HP required to pull hills

ShinerBock wrote:
Your calculations may be a little off because my Excel shows that you can't even do 65 mph with 150 hp up a grade 7 and a truck and trailer total weight of 3,000 lbs.

It's probably correct, since it factors in the frontal area for a full size fifth wheel. It takes lots of horsepower just to punch that much frontal area through the air at 65 mph and doesn't leave a low hp rig much power to climb the hill.

Your calculations may be a little off because my Excel shows that you can't even do 65 mph with 150 hp up a grade 7 and a truck and trailer total weight of 3,000 lbs.

The results seem like very low numbers. A 150 HP truck should do almost anything.

wanderingbob wrote:
While you guys are doing the math I done drove back and forth over that hill several times !

Wow! Your truck must go 1,000 mph, because it only took seconds to do the math. Plug it into Excel and it is even faster.

While you guys are doing the math I done drove back and forth over that hill several times !

4x4ord wrote:

Cummins12V98 wrote:
I will be pulling my 35k combined double tow thru 6% grades next week. What should my low speed be?

44 mph if you hit a long steady 6%. Sometimes there are short sections with a 6% grade where the sign is but the overall grade is considerably less. To really know the grade of the hill you'd have to know the elevation at two points on the hill and measure the distance between them. Here is a link to an elevation tool.

Edit: I was thinking you had 3.42 gears so 44 mph was figuring you'd be approaching the redline in 2nd gear. You've actually got 4.10's. The 4.10 gears will keep you in 3rd at a nicer rpm but you'll only be at about 40 mph.... maybe a touch over.

Must be that good AMZ/OIL top to bottom that nets me 5mph more than your calculation. The slowest speed from NW WA to SoCal was 45.

Could also be that the Cummins delivers more of it's advertised HP to the ground than what you calculated. This is at 35k combined double towing my MC trailer behind RV.

You are correct there are times that the 3.42's will out pull the 4.10's. I have owned both and have experienced this.

Another thing to consider is purposely derated power numbers similar to the "gentleman's agreement" between the Japanese carmakers during the 90's and early 00's to not go over 276 hp even though many of their vehicles clearly had more than 276 hp.

Japan Dumps 276-hp Pact

SAE standards and advertising laws only states that you cannot go over the tested number. It doesn't say anything about advertising below that number. There have been other instances of manufacturers doing this based on wheel end dyno numbers, but these manufactures never confirmed.

Which SAE horsepower certification does that go by since both use different methods and can have the same engine with two different power numbers using either J1995 or J1349?

4x4ord wrote:

Cummins12V98 wrote:
I will be pulling my 35k combined double tow thru 6% grades next week. What should my low speed be?

44 mph if you hit a long steady 6%. Sometimes there are short sections with a 6% grade where the sign is but the overall grade is considerably less. To really know the grade of the hill you'd have to know the elevation at two points on the hill and measure the distance between them. Here is a link to an elevation tool.

Edit: I was thinking you had 3.42 gears so 44 mph was figuring you'd be approaching the redline in 2nd gear. You've actually got 4.10's. The 4.10 gears will keep you in 3rd at a nicer rpm but you'll only be at about 40 mph.... maybe a touch over.

Thanks, I will report back. The extra 2K and extra axle does slow it a bit compared to the 33k towing just the 5er.

valhalla360 wrote:
Another consideration is gearing.

Especially with older trucks, they may have difficulty hitting peak HP if they don't have a gear ratio that allows the RPM to reach the engines peak output RPM.

You're right. Taking an engine's torque and HP specifications describes two points on its power curve. The rest of the curve needs to be interpolated.