Four blade prop

[rodbolt17]

your simply to dense to understand.

lets take a s225 turt and an F225txrb.

one displaces 3.1L the other 3.3 l.

not a large difference.

both produce an advertised HP at about 5500 RPM.

the s motor intakes,copress's,fires and exhausts all 6 cylinders in 360* of crankshaft rotation.

the F motor takes 720* of rotation to accomplish intake, compression fireing and exhausting all 6 cylinders.

means that every other time that F motors pistion comes up its cooling down.

that is the second function of the piston rings on both the s and F motor, dissipate the heat from the pistion to the cyl wall.

in theory the piston never touchs the wall on either engine.

so both engines are burning roughly 25 gallons of gas at 5500 RPM.

one ,the s motor,is fireing and combusting fuel every 5500 times per min.
the F motor does this power cycle only 2750 times for the same 5500 RPM.

yep not a lot of displacement difference between the 3.1L 2 stroke smokey and the F225 3.3L.

world of difference in hole shot and low end grunt.
the 3.1L will walk away from the 3.3 anyday of the week and do circles around it on sunday.

but the latest F225 with a single throttle body AND variable cam timing is another monster.

but ya really really need to understand the difference between two and four stroke motors and how the intake,compress,ignite and exhaust.\

at the end of the day.
suck squeeze bang and blow that's just how they go.

the thermodynamics come in to play so the more heat you can generate WITHOUT destroying it, the more power that same displacement can produce.

yes Virginia,,,, its that simple.

and remember 360* is one circle/revolution.
720 is two circles or two revolutions.
on a 2 stroke V6 one 360* turn of the crank each piston has done a power stroke.
on a four stroke V6 at 360* rotation only 3 pistons have done a power stroke.
the other 3 have been just dragging along.

[zenoahphobic]

your simply to dense to understand.

lets take a s225 turt and an F225txrb.

one displaces 3.1L the other 3.3 l.

not a large difference.

both produce an advertised HP at about 5500 RPM.

the s motor intakes,copress's,fires and exhausts all 6 cylinders in 360* of crankshaft rotation.

the F motor takes 720* of rotation to accomplish intake, compression fireing and exhausting all 6 cylinders.

means that every other time that F motors pistion comes up its cooling down.

that is the second function of the piston rings on both the s and F motor, dissipate the heat from the pistion to the cyl wall.

in theory the piston never touchs the wall on either engine.

so both engines are burning roughly 25 gallons of gas at 5500 RPM.

one ,the s motor,is fireing and combusting fuel every 5500 times per min.
the F motor does this power cycle only 2750 times for the same 5500 RPM.

yep not a lot of displacement difference between the 3.1L 2 stroke smokey and the F225 3.3L.

world of difference in hole shot and low end grunt.
the 3.1L will walk away from the 3.3 anyday of the week and do circles around it on sunday.

but the latest F225 with a single throttle body AND variable cam timing is another monster.

but ya really really need to understand the difference between two and four stroke motors and how the intake,compress,ignite and exhaust.\

at the end of the day.
suck squeeze bang and blow that's just how they go.

the thermodynamics come in to play so the more heat you can generate WITHOUT destroying it, the more power that same displacement can produce.

yes Virginia,,,, its that simple.

and remember 360* is one circle/revolution.
720 is two circles or two revolutions.
on a 2 stroke V6 one 360* turn of the crank each piston has done a power stroke.
on a four stroke V6 at 360* rotation only 3 pistons have done a power stroke.
the other 3 have been just dragging along.

Oh common don't resort to insult.

Your understanding of thermal dynamics as you explained previously does not meet your argument put. You don't mention which engine produces more heat anymore; which was BS anyway.

Thankfully you're shifting closer to what the original OP wanted, but it was to do with 4 bladed prop.

Don't assume what I don't know. It would be far more useful if you correctly explained what heat is and how this relates to temperature.

It is not the heat generated, both engines essentially create the same heat!!!!!!

Explain to those that are continually confused on this subject.

It is TEMPERATURE that destroys engines not the DAMN heat! Think more clearly about conservation/transfer of energy (Physics Man!).

[rodbolt17]

think mon.

if both similar displacement engines are burning a similar amount of fuel at a similar RPM but one spends 1/2 its time exhausting NOT creating heat which engine design will produce more heat.

temperature control of the metal is a function of cooling system design.

has nothing to do with heat generated.

can you overheat a 4 stroke?
yep.
can you heat it enough to pop a head gasket?
yep.

however its very rare to overheat that 4 stroke to the point of piston seizure while its fairly common on a two stroke.

pull the tstat on the 4 stroke and at WOT it will over cool.
pull it on the two stroke and it will still come close to operating temp at wot.

goes back to the 2 stroke lights a fire EVERY time the piston comes up.
the four stroke every OTHER time it comes up. the OTHER time the 4 stroke comes up the rings are cooling the piston and the head and cyl walls are cooling the ex gas.
no fire no heat,no heat and it wants to cool.

[zenoahphobic]

think mon.

if both similar displacement engines are burning a similar amount of fuel at a similar RPM but one spends 1/2 its time exhausting NOT creating heat which engine design will produce more heat.

temperature control of the metal is a function of cooling system design.

has nothing to do with heat generated.

can you overheat a 4 stroke?
yep.
can you heat it enough to pop a head gasket?
yep.

however its very rare to overheat that 4 stroke to the point of piston seizure while its fairly common on a two stroke.

pull the tstat on the 4 stroke and at WOT it will over cool.
pull it on the two stroke and it will still come close to operating temp at wot.

goes back to the 2 stroke lights a fire EVERY time the piston comes up.
the four stroke every OTHER time it comes up. the OTHER time the 4 stroke comes up the rings are cooling the piston and the head and cyl walls are cooling the ex gas.
no fire no heat,no heat and it wants to cool.

I have no problem with what you say above except for how you imply one produces more heat than the other. This is poor expression of what you mean. It will be said again: if both engines burn the same rate of fuel they will create the same amount of heat (irrespective of their design or HP output).

I appreciate that you have found more twostrokes seize than fourstrokes, but that is/was not the case in the other worlds where these engines operate. I might suggest two things. 1. 4st are tending to supercede old 2st; therefore greater technology invested in 4st to prevent such failures. 2. Two stroke seizures tend to be more "memorable" in that they invariably break rings which are closer to the piston tops as well, causing massive scoring of the bore, therefore involving more work.

The other exception I take, again poor thermal dynamic explanation, is with this "secondary purpose of rings is transferring heat from pistons'. I've heard this often and what is implied is WRONG.
I'm not denying heat transfers between cylinder wall, ring and piston. Thermally with such a small contact, the less conductive ring simply cannot transfer so much heat. The massively greater surface area and more heat conductive piston transfers its own heat directly to the cylinder walls. (I know they don't touch, so doesn't the ring). Sure the ring has to conduct heat to the cylinder walls; but this is for it's own preservation. It might even surprise you that there are times when the rings themselves transfer their heat to the piston (the other way around)!

I am not sure what your resultant point is. You seemed to have advised the OP against using a 4 bladed prop, presumably because the 2st has no power, but you have argued they have more power than 4st's, but then you went on a thermal tangient seemingly to suggest that 4st are powerful or atleast seems to be an argument why 4st are able to be more powerfull!

Sorry for taking you to task, but????

[zenoahphobic]

It would be an interesting, and far more informative to actually look at all the differences (not similarities) between the engines Rodbolt last quoted.

Clearly, if they have the same power at the same maximum revs the fourstroke must be getting twice the fuel air in on it's powerstroke.

I believe there are many differences including incorrect statement of HP. it would have many "2% ters" making them become similar in HP.

New thread maybe?

[rodbolt17]

Dude
do you understand piston to wall clearance and why it is there?????>

the piston should NEVER touch the cyl wall.
it will sometimes but not by desighn.
TWO things and TWO things only control piston heat.
the contact between the rings and the piston and the cyl wall.
and the amount of cooling from underneath the piston.

and yep that is IT, nothing else.

as to clarification.
how can I make it more clear?

the f225 displacing 3.3 L for every COMPLETE 720* cycle burns about the same amount of fuel as an S225 completing the cycle in only 360 degrees.

this aint difficult, it is hard to see in 3d space.
but that is how it works.

the s225 in ONE 360 revolution of the flywheel has ignited,fired, lit the candles on ALL 6 cylinders.

the F225 in ONE 360* rotation has only lit,fired or made a power stroke on THREE out of SIX cylinders.

which one ya thinking may produce more heatums ?????

if that piston aint going down on a power stroke, its dragging cause the ring friction and the camshafts still must turn
.

next time ya get a chance.
try rotating the F225 with all plugs removed.

then try a two stroke v6 with all plugs removed.

see how much HP the CAMS eat?????

[zenoahphobic]

Dude
do you understand piston to wall clearance and why it is there?????>

the piston should NEVER touch the cyl wall.
it will sometimes but not by desighn.
TWO things and TWO things only control piston heat.
the contact between the rings and the piston and the cyl wall.
and the amount of cooling from underneath the piston.

and yep that is IT, nothing else.

as to clarification.
how can I make it more clear?

the f225 displacing 3.3 L for every COMPLETE 720* cycle burns about the same amount of fuel as an S225 completing the cycle in only 360 degrees.

this aint difficult, it is hard to see in 3d space.
but that is how it works.

the s225 in ONE 360 revolution of the flywheel has ignited,fired, lit the candles on ALL 6 cylinders.

the F225 in ONE 360* rotation has only lit,fired or made a power stroke on THREE out of SIX cylinders.

which one ya thinking may produce more heatums ?????

if that piston aint going down on a power stroke, its dragging cause the ring friction and the camshafts still must turn
.

next time ya get a chance.
try rotating the F225 with all plugs removed.

then try a two stroke v6 with all plugs removed.

see how much HP the CAMS eat?????

"heatums" now you're getting too scientific!

Seriously you're two things con*****ing piston heat (and TWO things only, and yep that's IT nothing else, you say) you really state as three? (rings piston cylinder wall and underneath). But are also actually five.

You forgot what the incoming charge of fresh fuel and air does to the piston heat!!

Yes telling me nothing, cams eat power. Difficult to turn a fourstroke, but don't forget the potential energy put into the valve springs is given back pushing the cams with the engine rotation after passing. Again not an accurate demonstration of how much power cams actually use.

Next you might tell the readers "try turning over a diesel engine..... much much harder to turn over than a petrol motor..... so diesel motors eat more horsepower".

[rodbolt17]

I am trying not to be offensive.
but are you sure you understand the difference between 2 and 4 stroke outboards and how and why the pistons go up then down then up again?

on the two stroke smoke ums.
how does the pistion dissapaste het.
answer that and you will find I am right.

on the 4 stroke green motor its simply the same only it takes twice as long and NO underneath piston cooling.

dude your gonna allow me to back you into a corner and just like playing chess.
chess is a very good **** to allow your opponent to simply basck themselves into the corner.

but trust me if you burn 2ltr of fuel in 1 360* rev or burn 2ltr of fuel in 720, which just made more heat?

[99yam40]

Rod it is not worth your time,
when he 1st showed up I thought he was just a *****.
just going on and on about some nonsense he had in his mind, just likes to argue.
stay on the subject the OP stated and forget about him

[RayBersch]

Rodbolt & zeno,you guys are speaking the same different language together at different times but none of it helps the OP. Rodbolt, trust me, one 2 ltr of fuel will produce the same amount heat as the next 2 ltr of fuel but your point introduces a time element that impacts heat dissipation or accumulation, however you want to slice it. Zeno, I have no idea where you are going with the heat/temperature thing and where air comes in to play with two engines of the same horsepower but otherwise your logic is, well, logical. Lets see if we can provide more helpful information to the OP.

dngharvey, my reference to your being unhappy concerned your reason for posting, you are not happy with your hole shot when loaded. My comment was that I believe you are underpowered for what you would really like to achieve while loaded and I don't believe you will get much improvement with a four blade prop.

Fortunately, when I was purchasing my boat I had good information supplied by the manufacturer in the form of Performance Bulletins. Because I did not think I needed a 150 hp I looked long and hard at the F115 vs the F150 vs the 150 Vmax (two stroke) for this boat (our boats are approximately the same weight, slightly different hull) I looked at the Vmax because it was already on the boat - I have attached all three PBs and, dngharvey, if you look at the performance of the F115 vs the F150 you will see why I chose a 150 - you can see where the jump occurs (i.e.: the boat jumps on plane) with these power configurations - vastly different 3500 rpm vs 2500. Your 2 stroke will perform slightly better because it revs faster but not that much and this is where your added weight will prove to be a penalty. If you add a 4 blade you may actually find it worse (if you go for a four blade, talk to the prop guy about getting a vented prop to help produce RPMs faster.)

You can see the difference between the 2 stk vs 4 stk by comparing the F150 with the Vmax 150 which produced more speed and jump on plane at 2000 vs about 2500 for the F150. You should also note the greater speed for the Vmax - 56.2 vs 55 for the F150 at similar RPM's.

Now back to rodbolt and zeno - look at the two 150hp bulletins - The F150 produced 55 mph using 16.1 mph resulting in 3.43 mpg - the Vmax 56 using 20.3 gph and 2.7 mpg - so, rodbolt, you win - the two stroke used more fuel at about the same rpm and speed and much less efficiency. More fuel = more heat no matter how many bangs are involved.

By the way, dngharvey, try adding some weight up front when loaded to see if that brings the bow down a bit and lifting the stern - could help increase RPMs faster. And you may be happier if you add power more gently until some speed is gained and then floor it - far less inertia to overcome.

Ray

[zenoahphobic]

Rod it is not worth your time,
when he 1st showed up I thought he was just a *****.
just going on and on about some nonsense he had in his mind, just likes to argue.
stay on the subject the OP stated and forget about him

Com'on 99yam40, fairdinkem, don't show your ignorance and propensity to namecall.

If you must, go for the ball and not the man; stick to polite and simple rules of social engagement. Contribute but stick to the merits of an argument.

Read back, I did not start this nonsense Rodbolt has brought up about his distorted view on heat. I did ask him what this does to address the OP question.

I apologize if you cannot follow what I have written.

[zenoahphobic]

Rodbolt & zeno,you guys are speaking the same different language together at different times but none of it helps the OP. Rodbolt, trust me, one 2 ltr of fuel will produce the same amount heat as the next 2 ltr of fuel but your point introduces a time element that impacts heat dissipation or accumulation, however you want to slice it. Zeno, I have no idea where you are going with the heat/temperature thing and where air comes in to play with two engines of the same horsepower but otherwise your logic is, well, logical. Lets see if we can provide more helpful information to the OP.

dngharvey, my reference to your being unhappy concerned your reason for posting, you are not happy with your hole shot when loaded. My comment was that I believe you are underpowered for what you would really like to achieve while loaded and I don't believe you will get much improvement with a four blade prop.

Fortunately, when I was purchasing my boat I had good information supplied by the manufacturer in the form of Performance Bulletins. Because I did not think I needed a 150 hp I looked long and hard at the F115 vs the F150 vs the 150 Vmax (two stroke) for this boat (our boats are approximately the same weight, slightly different hull) I looked at the Vmax because it was already on the boat - I have attached all three PBs and, dngharvey, if you look at the performance of the F115 vs the F150 you will see why I chose a 150 - you can see where the jump occurs (i.e.: the boat jumps on plane) with these power configurations - vastly different 3500 rpm vs 2500. Your 2 stroke will perform slightly better because it revs faster but not that much and this is where your added weight will prove to be a penalty. If you add a 4 blade you may actually find it worse (if you go for a four blade, talk to the prop guy about getting a vented prop to help produce RPMs faster.)

You can see the difference between the 2 stk vs 4 stk by comparing the F150 with the Vmax 150 which produced more speed and jump on plane at 2000 vs about 2500 for the F150. You should also note the greater speed for the Vmax - 56.2 vs 55 for the F150 at similar RPM's.

Now back to rodbolt and zeno - look at the two 150hp bulletins - The F150 produced 55 mph using 16.1 mph resulting in 3.43 mpg - the Vmax 56 using 20.3 gph and 2.7 mpg - so, rodbolt, you win - the two stroke used more fuel at about the same rpm and speed and much less efficiency. More fuel = more heat no matter how many bangs are involved.

By the way, dngharvey, try adding some weight up front when loaded to see if that brings the bow down a bit and lifting the stern - could help increase RPMs faster. And you may be happier if you add power more gently until some speed is gained and then floor it - far less inertia to overcome.

Ray

Thankyou RayBersch,
as I wrote above I did not start this "heat" argument.

One point (if I may dare) less efficiency may well mean unburnt fuel leaving the engine , therefore not adding to heat creation, and then indeed aids cooling of that twostroke engine.

Back to OP, I would have suggested that a 4blade in theory would help on a 2st115, but how much gain, or is it worth while on that setup?. I was trying to tease out the discussion to address the actual HP available, not what it is at WOT.

[zenoahphobic]

I am trying not to be offensive.
but are you sure you understand the difference between 2 and 4 stroke outboards and how and why the pistons go up then down then up again?

on the two stroke smoke ums.
how does the pistion dissapaste het.
answer that and you will find I am right.

on the 4 stroke green motor its simply the same only it takes twice as long and NO underneath piston cooling.

dude your gonna allow me to back you into a corner and just like playing chess.
chess is a very good **** to allow your opponent to simply basck themselves into the corner.



but trust me if you burn 2ltr of fuel in 1 360* rev or burn 2ltr of fuel in 720, which just made more heat?

Thanks for your politeness,
But now you say there is no underneath piston cooling in 4st green motors??? Yes I do understand the lesser ability in this regard due to closed crankcase. But surely the oil takes some heat away under the piston region.

I'm trying to understand (reading between all the lines) what you're saying but I have attempted to draw out of this discussion the relevance, and how this relates to the bottom end HP (holeshot ) torque, not equal fuel used at WOT, and lead to why you would or would not use a four blade prop for either a 2st (as requested by OP) or 4st (as you seem to suggest).

You started this "heat" and power pulse timing debate, and imply I have no idea about the very simple and basic mechanical differences; which I cannot see where you get such an idea.

Read what is recently said by myself and others, you don't need to repeat yourself, I simply disagree on your expression of, and your version of thermal dynamics.

Last point:
everything stops starts, pulses, accelerates, decelerates, goes hot, goes cooler, goes up goes down, etc. etc.
So it's a wonder why it is possible to create any engine with a reasonable stable (smoothed out) and con*****able RPM's!
Same story how electricity is created. Same story with everything in nature. Everything is in a constant state of flux!!

[rodbolt17]

4 strokes are way more sensitive to over propping. EFI can get a bit better than carbs if over propped.
overpropped EFI 4 strokes tend to make oil as raw fuel gets pushed passed the rings due to the increased combustion pressures.

the MOST efficient prop blade design is a single blade.
however it vibrates a bit.
the three blade is a compromise.
add that 4th blade and it not only adds resistance to turning in the water but tends to pull in the direction of rotation harder.

going back to the power pulses.

both the F225 and the ss225 just ran one hour at 5000 RPM,close to the 225 HP rating for both engines output.

the S225 just lit the candles,burned the flame had a power stroke 300,000 times. yep the ign system worked flawless.

the F225 just lit the candles,burned the flame had a power stroke 150,000 times. it too had a flawless ign system.

both burned roughly the same amount of fuel.

which engine spent more time with the flame burner on ?

kinda mind boggling that the ign system worked .

without single throttle body injection and variable cam timing, this is why typically you cant use the same prop on the F115 and the s115 or the s225 and the f225.
its all in how the engine makes power and how long it takes to generate the RPM nessasary to make it to the power band.

[RayBersch]

the three blade is a compromise.
add that 4th blade and it not only adds resistance to turning in the water but tends to pull in the direction of rotation harder.

Yes, and this is a good point for the OP to understand if he pursues the effort. It took me three tries to get the right 4 blade. The first really improved stern lift but could not approach the 6k WOT RPM needed for the F150. The third compromised the stern lift and lower speed on plane I was looking for but got me to 6k WOT so I am comfortable with it - and I added hydraulic steering to overcome the prop torque. So, changing props to accomplish a specific goal is not a one and done thing.