Thread:

Horsepower vs Torque, getting the most from your combo...

Got in an interesting conversation today with a guy about which makes a faster boat, This guy tells me "torque" is what you want and I kind of disagreed with him. He says torque is what pulls you up to speed and horsepower doesn't count. So I was thinking... torque is optimum for heavy vehicles going fast, overcoming the wrong gears, or running it in a parking lot.

I contend that in a boat the size and weight of most flattys "horsepower" is what makes the boat sing and lets face it, most boats with medium layup don't weigh more than 1500 to 1800 lbs and in my book that's where horsepower can, does, and will outrun a boat that's 2500 lbs with a torque monster for a motor. Since boats are so light, it makes sense to be able to spin up your motor (s) to a higher rpm to gain the increase in rpm as fast as possible and spin the hell out of your prop enabling it to take a quicker set and just plain be faster over a torque motor. I would rather spin one up as fast as possible to let the prop do it's job at the max rpm you run WFO. I believe the more aggressive you get in the rpm band by selecting your components to compliment each other, the sooner you are hauling ass. So what are your thoughts on the torque vs horsepressure issue based on having a boat that's usually half the weight of a car, and the lower the weight... the faster the car "or boat" almost 100% of the time. What I also told him was, he needs to make sure his combo makes peak power in the rpm range the boat is expected to run @ speed, (by the way, we are talking about a flatty here). I learned that to make a 18' flatty fast you have to wind it up quick to make it get out of the water, take a set and just plain leave the guy next to you sitting there. On the otherside of the coin, if you are running a 21' daycruiser, because of the weight difference you need torque to get any kind of speed out of it, and rpm has less effect on speed than brute torque in a heavier boat. So what do you guys think... and PLEASE, I want your answers based on FACTS, not what you think or believe as we all view the same things differently, hopefully based on experience and of seat of the pants been there, done that. I'm sure some of you have hurt a motor, changed things up when you built a new one and could tell the difference between different levels of your build. You guys will either shoot me down in flames, or reinforce my theory by common sense or help my buddy shit in my neck. Share your combos, speed and weight of your boats and lets compare similar weight boats by estimated hp & tq and maximum RPM @ top speed. I really want some good input here, because if I'm talking out my ass I might need to change my combination of compression, heads, cam, intake & CFM of the carbs, in hoping I can gain 5 or more MPH based on the hp/tq argument. Thanks for giving your input on this and maybe teaching all of us we may be going about making our boats fast the wrong way, you are never to old to learn something and most of you guys know your shit, willing to share, and help some of us from spending money needlessly to gain nothing. ~You're opinions are priceless~ ... Larry

You are both somewhat right.

Actually the working power of an engine that you have to work with is Torque. Torque is the measured output. Horsepower is a derived term of power derived from Torque X RPM / 5252. At 5252 RPM in any engine the Torque and HP will be the same. So, now what we need to derive is what is the application for the engine. What is the desired RPM range? And now we need to select components to maximize Torque in the RPM range (powerband).

Now it is true if we can MAINTAIN torque at a HIGHER RPM, then the HP will be HIGHER. And the multiplier starts to work for us. Again this is useful if you can operate the engine effeciently in the RPM range and the components will withstand the stresses of the higher RPM use. In a jetboat, the pump will operate most efficiently in the 5800 to 7200 RPM range. Build and engine to make the most torque in this range which will also extrapolate the the most HP and then size your impeller to run close to the peak HP.

Same thing with a v-drive, car, prop job, etc. Gear/prop to run in the best powerband of the engine and components. Now the big job is selecting the correct components to meet your needs within your pocketbook and expectation of other areas such as fuel requirements, etc.

Modern day Pro Stocks are one of the most effecient big cubic inch V-8 engines. Most of them exceed 1300 HP with 500 cid... How do they do it? They maintain torque at an extremely high RPM. Their peak RPM these days exceeds 10,000 RPM and they have a narrow powerband. These are very expensive, fragile, high RPM engines for a specific use. One of these things would not fall out of a tree in a jetboat at 6000 unless there was a gear reduction or some redesign of the engine.

Hope this helps.

Gear

Originally Posted by Gearhead

Modern day Pro Stocks are one of the most effecient big cubic inch V-8 engines. Most of them exceed 1300 HP with 500 cid... How do they do it? They maintain torque at an extremely high RPM. Their peak RPM these days exceeds 10,000 RPM and they have a narrow powerband. These are very expensive, fragile, high RPM engines for a specific use. One of these things would not fall out of a tree in a jetboat at 6000 unless there was a gear reduction or some redesign of the engine. Hope this helps.
Gear

Those high winding pro stock engines make impressive HP, but the torque number is not impressive at all,


It takes boost pressure to make big torque numbers over a broad rpm range.

Originally Posted by Unchained

Those high winding pro stock engines make impressive HP, but the torque number is not impressive at all,
It takes boost pressure to make big torque numbers over a broad rpm range.

It doesn't take boost pressure to build big torque, It takes volumetric efficiency and displacement to build big torque. Forced induction certainly helps, but don't for a minute think you can't build big torque numbers over a wide rpm range without it. All forced induction dies is add false displacement. As far as the PS engine, It doesn't matter if the torque numbers are low, the power (not tq, not HP, but power) is impressive. Unfortunately, it's only available in a very narrow window, but to generate the VE with that many cubes to make that much power, it has to be that way.
Torque and HP are both relative but they both work together to build power, and the most usable power in your application is what will be most effective and win most races in 99% of the racing community. One is the result of the other but neither is 100% definitive of an engine's capability.

Originally Posted by Sanger Flatbottom

Got in an interesting conversation today with a guy about which makes a faster boat, This guy tells me "torque" is what you want and I kind of disagreed with him. He says torque is what pulls you up to speed and horsepower doesn't count. So I was thinking... torque is optimum for heavy vehicles going fast, overcoming the wrong gears, or running it in a parking lot.

Well before I read anything else I'll say....tell your friend if trq is it then build a small diesel engine that makes 850 lbs ft at 3,500 and redlines at 4,400 and see how fast it goes in a jet boat or v-drive for that matter

I'll read some of the others later.

S CP

Jon

Originally Posted by steelcomp

It doesn't take boost pressure to build big torque, It takes volumetric efficiency and displacement to build big torque. Forced induction certainly helps, but don't for a minute think you can't build big torque numbers over a wide rpm range without it. All forced induction dies is add false displacement. As far as the PS engine, It doesn't matter if the torque numbers are low, the power (not tq, not HP, but power) is impressive. Unfortunately, it's only available in a very narrow window, but to generate the VE with that many cubes to make that much power, it has to be that way.
Torque and HP are both relative but they both work together to build power, and the most usable power in your application is what will be most effective and win most races in 99% of the racing community. One is the result of the other but neither is 100% definitive of an engine's capability.

Show me those N/A big torque numbers with a BBC like we would use around here.

Originally Posted by Unchained

Show me those N/A big torque numbers with a BBC like we would use around here.

Mark, everyone knows how you feel about turbos, but that's not what this thread is about.

Originally Posted by Sleeper CP

Well before I read anything else I'll say....tell your friend if trq is it then build a small diesel engine that makes 850 lbs ft at 3,500 and redlines at 4,400 and see how fast it goes in a jet boat or v-drive for that matter

I'll read some of the others later.

S CP

Jon

X2 But don't stop at some wimpy ass small diesel. Get with the program. Go for a Catepillar D9 with approx 3000 lbs ft @ 1200 rpm. Now that will get that flattie hauling

Originally Posted by Unchained

Those high winding pro stock engines make impressive HP, but the torque number is not impressive at all,


It takes boost pressure to make big torque numbers over a broad rpm range.

Originally Posted by Unchained

Show me those N/A big torque numbers with a BBC like we would use around here.

Mark, torque is 100% tied to VE. You can artificially stuff it, or do it N/A. Bottom line is it is the amount of air ingested, and the energy of the fuel being used. In fact you can compare bore/stroke combos for the same cid and the peak torque will be almost the same. The peak will just occure at different RPM, which translates into different HPs. But the peak torque produced will be very close.
LINK: 1460 lbs ft @ 6100