The issue of increasing the power of the outboard motor from 5 to 10 horsepower remains one of the most discussed in the community of water engines. Many owners of PVC boats purchase units with a capacity of 5 hp. it is with the expectation of subsequent modernization to avoid mandatory registration in the GIMS, but at the same time get enough traction to plane with the passenger.
The procedure, popularly called “swelling,” is technically possible on many Chinese and some Japanese engines, as they are often structurally identical to the more powerful versions. automatically cancels the guarantee manufacturer.
In addition, the operation of a technically modified self-propelled vehicle on water can entail legal consequences if the inspector of the GIMS detects a discrepancy between the declared power and the real one. In this article, we will discuss in detail the technical nuances, implementation methods and risks associated with this procedure.
Design features of the 5 hp motors
Most modern two-stroke 5 hp engines are based on the same cylinder-piston group as their 8-10 strong counterparts, the difference lies in the intake and exhaust system, as well as in the carburettor settings. Manufacturers artificially limit power to create market segmentation and meet the requirements of the laws of different countries for registration of small craft.
The main element that prevents the free passage of the fuel-air mixture is often a petal valve or a special gasket-limiter installed between the carburetor and the cylinder. Tohatsu, Yamaha And their Chinese counterparts (Parsun, HDX, Sea-Pro) use similar flow throttling principles, in some cases, the limiter is the valve in the exhaust system or the modified phases of the gas distribution.
It is important to understand that engine When you're working at higher speeds, you're going to get rid of it, and the piston rod and crankshaft bearings are designed for loads, and forcing them causes accelerated wear, and if you're going to be using the motor in high-intensity mode, you might want to think about replacing the lubricant more often and using high-quality oils.
Mechanical ways to increase power
The most common method of scenting is to physically remove or modify the intake limiters, and many models have a metal plate with a smaller opening or an additional valve between the carburetor and the cylinder that covers part of the petal valve, and removing this part allows the mixture to enter the cylinder in greater volume, which directly affects the power.
The second step of mechanical intervention involves the exhaust system. Often there is a "narrowing" or an additional partition in the muffler or exhaust manifold that creates backpressure. Cutting off this partition or replacing the exhaust manifold with an analogue from the 10-horsepower version of the engine It greatly improves the purging of the cylinder, making it easier to get the engine to maximum speed.
The third, more sophisticated method involves replacing the piston. In some cases, 5-horsepower engines have a piston with a lower compression ratio or other bottom parameters, and replacing it with a piston from the 10-horsepower version (if they are compatible with the finger and rings) gives a noticeable increase in traction, but requires a complete disassembly of the engine and the presence of special tools.
Setting up the carburetor and fuel system
After removing the physical limiters, the standard carburetor settings are not enough, the engine begins to choke at high revs due to the dimness of the mixture, since the throughput of the jiclairs is designed for a smaller volume of air, you need to adjust the quality and quantity of the mixture.
First, you need to twist the screw quality of the mixture (usually located at the bottom or side of the carburetor) 1.5-2 revolutions from the position of light stop. Then, heating the engine on the water, you need to sample the optimal position of the screw. If the motor stalls when the throttle is opened sharply, the mixture is too poor - the screw needs to be twisted. If it "chokes" and smokes, twist.
In some cases, the main fuel jelly is replaced with larger hole diameters, which allows more fuel to burn the increased volume of air, but there is a risk: too-mix will lead to the formation of soot on the candle and piston, and also increase fuel consumption.
☑️ Post-refinement verification
Table: Comparison of parameters before and after modernization
The following are indicative data showing the change in performance of a typical two-stroke engine after the limitations are removed. Figures may vary depending on the specific model and performance.
| Parameter | Factory version (5 hp) | After modernization (up to 10 hp) | Units of measurement |
|---|---|---|---|
| Maximum speeds | 4500 - 5000 | 5500 - 6000 | min |
| Fuel consumption | 1.5 - 1.8 | 2.5 - 3.2 | l-hour |
| Boat speed (PVC 3.2m) | 18 - 22 | 28 - 32 | km/h |
| Noise level | Medium. | Highly | dB |
Legal aspects and GIMS
From the point of view of the legislation of the Russian Federation, the engine power is indicated in the technical data sheet (PSM) and in the boat's ticket. If the documents indicate 5 hp, and in fact the engine produces 10, formally you operate an unregistered vessel with an engine of more than 10 hp, if the total power exceeds the registration threshold (now 10 hp for boats up to 200 kg, but the rules may change).
Inspectors GIMS rarely measure the power of the motor on the water with dynamometer washers, but they can pay attention to external signs: the absence of factory seals, traces of carburetor opening, the characteristic sound of the exhaust. If you draw up a protocol, you may be required to undergo technical examination at your own expense.
⚠️ Attention: In the event of a traffic accident or a water accident, the examination will show an interference with the structure, which may be grounds for finding you guilty, even if the rules of navigation were not formally violated, because you were driving a technically defective or modified vehicle.
Risks and consequences for the engine
Increased power is always a trade-off between performance and reliability. Engines originally designed as 5-horsepower engines (even if the unit is 10) may have differences in the lubrication system. In two-stroke engines, lubrication is done with oil added to gasoline. When forcing, the cylinder temperature rises, and the standard oil mixture may not be enough to protect the rubbing vapors.
Overheating is the main enemy of the swelled motor. Make sure the cooling system (pump, impeller, thermostat) works perfectly. Often, when upgrading, they change the thermostat to a lower opening temperature or remove it altogether, which leads to underheating in winter and to saving from boiling in summer.
Impact on the piston resource
When working at the maximum speeds, the resource of an aluminum piston can be reduced by 30-40%. It is recommended to use tinted pistons and a skirt with graphite spray to reduce friction.
Also worth mentioning is vibrations. Imbalances caused by changing operating modes can lead to fatigue breakdown of the elements of the lower unit or even cracks in the body of the lower unit. Regularly check the tightening of the motor mount bolts to the transom and the condition of the antivibration gaskets.
Use AI-95 or AI-98 gasoline with an octane rating not lower than recommended. When you force the engine, the tendency to detonate increases, and low-octane fuel can quickly destroy the piston.
Practical advice on modernization
If you're determined to upgrade, you're going to do it consistently. Don't try to remove all the constraints at once. Start with the petal valve, run the engine, listen to it, then go to the exhaust, and this approach will allow you to monitor the state of the engine at every step.
Make sure to use quality components. If you change the gaskets, use paronite or special materials that are resistant to the effects of gasoline and oil. Thin cardboard or paper can burn, which will lead to air sucking and instantaneous engine failure (bullyers).
⚠️ Warning: Never upgrade with a warranty motor. Even if you carefully collect everything back, the presence of bolts unscrewing marks (torn paint, scratches on the edges) will be a reason for denial of warranty service.
For those who are unsure of their abilities, there is an option to buy ready-made tuning kits or order services from specialized workshops, but the cost of such work can approach the price of a new engine of higher power, which calls into question the economic feasibility of the idea.
The main conclusion: The scattering of the 5 hp engine is a real opportunity to get planing, but it requires technical skills, carries the risks of breakdown and legal responsibility.
Frequently Asked Questions (FAQ)
Will the fuel consumption increase after the swelling?
Yes, the consumption will increase in proportion to the increase in power and revolutions. If you used to use about 1.5 liters per hour at cruising speed, then after the modernization, the consumption can be 2.5-3 liters, which is due to the need to enrich the mixture to cool the combustion chamber and burn more air.
Can the engine be returned to factory condition?
Theoretically, yes, if you kept all the parts removed (plates, jelly pads, pads), but the traces of interference (thrown bolt faces, scratches, changing the color of the pads from heating) will remain.
Which engine is better for swelling: Tohatsu or Chinese analogues?
Japanese engines Tohatsu/Mercury Chinese engines (Parsun, Sea-Pro) are simpler and easier to find iron limiters on, but the quality of casting and assembly may be lower, which increases the risk of problems after modernization.
Should I change the spark plug after increasing the power?
Preferably, when operating at elevated speeds and temperatures, a standard candle may not have time to clean itself or, conversely, overheat. It is recommended to install a candle with a potassium number one step "colder" than the plant recommends for the base version, especially if you plan long transitions on full gas.
Is it true that after the swelling the engine will stop starting?
No, it's a myth if you do it right. You can only have problems starting if you're not setting the carburetor (too poor or rich mix) or if you've made mistakes in the assembly (tightness of the intake tract) and if you're properly tuned, you start the engine normally.