MS391 Muffler Mod Tips (5 Expert Hacks For Better Cuts)

MS391 Muffler Mod Tips (5 Expert Hacks for Better Cuts): A Deep Dive into Performance and Cost

Let’s talk chainsaws. Specifically, the Stihl MS391. It’s a workhorse of a saw, reliable and powerful enough for a wide range of tasks. But like any tool, it can be optimized for even better performance. One popular modification is tweaking the muffler. Why? To improve exhaust flow, which, in theory, translates to more power and faster cuts. This article isn’t just about how to do it, but also about understanding the potential benefits, the risks involved, and, crucially, whether the cost (both in terms of money and potential damage) is worth it for you.

I’ve spent countless hours in the woods, felling trees, bucking logs, and processing firewood. I’ve seen firsthand the difference a well-tuned chainsaw can make. I’ve also seen the frustration of a saw that just doesn’t quite have the oomph you need. So, let’s dive into the world of MS391 muffler modifications, weighing the pros and cons, and exploring how it all ties into the bigger picture of wood processing costs and efficiency.

Understanding the Muffler Mod: More Than Just Noise

The goal of a muffler modification is to reduce backpressure on the engine. The stock muffler is designed to meet emissions standards and keep noise levels down. However, this often restricts exhaust flow. By opening up the muffler, you allow the engine to breathe more freely, potentially increasing horsepower.

Potential Benefits:

Increased Power: A more efficient exhaust system can lead to a noticeable increase in power, especially when cutting hardwoods.
Faster Cutting: That extra power translates to quicker cuts, meaning you can process more wood in less time.
Improved Throttle Response: The engine may feel more responsive, making it easier to control during delicate cuts.

Potential Risks:

Voiding Warranty: Modifying your chainsaw can void the manufacturer’s warranty.
Engine Damage: Incorrect modifications can lead to overheating, lean running conditions, and ultimately, engine damage.
Increased Noise: A modified muffler will be significantly louder, potentially violating noise ordinances and disturbing neighbors.
Emissions Violations: Altering the exhaust system can cause the saw to fail emissions tests, where applicable.

Expert Hack #1: The Simple Screen Removal (Low Risk, Low Reward)

This is the most basic modification and involves removing the spark arrestor screen from the muffler. The screen is designed to prevent sparks from escaping and potentially starting fires. However, it can also restrict exhaust flow.

How to do it:

Locate the spark arrestor screen on the muffler.
Remove the screws or retaining clips holding the screen in place.
Carefully remove the screen.
Reassemble the muffler.

Pros:

Simple and easy to do.
Minimal risk of engine damage.
Slight improvement in exhaust flow.

Cons:

May not result in a significant performance increase.
Increases the risk of starting fires.
Doesn’t address the core restriction of the muffler itself.

Cost Consideration: This hack is essentially free, requiring only a screwdriver or wrench. However, consider the potential cost of starting a fire – fines, property damage, and potential liability.

Expert Hack #2: The “Drill-Out” Method (Medium Risk, Medium Reward)

This involves drilling additional holes in the muffler to increase exhaust flow. The key is to drill strategically and avoid damaging the internal components.

How to do it:

Remove the muffler from the chainsaw.
Carefully inspect the muffler to identify areas where drilling will not damage internal components.
Use a drill bit slightly larger than the existing exhaust outlet.
Drill additional holes in the muffler, focusing on areas that will maximize exhaust flow.
Deburr the holes to remove any sharp edges.
Reinstall the muffler.

Pros:

More significant improvement in exhaust flow compared to screen removal.
Relatively inexpensive.
Can be done with common tools.

Cons:

Higher risk of engine damage compared to screen removal.
Can be difficult to drill accurately without damaging the muffler.
May not result in a significant performance increase if not done correctly.

Cost Consideration: The cost is minimal – drill bits typically cost a few dollars. However, the risk of engine damage is higher, potentially leading to costly repairs or replacement.

Expert Hack #3: The “Deflector” Method (Medium Risk, Medium Reward)

This involves adding a deflector plate to the muffler to direct exhaust flow away from the engine and improve cooling.

How to do it:

Remove the muffler from the chainsaw.
Fabricate a deflector plate from sheet metal.
Weld or bolt the deflector plate to the muffler.
Reinstall the muffler.

Pros:

Improved exhaust flow and cooling.
Can be customized to optimize performance.

Cons:

Requires welding or metal fabrication skills.
Higher risk of engine damage if not done correctly.
Can be more expensive than other methods.

Cost Consideration: This method involves the cost of materials (sheet metal, welding supplies) and potentially labor if you need to hire someone to weld the deflector. The risk of engine damage remains a factor.

Expert Hack #4: The “Dual Port” Modification (High Risk, High Reward)

This involves adding a second exhaust port to the muffler, significantly increasing exhaust flow. This is a more advanced modification that requires careful planning and execution.

How to do it:

Remove the muffler from the chainsaw.
Carefully cut a second exhaust port into the muffler.
Fabricate a new exhaust outlet for the second port.
Weld the new exhaust outlet to the muffler.
Reinstall the muffler.

Pros:

Significant improvement in exhaust flow and power.
Can result in a noticeable increase in cutting speed.

Cons:

Requires advanced welding and fabrication skills.
Highest risk of engine damage if not done correctly.
Can be more expensive than other methods.

Cost Consideration: This is the most expensive and risky modification. It requires specialized tools, welding skills, and a thorough understanding of engine dynamics. The potential for engine damage is significant, and the cost of repairs could easily outweigh the performance gains.

Expert Hack #5: The “Aftermarket Muffler” Solution (Low Risk, Medium Reward, Higher Initial Cost)

Instead of modifying the stock muffler, you can purchase an aftermarket muffler designed for improved performance. These mufflers are often engineered to provide optimal exhaust flow while maintaining acceptable noise levels.

How to do it:

Research and purchase an aftermarket muffler specifically designed for the Stihl MS391.
Remove the stock muffler from the chainsaw.
Install the aftermarket muffler according to the manufacturer’s instructions.

Pros:

Relatively easy to install.
Designed for optimal performance.
May offer a better balance of power and noise.
Reduced risk of engine damage compared to DIY modifications.

Cons:

More expensive than DIY modifications.
May still void the warranty.
Performance gains may not be as significant as with more aggressive modifications.

Cost Consideration: Aftermarket mufflers typically range in price from $50 to $150. While this is more expensive than DIY modifications, it offers a safer and potentially more reliable way to improve performance.

The Cost of Wood Processing: A Holistic View

Now, let’s zoom out and consider how a muffler modification fits into the overall cost of wood processing. Whether you’re a professional logger or a homeowner cutting firewood, understanding your costs is crucial for profitability and efficiency.

Key Cost Components:

Timber Purchase or Harvesting Costs: This includes the cost of buying standing timber or the expenses associated with harvesting trees on your own property (permits, equipment rental, labor).
Tool Costs: Chainsaws, axes, wedges, splitting mauls, log splitters – these are all essential tools, and their cost can add up quickly. Don’t forget maintenance!
Fuel and Oil: Chainsaws are hungry beasts. Fuel and oil consumption is a significant ongoing expense.
Labor Costs: If you’re hiring a logging crew or firewood handlers, labor will be a major cost factor.
Transportation Costs: Hauling logs or firewood requires trucks, trailers, and fuel.
Equipment Maintenance and Repair: Chainsaws break down. Log splitters need servicing. Factor in regular maintenance and potential repairs.
Drying and Storage: Firewood needs to be properly dried and stored, which may involve additional costs for tarps, sheds, or covered storage areas.
Personal Protective Equipment (PPE): Safety gear like helmets, chaps, gloves, and eye protection are essential and should be factored into the cost.

The Impact of a Muffler Mod on Overall Costs:

A muffler modification, in theory, can reduce the time it takes to process wood. This translates to lower fuel consumption and potentially reduced labor costs if you’re paying by the hour. However, the potential for engine damage could lead to costly repairs, negating any savings.

Let’s consider a hypothetical scenario:

Scenario 1: No Muffler Mod
- Time to process 1 cord of firewood: 4 hours
- Fuel consumption: 1 gallon
- Labor cost (if applicable): $25/hour
- Scenario 2: Muffler Mod (Increased Efficiency)
- Time to process 1 cord of firewood: 3.5 hours
- Fuel consumption: 0.85 gallons
- Labor cost (if applicable): $25/hour

Cost Savings:

Fuel savings: 0.15 gallons per cord
Labor savings: 0.5 hours per cord (if applicable)

Assuming a fuel cost of $4/gallon and a labor rate of $25/hour, the muffler modification could save you $1.60 in fuel and $12.50 in labor per cord. However, if the modification leads to engine damage requiring a $200 repair, you would need to process approximately 15 cords of wood to recoup the cost.

Data-Driven Insights into Wood Processing Costs:

Timber Prices: Timber prices vary widely depending on species, quality, location, and market demand. According to the USDA Forest Service, the average stumpage price (price paid for standing timber) for sawtimber in the United States in 2022 was around $300 per thousand board feet. However, prices can range from less than $100 to over $1000 depending on the factors mentioned above.
Firewood Prices: The price of firewood also varies depending on location, species, and whether it’s seasoned or green. According to various sources, the average price per cord of seasoned firewood in the United States in 2023 is between $200 and $400.
Equipment Rental Fees: Renting a log splitter can cost anywhere from $50 to $150 per day, depending on the size and power of the machine. Chainsaw rental is less common, as most professionals and serious hobbyists prefer to own their own saws.
Labor Rates: Labor rates for logging crews and firewood handlers vary depending on experience, location, and the complexity of the job. Expect to pay anywhere from $20 to $50 per hour for skilled labor.

Original Research: Budgeting for a Firewood Project

I recently undertook a firewood project, processing approximately 5 cords of oak for personal use. Here’s a breakdown of my costs:

Timber: Purchased standing oak trees for $150 (negotiated a good price with a local landowner).
Fuel and Oil: Approximately $40 (chainsaw, log splitter).
Chainsaw Maintenance: $20 (new chain, sharpening).
Log Splitter Rental: $100 (rented a hydraulic splitter for two days).
Transportation: $30 (hauling logs and firewood).
Total Cost: $340

This translates to a cost of $68 per cord. Considering that seasoned oak firewood typically sells for around $300 per cord in my area, I saved a significant amount of money by processing it myself. However, this doesn’t factor in my time and effort.

Cost Optimization Tips:

Shop around for timber: Get multiple quotes from different landowners or timber companies.
Maintain your equipment: Regular maintenance can prevent costly repairs and extend the life of your tools.
Season your firewood properly: Properly seasoned firewood burns more efficiently and produces more heat, reducing the amount you need to burn.
Consider alternative heating sources: If firewood prices are high in your area, explore alternative heating options like propane, natural gas, or electric heat.
Buy in bulk: Purchasing firewood in bulk can often save you money.
Negotiate prices: Don’t be afraid to negotiate prices with firewood suppliers or timber companies.
Take advantage of free resources: Look for free sources of firewood, such as fallen trees on public land (with proper permits).

The MS391: A Reliable Workhorse

Before we get too deep into modifications, let’s appreciate the MS391 for what it is: a solid, dependable chainsaw. It’s not the lightest saw on the market, but it packs a punch and is known for its reliability. Its 59cc engine provides ample power for felling medium-sized trees, bucking logs, and processing firewood.

Key Features:

Engine: 59cc, 3.9 bhp
Weight: 12.3 lbs (without bar and chain)
Bar Length: 16-20 inches
Fuel Capacity: 19.3 oz
Oil Capacity: 10.1 oz

Maintenance Tips:

Clean the air filter regularly: A dirty air filter restricts airflow and reduces engine performance.
Sharpen the chain frequently: A sharp chain cuts faster and more efficiently, reducing strain on the engine.
Use fresh fuel: Old fuel can cause starting problems and reduce engine performance.
Check the spark plug: A fouled spark plug can cause misfires and reduce engine power.
Lubricate the bar and chain: Proper lubrication prevents wear and tear and extends the life of the bar and chain.
Store the chainsaw properly: Store the chainsaw in a dry place with the bar and chain protected.

The Verdict: Is a Muffler Mod Worth It?

The decision to modify your MS391 muffler is a personal one. There’s no one-size-fits-all answer. Consider the following factors:

Your Skill Level: Are you comfortable working on engines and performing modifications?
Your Risk Tolerance: Are you willing to risk engine damage for a potential performance gain?
Your Budget: Can you afford the cost of repairs if something goes wrong?
Your Needs: Do you really need the extra power? Or is the stock saw sufficient for your needs?
Your Local Regulations: Are there noise ordinances or emissions regulations in your area that could be violated by a modified muffler?

If you’re a skilled mechanic with a high tolerance for risk and a genuine need for more power, a muffler modification might be worth considering. However, if you’re a novice or simply want to improve the performance of your saw without risking damage, an aftermarket muffler or simply ensuring your saw is properly maintained and sharpened might be a better option.

Actionable Takeaways:

Assess your needs: Determine if a muffler modification is truly necessary for your wood processing tasks.
Research thoroughly: Before attempting any modification, research the potential risks and benefits.
Start small: If you decide to modify your muffler, start with a simple modification like screen removal before attempting more complex modifications.
Prioritize safety: Always wear appropriate PPE when working on your chainsaw.
Consider an aftermarket muffler: An aftermarket muffler offers a safer and potentially more reliable way to improve performance.
Maintain your chainsaw: Regular maintenance is crucial for ensuring optimal performance and preventing costly repairs.
Factor in all costs: Consider the potential costs of engine damage and repairs when evaluating the cost-effectiveness of a muffler modification.

Final Thoughts: A Balanced Approach

Modifying a chainsaw is a bit like adding spice to a dish. A little can enhance the flavor, but too much can ruin the whole thing. The key is to approach it with caution, knowledge, and a clear understanding of the potential consequences. Whether you choose to modify your MS391 or not, remember that proper maintenance, a sharp chain, and a good understanding of wood processing techniques are the most important factors for achieving efficient and safe results. And always, always, prioritize safety. A chainsaw is a powerful tool, and respect for its capabilities is paramount. So, get out there, process some wood, and enjoy the satisfaction of a job well done – safely and efficiently.

MS391 Muffler Mod Tips (5 Expert Hacks for Better Cuts)