Torque? Let me tell you Thats where it is . I recently put 2 540,s im my Formula . I have been dissatisfied with my dyno numbers , 575 hp and 630 ft lb of torque. I just compared my stats with that of the chief engines 540 . My torque is much higher . My old 454,s put out 535 hp but not nearly as much torque. I jumped up 5 prop sizes only went up 40 more hp. But the torque was almost 100 foot poiunds . Not totaly dialed in yet . I ran out of weather . But the torque gain from an 850 to a dominator was so impressive I alomst idled on plane on my last sea trial .So ther bottom line is torque will pick your as- up and hp will get your as- at the top end....

Hey Boat .... what Formula and some numbers before and after ? Ballpark ...

speaking of prop tuning ... in my 311/454mags I went to 23 Hydromotives ...I can get to 5000 but it takes some fine tuning ...triming ect ....should this be right or should I pretty much be able to spin right up to 5000 .... I have heard some like to underprop some so you will have throttle left ...then at heavier loads you would have better perfromance .... Matt at Throttle up calculated about a 22 prop but that was with very rough numbers ...these props are stock ....so there is room for matt to tune I suppose .....

Only every engine on the plant that can spin 5250?
(Actually it's really 5252...)

ONE horsepower is the power needed to raise 550 pounds ONE foot vertically in ONE second. (Supposedly this "unit" was derived from the mining industry which used horses and mules to haul buckets of ore out of the mine shafts.)

So:

1hp = 550 pound-foot per second.
or
1hp = 33,000 pound-foot per minute.

In a rotating motor, you gotta sort of work backwards..

Each revolution of the motor, at a "1 foot" lever arm (or pulley with the same radius), you circumscribe a path of (2 x Pi x 1foot) 6.283 feet. (Perimeter=2 x Pi x Rad, and for this example Pi will be rounded to 3.1415)

So a motor with "T" lb-ft of torque can lift "T" pounds a distance of 6.283 feet per rev.
At 1 rpm, that motor will lift "T" pounds 6.283 feet per minute.
So, you can take that and rephrase that as:

"H" hp = ("T"/33,000 pounds) x (6.283 feet per rev) x (1 revs) per minute.
or
HP = Torque x (6.283/33000)RPM = Torque x (1/5,252)RPM
or finally
HP = Torque x RPM / 5252

mc

OK, I am going to respectively disagree with a few of you here. I don't see any relationship between best cruise speed and peak torque, unless you define best cruise speed as the speed in which you feel the most surge in acceleration when you hammer the throttle.

The term "best cruise" is a bit nebulous anyway. I would venture to guess it would be the most economical running speed in terms of miles per gallon. That can only be determined through boat tests for your particular boat, engine, prop, etc.

As far as horsepower and torque peaks crossing - don't concern yourselves with this one either. In Europe, they measure in kilowatts, and Newton-Meters. Now what? The torque and horsepower curves are going to cross at a different RPM. That crossing is completely dependent on the graph scale, tells you it is bogus.

As far as peak horsepower, and best top speed, many of you got it correct. It is at the horsepower peak. Engine torque is one of those figures which is interesting on the dyno, but not important overall, because we have transmissions to change horsepower into drive torque. If it was important, we wouldn't have Formula 1 cars with their little 183 cu. in. engines doing 0-100 mph in 3.6 seconds.

Michael

You may be right but if you pick the right conversion to Newt/mtrs and kilos I don't see how the equation could come out different. Trouble is I saw about 30 kinds of kilowatts and several NMs in my "pocket ref" so I'll leave it to MC to prove this.

1 W = 1 N x m /sec
okay, what's a Newton? It's (1 Kg x m /sec^2).
so
1 W = 1 kg m^2 / s^3, but for Shts and Giggles, we'll leave Newton-meters as the unit of torque.

so

1 W = 1 N m /sec = 60 N m / min

So, a 1 meter radius pulley will lift a load 6.283 meters per rev.(we already did that math).

1 Watt = ("T"/60 Newtons) x (6.283 meter per rev) x (1 revs) per minute.
1Watt = T x (6.283/60) RPM = T x (1/9.55) RPM
1 Watt = T x RPM / 9.55
1 kW = T x RPM / 9550

Therefore, torque curve crosses the power curve at 9550 rpm when using Newton-meters and Kilowatts.

Let's see you try to prop for that......


mc

That is great! Glad to see no one has lost their sense of humor during these technical discussions.

Michael

Torque is measured, HP is calculated.
Torque ='s the amount of work that can be done
HP= how fast the work is done.

A boat needs a broad powerband since it is limited to a single gear ratio and limited by a narrow range of props sizes and pitches. In comparison a car has transmission gear choices, rear gear choices, and tire size choices. The broad power band is needed in the boat to plane, to cruise, and for top speed. We can not throw the throttle to 5K rpm and drop the shifter into gear.. . .a race car can.

So when building a marine engine, you better off to ask how broad is the power band then to ask what is the calculated HP.

Chris

I'm just glad I ain't got no furrin motors. Can you imagine trying to find a 56" pitch Mirage,,much less controlling valvetrain float
Yeah, I know, I know.