Torque vs. Horsepower

[thgoodman]

My '06 Beaver Patriot Thunder has a C-13 Cat rated at 525hp. The guy parked next to me last week had a similar size MH (looked like a Prevost but wasn't). It also had a Cat C-13 but it was rated at 475hp but with more torque. I know Cat can change engine ratings both mechanically and electronically (i.e., injector timing?) but I don't know why the coach builders' design specs call for different ratings.

What I don't understand is how the torque/horsepower trade off affects vehicle performance and if there would be any advantage to going back and paying Cat to making a change to my engine specs (what would I ask for?). How do the changes affect hill pulling, towing, city vs country driving, fuel mileage, etc? Could the average Joe sitting in the driver's seat even feel the difference if the modifications were made?

[neil57]

Cat engines come in many power levels,some ratings are motorhome specific or because of cooling or transmission capacity. If you feel you are lacking power(525 is probably lots) Cat can put it on their chassis dyno and give you a detailed report. A reflash of your computer is $5-600 plus cost of dyno time. Your right foot and road speed has more to do with fuel economy than any engine rating. Unless you are pulling a large trailer behind,100 lbs. torque would not be felt in the drivers seat. Hope this answers your questions.

[wolfe10]

hone eagle wrote:

wolfe10 wrote:

hone eagle wrote:
Nobody mentions that Cat 'gives' the power it thinks the chassis can cool,the better they think the cooling system is the higher they will set the power.
Check out marine installations ,much much higher power and boats are always going uphill.

Common across the industry. Same goes for Cummins. In marine applications where cooling capacity is infinite and engine load is much more constant, AND emission standards are lower, indeed power is higher than in on-highway applications.

OK the OP asked if the power can be changed ?He was comparing his installation to another different builder ,its possible his at the limit for his chassis and the other has a higher capacity cooling system?
apples and oranges but still fruit ?

Absolutely. Cooling system, transmission, etc could certainly be different. And, different year models of the same engine (but with different emission specs) can and are often different.

Since this is a Caterpillar, I would start with a call to Caterpillar (877 777-3126) with the engine serial number. They can tell you exactly what HP your engine made on the dyno before leaving the Caterpillar factory. Not just what is SHOULD make, but what it actually made.

They can also tell you if an upgrade is possible.

Be sure to ask if it changes torque and HP at "normal RPM"-- many higher-HP engines only make the additional power way up in the RPM range.

[hone_eagle]

wolfe10 wrote:

hone eagle wrote:
Nobody mentions that Cat 'gives' the power it thinks the chassis can cool,the better they think the cooling system is the higher they will set the power.
Check out marine installations ,much much higher power and boats are always going uphill.

Common across the industry. Same goes for Cummins. In marine applications where cooling capacity is infinite and engine load is much more constant, AND emission standards are lower, indeed power is higher than in on-highway applications.

OK the OP asked if the power can be changed ?He was comparing his installation to another different builder ,its possible his at the limit for his chassis and the other has a higher capacity cooling system?
apples and oranges but still fruit ?

[wolfe10]

wny_pat wrote:
And it really gets complicated when one manufacturer measurers torque/horsepower at the flywheel and another measures it at the wheels.

Not aware of any engine manufacturer who measures at the wheels. Not even sure how that could be done. With the same engine, the chassis builder makes many decisions that affect HP at the rear wheels:

Alternator size/output-- the larger the output, the more HP it takes.

Dash A/C compressor size-- same issue.

Rear mounted fan (solid) vs clutched fan vs hydraulic pump for side radiator.

Air compressor for air brakes and/or suspension vs no air pump.

Bottom line, WAY too many chassis builder options for an engine manufacturer to rate "at wheel HP" even if they wanted to.

[wolfe10]

hone eagle wrote:
Nobody mentions that Cat 'gives' the power it thinks the chassis can cool,the better they think the cooling system is the higher they will set the power.
Check out marine installations ,much much higher power and boats are always going uphill.

Common across the industry. Same goes for Cummins. In marine applications where cooling capacity is infinite and engine load is much more constant, AND emission standards are lower, indeed power is higher than in on-highway applications.

[hone_eagle]

Nobody mentions that Cat 'gives' the power it thinks the chassis can cool,the better they think the cooling system is the higher they will set the power.
Check out marine installations ,much much higher power and boats are always going uphill.

[wa8yxm]

Gee, I always thought Torque was a measure of how much "Twist" (Torque) it could put on the output shaft and Horse Power was how many 33,000 pound train cars it can lift one foot in one minute... (A very very old way of measuring horse power). (NOTE: I actually looked this up. 33,000 foot pound/minute

So torque is foot pounds but static, HP is dynamic.

[wny_pat1]

And it really gets complicated when one manufacturer measurers torque/horsepower at the flywheel and another measures it at the wheels.

[Koop]

As someone already mentioned, torque is force that can be measured on a dyno. Horsepower is a calculated value that represents work over time (power).

The formula for SAE horsepower is torque (measured in lb/ft) X RPM /5252
(torque times RPM divided by 5,252)

This formula illustrates how two engines with the same peak torque can have different horsepower ratings. It depends on what rpm that peak horsepower is achieved at. The torque curve influences which at which RPM we achieve maximum horsepower.

I hope this simplified explanation helps.

[wa8yxm]

Oldme wrote:
Another analogy I like:
HP= how fast you can hit a wall
Torque- how far you can push that wall.

I like it Oldme. I like it.. A good rewrite of what I posted. 🙂

Kind of like what I say about 4-wheel drive in bad weather.

Yes, A 4-wheel drive can "Go like the wind" on roads where a 2-wheel drive would be stuck.

Problem is: it also STOPS LIKE THE WIND (When it hits something).

[Seamutt]

You folks want to talk Horse power and torque, check this out

http://www.gizmag.com/go/3263/

[davebrown]

bobman wrote:
The combustion temperature is determined largely by the correct mixture ratio of fuel to air if the boost goes up ( meaning more air is being packed into the cylinder ) then the computer must compensate by lengthening the time the injectors are open to inject more fuel and keep the proper mixture

If that didn't happen the engine would run lean and if lean long enough the exhaust temp will exceed the rating the valves are designed for

yes I know how the system works I have just never seen it protrayed the way u did,Its called EGT and it for valves and pistons etc just never seen it as :Fuel delivery has to match the combustion volume to keep the valves in the correct temperature range

[Oldme]

Another analogy I like:
HP= how fast you can hit a wall
Torque- how far you can push that wall.

[wa8yxm]

Basically TORQUE is how fast you accelerate, HP is how fast you can go (Within some limits like valve float).

Another factor.. With more POWER (HP that is) the engine is less stressed at highway speeds.