. 
• Maxflow provides high volume covers to fit the Pro and Legacy Series kits. No other manufacturer takes the time and expense to assure complete protection in the worst elements for year round use. The Pro Series black covers are visible in countless professional videos and reels.
•  MaxFlow filters are stocked by many Stihl dealers worldwide

As MaxFlow® has remained the leading aftermarket filtration system for decades, it’s natural that new competitors try to gain attention—especially in online spaces. Some of the recent criticism circulating on forums and social platforms isn’t based on real‑world testing or professional experience. Instead, it often comes from:

• Untrained operators who may not understand filtration principles
• Operators who run their filters without oil (hard to believe, but it is true)
• AI‑generated or AI‑amplified posts designed to create doubt and clicks
• Competitors promoting their own products through anonymous accounts
• Misinterpretations of foam density, oil capacity, or sealing design
• Short‑term impressions rather than long‑term performance data

Online discussions can be useful, but they don’t always reflect the engineering behind a product or the conditions professionals work in. Filtration performance depends on factors that aren’t obvious at a glance—foam structure, oil‑holding capacity, airflow characteristics, sealing geometry, and durability under heavy use.

MaxFlow’s reputation wasn’t built overnight. It was built on decades of field‑proven performance in harsh, real‑world environments, widespread professional adoption, a strong dealer network, and two U.S. patents that helped define modern undercover foam filtration. These innovations set the foundation for the filtration standards many operators now take for granted. 

Isolated online comments—especially those lacking technical understanding—don’t outweigh the long‑term trust MaxFlow has earned from the people who rely on their saws for a living. 

They should be, but just looking at high numbers can be deceiving. Thin foam elements, covers or sleeves show high airflow on a bench test because they offer very little resistance — but they also offer very little filtration because they can't retain enough oil. Other thick filters offer low numbers, but perform filter poorly because of restricted airflow.  Effective filters must balance airflow, foam density, oil capacity, and sealing integrity. All MaxFlow Filter elements are engineered to deliver that balance.

Several foam filter kits on the market were originally designed as filter covers for H/D filters (read the fine print) or dust sleeves, not as primary filters. When used alone with non‑filtering 3D printed cages, (rather than the Injection molded MaxFlow support cage) they may not seal at the ends or at the mounting stud, allowing dust to bypass the foam entirely. MaxFlow filters use a patented sealing system that prevents end leakage and ensures consistent filtration.

The MaxFlow MINI filter for under-cover applications was developed over a multi-year time frame to assure filter performance consistent with their Pro and Legacy Series. All MaxFlow filters use a full‑thickness foam element constructed in the USA from proprietary 60 or 80PPI foam and mounted over a high strength injection molded cage. Each kit has our patented sealing system designed specifically for the MS500i and  MS661. Keeping these specifications was the goal, and the MINI achieved all the performance objectives.

Yes — for many users. The limitation is not based on skill level, but rather on the amount of time a saw runs a week. Operators burning 10+ tanks of fuel per week or working in wildfire, heavy dust, or abrasive environments will benefit from the Pro Series MF500i and MF661 kits, which include an extra‑volume cover and high‑flow impact resistant MAX filter support cage for extended service intervals.

No. MaxFlow OEM replacement elements are typically about half the cost of many aftermarket replacements, while offering superior foam mass, oil capacity, and sealing performance. 

Because of the tight tolerances on today’s saws, a small amount of shroud trimming is sometimes necessary.

• MS500i: Pro Series  A minor trim of the cylinder shroud is required for anti‑vibe clearance.
• MS500i: MINI We suggest removal of the small clearance pins inside the filter lid.
• MS400 / MS362: A more significant modification is needed to accommodate the rear‑mount cover.
• These adjustments ensure the filter and cover fit properly while delivering the airflow and durability MaxFlow systems are known for.

Some History

When the first MaxFlow® (Holeshot) Filter Systems were introduced nearly 40 years ago, they were hand‑built and sold without covers. A simple nut plate held the filter to the saw. Over time, loggers started making their own improvised covers—often the end of a bleach bottle with a hole cut in it—to keep rain off the element. To offer a better solution, we created the original square 064 cover, which we still sell today. This was long before CNC machining; the covers didn’t need to be pretty, they just needed to work. And they did.

Our design philosophy has always been the same: use the largest possible filter surface area that can fit on each saw. More surface area means longer run time between cleanings and better overall performance. The only real constraint is avoiding interference with the saw’s operation or the user’s sight lines.

Modern saws, however, are far more compact, with shrouds that tightly contour around internal components. To maintain maximum airflow and filter size, most of our kits (except the MaxFlow MINI) include custom CNC‑machined covers designed for both performance and a clean fit.

Not necessarily, but if you’re replacing a dirty stock filter, performing the factory reset procedure is recommended so the saw can adjust to the increased airflow.  On a carb equipped saw, you should check the WOT rpm and adjust according to the factory spec.

Absolutely not. You will experience all the power your saw can give with a factory exhaust system. Unlike a turbo or supercharger, air filters cannot add air to a saws intake system A MaxFlow air filter has no method of increasing the heat output of an exhaust component or outflow to more than the factory stock filter. However; MaxFlow filters provide 100% of the air necessary for the saw to breath at its maximum output for longer, and this is its most important feature.

Factory mufflers have to perform significant noise reduction duties, and a small exhaust hole helps with this function. Opening up this hole can increase the NOISE of the saw significantly, giving the sensation of more power. Whether additional noise and the feeling of power is important to you is your choice.  But it is NOT necessary to change your muffler for a MaxFlow filter to work properly.

Fun facts on exhaust flow on a two stoke chainsaw engine. or why the exhaust outlet is smaller than the intake port.

Exhaust gas leaves under pressure, intake air enters under vacuum

• Exhaust is pushed out by expanding combustion gases.
• Intake air is pulled in by the piston’s very weak vacuum (and in a two‑stroke, that vacuum is even weaker because the crankcase is doing the pumping).

Because the exhaust has positive pressure, it doesn’t need a big hole to escape. Because the intake relies on negative pressure, it needs a larger area to reduce restriction.

Exhaust ports are generally tuned for velocity, not volume

A smaller exhaust outlet increases gas velocity, which improves:

• Scavenging
• Pulse timing
• Wave reflection
• Powerband shape

Intake ports must be larger because air is dense and slow

Fresh air/fuel mixture is:

• Much denser than exhaust gas
• Much slower-moving
• Entering under weak vacuum

To get enough mass flow, the intake port must be larger.

Thermal expansion makes exhaust gas “bigger”

Hot exhaust gas expands dramatically. Even though the port is smaller, the gas is:

• Hot
• Thin
• Moving fast
• Under pressure

So it still escapes easily.

Two‑stroke timing demands a smaller exhaust port

If the exhaust port were as large as the intake:

• Blowdown would be too fast
• Scavenging would collapse
• The engine may lose torque and over‑scavenge fresh charge

A smaller exhaust port preserves the timing window the exhaust muffler is designed around.

The simple summary

Intake = low pressure, dense air → needs a big opening Exhaust = high pressure, hot gas → works better with a smaller, high‑velocity opening

The size difference is not a flaw — it’s a deliberate balance of:

• Pressure
• Temperature
• Gas density
• Port timing
• Wave dynamics

And in two‑strokes, that balance is everything. This is exactly why carburetors, intake boots, and filters are always the biggest restriction in the system — and why MaxFlow filters work so well to improve performance of your saw.

After installing a MaxFlow® filter, you’ll eventually need to clean and re‑oil the element. Since the filters must be run with oil, we recommend having filter oil on hand and pre‑oiling your element before its first use.

We do offer pre-oiling on certain Semi-Pro Series filter kits.  However,  pre‑oiling at the manufacturing stage sounds convenient, but it’s surprisingly expensive and ultimately not cost‑effective for customers. In fact, providing a pre‑oiled element costs more than an entire quart of high‑quality foam filter oil. Rather than raise prices, we chose a better solution: While one of our kits includes one pre-oiled element,  Most MaxFlow kits include two filter elements. This way, you always have a fresh, clean element ready to swap in after you oil them, and we can keep overall kit pricing reasonable.

All MaxFlow elements are manufactured in Oregon, USA. They’re built from our proprietary high‑flow foam, capable of holding up to six times more oil without restricting airflow. Each element features seamless construction and consistent wall thickness, delivering the highest performance and durability in the industry.  

All MaxFlow® filters are engineered with USFS SAE J335 compliance in mind. Exhaust systems, however, are a different story. To our knowledge, no aftermarket or “loud” replacement mufflers meet SAE J335 or USFS 5100A qualification standards. Compliance involves far more than simply having a spark‑arrestor screen, and any saw operated on USFS or BLM lands must meet these requirements. Users should keep this in mind when modifying exhaust systems.

If you’re running your saw on private property, how you configure your equipment is ultimately a personal choice. Just like bar length or brand preference, we can’t tell you what you can or can’t install. What we can speak to is performance. To date, we have not seen any dyno testing showing a loud exhaust producing a measurable horsepower increase beyond the 5% margin of error of a high‑quality dynamometer. We are also not aware of any certified dynos (such as SuperFlow) being used for chainsaws. Water‑brake dynos like the Dyno‑Mite simply aren’t accurate enough at low horsepower to produce repeatable torque or acceleration curves. They can show a peak power point within about 5%—and yes, some muffler mods may bump that slightly—but you’ll also be dealing with bone‑conducting 130 dB noise.

MaxFlow® filter kits already provide 100% of the airflow required for Stihl saws to achieve maximum power, while extending run time between cleanings. Our recommendation is simple: install your MaxFlow first and feel the throttle response and torque. In most cases, adding a loud exhaust afterward won’t produce a noticeable performance gain—just a dramatic increase in noise.

Hearing safety is also a major concern. Our findings indicate that prolonged exposure to aftermarket exhaust noise can contribute to permanent hearing damage and increased operator fatigue. We encourage users to prioritize modifications that improve efficiency and reliability without compromising comfort or long‑term health.

For many years MaxFlow worked directly with the USFS during the era when SAG approval was required. All MaxFlow filters comply with the published regulations for components under SAE J335 or USFSA 5100A.  From 2003 to 2021, MaxFlow filters were specifically listed in the SAG under 

approved aftermarket filters.

Regarding aftermarket mufflers, the USFS guidance is clear:

“Any modification or damage to any part of the stock configuration or exhaust system as it was presented for testing voids the qualification of the spark arrester… Modifications usually consist of removal of screen or change in exhaust outlets.”

Based on this, and on current available information, we are not aware of any loud exhaust system that has passed SAE J335 or USFS 5100A qualification for legal operation on USFS or BLM land