I've read the basic explanations and get that HP is top end torque is power and quickness. What I'm not correlating is real world applications. I'm doing some tire kicking and research. Assume the tow vehicle weighs 4000 lbs and the trailer 1500.

Am I correct about the effects of the following combinations?

200 HP and 300 ft lbs.

300 HP and 300 ft lbs.

The above would mean a higher top end but the same towing capability and acceleration. There might be a little help from the higher top end in that one could make a run going up a hill. Instead of starting at 60mph and slowing to 50 under a heavy load the higher HP would allow starting at 70 and slowing to 65, yes??


200 HP and 200 ft lbs.

200 HP and 300 ft lbs.


The second comparison would be the same top end but increased torque would tow more or accelerate quicker. Also maintain speed going up a hill, yes??


As for the rear end... going from 3.21 to 4.30 decreases mpg and increases torque. Is it correct to say that the differential only keeps the torque applied at a constant rate (the amount of torque controlled by the gas pedal)??

Dan

I have a 1985 Monte Carlos SS that I used to tow a 24 foot Searay Mid Cabin Cruiser for j22 years.



The original engine as a 305 V8 with 180 HP and a whopping 240 ft.lbs. of torque. Boat and trailer weighed in at 5200 lbs. Note, I used a dead weight hitch for the first 3 years and went to weight transfer for the remainder of years I had the boat. Any trailer over 3000 lbs. of towed weight I recommend using a weight transfer hitch because the increase in stability is worth every penny.

Towing with the 305 required running the transmission in drive and holding speed to 55-60 mpg. On a 720 mile tow that seems like a snails pace. Engine speed with the 373 rear in the Monte had the engine revs at about 3000 RPM and mileage was 10-12 mpg depending on the quality of the fuel. BTW, Sunoco on the New York Thruway was nothing but Octane Cheaters running 86 octane in the premium fuel tanks. Used to call the State Police and complain about it and it never changed, I'll bet they still get kickbacks from Sunoco because their premium is NOT a higher octane fuel.

In 1995 that old 305 was getting tired and starting to use some oil so I purchased a junkyard 350 out of a C1500 pickup. Went full house on that 350 and the Fuelie Heads my brother donated and ended up with over 400 HP and more than 350 ft.lbs. of torque from 1700-5200 RPM. Note, when you build an engine for Torque you can end up with a heck of a strong motor for any type of use. In this case I could not use full throttle in second gear because it would slip. Tried an Art Carr race spec. tranny and it blew up after 15K miles. Anyhow being mindful with second gear that engine worked well for tow duty. Installing a NASCAR grade Becool radiator also helped. Overheating in any condition did not happen. With this engine I would put it in overdrive and set the cruise control at 68 mph and just roll. Fuel economy was about 1 MPG better than the 305 at 11-14 MPG. Still had to run premium so I would arrange my stops so I could avoid the thieves at Sunoco. Best gas for economy was either BP or Shell.

In 2007 a valve seat fell out on the #3 cylinder and wiped out the engine. Scored the cylinder and chipped a piston, so I had a dealer in Lake George NY order in a HT383 from GMPP. Total cost was 5500 bucks installed but it's a strong motor with good torque and it's a bit less sensitive to octane than either the 305 or hand built 350. It's also a bit less powerful than the 350 so I can nail the gas from a stop and never feel any slippage from 2nd gear. BTW, Popular Hot Rodding took the HT383 and machined the valve guides for 0.030 inch more lift and slipped in a hotter cam and hit 497 HP with this engine. If I had an extra 12 grand for a transmission and controller I could have a pretty darned fast Monte Carlo.

My examples are all over the board, but may help you understand. Think of torque as the amount of power to get you going from a stop (low RPM), and HP is the amount of power to keep you going (higher RPM). There are many variables in determining HP and Torque, like camshaft lift & duration, heads, etc... But there's also stroke. Not what you are asking, but compare 2 different engines, a Pontiac (long stroke) and a small block Chevy (short stroke)

A Pontiac is a long stroke motor, and will produce most of its power low in the RPM range. In a drag race, the Pontiac will generally take off the line quicker as it will generally have more torque. The Chevy engine has less torque, but probably more HP, and the HP will come in at a higher RPM. The Pontiac may jump out to an early lead, but the Chevy will catch up to it by the end of the 1/4 mile.

High torque engines will also generally have a lower max RPM. My GTO runs out of power at about 5,200 RPM, but a small block Chevy makes tons of HP above 5,200.

As an extreme example, consider a tractor trailer. It will have a few thousand ft-lbs of torque, but maybe only a few hundred HP. It needs the torque to get 80,000 lbs moving. All low RPM "pulling" power and probably won't rev much of 2,500 RPM or so (guessing here).

If you're talking about the differences in the same engine, a camshaft with a shorter duration @ .050" lift will have more torque, usually called a towing or RV camshaft. It will make most of its power in the low to mid RPM range. A "race" camshaft will have a longer duration at .050" lift and produce more power at higher RPMs.

Countless articles have been written on camshaft & engine theory and how it relates to muscle car engines!...My area of interest!

Horsepower = torque x RPM/5252.

You will need manufacturer's engine curves (RPM vs. Torque/Horsepower. Choose engine having greatest torque at a given RPM level.

You are correct gearing can only multiply engine crankshaft torque. Lower gearing (numerically higher ratios) multiply torque while increasing RPM and decreasing vehicle speed (and gas mileage).

As a "rule of thumb" you would like the engine RPM to be 1600-1700 RPM cruising at highway speed.

Not sure if this helps Detroit Diesel DD16 is rated at 2050 pound feet torque (850 rpm) and 600 hp (1700 rpm). Dodge Hellcat 807 hp and 707 torque.

One pulls 100,000 lbs uphill the other pulls 9 second quarter mile times. Horse power is a deceptive figure, it is a mathematic calculation meant to describe how fast work is being performed. Torque on the other hand is how much work is being performed.

Dad always said torque was what lifted your heels when you bended it down to pee in the morning.

You’re going to want your torque peak to be inside the rpm range that you expect to use while towing. I would not expect to run an engine used to tow for extended distances at much more than 3000 rpm. High torque at low rpm will calculate to modest horsepower but the engine will be easy going and strong. A lower torque figure at high rpm may calculate to the same horsepower but the high rpm engine will be less enjoyable to use for extended towing.
Gearing makes a huge difference if your engine is designed for the rpm at which you'll end up towing. More mechanical advantage and higher rpm which on average means more engine power for any given speed.
There is no substitute for diesel or cubic inches for towing. Less shifting, easy going rpm range, and a long service life.

Please remember that torque multiplied by engine speed divided by a numerical constant equals power.

Power (hp) = torque (lb - ft) x speed (rpm) / 5252

This guy breaks it down pretty well.

https://www.youtube.com/watch?...EngineeringExplained