FourStorke vs TwoStroke

DJL · 12 November 2002, 18:47

Here are my findings on the topic, they will only really apply to mid range engines, as there isn't the option of hightech 2-strokes, such as optimax.

Situation: I recently changed from a Mercury 60HP 2-stroke (100kg) to a Mercury 60HP 4-stoke EFI (112kg)

Noise: The fourstroke is much quieter throughout the RPM range. A normal conversation can now take place at full throttle.

Top Speed: Surprisingly my top speed has increased by 1/2knots. I am using the same pitch/dia prop. The engines do however have difference gear ratios/WOT engine speeds – leading to the prop on the fourstoke spinning slightly faster.

Power: Acceleration seems very similar (probably due to the EFI), although it’s difficult to tell though because you don’t have the raw power sound that you get with a 2-stroke. The boat performs much better at low to medium planning speeds, the fourstroke doesn’t labour and drink large amounts of fuel like the 2-stroke. The fourstroke is also very nice in rough weather, the smoothness of the power makes for a more comfortable ride when working the throttle. Having said that you do need to move the throttle further as the power is spread more evenly over the rev range. It will be intresting to try waterskiiing / ringing.

Fuel Consumption: Its hard to say at the moment because the engine is being run in and the RPM had to kept low and varied. However for the first time in the life of the boat a full payload of fuel kept the boat going for two days, even though similar hours/miles were covered. Will have to wait until I cruise normally for accurate figures.

Starting/Idling: Mainly down to the EFI and computer control, the engine starts first time, applying choke and throttle automatically. Over the first few minutes as the engine warms the revs drop to an idle speed of about 800rpm.

I am very surprised about how the fourstroke performs. I was ready to except a loss in performance for the fuel savings but I havn't needed too. From my experiences this weekend I have no idea why a 2-stroke would be bought over a 4-stroke – apart from initial cost. The 4/ is clean, quiet, more efficient, smoother, has loads more torque at low speeds and is just as powerful. Although they do feel quite difference to drive, I much prefer the 4/, and I’m not just say that cause I just bought one. I just hope I’m still happy after the bill for the first service.

JCW · 12 November 2002, 19:39

I knew you would not be dissapointed.

Enjoy.

Robert1 · 12 January 2004, 17:56

Daniel,

A year on and are you still chuffed with your engine? I have the same but yet to get it out on the water - yet to even run it in! Also, after your season, how have you fared with water sports and particularly fuel consumption? We have similar size boats so your knowledge would be very useful to me!

Thanks, Robert

Phil Davies · 12 January 2004, 18:43

Well done for dredging that thread up, Robert - you must have set one of those bleeping devices on your computer to remind you a year down the line

Seriously, though, it's a fascinating subject and particularly pertinent in my case since I'm currently dithering over whether to fit a Suzuki 50 Efi 4-stroke or Evinrude E-Tech direct injection 2-stroke to my 4m Searider. It should be pointed out though that a lot of Daniel's comments about 2-strokes are not necessarily applicable to direct injection technology.

simmons0 · 12 January 2004, 20:02

PD wait too see about the E-tecs. If heard only good things about them, they are tiny! weight very little, should give comparable fuel consumption but wait for them to be throughly tried and tested before buying.
The fourstroke is a safe bet.

gtflash · 12 January 2004, 20:44

after my visit to london boatshow, all the gumf says that optimax, hpdi etc etc are very fuel efficient and the figures the suggest compare with 4stroke. But i have a friebd who has a modern 2strke rude and although it is very cheap on fuel he seems to be constantly putting oil in it. Surely that outweighs the cost making 4stroke a winner again??

ta gt

DJL · 12 January 2004, 21:02

The engine has been great and even without the fuel savings it would have been worth the money. Generally its nice just to have an engine that’s quiet and starts instantly. Plus the extra few knots ain't bad either.

Fuel consumption has decreased by about 35%, giving around 2 to 2.4 nmi per litre. If you push it hard, 5500->6000 RPM it drops to around 1.7/1.8nmi per litre.

Water sports have been great - I started to learn how to wakeboard this yeah. The boat has loads of pull in it, in fact you have to be quite gentle with the throttle, much more so than with the old two stroke. Its also noticeably easier to get the ring on the plain too. I do have a stainless prop now though.

It was interesting to read what Pitkis wrote in the gallery about the Finnish Atlantic 21 being fitted with a pair of Mercury F60s. I will be intesting to know how they get on with them.

DJL · 12 January 2004, 21:37

Quote:

Originally posted by gtflash
But i have a friebd who has a modern 2strke rude and although it is very cheap on fuel he seems to be constantly putting oil in it. Surely that outweighs the cost making 4stroke a winner again??

Quicksilver 2 stroke oil adds about 4p per litre - a saving of £1 per tank of fuel used (25L)

Rogue Wave · 13 January 2004, 10:34

Do the maths

Most rib users are weekend warriors, and then mostly in the summer, spring and autumn. so the average boat only goes out for two days a week say for 30 weeks a year (bull, it's more like 15 weeks a year). Check your logs and you'll se what I mean

If your cruises average a 100 miles a day that's 3000 miles a year tops. The difference in performance betwen a two stroke Opti and a 4 stroke is marginal say + or minus 5%. given that you get about .8 of a ltre per mile and that 4 strokes were marginally more fuel efficient and adding a further !% for 2 stroke oil.

The four stroke 3000 miles at . 8 litres per mile = 2400 litres
The two stroke (opti) 3000 miles at .84 litres per mil = 2520 litres
So the 2 stroke on 3000 miles pops 120 more litres of fuel.

Thats about £90:00 a year extra in fuel for a 2 stroke. if your 4 stroke was just a grand deared than the new technology 2 stroke then you are only going take 12 years to recover that grand

If on the other hans you are a Dive Club, River Police, Sail Club
or small ferry operator then 4 stroke has got to be a winner if you are doing slow speed stuff all the time.

Manos · 13 January 2004, 10:59

Stuart I am in agreement with you and there were many threads debating this issue I remember this one

2 vs 4

In general I think if economy and weight are the only (or the major) issue, then it does not worth the trouble of buyng a 4 stroke which is more expenssive than a 2 stroke.
If however, there other issues such as less noise, slow speed at long periods of time i.e. dive club as you mentioned (that's it really can't think of anything else) then a 4 stroke is a serious consideration.

In any case I am sticking with 2 stroke engines whatever else is going on (call me old fashioned and all that)

PS I think that 100 miles average a day for a private individual is quite a bit (as you say the very VERY max). Better do your sums for about 40-60 miles tops.

PS Is it also correct in saying that in smaller engine size (50-110 bhp) there is not a big (or not at all) difference in consumption?? Just asking

The Jackeens · 13 January 2004, 11:24

rogue,

Is the small differance in fuel consumption only at 3/4 cruise speed. At wot is the differance alot more, doesn't the modern 2 stroke act like a normal 2 stroke and suck in tons of fuel ?? I remember someone saying that to me (i think).

Also how much oil (cost) over 3000 miles

paul

DJL · 13 January 2004, 11:45

Stuart,

Don't forget we are talking about the mid range here and therefore don't have the choice of opti/HPDI etc yet.

Its not just saving money on fuel its the extended range that comes with it. I save about £12 on a normal day, plus I get another >40nmi range out of my tanks.

It may be different further up the power scale but I would never ever buy a 2-stroke in the 40/60HP range again. Plus the 2-strokes are still noisy and smelly, which every technology you get.

Rogue Wave · 13 January 2004, 16:18

Hi Daniel and Paul.

Hmmm 2 strrokes are noisy and smelly....agreed but enough of the good points.

I agree that medium 2 strokes engines are better being four strokes, but the new technology is getting down into the 90 hp region now. your point about extended range is noted however what if you had a 150 4 stroke which guzzled more than a 150 Opti (which is actually quite likely)

Paul The oil consumption is a good point and for 3000 miles
you would need 25.2 litres of oil and that's about 120 quid. Although the 3000 miles is a generous amount of mileage.
but say you needed a litre every 100 miles then thats about £150 .

Paul I'd be very interested to know how many miles you tooz did this year as you are never off the water and that would give us a good rule of thumb.

I push my engines quite hard and I think all engines consume more when the throttle opens up. However the Opti is stunning on fuel. when we went to Yarmouth and back that night we burned about 40 litres. which I think is very reasonable.

I am not attacking Daniels engine I think he bought the best engine around at that size. I also think your is an excellent engine, but they have a 75 Opti on the way

Robert1 · 13 January 2004, 16:21

I think the new E-tecs give the midrange 2strokes the direct injection technology of larger engines. However, the F60 is EFI anyway (not quite direct injection, but better than carb).

Also an often overlooked point I feel is that fuel tanks on boats (taking the midrange 4stroke engines) are never large. This is where a 4stroke would be preferable as you can go a whole days boating without having to fill up half way through! This was certainly one of the factors that made me choose a 4 stroke. After all, 60hp is 60hp whether its two or four stroke.

Prop selection is surely more vital when it comes to performance so why not have the right prop for performance and have the 4stroke for a uninterrupted day on the water?

Robert

Rupert Bear · 13 January 2004, 16:48

I have never run a 4 stroke so have no experience of them, however I only use around 1lt per mile at WOT with the boat fully loaded with 4 folk, 4 sets of dive kit and 8 cylinders.
In the future I may consider a 4 stroke mainly for the lack of noise but I like the ability to strip and maintain the 2 stroke, something I am being told is not practicable with all the black boxes on the current 4 strokes.

Rogue Wave · 14 January 2004, 12:16

To be honest ,and not wishing to compromising my memebrship of the 2 stroke supporters club, I must say that the new technology outboards are as conplex as a fourstroke in terms of electronics and injection rails. etc

Phil Davies · 14 January 2004, 12:24

You've had a busy week on the forum Stuart with all these engine threads going on! Keep it up, your advice and experience is always well worth listening to!

Rupert Bear · 14 January 2004, 15:09

Quote:

Originally posted by Rogue Wave
To be honest ,and not wishing to compromising my memebrship of the 2 stroke supporters club, I must say that the new technology outboards are as conplex as a fourstroke in terms of electronics and injection rails. etc

My outboard has one black box for the EMS, one of the advantages of a, how do I say it, more elderly motor

Not being able to strip and maintain myself is not my cup of tea.

Rogue Wave · 14 January 2004, 18:32

Agreed Mr Bear,

I feel a lot happier servicing and maintaining the Yamaha 3 pot 70 than any of the other ones. In fact it's the only one I haven't broken lately