Clearly I'm missing someting. I'm shopping for a new outboard. Beside the price, I have not been able to figure out the difference between the 4hp, 5hp and 6hp Nissan 4 stroke motors. Each model has the exact same displacement (123cc), stroke (59X45mm) and gear ratio (2.15:1). I've checked other manufactures also (Tohatsu, Johnson, etc) and the 4hp-6hp have the same specs too. They also have the same prop size, gears (F-N-R), tiller controlls, weight, etc. Why would I pay more for a 6hp when the 4hp appears to be the exact same motor? Everyone I ask says, "The 6hp is bigger and more powerful than the 4 hp." But they scratch their head when I show them the specs. Anyone know why this is so? I'm sure I'll feel stupid when someone tells me what I'm missing.
4hp vs 5hp vs 6 hp?
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De-tuning engines and Electronic control units
Funny you should ask. Outboard manufactures have for years produced different HP engines based on a common model. They claim to "de-tune" to produce a lower horsepower output with similar engine specifications. There is an article in the current issue of Soundings (September, 2004) regarding large 4-stroke outboards. Mercury has come out with four new Verado 4-stroke engines, 200, 225, 250 and 275 HP. The electronic control unit is the only component that is replaced or modified to alter the horsepower ratings on the different models. There are no differences in displacement, compression ratios or cam timings with the different engines. Could be that the same applies to smaller engines.
Funny you should ask. Outboard manufactures have for years produced different HP engines based on a common model. They claim to "de-tune" to produce a lower horsepower output with similar engine specifications. There is an article in the current issue of Soundings (September, 2004) regarding large 4-stroke outboards. Mercury has come out with four new Verado 4-stroke engines, 200, 225, 250 and 275 HP. The electronic control unit is the only component that is replaced or modified to alter the horsepower ratings on the different models. There are no differences in displacement, compression ratios or cam timings with the different engines. Could be that the same applies to smaller engines.
Fuel
The fuel system is different on each one, therefore providing the different horsepower ranges.
The fuel system is different on each one, therefore providing the different horsepower ranges.
Carb Jetting
I understand this is most often the difference. This is not to say you are better off using an apparently same 8HP motor on a boat that calls for a 4HP one. You will not get more performance. You’ll use more fuel and not probably be able to control your speed as well as if you used the 4HP motor.
I understand this is most often the difference. This is not to say you are better off using an apparently same 8HP motor on a boat that calls for a 4HP one. You will not get more performance. You’ll use more fuel and not probably be able to control your speed as well as if you used the 4HP motor.
Don't Feel Stupid!
Like the man said; they have done this for years! Yet I have not found a mechanic who knows how to "upgrade one" hope somebody in the industry weighs in.
Like the man said; they have done this for years! Yet I have not found a mechanic who knows how to "upgrade one" hope somebody in the industry weighs in.
kicker
Don't know what you're driving or what she weighs,but my two tonner does better than I imagined with a four blade working prop on my 4 stroke, and I can imagine that at 9.9 she's somewhat overpowered. Doesn't suck down the stern at 3/4 throttle anymore. HP is a consideration, but so is prop pitch.
Don't know what you're driving or what she weighs,but my two tonner does better than I imagined with a four blade working prop on my 4 stroke, and I can imagine that at 9.9 she's somewhat overpowered. Doesn't suck down the stern at 3/4 throttle anymore. HP is a consideration, but so is prop pitch.
Nissan 4 HP
I bought the 4 HP primarily because it is the only one with an internal tank (comes with the fitting to add an external tank).It's big enough for my needs.The factory prop is a lower pitch than the other two so it gives up some potential speed for power.
I bought the 4 HP primarily because it is the only one with an internal tank (comes with the fitting to add an external tank).It's big enough for my needs.The factory prop is a lower pitch than the other two so it gives up some potential speed for power.
Tohatsu makes Nissan, Mercury
The Tohatsu, Nissan and Mercury 4/5/6 are all made by Tohatsu. Same machine for all three. I bought the Mercury 6hp 4stroke, and paid extra for the "name". Nissan and Tohatsu sell the same model for less. They can vary the fuel, ignition and prop to get a different hp rating. My Mercury 6hp is "ok": been reliable so far, runs quiet, no smoke. I would rather have the shift on the front of the engine, or some option to set this up, but no luck. Mercury has a new 8hp model with shift on the handle.
The Tohatsu, Nissan and Mercury 4/5/6 are all made by Tohatsu. Same machine for all three. I bought the Mercury 6hp 4stroke, and paid extra for the "name". Nissan and Tohatsu sell the same model for less. They can vary the fuel, ignition and prop to get a different hp rating. My Mercury 6hp is "ok": been reliable so far, runs quiet, no smoke. I would rather have the shift on the front of the engine, or some option to set this up, but no luck. Mercury has a new 8hp model with shift on the handle.
The 8hp 10 hp engine
I will throw another variation into the 'how do they get 10-hp out of an otherwise 8-hp engine?' The answer is a takeoff on the 'de-tuning' myth. The lower hp motor often has a small tang on the throttle that simply restricts the throttle 'stroke'. Check the hp at rpm ratings between motors. Often the only difference between motors is that the higher hp motor is rated at a higher rpm(without the tang!). We could then start talking about hp ratings of dinghys and other boats and wonder where the same weight motors of different hp ratings fit in there?? Other than for risk management and liability purposes for the manufacturers........ but.......nevermind !!! fair winds, Dave
I will throw another variation into the 'how do they get 10-hp out of an otherwise 8-hp engine?' The answer is a takeoff on the 'de-tuning' myth. The lower hp motor often has a small tang on the throttle that simply restricts the throttle 'stroke'. Check the hp at rpm ratings between motors. Often the only difference between motors is that the higher hp motor is rated at a higher rpm(without the tang!). We could then start talking about hp ratings of dinghys and other boats and wonder where the same weight motors of different hp ratings fit in there?? Other than for risk management and liability purposes for the manufacturers........ but.......nevermind !!! fair winds, Dave
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