502 power VS torque
Posted: Tue Feb 20, 2018 11:56 am
Question for the group. I have a 21ft dixie airboat. I m planning on putting a chevy 502 in it. what kind of power do I need to push this size boat?
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Here is what to do:nolaboat wrote:I havent purchased a prop or reduction gears as of yet. So Im open to suggestion on that as well.
Where to start....ladyblackwater wrote:OneBCF HP. doesn't move a boat. Torque does, horse power sustains the torque. The best motor you can get is one that pretty much goes square around the Rpm you want to run. This meaning the HP and torque are about the same numbers at let's say 4800rpm (if that's the range you are looking for) If you have a motor that builds HP and hardly any torque or vice versa than you will have a useless motor for an Airboat.
Well, this one is easy because I don't think you realize that HP is actually work. Therefore, any electric motor is providing the same power as any other type of engine to accomplish the same "work" and "carry a load". If you can point to a specific example of an electric motor requiring less power to perform the exact same task as another engine, I would like to see it.Please explain to me how an electric motor can do more work and carry a heavier load with less HP than an equivalent gas motor?
Well, again, this is a common fallacy. For any engine a higher torque equates to a higher cylinder pressure. Cylinder pressure is a major contributor to fatigue and component stress as well as overall wear. This is why you don't "lug" engines at low RPM and high load. It's why trucks down shift to go up hills. The cylinder pressure is reduced and the engine turns more RPM to make the required power.Also the one with more torque is going to live much longer than the motor that is working it's butt because it has HP but not enough torque. It's called the big HP motor with little torque will be crusing and running at a much higher rpm and will have to run more rpm to stay with the motor that has good HP but equivalent or higher torque to the HP.
I'm not going to go into the derivation of the equations but there is a direct relationship between torque and horsepower.SWAMPHUNTER45 wrote: On another note can one of you fuzzy math geniuses educate me on the 5250 dynamic?
Why does horsepower "always" eclipse torque at an rpm above 5250 and as as such would torque not then be more relevant to usable power and therefore of more value in an airboat?
An A/C motor makes lots of torque and turns half the prop as a 600 HSP car motor. Should you put an A/C motor on a 21 foot boat?ladyblackwater wrote:OneBFC I have one question for you because I'm done going back and forth with ignorance. How many airboats have you own and built that were 18' or bigger? Maybe his best bet is to build a 800hp Ecotech for his boat LMAO. Explain to me how an AC motor works with HP and Torque. Yelp they are torque motors a 300hp O540 puts out around 700+ torque. This should explain it very well.
I will take the bait here. I tried to keep it simple, but this is a bit long. If you want math to back this all up, I can do plenty of math, but I don’t want to complicate this discussion. I have been paid good money to apply the following information in practice, so I don’t know why I’m giving it away for free…OneBFC wrote:Where to start....ladyblackwater wrote:OneBCF HP. doesn't move a boat. Torque does, horse power sustains the torque. The best motor you can get is one that pretty much goes square around the Rpm you want to run. This meaning the HP and torque are about the same numbers at let's say 4800rpm (if that's the range you are looking for) If you have a motor that builds HP and hardly any torque or vice versa than you will have a useless motor for an Airboat.
Well, quite simply, your wrong here and some math will explain. I'm doing this not to put anyone in their place, etc, but rather to help keep a common belief that is compeltely wrong from spreading through misunderstanding how things actually work.
Engine A has 600 lbft of torque between 1500 and 3000 RPM and spins a maximum of 3000 RPM
Engine B has 400 lbft of torque between 2500 and 6000 RPM and spins a maximum of 6000 RPM
Which engine will produce more thrust to move "a boat?"
Given that Hp(power) = (Torque x RPM)/5252
Torque is a Force
To turn a shaft at a given speed requires Power.
(Force x RPM) = Power
To get to the standard unit of "Horsepower" we divide by 5252 as a constant.
If you want to understand how Horsepower is derived see herehttps://en.wikipedia.org/wiki/Horsepower
So, the answer to the above question of "Which engine will produce more thrust to move a boat" is the engine that makes the most POWER, which is engine B. Engine A is roughly 343hp. Engine B is roughly 457hp.
Engine B will move a boat better because it will make more thrust from a propeller.
Torque by itself means nothing. You can generate 10,000 lbft of torque at 10 RPM and it's still less than 20hp.
So, I challenge you, or anyone else for that matter, to explain, exactly, how any engine with more torque but less power will "move a boat" better than an engine with more power and less torque.
I look forward to the response!
Ok first off, show me once where I recomended any platform anywhere in this thread? Get the bias out of your minds, just because I currently use platform A doesn't mean I am trying to say everyone should use it? What the heck? Maybe go back and read what I have said in this thread again?So, feel free to go back to arguing 4 cylinder ECO, vs. LS vs. big bore/stroke V8, vs. boost vs. my johnson is bigger than yours vs. blah blah blah. But do it while considering the above information. In the meantime, my O-540 will just cruise along fine, no issues, no argument.
I gave him an answer that he can use to make a working boat. I did not say use this engine or that engine or anything else. He wants to know how much power he needs and he got an answer of "you need lots of torque." If he just builds an engine with good POWER he will get plenty of torque as a by product. If he builds an engine with good TORQUE, he very well may end up with less POWER than he could have for the same money and ultimately end up with LESS usable thrust because of it and an engine that will not be as reliable!Question for the group. I have a 21ft dixie airboat. I m planning on putting a chevy 502 in it. what kind of power do I need to push this size boat?
We are on the same page here, the power curve does dictate acceleration characteristics. In fact the example given did show that a lower hp system (engine and gear) which produces higher (prop) torque at all speeds can produce more thrust during the acceleration phase. In my opinion this is a key element of a well performing boat.my bet was to show an example of a lower hp engine that has more torque producing more thrust than a higher power engine with lower torque. ALL you have said is that the power curve dictates acceleration characteristics (of course?)
My argument is that the acceleration (snap) characteristics of the set up does dictate performance of the boat for all around use, not just racing. These characteristics are seen when getting on a plane, turning, flipping around to stop and particularly when running ground and especially for my sore back. It improves the operators ability to control the boat. As several people have noted, most airboat engines do not operate at a steady state, these are dynamic applications.Torque will give you lots of "snap" that isn't used most of the time by most people that are not racing. Power is the determining factor in how much thrust you will get and is what most people need most of the time.