The modern outboard motor market offers many solutions for small vessels, but it is the only one that can be used. Tohatsu 9.8 It's a well-deserved "king" among budget four-strokes, and owners often wonder about boosting, because it's structurally almost identical to the older 15-strong model, the only difference is the software constraints and the throttle that physically prevents the throttle from opening to full capacity. Tohatsu 9.8bhp One of the most popular and technically justified events in the world of water-motor technology.
The process of improving productivity requires not only mechanical intervention, but also a deep understanding of the work. fuel-injectionIlliterate modification can lead to overheating of the piston group or failure of the electronic control unit. In this article, we will discuss in detail all the stages of modernization, from removing mechanical constraints to fine-tuning the fuel card, so that you can safely and efficiently increase the power of the fuel card. motor-power up to the declared 15 horsepower.
It's worth noting that any interference with the factory design removes warranty obligations. However, if your warranty period has expired or you are ready to take responsibility, the result is worth it. The speed of going to the sleeve is reduced, and the maximum speed of the PVC boat or aluminum boat increases significantly. Let's look at which nodes require your attention.
Technical features and hidden potential of the model
Engine. Tohatsu MFS9.8B built on the basis of a time-tested cylinder block, which was originally designed with a margin of safety under 15 hp Engineers company just software "strangled" the engine, limiting the angle of opening the throttle and adjusting the angle of ignition advance. Electronic throttle In this model, it's controlled by a microprocessor that reads the position of the gas handle and signals to the servo, and that's where the first and most important limitation lies.
The second important aspect is the cooling system, and when you increase the load, the heat transfer must be efficient. The factory pump can handle 9.8 hp with the margin, but when you run at full speed after tuning, the condition is very high. pump-dip The cleanness of the cooling shirt comes to the fore, and if you plan to keep the motor in the forced mode constantly, it is recommended that you prevent the cooling system before you start work.
And there's also the fuel system, which is that the regular fuel pump and the injector are designed to be a certain amount of supply. fuel And it's going to increase, and the capacity of the standard might not be enough to make the perfect high-speed mix, but in most cases, if you're fine-tuned, the regular components can handle the increased load without having to be replaced.
⚠️ Warning: Before starting any work, make sure that the battery is fully charged. Sharp voltage surges when flashing the ECU can lead to irreversible damage to the electronics of the motor.
To understand the scale of the changes, you can compare the basic parameters of the stock and tuning version, and the difference in weight of the boat on the planing will be felt immediately after the revision.
| Parameter | Tohatsu 9.8 (Stoke) | Tohatsu 15 (After tuning) |
|---|---|---|
| Maximum power | 9.8 hp at 5,500 rpm | 15 hp at 6,000 rpm |
| Workload | 169 cubic centimetres | 169 cubic centimetres |
| Number of cylinders | 1 | 1 |
| Maximum speeds | Limited SOFTWARE (~5700) | 6000-6200 rpm |
Mechanical refinement of the throttle valve
The first step to increasing power is to remove the physical throttle limiter, and in the runoff, the throttle lever rests on a special screw limiter, preventing the throttle from opening more than 60 to 70 percent, and your job is to dismantle that stop or modify the drive to ensure full speed. throttleThis will allow the motor to consume more air, which is the foundation for power growth.
The process requires precision. You need to remove the top casing and find the gas cable going to the carburetor or throttle block (depending on the year of release and the injection modification), you will see a control screw on the drive lever, it must be twisted or replaced with a shorter analog, or you need to put the washers under the base of the cable attachment, changing the geometry of the stroke.
After mechanical adjustment, be sure to check the flap's progress visually, it should open to a stop of 90 degrees relative to the air flow, if the flap does not open fully, the desired gain. motor-power It will not happen because the engine will suffocate at high speeds.
☑️ Testing throttle mechanics
Remember, after mechanical intervention, the motor will start to consume more air, and if you don't adjust the fuel supply programmatically, the mixture will become too poor, which will cause the piston to burn, so the mechanical part is only half the battle.
Software and work with ECU
The most important stage is re-flashing electronic control unit (ECU) It is the motor's brains that know that they have a 9.8-horsepower version, and limit the fuel supply and ignition angle. You will need a special adapter (often an RS-232 or USB-based one) and licensed or specialized software such as Tohatsu Diagnostic Tool or its analogues from third-party developers.
The process is this: you connect the adapter to the diagnostic connector of the motor (usually hidden under the lid) and connect to the laptop. In the program menu, you need to find the option to change the engine configuration. You need to change the maximum power setting from 9.8 to 15 hp or select the appropriate model from the list.
It's important to understand that firmware isn't just about lifting a limit; it's about changing algorithms in a complex way. Ignition advance angle At high revs, it will be exposed more aggressively to better burn the mixture, and the fuel injection time will increase, and an error in this process can lead to unstable operation or detonation.
Risks of reflashing EBU
Self-flashing carries risks. If you're writing a firmware file or a cable fails, the ECU can turn into a brick. Recovery requires expensive equipment and a dedicated service, and if you're not sure about your abilities, you'd better leave it to the professionals.
After a new firmware is successfully recorded, it needs to reset the errors and adapt the process, and the motor needs to "understand" that it is now running in a new mode, often requiring it to be allowed to idle for 10-15 minutes to stabilize the parameters.
Tuning of the fuel mixture and ignition
Even after flashing, fine-tuning may be required. Factory settings often make the mixture a little richer for ecology and reliability, but you need balance to maximize the impact. If you notice that spark plugs after a race have white coating (overheating) or, conversely, black carbon (rich mixture), you need to adjust through diagnostic software.
You can change the fuel correction factor in the setting menu, and increasing this will enrich the mixture, which is useful for long-term full-gas operation with a full load of the boat. fuel-flowThe optimal color of the candle insulator is brick brown.
Also worth paying attention to is the octane number of gasoline. A forced engine with earlier ignition becomes sensitive to fuel quality. Using AI-92 gasoline can cause detonation under load. Switching to AI-95 or AI-98 with the appropriate octane corrector (if there is one in the firmware) will allow you to squeeze the maximum out of the engine without the risk of destruction of the piston group.
⚠️ Warning: Never use a motor with signs of knocking (a sound metal knock under load) is a sure way to destroy pistons and rods in minutes.
To monitor the condition of the engine after tuning, it is highly advisable to install additional sensors, if they are not provided for by the design of your boat, Control of temperature and revs will help to avoid fatal errors.
Install an external tachometer with Hour Meter function, which will allow you to accurately track the engine life and oil change intervals, which after tuning is better to reduce by 15-20%.
Refining the exhaust system and anti-cavitational stove
Many people overlook that a standard exhaust system can also choke the engine. The standard muffler and exhaust pipes have a certain cross section. As the power increases, the exhaust volume increases, and backpressure in the system can reduce the efficiency of cylinder purging. Replacing the exhaust pipe with a model with an increased diameter (if available from the 15-horsepower version) can give an additional increase of 0.5-1 hp.
Anti-cavitational stove also plays a role. On stock 9.8 hp, it can have geometry differences from 15-horsepower counterparts. Installing the stove from the older model will improve exhaust exhaust exhaust exhaust exhaust and reduce propeller cavitation at high speeds, which indirectly affects the final speed of the boat.
Special attention should be paid to the propeller. The native propeller from 9.8 hp has a pitch designed for less power. Once forcing, the motor can spin a screw with a larger pitch or diameter. Replacing the propeller with a more traction or speedy one (depending on your goals) is mandatory for the realization of potential.
If you are planning a serious tuning, consider installing stainless-steel screwSuch screws are thinner and have a more accurate geometry of the blade, which increases the efficiency of the screw by 5-10% compared to aluminum counterparts.
Legal aspects and safety of operation
Before you start upgrading, you should be aware of the legal consequences. In the documents (PSM, GTD) your engine is listed as 9.8 hp The actual increase in power to 15 hp makes the operation of such a vessel illegal without proper registration and category B rights (for engines over 10 hp and speeds over 15 km / h, although the rules of the GIMS periodically change, the risk of fine remains).
GIMS inspectors can measure the speed of the boat or require an examination, and in the event of an accident or an emergency on the water, the presence of an abnormal modification of the engine can be grounds for the insurance company to refuse payment or shift all the blame to the owner of the boat.
Technically, the life of the forced motor is always lower than that of the stock motor, and working to the limit of your ability causes the crankshaft rings, liners and bearings to wear faster, and you have to reduce the intervals of oil change and monitor the temperature more closely.
Tohatsu 9.8 tuning is technically simple and effective, but requires an integrated approach (mechanics + software) and awareness of legal risks.
If you're using a boat exclusively on private waters where there's no GIMS control, or if you're willing to accept the risks, this tuning will give you a whole new experience of riding, and the boat starts glides almost instantly, even with two passengers on board.
Frequently Asked Questions (FAQ)
Will the warranty work after the flashing of the ECU?
No, you lose 100% of the warranty, and the official dealers have access to the service history and can see a modified version of the software or mechanical traces of interference in the throttle node whenever they access the service.
Should I change the oil in the gearbox after tuning?
The power on the lower unit is transferred the same (torque increases slightly), so the gearbox is not required. However, due to the increased load on the screw, it is recommended to check the condition of the oil in the gearbox more often, for example, every 25-30 hours.
Can we get everything back to factory?
The mechanical part (the limiter screw) can be returned in 10 minutes. The software part is more complicated: to return the stock firmware, you will again need to connect to the computer and have the original firmware file for 9.8 hp, which is not always easy to find in the open access.
What is the real speed gain that can be achieved?
On a PVC boat with a length of 320-360 cm with one passenger, the speed increase will be from 3 to 6 km / h depending on the propeller and loading. The time to get on plane is reduced by almost half, which is especially noticeable on heavy boats.