hears one for the team, i am in the market to up grade my motor, i have decided to go yamahar for one reason only as there is not a lot difference between brands, yamahar have a much better setup on the tiller handle with all controls at your finger tips, the weight difference between the 2stroke and 4stroke is only 9kg so no real advantage there.
so here is the kicker which is better 2 stroke or 4 stroke

Smaller motors 2 stroke, Larger (90+) 4 stroke

Most smaller boats I have been in with 4 strokes have been underpowered, which can be fixd with a bigger HP, however there goes your weight and cost!!

Modern 2 strokes are nearly as fuel efficient and I personally think more reliable in smaller applications. Ie, they can cop a bit more punishment.

Yamaha! Agreed, THE BEST, all my motors will be Yamaha, Same as My Bikes!

Poly, if you want more power than you have now try comparing a 40hp two stroke to a 50 hp four stroke as the lack of acceleration power in the 50hp 4 stroke would make it equivalent to the 40hp 2 stroke so do your sums again on the weight difference 50hp 4stroke114kg ::40hp 2 stroke 84 kg making a 30kg difference to achieve the same Torque.

I tried out my 'new' 40hp Merc yesterday. What a buzz. It really powers the 4.2m quintrex at a high speed. I also trolled for 40 mins at just above idle speed, and it didn't foul up the plugs. I think I will need a sandbag up front though, when I go out on my own. My wife says a better option would be to lose some weight
I was really keen to get a 50hp 4 stroke, but I am very happy with the 2 stroke I got, and after an hour plus of running around, used less than 1/4 tank of fuel. The old 25hp ('76 model) would have used 1/2 to 3/4 of a tank.
So poly - I'm with 'The Chadd'. If it is a smaller motor, stick with the 2 stroke.

Sumo i asked the bloke about prop size for the two motors and he told me it would be the same for both motors, i do agree that the two stroke should have a better hole shot but over all the top end should be the same as they both have the same revs but i will check it out a bit more

You hear this all the time (2 strokes being more powerful than 4 strokes), it just doesn't make sense.
A 50 HP 2 stroke should be the same as a 50 HP 4 stroke.... end of story.

Judge Judy says, "If it doesn't make sense then it's not true".

Perhaps people are being fooled by the motors developing their power at different rev ranges?

If weight is not a factor and unlimited finances I'd buy the 4 stroke.

power is calculated as a MAX at the engine,

While they may have the same HP Reading they will not have the same torque! Which give the thrust to drive the boat forward, Thus the reason most 4's have smaller props.

Compare Cars to Diesel's

A HSV 5l V8 Might have Heaps more HP, But you would do better pulling a large load with a diesel with less HP (most semi's only have around 400 or less, where v8 HSV might have more HP but will never pull the load!

Some trucks still runs 2 stroke engines also due to the power curve of the engines!

Compar bikes also.

A 250 2s has less power but is quicker and can pull harder than a bigger 4s

Outboards have been rating HP at the prop for the last 20 years.


Sure, you can have different props and different gear ratios but at the end of the day 50 HP at one prop equals 50 HP at the other prop.


500 HP will outpull 400 HP every day of the week.
It's all in the gearing.


That's comparing apples to oranges, weight and gearing in different bikes changes everything.

If it doesn't make sense then it's not true

Ok, Ive trid to word it simply and simplified it to much!

My mistake on the engine and prop, however that make no differance, and the gearing also makes no differance to what we are comparing.

My point is that 2 stroke engine have a higher power output than 4 stroke engines with th same rated horsepower.

To start, Horsepower is simply a mesurment from made from torque ie:

Torque x RPM
HP = ------------
5252 (= 33000 foot pounds per min = 1hp , at 5252 HP and Torque are always equel)


Get a print out of the power and tourque curves of the 2 engines and compare them, See how much longer the 2s power curve is at full or near to full power compared to the 4 stroke.

While horsepower ratings may be the same they are simply a meausurment, 2s engines deliver the power (torque) in a differant way to a 4s, The power curve is held in a higher range for much longer simply because a 2 stroke engine makes power (torque) EVERY Cycle where a 4 stroke makes power every other cycle. While there is load on the engines the
2stroke is driving EVERY STROKE, wheras the 4stroke has a rest each cycle.

Large capacity engines improve on this with heavy flywheels and pistons which help to hold momentum, (ie trucks)

I can get MUCH MUCH More technical if you would like but most peeps (thats for you jumpy) would not understand.

a 500hp V8 Holden would get smashed by a 400hp Diesel SIMPLY Because the Holden motor could not hold it engine at full HP Due to th power only peaking for a very small rev range, where the diesel has a much longer peak. (unless you could hold the engine on the same revs for long periods which creates its own problems)

This equates to boats as you are on and off the throttle and thats where the 2stroke wins, UNLESS your in a big boat with Big outboards!

Hopefully Ive comvered this in slightly more detail, im busy and i have rushed my reply so i will re reaad it later and check!

Poly, if you believe that it doesn't matter just ask the Dealer which one he makes the most money from, The motors both have the same HP BUT there is a lot of difference in torque, as an example if you were going 50klms the two stroke will get on the plane a lot quicker than the 4 and be two kilometers away before the 4 stroke gets you on the plane,;; sure once the four is on the plane it will develop the same power and always be 2 klms behind BUT if you are only going 2 klms GUESS WHAT.

and dont forget

that that it all comes into effect everytime you are on and off the throttle to slow down for a wave or cause you dropped your beer!

Slower response time!

there are other things to consider other than hole shot, yes i do agree that the two stroke will have better acceleration but we are not talking about a race boat, with fishing as it's main roll i would think that the quieter the better and at idle the four stroke will be almost silent fuel should all so be considered, the little 30hp is capable of draining a 25lt tank in a 3hr session so i beleave thease things must be taken into acount, what do u think

you are upgading from a 30hp 2 stroke to a 40hp 4 stroke????

That changes things, as you should expect similar performance from the two engines,
however like you say, better fuel economy and quieter..

The 40hp 2 stroke will give you better performance but if the 30hp pushes it along fine
then the 40hp 4 stroke should be more than adequate.

Poly, it will also depend on your use of the boat, If your crossing bars or heading outside,
then more power the better. Especially when crossing bars when you might need the quick
respose of a 2 stroke. Though again, I didnt realise you were upgrading to a 40 from a 30
so It shouldnt be a problem..

no chad the power is not adequate that's why the up grade in the first place + the need for p t&t as she holds her head up to high when running into a chop.
at 4.1mts i will not be crossing to many bars, well maybe the odd pub bar
that is why i asked the question in the first place, now if i under stand what u are telling me the 40hp 4 stroke will be about the same as a 30hp 2 stroke in performance is that right or can i expect a bit more grunt, thanks :o :o

Never driven the two of them poly, but i know going from a 25hp 2 stroke to a 30hp 4 stroke was like going back to rowing!

the 30hp struggles to put the 4.1m boat on the plane with 3 medium sized people!
I must say though that it is VERY quiet and great for trolling and fuel efficiant...
But i have been caught in some big chop and it did not have the power to get over the waves when I would have liked..

Have you posted this on the Poly Forum and spoken with anyone with the same boat?

poly want a motor, whats the diference {price} of a 40hp - to a 50 hp 2 stoke if the price is not mutch I would go the 50 reason being you are not pushing the motor , making it work . and if you need to get out of some where in a hurry the power is there . always better to have more than not . and at normal working pace the motor is just huming along.

I'm with you Poly, hole shots, who needs them, certainly not a 4.1M tiller steer being driven by an old fart.
I'd turn the boat into a little centre consol while you have this opportunity of a new motor.
Have you thought about starting again with a whole new boat, there's a lot to said for boats with some shelter from the elements especially if you take your Missus out.

RDnR, do you think the 40hp 4 stroke would have a higher top speed than the 30hp 2 stroke?

Speed is irrelevant as it is to do with gearing, NOTHING to do with Torque or HP

What I am saying is that the response and power of the two 40hp's Is NOT the same,

And this can be important, NOT for hole shot speed but in the case where you need then quick power
in big chops or when crossing a bar, Better to have it when you need it than not to have it at all..

Calm down mate I'm only asking your opinion.

I would assume the 40 may have slightly more, depending on gears, prop size and hulls. However I beleive the 30hp 2 stroke would have better response.

Im Calm FED Just making my point clear.

Do you think that if there was water in the fuel tank that it would make a differance? ;)

i got this reply on the poly oners sight and i think itcovers it very well
As RBF noted, I have a 4.1/40 honda. The 4.1 carries my honda on the back no worries and I have 2x25litre fuel tanks, a heavy duty battery, extra decking and 15kg of foam filler, plus me sitting down the back.

Go the 40 yamaha (or whatever brand of 4st you have available) as your boat will be lighter than mine and will be quite nimble. I played with props, engine height and foils to get the max performance out of my boat and ended up with an 11pitch solas SS prop and permatrim - which runs out at 5900RPM with 2x85kg fishermen on board (plus all gear).

The permatrim is a no-brainer, bolt one on from new - they make a big difference.

Also think about a stainless prop. The SS significantly reduces cavitation and allows engine height to be increased at least one hole, which gives better lift.

I would say that 30hp is a bit light on for power.

Send me an email or phone call and I can try to answer any other questions.
_________________
===============================

yep . like I said pol even a 50 yamy would suit a bit more there if you want.

yours prob should have had a 40 on from start. and you might even have said . Iwouldn't mind a fifty just for that bit extra. and like i said you wouldn't be straining motor. whitch in turn last a lot longer

Judge Judy would not be impressed with this little gem.

What are you really trying to achieve from this upgrade Poly?


This guy has too much weight in the back of his boat, if it was set up properly he wouldn't need one.


Just because you read it on the net don't take it as gospel Poly, these guys weave their own web and convince themselves of lies.
Think about it, how does lifting the motor 1 hole give you better lift?
Smoke, mirrors and voodoo.

personally id say at around that size , id go for a 2 stroke,

FED i don't wont to get into a big discussion over this the idea about the permatrim is not to give better lift,there is a problem with the 4.1s as the horse power is increased towards maximum the boats have a tendency to porpoise and the permatrim solves this problem as i only posted 1 of the replies i received on the poly boat owners site all those running 40 horse power and above have recommended strongly that one should be fitted.
as for lifting the motor one hole i really don't know if this can be done or not.i will just have to wait and see how she performs with the standard 12inch prop.thanks for your input mate its very much appreciated.
HUSTLER 57 as i said in a earlier post the hole shot is not very important to me as i place a greater emphasis on our fishing,the additional stealth i will achieve with a 4stroke motor for me far out ways everything else

Stealth If you didn't go dancing around trying catch fish and have a more sensible aproach there's your stealth Iv'e seen you dance poly it aint pretty

STEVE i can only dance as well as the teacher can teach just ask SUMO

Orrrrr grasshoper , but you need more lessons

:drop the daks:

poly it's JG

Honestly I think you've been listenting to to much BULLSH*T from that guy on the poly site

He knows Sierra Foxtrot Alpha about motors or boat performance & he cares to debate me about the crap he's been telling ewe tell him to come aboard & I'll sort him out

ps ] SUMO & I R having a good laugh @ what he's told you

Stealth sounds like a plan to me Poly have you got a leccie?

The other guys are probably lifting their motors up to reduce drag and get more top end speed but the trade off is porpoising because lifting the motor starts to reduce the effect of the cavitation plate and they're putting permatrims on to counteract this.
Could these guys be Yankee revheads?

If I was buying a new motor I'd be looking for... quiet (4 St), smooth (4 Cyl) and power trim but I don't know if that configuration is available in the range you're looking at.

hear are the specks for the yammy motor i am buying i believe it will do the job nicely

SPECIFICATIONS



GENERAL
O/M Transom Height (mm/in) 533 (21.0)
Weight (kg) with prop. 96.9
Engine Type Inline 3 Cylinder
Displacement cm³ 747
Bore x Stroke (mm) 65 x 75
Output (hp/kw) 40 (29.4) @ 5500 rpm
Max. Operating Range (rpm) 5000~6000
Compression Ratio 9.87
Scavenging Single Overhead Camshaft
Ignition CDI microprocessor
Gear Ratio 2.0 (26/13)
Fuel Management 3 - Carb with Acceleration Pump
Oil Pan Capacity (litres) 2.0
Max. Fuel Consumption 15 l/h
Spark Plug DPR6EA-9
Steering 40° Each Direction
Gear Shift F-N-R
Exhaust system Through Propeller Hub (Jet)
Prop. Engagement Spline
FEATURES
Operation Method Tiller Handle
Lubrication Wet Sump
Starting System Electric
Tilt & Trim Method Wide Range Power Tilt & Trim
Prime Start™ Standard
Engine Stop Watch Lanyard Yes
Shallow Water Drive Standard
Alternator 12V-15A (M:6A (85W))
Rectifier Not Installed
Rectifier Regulator Standard
2 Pin Connector Not Installed
Start in Gear Prevention Standard
Overheat Warning Standard
Over Revolution Prevention Standard
Remote Control Box Not Installed
Speedometer Not Installed
Tachometer Not Installed
Trim Meter Not Installed
Propeller Standard
Fuel Tank Remote
Separate Fuel Tank Capacity (litres) 24 l
Emergency Start Rope Standard

CDI-E:CDI-Electronic Automatic
CDI-M: CDI-Mmicrocomputer
TCI: Transistor Controlled Ignition
Above specifications are subject to change without notice

J G as i said to FED the reason for the prematrim is to prevent porpoising and not to increase lift, however it will be a bonus i would think, as for the SS prop i will wait and see how she go's in stock trim before i start to change things

Poly, The Permatrim is a total waste of time and money, If the motor height is set correctly and the motor angle is correct, THERE IS NO way that the boat will Porpoise. I notice that you have Posted the Specifications for the 40HP four stroke. this motor has POWER TILT & TRIM so therefore you would not require a powertrim unit. and this motor would probably not perform much better than the 30Hp two Stroke you have. Have a Good look at all the engine specs you have listed there is NO MENTION of TORQUE Specs.

POLY, I forgot to mention, I noticed that your SPECIFICATIONS state that this engine is 3 carburetter, how far obsolete is this motor with CARBIES????

george my dearest friend,let us start with torque,none of the engine manufactors list figures for torque so i am assuming that the engine torque will be created somewhere between 2500r.p.m and 4500r.p.m placing them far higher in the rev range compared to a2stroke where torque would normally commence between 1500 and 1800r.p.m beginning to taper at somewhere between 2500 and 3000r.p.m where overall horse power takes over giving the engine the impression of been more powerful.however this is actually an illusion.at 5500r.p.m a 40 horse power engine regardless whether it is 2 stroke or 4 stroke if they are both turning a 12inch propellar on the same hull the top end speed has to be the same.the difference is the 2 stroke gets there quicker.
i do sincerely hope that u can see i do understand the difference between the 2.
carbs george this is a HARD ONE we run a high performance motorcycle well should i say our son does.it has been built to do one thing and that is for maximum performance over a 4 mile straight.in other words he is looking to go as fast as he can on a 2 cyclinder 750cc motorcycle.the only way this can be achieved is through the use of carbaraters as fuel injection cannot not supply enough fuel at any given point in the rev range to reach a maximum r.p.m with the given gearing of the bike.also carbs.are far simpler to work on then c.d.i lets face it if c.d.i shits itself midstream u will be paddling. if cards blocks up just blow out the jets keep going.okay i hope this answers your questions
thanks mate for all your suggestions much appreciated.

Hey guy's been stay'n outta this as i don't have much experiance with large motors(6hp+ ),sure i've been in many but never owned any.


I'm just a bit dumbfounded by the above quote .


How does a certain material prop make a differance in cavitation??

Does'nt it have more to do with where the motor is placed and the pitch of the prop??


Poly i'm not trying to rrubbish your mate BTW,just curious.


SMELLY

It's due to the strength of SS Smelly, a SS prop being stronger can be made with thinner & sharper blades which makes them more efficient.
Imagine if you had a prop made of wood, the blades would have to be very thick so they wouldn't work as well at slicing through the water.
Nowdays there's not a great deal of difference between SS & Alloy as the alloy materials they are using are getting better all the time.

Poly, how much does your existing motor weigh, I hate to see you turn the boat into a dog.
Have you thought about holding out for a whole new rig, maybe one that has a steering wheel?

FED thank u for your concern, possum and i have given that a gr8 deal of thought in the past few months and have desided against it.
the 30 suzi weighs in at 68kg i think and the new motor will be 96.9kg well within the manufacturer's spec's, i could go up to a 50hp yammy if i wish as it is the same weight as the 40hp how ever it would make it a lot harder for me to work on the motor as they have E F I fuel injection.
thank u all so for explaining why ss props work better as it had me scratching my head to

testing edit button all is ok.

I think that you are not getting ahead going the 4st 40 for the reasons i have said, performace wise the 4st 40 will give No benifits over your 30, however you will have more stealth. Put a leccy on it instead!?

Or get the 40hp 2 stroke for more performance. and a Leccy!

Has very little to do with it Fed esp on a toy motor like the one poly is looking @ getting

Only advantage you would get out of a stainless prop on a motor that size will be wear & tear the stainless one will outlast the alloy one

Down side to having a stainless opposed to a Alloy prop is the stainless wont snap the blade as easy as an Alloy prop if you hit something & I'd rather replace a prop than a gearbox any day of the week if thiis happened

Has very little to do with what Jumpy?
Did you even read the question?

Bloody oath I read the Question

Smelly quoted this



Then you went on to say that it's due to the strength of S/S which dosen't cause the motor to cavitate as much then I pointed out material contruction has nothing to do with it.

Exept in your case cause you use a wooden prop which would tend to float alot more thus causing cavitation

The question.



The answer.


I made the important part bold to help you understand it mate.

Nothing to do with it Fed !

Go out & have a good look @ new props not used oneswhere the stainless has been worn down or had the sh*t polished out of it thats what you've seen

AS a matter of fact you've got more chance of a stainless prop distorting under load than a Alloy the Alloy prop would be more likely to snap

I think you will find that stainless ones are generally more shiny!!

therefire faster, paint a alloy prop red and see what happens!

strike me lucky rum now i am confused, :huh: i think i will take up the grog again