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Review of Nissan / Tohatsu 1 cylinder 4 stroke 6 HP engines MFS6BUL NFS6B2 performance data

I had the opportunity to work with a friend on his boat yesterday and I took the inline scale and a tachometer with me to test the performance of the engine in a static thrust test. We also did this with both the stock 8 pitch prop and a 6 pitch prop.

The tachometer is a Sendec unit good to 7000 rpm in 10 rpm increments.
The scale is a 3000 lb loadcell scale accurate to the nearest 1 lb increment.

I have been wanting to do this for a while as I have the same engine only marketed under the tohatsu brand and it has run weak since I got it. I had assumed that there were problems with my engine but based on the test results I think that there is a much larger issue.

The Nissan engine produced identical test results in RPM and thrust for the static tests with both the 6 pitch and 8 pitch props as my Tohatsu. Both engines with the 8 pitch prop could only turn 3700 to 3800 rpm and produce an average 124 lbs of thrust. With the 6 pitch prop they both turn about 4300 rpm and produce an average of 165 lbs of thrust. With the 6 pitch prop this does produce more thrust at low rpm and in static tests. However on the water this does not equate to better high end performance. The drop in pitch actually needs the engine to turn more rpms to maintain the same speed at the top end. Unfortuanatly even with a 6 pitch prop the engine does not produce enough power to even match the manufactures specified nominal 5500 rpm.

For this engine to output 6 hp it has to be turning the prop at 5500 to 6000 rpm. On the water not tied to a dock the engine will produce a little more rpm.. It will with the 6 pitch prop get to around 4700 rpm. This is still 800 rpm below the 5500 rpm nominal and 1300 rpm below rated max rpm. The difference in 800 rpm on the thrust produced is large, 1300 is simply huge.

My conclusions based on these tests is that Tohatsu/Mercury/Nissan all the names this engine is branded under are over reporting the power produced. Their 6 hp engine produces approx the same output as a 4hp 2 stroke engine.

When I replaced my old 4hp engine with this one I was looking for more power, better fuel economy and queiter operation.

1. Power

The power is the equivalant of a 4hp 2 stroke engine based on static thrust tests (based on testing two engines-one Nissan and one Tohatsu) at the dock. On the water on the same boat that the 4hp engine was pushing the week before , the boat actually lost about 10% of its through the water performance. Going from a top average over the water speed of 5.76 knots to 5.35 knots. I had actually lightend the boat during this time period also in cleaning out a bunch of stuff that had accumulated on the boat. My expectations were sadly let down with this engine. It not only doesn’t give me the extra safety margin I had looked for in a engine 50% more powerfull than my old one it actually is just slightly less powerfull.

2. Fuel Economy

I have to give the new engine top rating for comparative fuel economy. A three gallon tank will give almost 30 nautical miles range with the new engine. This is more than twice the range I had with the old engine. It meets the stated .5 gallon per hour fuel consumtion give by the manufacture.

3. Noise and Vibration

I was expecting a much quieter operation with the new engine and it failed to give that. It is almost as loud as the 2 stroke at WOT (wide open throttle) which is the normal operating speed needed to fight the currents here. Also the engine vibrates even more than the two stroke. The Manufacture told me that this is normal as it is a one cylinder engine. The vibration is bad enough that it vibrates the whole boat at speed and if holding it the engine tiller handle will numb your hand after a while becuase of the vibration.

Another effect of the vibration and a badly designed friction adjustment on the unit is that it will not hold itself straight unless you hold onto the tiller handle. ( the friend with the Nissan version reports the exact same issues) At low rpms the torque of the engine running will instantly turn the engine  to the side if not held and at WOT it will gradually twist sideways. For those in dingys and such that use the engine to turn/steer with this shouldn’t be that much of an issue as you are constantly holding the engine tiller handle anyways, but on sailboats (which it is marketed to in the long and ultralong shaft designs) it is a major problem. We have a boat tiller or wheel that we steer with, not the outboard.  If not closely monitored it will introduce course changes when your not expecting it while under power.

I would imagine that this data holds true over the entire line of the 6hp engines having these model numbers. Mercury also puts these engines out but I don’t have the model numbers offhand. As to the 4 and 5 hp engines that are based on the same engine and chasis, I have no test data to say how they perform. I can only think that they will be quite weak, as well as having the same issues with vibration and noise.

MFS6BS, MFS6BL, MFS6BUL for the tohatsu’s
NSF6B1, NSF6B2, NSF6B4 for nissan

83 comments to Review of Nissan / Tohatsu 1 cylinder 4 stroke 6 HP engines MFS6BUL NFS6B2 performance data

  • Phil Piraino Windows Vista Internet Explorer 8.0

    I have a Nissan 4 hp I purchased in Jan 2010. Ive been having a problem with it and i cant solve it. When trolling the motor it will run fine for a while , than it will stall. Than it wont restart unless I change the Spark plug. The used plug has a black residue on it. Some of my friends told me to lean the mixture on the carb. How is this done since I cant find a mixture adjustment screw ? Phil

  • Phil Piraino Windows Vista Internet Explorer 8.0

    Thanks Scot for the advise on the 4 hp Nissan . Im having the Nissan dealership take a look at it next week. Thanks again .Phil

  • no problem.. i hope its a simple fix.

  • Peter Lawrence NEW ZEALAND Windows XP Internet Explorer 7.0

    New into boating… have taken all the rigging off a 14 foot fibreglass sailing catamaran. bolted 2 sheets of 2.4m x 1m marine ply sheets on top. added a transom at rear. fish finder. 4 rod holders, cooler bin, tool box and two old swivel seats. Still pretty light…….. any suggestions what sort of motor to throw on it? I am thinking a 6hp? I tried a 4hp Yamaha that pushed it along ok in the river but think another couple of horses would be handy out in the bay. Worried that maybe 4 stroke weight will tip it backwards? the twin hulls are not very wide at the back. I plan to set a longline from it, maybe a net? I have built a bracket under the deck that holds a 20l bucket into the water to hold ‘live’ bait when stationary. The front has a panel cut out that just fits a standard fish bin (also when stationary) I plan to have a toughened glass window sealed into the bottom so that it becomes a viewing window to see whats happening underneath when fishing near rocks etc. anybody done anything like this?

  • If the 4 hp didn’t satisfy you then you are going to need to go up in hp.. to check how the weight will affect it just get a bucket and put the same amount of weight that the engine and fuel tank will be based on the manufactures specs and the weight of how much fuel you plan on carrying and place the bucket on the boat where you will mount the engine. This will allow you to see how it affects the craft. obviously an old 2 stroke will be more powerful per HP rating than a 4 stroke as well as lighter. However your fuel economy will be about half of a 4 stroke. Old 2 stroke will probably be much cheaper as well.
    scott

  • Josh Windows XP Mozilla Firefox 3.6.10

    I have the Tohatsu 6 HP 4 stroke from 2006. I have a tach on mine (tinytach) and routinely get it up to 5990 rpm in my inflatable (about 20 mph on the GPS), I will note that this is when I am on plane, and not slogging through waves with 4 people in the boat, then I only get 3500 rpm or so.
    I am not so sure your test is actually valid, have you had it on plane?
    My engine has over 100 hours on it, runs great, and always starts.

  • it was a small rib that I tested on so it should be valid.. I did get it up on plane but it didn’t go nearly as fast as your describing. I would say the best speed I did was about 10 or 11 knots. however I didn’t have a gps with me doing the dingy test.

  • dave Windows 7 Internet Explorer 9.0

    I bought the 2011 6hp tohatsu sail pro 25inch shaft and can’t get full rpm range out of it. It is pushing a 2100lbs macgregor sail boat 1976 25foot. I am happy with the motor because it pushes the boat fast enough to get to sea, Im in san diego and mission bay channel can get rough sometimes. I was thinking about trying a different prop to get more rpms, but if the prop I have now works will a different prop get me more speed?

    I am happy with the weight, 58lbs, speed is ok but we are always looking to improve. Going to try and change the prop. Electric out-put 12V 60W 5A.

  • You will never get full specified power out of one of these engines but if your mostly happy with what it actually puts out then it will do well for you.. We saw significant performance increases when we went to the 5.99 pitch super high thrust prop. We did gain a bit of rpm and the torque was amazing starting and stopping the boat. We also picked up fraction more speed at the top end with it. Unfortunately it still was a 1000 rpm under rated maximum rpm that would have given us the full 6 hp.

  • BDFlorida Windows Vista Internet Explorer 9.0

    I have a 2007 6hp Nissan NSF6BS1 with factory prop on my 2007 Mercury 340 Hypalon inflatable. The boat gets on plane with 2 adults, light gear (full cooler, emergency supplies, misc), & full bimini. GPS speed 13-15 MPH @90% WOT. Engine weight is a key priority as I transport engine from car to boat. Vibrations are higher than expected. Better now with a foam insert from an electric trolling motor on the tiller (closed cell AC insulation should work just as well). Motor is quieter than equiv 2stk on my friend’s boat. However, it runs much quieter at 90%vs100%WOT. Gas consumption is amazingly low. Overall, I am pleased with motor. I am planning on moving up to 9.8 hp as I anticipate the addition of a teenager. Will also try slight choke with current 6HP at 90% WOT as recommended previously. Was considering another Nissan/Tohatsu as light weight is paramount. Boat is rated for 15hp. recommendations welcome.

  • I think other than the weight of the motor you will like the 9.8 much better as it is a 2 cylinder and runs very smooth.. I have never tested them though to see if they can meet rated horse power like the 6hp engine. Honda makes a great engine in that range.. though it is a bit heavier than the tohatsu.
    scott

  • Jeff Windows XP Mozilla Firefox 11.0

    Waking up an old thread. The Tohatsu/Nissan/Merc 4hp,5hp,6hp are all the same exact motor. The only difference is the car. You can stick a 6hp Tohatsu carb on a 4hp motor for about $140 and turn it into a 6HP motor.

  • Yep they are the same motor. However there is differences in some of the lower units such as short, long or super long shaft. The super long 25 inch shaft for sail boats only come on the 6hp engine. I have heard of people just changing out the jets on the carbs to change the engine from a 4hp to a 6hp.

  • Sir

    I just purchase a 2003 Nissan 6hp 4stroke NSF 6A2S. IT WAS STILL IN THE SHIPPING CRATE THEREFORE NEW.

    MY QUESTION; Is there any differance in the 2003 Motor as opposed to the same motor made in 2011

    THANKS, BILL

  • I honestly couldn’t say Bill, I haven’t seen the newer ones. However in a quick perusal of the web I see that there are some new features on the 2012 model such as longer handle, integral fuel tank with external fuel tank port and a couple of other features. However I don’t seem to see any revolutionary changes. I think the basic engine and carb are probably identical. You could give internetoutboards.com a call and ask them. They have always been very good about answering technical details.
    Scott

  • Walt Linux Safari 534.30

    How do you think the tohatsu 6hp compares to a suzuki 6 hp , both are four strokes

  • Walt,
    I haven’t every actually used a suzuki 6hp so couldn’t give a good answer to that.
    scott

  • Ken Windows 7 Google Chrome 20.0.1132.57

    Just purchased the Nissan 6 hp short shaft with the internal tank for a 12 foot aluminum boat for use on a lake. I am still in the 10 hour break in period and not running it above 75% power. I already see little difference in the RPM between 60% throttle and 75%. It just does not have the torque to move the boat and get the RPM up to the rated range and power. I think the builder is a little overly on the HP rating to the engine for normal use. It will get the boat up on plane with one person but not 2. It starts fine on second pull most times but do not use the choke at all unless it is cold out. My engine floods real easy (1 pull) and then it takes 20 minutes to start. The engine does vibrate as it is a single cylinder and that is to be expected. Overall I am happy with the Nissan 6 HP as I bought it for the fuel economy, 4 stroke, and lower weight that a 2 cylinder.

  • Magne NORWAY Windows Vista Internet Explorer 9.0

    To move a heavy boat with these motors (Nissan/Tohatsu/Mescury 4-5-6) use the SailPro propeller Tohatsu part 399B64512-1. It has a much larger blade area and will produce more thrust at low speed.

    The standard propellers are designed for light boats and relatively high speed, like this: http://www.youtube.com/watch?v=Yo2PtXj_OIQ

  • Hi Magne,
    If you read the whole exhaustive thread and article you will see that I did use one of these. It’s what I have on the engine currently. It helps a lot but still doesn’t allow the engine to meet its specified rpm range. If your going to use this engine then the super high thrust low pitch prop is what you want.

  • Jimmy Windows 7 Google Chrome 26.0.1410.64

    Have these engines you’ve tested been broken in properly? If not, that may be the cause for the low power output. How was the compression?

  • Yes they have been broken in properly. Compression is good.

  • wendy Linux Safari 534.30

    I have a brand new (out of the box) merc 6hp 4stroke on a 10’6″ inflatable boat. The first month l was very happy with the speed l was getting out of the motor. Two months into ownership, the motor is only running at 1/8 the original speed. In naugtical language I’m gettin about 60 rpms instead of 6600. Why is my motor so slow now?

  • I haven’t had that issue.. I would check your oil levels. If you have run it with out enough oil you might have damaged the rings on the pistons and have low compression now. The other thing to check is the carb.. runs some carb cleaner or fuel treatment like seafoam through the gas and see if after a tank of treated fuel it starts running better. Past that I would take it to a dealer. Actually if it is brand new I wouldn’t mess with it but take it to a dealer/service center now. It is under warranty the will look at it and fix it for free.

  • JB Windows Vista Google Chrome 29.0.1547.57

    FWIW, Tohatsu/Nissan now offer a steering lock kit that locks the motor in place and allows the boat to be steered by the boats rudder. Takes about 5 minutes to install. Once it’s installed, the motors tiller cannot be used to steer, only the boats rudder. The “friction” knob that comes on the motor isn’t intended to lock the motor into a fixed position. Its only intended to tighten the friction it takes to turn the motor.

  • Joseph Burgdorf Windows 7 Google Chrome 39.0.2171.99

    Will boring out the carb jets on the Nissan 4 stroke 6 HP engine increase the fuel supply sufficiently to get more RPM’s and HP?

  • I believe it would but that is just a supposition on my part. I haven’t tried it and I am sure it is an at your own risk proposition. The 4 and 5 hp engines are identical to the 6hp one other than the carb’s. I think it is just different sized jets in them. Other than that they are the same engine as I understand it.

  • John Mac OS X Safari 600.1.4

    Ok so Iam considering buying a 2007 tohatsu 6hp motor for my dingy the guy wants 600.00 bucks is it worth it? Thanks

  • if it starts easy and runs smoothly then yes it probably is worth it. They are 1400+ new or were. I would still try to dicker and get the price down a bit more I would be happier paying 300 to 500 for an 8 year old motor but they are reliable engines and just sip fuel.

  • Larry Windows 7 Mozilla Firefox 38.0

    I have a new Tohatsu MFS6C with ultralong shaft, and have several observations about noise and vibration.

    1. One easy fix that made some improvement was to prevent the motor cover from vibrating. The forward catch and aft clamp have no adjustment. Sound was leaking under the loose cover, and its vibration also made a buzz. The fix was to wrap the forward catch with 7 or 8 wraps of rigging tape (epoxy mastic tape) for snug fit.

    2. The big problem is that the vibration isolation system between the drive shaft housing and the mounting bracket is poorly designed. The big rubber bushing between them may (or may not be adequate). I think the problem is that clamping device that provides steering friction is all metal, and it is a vibration short circuit between shaft housing and the bracket.

    I have this motor on a sailboat, so I need to have the friction clamp very tight — which is the worst situation with this design. You can see photos of the rubber bushings and the clamp in this blog: http://tillerfix.blogspot.ca/. This guy wrapped the clamp with Sunbrella fabric (and removed grease) to get tighter clamping. It may be possible to use some sheet rubber instead to dampen the vibration somewhat. It wouldn’t be much thickness, but may help some.

    3. Vibration transmission to the transom is through the tilt bolt and the two forward-facing legs at the bottom of the front half of the swivel bracket. The legs press against the thrust rod (that spear bolt with the toggle on the end that you use to adjust tilt angle), and I have just made a modification in this area. A pieces of the rubber fuel line that came with the engine is are a perfect fit over the spear bolt. 3/4″ long pieces fit well between the main sides of the bracket and the latch that locks the tilt for reverse gear. I filed off the tips of the latch (just a little – it doesn’t take much) to accommodate the thickness of the hose, so the latch will close and so the shifter can go into reverse. Hose I found at auto parts and hardware stores are too thick; the Tohatsu hose is perfect for this. I haven’t tried this yet. It may help some, but the main tilt bolt will still conduct vibration. Also, the spear bolt is metal-to-metal in its holes, and that could still be a source of noise.

    4. The problem is with the basic design of vibration control system. Tohatsu may be able to make some improvement with minor changes if it comes out with a D model. This would be to provide rubber isolation at the friction clamp, spear bolt and main tilt bolt. Look, for example, at how much isolation is provided where the tiller handle joins the motor housing. These other places need isolation as well. Better yet would be to set the motor back a few inches from the mounting bracket, with a very well isolated tiller yoke in between, as is done on two-cylinder engines. On the old Honda BF8A I just replaced with this motor, there are two vertical isolators and one thrust isolators between the yoke and the motor head, and two more isolators lower down between a leg on the yoke and the motor leg.

    The vibration of this motor is, I think, not so much due to it one-cylinder configuration as it is to the design of vibration isolation. And this relates to the noise level, too; from resonance in my boat as well as from the motor & its bracket. Some of the noise and vibration transmission probably also comes from the propeller, but for that the solutions are the same.

    If this is really going to be called a “SailPro” Tohatsu’s choice among these improvement options is crucial in my view. Sailboat motors need to be able to run many hours on end without discomfort and without potentially damaging the boat (mine wooden, and old).

  • Wow.. nice write up… I never had an issue with the cover vibrating so that’s a new one on me, but the rest of it is something that I never thought about as far as the vibration went. That engine does vibrate a lot. I can tell you gave this about as much attention and thought as I did to the rpm’s and hp issues :)

  • Larry Windows 7 Mozilla Firefox 39.0

    I put the motor back on the boat this weekend, after having it off for the first 20 hour oil and lube change and making two modifications. First, I added the two bits of rubber hose on the thrust bolt (see item #3, two messages above) so that hopefully less vibration would be transmitted to the transom. Also, I took my 8.3 inch diameter, 6 inch pitch to a prop shop and had the pitch reduced to 4 inches.

    The results are much less vibration, but still more than I would like. The prop modification got my WOT RPMs up from the previous more or less 4950 RPM to the 5500-5600 range. My earlier tests were in flat calm, reaching a max. of 5.3 kts. Yesterday I got 6.4 kts downwind and 5.4 kts upwind, so an average of 5.9 kts. RPMs were the same on both legs.

    I would like to reduce the prop pitch by another 1″ or 1.5″. That should give me 6,000 RPM or a bit more, respectively (not that I would use more, but that cushion would be nice). I have a TinyTach (inductive tachometer) on order. (I used a laser tach, with motor cover off, for the tests.)

    Also, if I can add some rubber vibration isolation in the swivel clamp, that should further reduce vibration and noise and will hopefully make the clamp more effective.

    This is with a wood lapstrake Folkboat. 25.2′ LOA, 19.7′ LWL, 7.2′ beam, spec. min. displacement 4250 lb (so maybe 4600 lb gross, as tested).

  • That’s nice to know about re-pitching the prop. That is good performance after changing the pitch for that boat. I will have to try that and see what happens on sea puppy if I ever put her back into the water. :) right now I am still in big boat land with our Downeaster 38 cutter.

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