Factory Horsepower ratings

[ron7000]

Re: Factory Horsepower ratings

sorry man I disagree. I'd have to say thrust is just a force, without having any distance included. Standard definitions of work and power are
work = force x distance
power = work / time; which is the rate of work, and horsepower is in units of power.

 

[QC]

Re: Factory Horsepower ratings

ron7000,

I agree on your definition of thrust as a force not work, but we need to seriously back up here as your analysis is fundamentally flawed yet you are very close.

Please note your previous comments about propping this thing at peak torque for wot. Horsepower is work as you have duly noted. Work is force over time (not distance). The HUGE mistake you are making is recommending that since peak torque is developed at 2800 RPM then that is where you should prop too for max speed. This is TOTALLY incorrect. Max speed comes from max work, not max force.

 

[Tail_Gunner]

Re: Factory Horsepower ratings

This is just to simple, if a prop is the mechanism that drive's both the tourqe and horse power i ask you this.

Would you place a bet on overall speed of a boat where a prop's turning 2800 rpm @ 229 hp ? Or a prop turning
4800 rpm @ 321 hp......... Hmm the loser dance's naked on main st.

Tourqe is defined as in laymen's term as a measurement to define twisting force, it is not defined as a rate of speed or travel, it just help's getting to a certain rate of speed the more tourqe the faster you achieve a given revoltion, but once it's there, it can do no more.

Perhap's if you think of it like this it maybe easier to understand, when a boat is dead still in the water it take's a lot of energy (tourqe) to begin moving it's mass, as the boat gain's speed less of the hul is in contact with the water requiring less energy (tourqe) to propell it. Now to a certain point the faster you go the less resistance is taking place allowing the hp to take over the work load................ Your never gonna be able to turn a huge prop over @ 2800 and get the same rate of speed @ 4800 because the rules are different it does not (the prop) become more efficent it actually starts to drag down because of it's phyisical size ( say a 28 pitch vs a 22 pitch.............. LOl i cant go on any more.......... This thread really needs to get on topic and help this guy out.............Fraser get a 850 doulbe pumper carb and you may want to post a new thread asking Don how far you can go with new gears in your stern.......... that motor you have there is a beast............

 

[180shabah]

Re: Factory Horsepower ratings

Yup, thrust is directly related to prop RPM. more spins = more thrust. And yes, I know this is oversimplified.

 

[calwldlif]

Re: Factory Horsepower ratings

I look at it like this :%
Torgue gets you going
Horsepower keeps you going

 

[fraserscrane]

Re: Factory Horsepower ratings

I look at it like this :%
Torgue gets you going
Horsepower keeps you going

 

[fraserscrane]

Re: Factory Horsepower ratings

Thank's again,first for a wealth of technical data,& second for a more simplfied definition!!.I feel a little overwhelmed with everything,,as qc posted...confusion!!.I have talked to the the guy that built this motor(for the record,he has been building race motors for 25 years,& is a very good friend of my father in law)so I trust him totally.He told me that this motor will handle a supercharger,but cannot garantee reliability,as the motor ages.He built this motor to be reliable.He suggests I run the boat & try to prop it accordingly.If I'm not happy ,he suggested installing a new intake manifold,with (as mentioned)a 850 cfm double pump carb.Apparently the bottom end has been built with future mod's in mind.WHAT I NEED TO KNOW IS WHAT PROP I SHOULD START WITH,BEFORE I DECIDE TO MODIFY A FRESH<RELIABLE MOTOR .I believe the boat weighs appox.4500lbs I also believe the hull has approx. a 25 degree deadrise (not sure though).I dropped the motor off tonight & I won't have the boat back until next weekend,so until then I have no knowledge of characteristics.WE also have a very short boating season up here,so the more time in the water enjoying life,the better.Thank's Fraser

 

[QC]

Re: Factory Horsepower ratings

Well we don't know the gear ratio, but I do think you have more horsepower than when you started. I would go 2 inches above what you had. If you don't know I would try around a 22" 4 blade SS to start . . . Could be totally BS, but you asked

 

[ron7000]

Re: Factory Horsepower ratings

Please note your previous comments about propping this thing at peak torque for wot. Horsepower is work as you have duly noted. Work is force over time (not distance). The HUGE mistake you are making is recommending that since peak torque is developed at 2800 RPM then that is where you should prop too for max speed. This is TOTALLY incorrect. Max speed comes from max work, not max force.

Would you place a bet on overall speed of a boat where a prop's turning 2800 rpm @ 229 hp ? Or a prop turning
4800 rpm @ 321 hp

thrust is directly related to prop RPM. more spins = more thrust. And yes, I know this is oversimplified

horsepower is not work, I said horsepower is "power", in units of power. Thrust, work, and power are all different measuring units and you guys are either mistyping words for what you mean or don't understand the definitions of what you're typing.

work = force * distance
power = work / time

that being said, if you really mean max speed comes from max work then that supports what I've been saying about propping at max torque.

229 hp @ 2800 rpm = 429 lb-ft torque
321 hp @ 4800 rpm = 351 lb-ft torque

he who makes a given amount of torque at the highest rpm wins in speed. But, because you can change prop pitch which will vary the thrust (force) the prop can give for a given rpm, you can make use of max torque at any rpm, within reason.

while thrust is directly rated to how fast you spin the prop, you can also increase the thrust by increasing the pitch. That has been my point from the beginning, you don't have to spin the prop fast to go fast.

 

[Mischief Managed]

Re: Factory Horsepower ratings

I think you'll find that if you break-in the engine properly, the whole torque curve will slide upwards as the engine loosens up. This could easily get you to 340 HP. You'll also find that air density will have a major effect. The engine was likely spec'd at sea level and some specific air temperature. Increase altitude or temperature from those original specs and power output goes down. Sometimes, a lot.

I'm pushing a 4500 lb or so, 24 degree deadrise, 25 foot long, 8 foot 6 inch beam, single-stepped-hull, pad keel boat with a 454 CI engine rated at 340 HP (at the crank, 310 HP at the propshaft). She tops out around 53 MPH on a cool day with a light load at 400 feet above sea level. Normal load and a normal summer day I'm seeing 49 MPH at the same altitude. I'm swinging a 26" SS propset with a 2:1 drive on a Bravo 3 leg. I am told I could gain maybe 2 MPH by going with a single prop Bravo 1 drive.

If you have less weight, less deadrise than 24 degrees, a narrower beam, and/or a bigger pad at the keel, you can probably expect higher speeds than I see, but I would not expect 60 MPH from what you have written.

Drag (and therefore HP requirement) increases with the square of speed. My boat would need 435 crankshaft HP to attain 60 MPH with a light load on a cool day, assuming prop selection was as efficient as I have now. With a normal load on a normal Summer day, I'd need 509HP to see 60 MPH.

Good luck, sounds like a sweet boat/motor you got there. Post photos.

 

[QC]

Re: Factory Horsepower ratings

ron7000,

The only reason that I keep this up is not to win an argument or beat a dead horse. It is to help people understand something that we are not communicating well.

Yes power = work / time. You have stated this more correctly than I have. I have been equating work and power. This is incorrect. My bad.

With that said, top speed comes from peak power, not peak torque. That has been the only real point I have been trying to make. If you gear (prop) any boat for peak torque it will be slower than if you gear (prop) it to operate at peak power. There are examples where peak torque and peak power are developed at the same RPM, but I have never seen that with a gasoline engine, only electronically controlled diesels and I believe steam engines. I do not profess to understand the power output characteristics of a steam engine. I do profess to understand the power output characteristics of gasoline, natural gas and diesel fueled engines.

Maybe I am missing your point, however, I believe you are recommending that people prop their boat to operate at peak torque because it will be faster due to more thrust. This is where we differ.

 

[Tail_Gunner]

Re: Factory Horsepower ratings

while thrust is directly rated to how fast you spin the prop, you can also increase the thrust by increasing the pitch. That has been my point from the beginning, you don't have to spin the prop fast to go fast.

Ok now calculate the drag of a 30 pitched prop vs a 22 pitch prop and what happens, you have something called mass which takes energy or Rob's. That is what is missing here and i for one am not a phyisic's geek. Take your time and figure it out, keep us posted.........8) Just kidding i wouldnt wish that on anyone other than a higly experienced tuner. As QC stated i was just trying to get to the end game and propping at max tourqe is not a good ideal in a boat the drive is final there are no stepping of the gears allowing the prop to achieve it's max rpm and still keeping the engine in its peak horsepower or more to the point tourqe band.

 

[Purduebarry]

Re: Factory Horsepower ratings

Horsepower is for bragging rights at cocktail parties...Torque is the transfer of the power generated from the engine. I'll take torque over HP, especially for a marine application. My comparison...take a Corvette, torque gets it up to speed quickly, HP makes it go fast once the torque gets it there. Get a good prop with lots of bite and hang on. You'll find that the raw power, up to plane, holeshot is awsome, top speed is a given, in a 22' you should see 60, but the prize is getting there quickly. That is if everything else holds together. What a kewl thread. Drop this combo in the prop forum I'd be interested to see what they recommend. And for goodness sake, keep us posted. All these opinions don't mean squat until you get it in the water.

 

[QC]

Re: Factory Horsepower ratings

Please Prudebbarry, do some research. Torque does in fact equal acceleration, but peak torque does not equal top speed. In a marine application, if I am not pulling skiers, horsepwower is waaaaaay more important if the boat will plane as is. I promise this is true. Quit trying to seperate the two. They are combined by RPM. Again, please note, you yourself can make 300 lb/ft. of torque., I guarantee you cannot accelerate a Corvette or a boat to any level of satisfaction.

 

[Purduebarry]

Re: Factory Horsepower ratings

Of course there is a relationship between the two, I was just adding my two cents. He has a big motor with lots of torque, this does not in and of itself mean it will have high top end speed. But it will get him on plane and up to speed quickly. However Fraiser started this tread with the question "what happened to my Horsepower". There are plenty of motors with high horsepower and low torque and vice versa. This motor is a pulling motor, boats need pulling power. Just like off-road, high horsepower is great but to get out of ruts and up steep inclines, you need torque! I do realize that there is a relationship and you can't really have one with out the other. New Corvettes have both, that is the challange with pushrod engines, getting both HP and torque high and to match closely, the best of both worlds! I got your reference BTW, strap me to your transom and we ain't going no where fast, LOL! Still a great thread.

 

[QC]

Re: Factory Horsepower ratings

Yup! It is just one of those things that advertisers have ruined the public's knowledge of . . . Kewl dude. Oh, BTW, the misspelling of your name was a mistake. I read Prudebarry, got it now

 

[Purduebarry]

Re: Factory Horsepower ratings

Freudian slip I'm sure, yea Purdue, lol, just a little engineering school in Northwest Indiana, yup I'm a Boilermaker!

I agree on the Advertising, at least they reeled this in a bit and tightened up the claims this year for HP ratings. Everyone is so damn fixated on HP they miss all of the other specs. My wife's new Minivan lost 5 HP from the same power plant from the year before. The claim was a bit exagerated as are most.

 

[lilmandavis]

Re: Factory Horsepower ratings

lugging down an engine is bad, prop it to go 4800 wot. i have a 460 in mine an its wot is about 6000 rpm. will i ever see that in the boat, no. but i will to show off bang it up to 52 or so. its far from stock and the curves im sure are like mountains. lets all go to the machinists handbook and read the equation section to figure all this out. 8) "cheerio mate!" i cant wait to repower my barge so i can put this thing in something worth it with a TRANSMISSION!!

 

[Tail_Gunner]

Re: Factory Horsepower ratings

8) Chit a barge8) your all missing the point, Don could you please step in here. Just what kind of gears can this guy put in that rear drive without blowing it (overing reving) that engine has enough tourqe to pull a huge prop and enough hp to spin it at very high rev's

:devil:Come on Don step into the fiasco and shed some light.................. ill get walleyhed aor dahdley to comment there both expert's when it come's to propping.

 

[Mischief Managed]

Re: Factory Horsepower ratings

Those of you who think HP does not matter and torque is all there is are incorrect. Torque is a function of HP and RPM. You can multiply torque with gearing but you can never multiply HP, for a given engine, it stays the same regardless of gearing and final torque output.

If you have an engine that produces 400 ft. lbs of torque at 3500 RPM, you can run it through a 10:1 gear reduction and get 4000 ft. lbs of torque at 350 RPM. You can run it through 1:10 gears and get 40 ft lbs of torque at 35000 RPM too. In all three cases, the HP remains the same. Do the math if you don't believe me.

Propping a boat to run WOT at the torque peak is a really bad idea and it will always run faster with a smaller pitch prop that allows the engine to get to it's HP peak.

I can easily apply 300 ft lbs of torque to my propeller shaft with my own strength and weight (and a lever) but I'll never be able to make even 1 HP for more than a second because I cannot spin the prop very fast for very long.