You dream of squeezing your own. 5-horsepower outboard motor More power, but afraid to turn it into a pile of scrap metal? You're not alone: owners of low-power outboard motors (see below).Yamaha 5FMHS, Mercury 5M, Toatsu 5BS And so, all the time, they're looking for ways to improve the dynamics without buying a new engine. practical methods of increasing powerfrom simple to radical, with a review of pros, cons and The most common mistakes that kill the engine in a single season.
It's important to understand that any tuning is a compromise between the increase in horsepower and the life of the engine. Honda BF5 or Suzuki DF5 They have a margin of safety, but it's limited. legality (adjustment of the carburetor, replacement of the screw) and extreme (cylinder waste, turbine) and why some “folk” methods (such as catalyst removal) do more harm than good.
If you’re willing to spend 10-15 minutes reading, you’ll know by the end of the article:
- 🔧 What engine settings can be optimized without disassembly (and how much L. S. would it give).
- ⚙️ What details to replaceto increase efficiency (screw, air filter, exhaust).
- ⚠️ What “improvements” reduce the engine life by 2-3 times (and how to avoid them).
- 📊 Real figures of power increase for each method (comparison table).
1. Adjustment of the carburetor: +0.3-0.7 hp without investments
The easiest and safest way to do this is to carburettingFactory settings are often "squeezed" to environmental standards, rather than to maximize impact. Yamaha 5FMHS and Mercury 5M It gives you an increase. 10–15% power.
What needs to be done:
- Find it. blend-wheel (usually marked as "L" or "H" on the carburetor)
- Start the engine and warm it up for 5-7 minutes at idle speeds.
- Smoothly twist the screw "H" (high revs) until the moment when the engine begins to "sneeze", then unscrew 1/4 revolution back.
- Repeat with the "L" screw (low revs), focusing on the stability of the idling.
⚠️ Attention: If you start to overheat after you adjust the engine (temperature above 90°C) or black smoke comes out of the exhaust, the mixture is too rich.
Pour out old fuel and pour fresh (octane number not lower than 92) | Check the state of the spark plug (gap 0.7-0.9 mm) | Clean the air filter from dust | Have a screwdriver with a flat sting at hand ->
2. Replacement of propeller: +0.5-1.2 hp due to the correct step
The wrong screw can "steal" before 30% capacityFor example, if you're on a motor. Toatsu 5BS pitched 9" instead of optimal 7–8"The engine will run at its limit, but the boat will not reach its maximum speed.
How to choose a screw:
- 📏 Diameter: For 5-horsepower engines - 180-210 mm. Larger diameter = better "capture" of water, but higher load.
- 🔄 Step: For light boats (up to 300 kg)
7"for loaded (300-500 kg) -8–9". - 💎 Material: Aluminum is cheaper, but stainless steel gives +5-7% efficiency due to lower resistance.
Example: on a PVC Killer 320 boat motorized Honda BF5 replacement 8.5×7" stainlessly 8×6" increased speed from 18 to 21 km / h (GPS measurements).
Before buying a screw, check its compatibility with the gearbox of your motor. Mercury not fit Toatsu Because of the different landing holes.
Modification of the exhaust system: +0.2-0.5 hp and better sound
The factory muffler restricts the flow of exhaust gases, which creates backpressure and reduces power. sport-gas (e.g. from Sierra or Stingermay increase to 5%But there are nuances:
Pros:
- ✅ The cylinder purging (less residual gases) is improved.
- ✅ The engine is more easily gaining momentum.
- ✅ The sound becomes deaf and bassier (important for fishermen).
Cons:
- ❌ In some models (e.g., Yamaha 5FMHS) requires a flashing of the ECU, otherwise there will be a check engine error.
- ❌ Cheap Chinese emissions often rust during the season.
The cost of quality exhaust is from 8 000 to 15 000 rubles. It pays off in 2-3 seasons due to fuel economy (consumption is reduced by 5-10%).
Installation of turbine or compressor: +2-3 hp, but the risk of overheating
It's most radicalIt's a very sophisticated engine, and it pumps extra air into the cylinder, which allows you to burn more fuel and get more power. It is fraught with a reduction in resource by 3-5 times.
What you need to install the turbine:
- Strengthen the piston group (replacement of pistons with forged ones, for example, from Wiseco).
- Install an intercooler to cool the injected air.
- Reconfigure the ignition system (increase the angle of advance by 2-3 °).
- Use fuel with an octane number not lower than 98.
Example: on the motor Mercury 5M turbine was installed Garrett GT08 at a pressure of 0.3 bar. The power increase was 2.8 hpBut 50 hours later, there was a knock on the rod bearings.
⚠️ Attention: Turbine on a 5-horsepower engine is like putting a turbine on a power plant. Oka: theoretically possible, but the practical consequences are predictable. If you are not ready for a major overhaul in the season, it is better to consider buying an engine for 8-9.9 hp.
5. Cylinder squandering and piston replacement: +1-1.5 hp, but expensive
Increasing cylinder displacement is a classic way of boosting, and for 5-horsepower engines, this means increasing the cylinder diameter by 0.5-1 mm and installing a larger piston.
What the germ does:
- 🔥 Increase the volume of the combustion chamber more fuel-air mixture more power.
- 🔄 The ability to install pistons with a greater degree of compression (for example, 10:1 instead of 8.5:1).
Cost of work (including details):
| Service/detail | Price, RUB | Note |
|---|---|---|
| Spreading the cylinder | 3 500–5 000 | Includes honing. |
| Wrought-iron (Pistons)Wiseco) | 6 000–8 000 | For compression ratio 9.5:1 |
| Piston rings | 1 200–1 800 | 3 ring set |
| GBC purification | 2 500–4 000 | Increased channel capacity |
Total: 13,000–18,000 rublesPower up to the next level. 1.5 hpBut the engine life is reduced by 20-30%.
What happens if you blow the cylinder too much?
If the permissible diameter is exceeded (usually +1.5 mm from the standard), the cylinder walls become thinner, which leads to:
- Overheating (heat sink deteriorating).
Risk of piston bullying (due to cylinder deformation during heating).
Possible wall damage (in extreme cases).
Like, on a motor. Suzuki DF5 maximum permissible scavenging - up to 58.5 mm (state diameter - 57 mm).
6. ECU Chip Tuning: only works on injection motors
If your motor is equipped with an electronic control unit (Yamaha 5FMHS 2018+ years or Honda BF5 s PGM-FI) can be done chip-tuning - Flashing the ECU to change the parameters of injection and ignition.
What's changing chip tuning:
- 🔥 Increased injection time richer mix more power.
- ⚡ Change the angle of ignition advance (optimum for 95+ gasoline).
- 📉 Disabling the speed limiter (if any).
Example: After the EBU has been installed Mercury 5M EFI capacity increased from 5 to 5.8 hpBut the fuel consumption increased by 12 percent, and the firmware cost was 5,000 to 7,000 rubles.
⚠️ Attention: On carburetor engines (Toatsu 5BSold Yamaha) Chip tuning is impossible - there is no ECU. Don't believe the "masters" who offer "to flash the carburetor" - this is fraud.
7. Alternative Ways: What Doesn't Work (and Why)
The Internet is full of power-enhancing tips that are either useless or harmful in practice.
Myth 1: “Remove the catalyst, 1 hp will be added.”
Reality: Catalyst on 5-horsepower engines (Honda BF5, Suzuki DF5) does not create any noticeable resistance. Removing it gives +0.1-0.2 hp, but you get:
- ❌ Violation of environmental norms (problems with GIMS).
- ❌ Increased toxicity of exhaust (important for fishing in closed waters).
Myth 2: “Pour the 100th gasoline, the engine will fly!”
Reality: If the motor is not designed for a high octane number (compression rate below 9:1), you will only overpay. 0%but
- ✅ Nana Yamaha 5FMHS There is no difference with a compression ratio of 8.7:1.
- ✅ Nana Mercury 5M 9.2:1 can be poured 98th to prevent detonation.
Myth 3: “Put a sports air filter – it will be +2 hp.”
Reality: On atmospheric motors (without a turbine), the zero drag filter gives +0.1-0.3 hp, but requires frequent cleaning (every 10 hours).
The safest and most effective way to increase power on a 5-horsepower engine is a combination of adjusting the carburetor, replacing the screw and installing sports exhaust. Together they give +1-1.5 hp without critical damage to the resource.
FAQ: Frequent questions about tuning 5-horsepower engines
❓ Can the engine power be increased? Toatsu 5BS 7 hp?
Theoretically, yes, but it will require:
- Cylinder drainage up to 60 mm (+1.5 mm from the state).
- Installation of a forged piston with an increased degree of compression (10: 1).
- Replacement of the carburetor with a model with a higher throughput (for example, with a carburetor) Yamaha 8bhp.).
Cost: ~ 25 000 rubles. the resource of the engine will be reduced to 300-400 hours (instead of 1,000-1 500 regular).
❓ What is the power gain of replacing the spark plug?
Minimum, like switching from a regular candle. NGK BPR6ES iridium NGK Iridium IX gives:
- ✅ More stable spark (especially at high revs).
- ✅ Reduce fuel consumption by 2-3%.
- ❌ Power gain. 0.1 to 0.2 hp (intangible).
The cost of an iridium candle is 800-1 200 rubles. It pays off due to fuel savings for 2-3 seasons.
❓ Is it legal to increase the power of the engine from 5 to 6 hp?
From the GIMS perspective:
- If the motor remains within the limits 5-5.9 hpRe-registration is not required.
- If the power is greater than 6 hpYou need to make changes to the technical data sheet of the boat and re-register.
- The penalty for non-compliance is up to 2 000 rubles (Article 11.8 of the Administrative Code of the Russian Federation).
Tip: if you plan to increase to 6+ hp, it is better to immediately buy an engine for 8-9.9 hp - this is cheaper than tuning + fines.
❓ Can I use motor oil for cars in a outboard motor?
No! Automotive oils (even synthetic ones) are not designed to:
- Working in high humidity conditions.
- Protection against corrosion during prolonged periods is simple (winter).
- Lubrication of bearings operating in water (in a gearbox).
Use only specialized oils for outboard motors:
- Yamalube two-stroke Oil (for 2-strokes).
- Mercury Premium four-stroke Oil (for 4-strokes).
❓ How much does a full tuning of the engine cost? Yamaha 5FMHS 7 hp?
Calculation for complex tuning (prices 2026, Moscow):
| Work/detail | Price, RUB |
|---|---|
| Cylinder waste + honing | 4 500 |
| Wrought-iron piston (Wisecocompression ratio 10:1 | 7 500 |
| Carburetor with enlarged diffusers | 5 000 |
| Sports exhaust Sierra | 9 000 |
Stainless screw 7.5×8" |
6 000 |
| Adjustment and breaking in | 3 000 |
Total: ~35,000 rubles. The increase in power is up to 6.5-7 hp, but the resource will be reduced to 400-500 motor hours.