Real World Testing 40hp 2 stroke vs 4 stroke

[miles]

Hi

I've been a member on this forum for almost 10 years, posting very little, but rather reading and absorbing as much knowledge as possible. I have a passion for semi-rigids and have had one for the last 10 years, in conjunction with my fibreglass boats.

I did this real world test for my local South African Boat Fishing forum and thought that i would share my findings here.

Makes for interesting reading:


When the discussion of 2 stroke vs 4 stroke is raised, there are a few common well known theories that we mention. The general consensus amongst boaters is that a 2 stroke has better performance, whilst a 4 stroke offers better economy, but lacks the grunt or low down hole-shot of a 2 stroke.

I can attest to this theory, as when i still drag raced motorbikes at Killarney Race Track, my buddy's would run 400cc 4 stroke motorbikes against 250cc 2 stroke bikes, and the 2 stroke bikes would ANNIHILATE them!! We all knew that 2 strokes were faster, even though they had smaller engines.

With the advancement made by the modern outboard manufacturers, has the PEFORMANCE gap been made smaller or is there still such a big difference?

I was in the perfect position to test this. I had aquired a 5.0m Gemini Semi Rigid and had fitted her with a 40hp 3 cylinder pull start Yamaha 2 stroke. My wife wasn't too impressed being asked to pull start the motor, even though it started with half a pull!! So, i was asked to look for a motor with electric start. As luck would have it, a second hand Honda 40hp electric start tiller steer motor came my way, at a VERY good price, and i acquired the motor.

My tests were to determine the PERFORMANCE of the motors.

0-10 knots. I slipped the boat into gear, then idled for a minute or so and then opened the throttle completely. The time it took to get to 10 knots was then recorded. This was repeated 15 times, alternating runs WITH the slight swell, as well as against the slight swell. The average of these times were taken.

0-15 knots. I slipped the boat into gear, then idled for a minute or so and then opened the throttle completely. The time it took to get to 15 knots was then recorded. This was repeated 15 times, alternating runs WITH the slight swell, as well as against the slight swell. The average of these times were taken.

0-20 knots. I slipped the boat into gear, then idled for a minute or so and then opened the throttle completely. The time it took to get to 20 knots was then recorded. This was repeated 15 times, alternating runs WITH the slight swell, as well as against the slight swell. The average of these times were taken.

WOT (Wide Open Throttle). I made 4 runs, at full open throttle. Two runs were with the swell and two runs against the swell. The highest recorded speed on the GPS was taken.

Fuel consumption. I filled my fuel tank to the FULL mark. Did the testing runs and after the trip, refilled the fuel can to the FULL mark. Total fuel used was recorded as well as total distance travelled according to the GPS's trip meter.

[miles]

Yamaha 40hp 2 stroke outboard

This motor belonged to a very good friend of mine and was in storage for the last few years. I took the motor to Anchor Boat Shop, who serviced her and replaced all the necessary seals, impellor, cleaned the carbs, etc, etc. For the test, i installed a new set of spark plugs. Motor was in very good working condition.

Model: 1995 Yamaha 40hp 2 stroke Autolube 3 cylinder long shaft
Weight: 75kg's
Displacement: 698cc
Prop: 12p Yamaha Prop

Boat: 5.0m Gemini Semi Rigid
Weight: 180kg's
Fuel: 25kg's
Safety Kit: 20kg's

Crew: 200kg's

Total Weight of Boat, Engine and Crew: 500kg's







0-10 knots. Average 5.1 seconds

0-15 knots. Average 6.1 seconds

0-20 knots. Average 7.5 seconds

WOT - Top Speed - 29.1 knots

Fuel Consumption. Distance Covered 8.40nm, Fuel Used 7.1litres = 1.18nm/ltr

[miles]

Honda 40hp 4 stroke outboard

Because this motor is an electric start, i had to add a battery to the boat. My daughter insisted on coming along, so we had a extra passenger, even though she only weighs 15kg's........




Model: 2011 Honda 40hp 4 stroke 3 cylinder long shaft
Weight: 97kg's
Displacement: 808cc
Prop: 13p Honda Prop

Boat: 5.0m Gemini Semi Rigid
Weight: 180kg's
Fuel: 25kg's
Safety Kit: 20kg's
Battery: Deltec 60amp 15kg's

Crew: 215kg's

Total Weight of Boat, Engine and Crew: 552kg's









0-10 knots. Average 4.4 seconds

0-15 knots. Average 5.9 seconds

0-20 knots. Average 9.5 seconds

WOT - Top Speed - 28.4 knots

Fuel Consumption. Distance Covered 9.04nm, Fuel Used 4.1 litres = 2.2 nm/ltr





And after a hard days testing!!

[miles]

Some issue's worth pointing out:

When i fitted the 40hp yamaha 2 stroke to the boat, she was mounted a tad bit too high. During tight turns, she would cavitate a bit. It didn't bother me and i left it like that. When i fitted the Honda 40hp 4 stroke, it was also mounted a tad bit high. The Honda however doesn't go down as far into the water as the Yamaha and i would get the odd occation of cavitation under acceleration. I will cut the transom down a bit and refit the motor, to eliminate this cavitation.

The Honda motor is 22kg's heavier than the Yamaha 2 stroke. I also added a battery to the boat, which weighed 15kg's. Furthermore, i took my daughter with, which was another 15kg's of extra weight, which i did not have on the initial test with the Yamaha 2 stroke motor. The second test was thus done with 52kg's extra weight.

The Yamaha 40hp 2 stroke had a 12p prop on and the Honda 40hp 4 stroke had a 13p prop on. I have requested a 12p loan prop from Honda Somerset West and they have ordered one for me. I will redo the entire test when the 12p Honda prop arrives.

[miles]

Initial Verdict

Performance:

I was convinced that the 40hp Yamaha 2 stroke would outperform the 40hp Honda 4 stroke by a large margin. When i took into account the 10% increase in weight in the second test, i was even more sure that the difference would be much greater, in favour of the 2 stroke Yamaha.

However, when i started comparing the data, i was very surprised to see that the Honda 4 stroke was actually FASTER during the 0-10knots test!! The Yamaha 2 stroke 40hp did the 0-10knots test in an average of 5.1 seconds, whilst the Honda 4 stroke 40hp did it in an average of 4.4 seconds. That makes the Honda 40hp 4 stroke 12% FASTER in the 0-10knots test.

During the 0-15knots test, the two motor are very close to each other, with the Honda 40hp 4 stroke being marginally faster, at 5.9 seconds compared to 6.1 seconds for the Yamaha 40hp 2 stroke. The Honda 40hp 4 stroke is thus 3% FASTER in the 0-15knots test.

During the 0-20knots test, the Yamaha 2 stroke 40hp was CONSIDERABLY faster, completing it in an average of 7.5 seconds, whilst the Honda 4 stroke 40hp did it in 9.5 seconds. Here, the Yamaha 2 stroke 40hp was FASTER by 21% in the 0-20 knots test.


Top Speed:

The Yamaha 40hp 2 stroke had a top speed of 29.1knots, whilst the Honda 40hp 4 stroke had a top speed of 28.4knots. That makes the Yamaha 40hp 2 stroke 2% faster on top speed. What is however impressive is that when testing the honda, the boat was 52kg's heavier.


Fuel Consumption:

The Yamaha 40hp 2 stroke used 7.1 ltrs of fuel to cover 8.40 nm, which equates to 1.18 nm/ltr. The Honda 40hp 4 stroke used 4.1ltrs to cover 9.04nm, which equates to 2.2 nm/ltr. The Honda 40hp 4 stroke is thus 46% LIGHTER on fuel when compared to the Yamaha 40hp 2 stroke. No surprise here, as that is what we all expected.


Conclusion:

This is NOT what i expected. I went and did a bit more research and found that Honda has BLAST on their motors ( Boosted Low Speed Torque, or BLAST, improves acceleration at low speeds. A quick movement of the throttle control activates the BLAST® system, advancing the ignition curve aggressively. "Hole Shot" is vastly improved as more horsepower gets the hull up on plane quicker. - as per honda website) This explains why the acceleration from 0-10knots and 0-15knots actually exceeds that of the 2 stroke Yamaha. The two stroke however keeps on powering on, when the BLAST system on Honda stops, which is why the 0-20knots is so much quicker for the Yamaha 2 stroke.

Not only has the newer generation 4 stroke caught up to it's 2 stroke counterparts in holeshot/low down acceleration, it has actually surpassed them!!

The fuel consumption figures are also not a true reflection of things, as most of the time the motors were tested at WOT, which is where a 4 stroke offers its worse fuel economy. If one was to cruise at 16-20 knots, the consumption would be MUCH better for the 4 stroke. Regardless, the economy is still BRILLIANT, saving you 46% of fuel at a MINIMUM.

Note:
I am in no way affiliated to either Yamaha or Honda. I do however have to say a BIG thank you to Neil and Dudley at Anchor Boat Shop for assisting me in rigging my boat with the Yamaha, as well as for their years of PHENOMINAL service!! GREAT guys and they will try their utmost to assist ANY boater. I can HIGHLY recommend them for all your Yamaha needs. Similarly, Jeremy and Andre and Honda Somerset West also offered AWESOME service and i have to thank them as well for assisting in the installation of the Honda motor to my boat. GREAT guys and would also recommend anyone wanting Honda's to go visit them. :mrgreen: :mrgreen:

[whisper]

Awesome post

[HUMBER P4VWL]

Good post but a 1995 2s vs 2011 4s isn't a fair test. 2s tech has come on leaps and bounds too!!

[Boatnomad]

Yes,really interesting post. Massive difference in Fuel Consumption and therefore boat-range.

[NSS]

As I've said before, I love my Honda 50. I was aware of the BLAST technology, though was a little sceptical as to how well it would work, but must admit that it seems to jump onto the plane when you whack the throttle open, and the fuel economy is exceptional.

PS. When you do the re-test, will you leave sleepy-head ashore so the only weight difference is the engine/battery?

[matt h]

Brilliant test but agree with HP .. It s not a fair test.. I dont mean that in a bad way so appologies i it came over like that.. Fantastic detail and effort!
I would like to see a test on a like for like set up.. A big well done for doing it!!

[miles]

Good post but a 1995 2s vs 2011 4s isn't a fair test.

I concur completely with this statement. However, this is the real world and that's the engines i had purchased. In a perfect world, it would have been awesome to test brand new engines against each other............

If this had been a test between the older 40hp carb model honda, from the same era, i have no doubt that the results would have been COMPLETELY different!! (i actually have 2x50hp carb model Honda's on my 18' cat and they are a bit sluggish out of the hole, even with low pitched semi-cleaver props on)

2s tech has come on leaps and bounds too!!

Yes and No on this point. In South Africa, Yamaha has decided to drop the 3 cylinder 40hp 2 stroke yamaha from it's range and now only offer a 2 cylinder single carb 40hp 2 stroke. Bulletproof engines, made for hardcore, middle of nowhere use. Heavy on fuel, but VERY reliable. The technology on the yamaha smaller class 2 strokes, ie. sub 100hp is pretty much the same as it was 15 years ago. Why mess with a winning recipe? hahahaha

Other manufacturers like Evinrude ETEC do offer direct injection on their smaller motors. Unfortunately, these motors are not popular here and i actually don't know of a single one of my friends who have them on their boats.

We unfortunately only get a few models of Tohatsu 2 stroke, carb models, so there isn't much new 2 stroke technology in our country to compare the 4 stroke to.

As I've said before, I love my Honda 50. I was aware of the BLAST technology, though was a little sceptical as to how well it would work, but must admit that it seems to jump onto the plane when you whack the throttle open, and the fuel economy is exceptional.

I also read about BLAST and LEAN BURN. All the modern manufacturers have some sort of new name, which the advertsing guys push hard. It usually take it with a pinch of salt and dont believe everything i'm told. In this case, the BLAST certainly does work!! It would be very interesting to test a 4 stroke, like say a 40hp Suzuki or Yamaha which does not have blast, just to see what the difference really is......

PS. When you do the re-test, will you leave sleepy-head ashore so the only weight difference is the engine/battery?

I will do even better!! I will get my buddy who did the first test with me to tag along. Unfortunately, he was spearfishing up the coast off his rib, so he wasn't available.

In theory, since the motor uses almost 50% less fuel, it means that theoretically i can carry 50% less fuel. Not a major saving in weight, but it will be close enough to offset the weight of the battery. Then the only difference is the physical weight between the two engines, which is 22kg's..........

Just for interest sake, sleepy head was 5 months old when she went 30nm offshore with me on my big boat.......... Besides, all the boats i own ACTUALLY belongs to HER!!

Brilliant test but agree with HP .. It s not a fair test.. I dont mean that in a bad way so appologies i it came over like that.. Fantastic detail and effort!
I would like to see a test on a like for like set up.. A big well done for doing it!!

As mentioned above, i COMPLETELY agree, but it's what i had at my disposal. I've been thinking about this type of test for a while and there are just soooooo many variables that i didn't take into account:
- the yamaha has a 12p prop, the honda a 13p. BUT, the Honda comes standard with a semi-cleaver prop, the yamaha not.
- even if both motors have the same size props on, the gearbox ratios are different, which would skew the results.

There is a few GENERALLY accepted facts that i've come to find to be completely inaccurate. Take my old 6.5m Hysucat for example. It was powered by 2x50hp Yamaha carb model 4 strokes. Boat was 2 years old when i bought her. Did 33knots top speed, whether boat was empty or had 600kg+ of fish and 4 crew onboard. My buddy had a 6.5m Mako rib, which was actually a copy of the PHANTOM hull from your side of the world. He also had 2x50hp 4 stroke carb model Yamaha's, but his motors had probably 2000hours+ on them. We would run out to our tuna grounds together and fish/spearfish together, so our trips were almost identical. Usual cruising speed was 18-20knots. According to the Hysucat marketing guys, it's a cat AND has foils, so it would be X% lighter on fuel than a comparable monohull rib of similar size. In reality, i was 30% HEAVIER on fuel than my buddy on his monohull!! Finally figured out that my motors had to work too hard to keep the boat on the foils, which meant i was running at higher rpm's than my buddy, hence the heavier fuel bill............

Anycase, i digress too much!!

6.5m Hysucat and Mako(Phantom):








ps. My next step is that i want to test various props on my rig, and see what the real world differences is. ie. 3 blade vs 4 blade. Standard vs semi-cleaver vs cleaver. Allum. vs Stainless. Trying to keep in mind what your AVERAGE boater is looking for, ie. not just top end speed, but rather comfortable cruising speed and economy. (this idea was bred by my local Yamaha dealer)

[beamishken]

interesting results but surely this just proves what we all realy know that two strokes & four strokes deliver their power in different ways & at different rates

they are both 40 hp & at some point they will both produce that 40hp,they are nothing like comparing motorbikes which are rated as displacement not hp so a 125 cc 2 stroke is almost identical in hp to a 250 4 stroke although they are both totally different machines to ride

the two stroke/four stroke debate is more down to personal preference & type of use & my own opinion of what id use personally changes with the type of boat id strap the engine too

for a rib personally up to about 40/50hp id chose two stroke as smaller boats struggle more with the inevitable weight disadvantage of a 4 stroke but over that size id probably go for a 4 stroke as it would probably be on a larger boat which would carry the weight better & you would probably want to go further afield & the range becomes more of an issue

I think the 4 stroke/ 2 stroke debate will continue for some time to come as I don't think there is a definitive answer as its all about personal preferance

[kerny]

Cracking pic s miles and thats an "Awesome" Tuna

[Exe treme]

Great thread Miles. You might not post much but when you do, its a worthwhile read.
Treat yourself to a nice mid-00's 2-stroke and post more of the same please!!

[9D280]

If you are planning a re-test - other things to add to the mix:

- Diameter of gearbox / width of leg "in the water". E.g my Merc has a gearbox on a par size wise with my old Suz 25. My old Yam 55 had a gearbox I swapped with one off a 90! - the drag through the water is significant.
- Do some fiddling to get the two identically below the transom (prop shaft centrelines at same depth)

Hows about a long distance fuel consumption e.g. (assuming you have the tank capacity) an hour or known distance each way at WOT / 4500rpm / etc. I realise this will be a longer time to get meaningful results as you will need to get the tide & weather to be similar....

Also If the 2- stroke is pull start I guess it's not power trim? if so & the 4-st is getting that angle similar would also make the comparison more meaningful.

And to make a totally fair comparison can compare the purchase cost of the two - I guess you can still buy "oldschool" 2- strokes new in SA? Also then check do I need to replace the boat as well due to the extra weight of the 4 - streoke eclipsing the transom's max capacity! (not that I speak from experience or anything My transom is 110Kg max, but I have a 5m boat that clocks in at 420Kg fully fuelled....I'd love to try a back to back alongside an O-Pro with a 4- stroke 60.) But I digress.


Initial testing is fantastic and I totally for your efforts.



I did get a comparison (same hull, 2 engines) between a 1970 Yam 2 cyl and my "new" clamshell. The Yam was a long throw crank & had shedloads of Torrque. It was also manual trim. The Clamshell (arguably a similar vintage of base design) is 20 odd Kg lighter, less grunty at the low end but was (is still) a good 0.35L/NM less consumption than the Yam. (Largs in the Yam I could just make Greenock Princes Pier before it ran dry. I can now get to Helensburgh & almost back to Kip.....)

[two stroke mick]

A great Post. I think very well put together for the real world boater. Very useful for someone considering changing an engine. I would not get bogged down in gear box pitch etc not prop pitch. Run the correct prop for the engine and boat combo not the same pitch on each engine.

TSM

[PeterM]

Great post & test . and pics (I've family in Fish hoek )

I think its a very real test as the older ( much older) 2 strokes start to fail for one reason or another and are replaced by more modern 4 strokes.

I think things like eclectic start/ PTT/ noise and smooth running all play a part in decision making when weighing up a change.

The modern 2 stokes just don't seem popular in the UK ( and that from a big optimax fan) . I think the latest range of 4 stroke have overcome the weight issues of early ones ( just comparing my 2006 50 yam to a 2014 50 Honda is interesting) .

[miles]

Hi

Thanx for the kind words!!

Sorry for taking so long to respond........was out fishin' with the family! (no internet!!)








Here in South Africa, we have a very different set of requirements that we would look at when choosing our outboards. On our East coast, most of the launching is done through the surf zone, which can be dead flat or on the other extreme, MONSTROUS. In these type of conditions, your hole-shot performance is what is critical.






The East coast boaters have for years complained about the 4 strokes being too sluggish and MANY boaters will buy new motors based on this premise. With the simple testing that i've done, it clearly shows that in this particular case, the 4 stroke actually has better low down performance, which is contrary to what most boaters here in SA believe (myself included!!)

- Diameter of gearbox / width of leg "in the water". E.g my Merc has a gearbox on a par size wise with my old Suz 25. My old Yam 55 had a gearbox I swapped with one off a 90! - the drag through the water is significant.
- Do some fiddling to get the two identically below the transom (prop shaft centrelines at same depth)

9D280, both gearbox's were standard gearbox's. The bigger BIGFOOT gearbox's would make for even more interesting testing, as it swings a MUCH bigger prop, which should give better low down power. Both gearboxes looks the same to the naked eye.

Unfortunately, most boating shops fit the engines and its not always fine tuned for its application. I like my cavitation plates to be a bit higher than the bottom of my keel. This allows me to get better fuel economy, as there is less drag, as less of the motor is in the water. Both motors were mounted at the same height, as my transom is a fraction too high. This meant that they both were fitted as low down as possible, with the brackets of the motor hanging onto the transom.

Also If the 2- stroke is pull start I guess it's not power trim? if so & the 4-st is getting that angle similar would also make the comparison more meaningful.

Both motors are non-trim and tilt. Both were set to the lowest pin. However the honda's lowest pin is a tad bit higher up than the yamaha's lowest pin, but very, very close!!

And to make a totally fair comparison can compare the purchase cost of the two - I guess you can still buy "oldschool" 2- strokes new in SA?

I purposefully did not mention the pricing factor, as my testing was done to determine the PERFORMANCE difference between the 2 and 4 stroke motors. However, i did eventually go into the cost side of things, and even though the 4 stroke is more expensive to acquire, the 2 stroke was actually more expensive to service!! Remember, 4 strokes service intervals is 100hours, where-as 2 stroke's service interval is every 50 hours. Looking at a avid fishermans fuel savings, two stroke oil savings and service costs, it would take this boater almost 2 years to break even. Needless to say, this was based on our pricing and servicing costs. (prices i used was general list price on motors, so as to keep it fair) I then went one step further and looked at servicing the motors yourself, when your warranty runs out and the 4 stroke servicing costs for the year STILL worked out cheaper than the servicing costs of a 2 stroke for a year.

for a rib personally up to about 40/50hp id chose two stroke as smaller boats struggle more with the inevitable weight disadvantage of a 4 stroke but over that size id probably go for a 4 stroke as it would probably be on a larger boat which would carry the weight better & you would probably want to go further afield & the range becomes more of an issue

beamishken, that was my view point too!! However, when one considers how close the difference is weight really is, the difference is maginal. In this case, the motor weighs 22kg's more than it's 2 stroke counterpart. However, you'll be using less fuel, so instead of carry 30ltrs of fuel, you can now carry 15 litres of fuel, for a trip. The fuel saving alone almost cancels out the difference in weight bewteen the two. If one was really into saving as much weight as possible, you can also start and run the 4 stroke on a motorcycle battery, which is VERY light in weight.....

[Locozodiac]

Were both engines sitting at opt transom heights and running top rpm factory stated for each brand engine at wot ? Max HP is achieved near it's max rpm for a given engine to compare 40 HP to 40 HP in equal conditions as if you vere racing against each other.

Happy Boating

[Locozodiac]

Originally Posted by Locozodiac

Were both engines sitting at opt transom heights and running top rpm factory stated for each brand engine at wot ? Max HP is achieved near it's max rpm for a given engine to compare 40 HP to 40 HP in equal conditions as if you vere racing against each other.

Happy Boating

For a perfect test will need same 2 light boats, with both drivers weighting same with same amount of fuel for each one, just with a different 40 HP engine brand, both engines must be well height seated and trimmed to have boat riding paralell to water surface at wot. Doesn't matter if each one has a different prop diam or pitch or gear ratio as long both delivers full wot rpm factory stated for each model to achieve full 40 HP. Add flat calm no wind water conditions and you'll be racing equally to compare 40 HP to 40HP.

Happy Boating