Forum Discussion
- To me, there are two difference types of power numbers. Peak power and usable power. What good is 400 peak hp if it is at such a high 5,000+ rpm that the only gear you could actually be able to use 100% of it with the torque converter locked at a reasonable road speed is 2nd gear? This is the case with most gas N/A truck engines. After third gear, you will never even come close to reaching that high of a road speed to get to the rpms to hit peak power with the TC locked. If the TC is not locked then you are not getting 100% of the engines power to the wheels depending on how efficient your torque converter is. This makes that peak power useless unless I was using my truck for racing.
In contrast, my diesel will hit its peak horsepower at 2,800 rpm in multiple gears and at reasonable speeds with the torque converter locked. It will hit peak horsepower in 2nd at 46 mph, 3rd at 59 mph, and in 4th at 81. This makes that peak horsepower more usable for towing and passing situations. RCMAN46 wrote:
4x4ord wrote:
Torque and horsepower ratings together help to explain the power curve of an engine They are both valuable numbers.
If a gasoline engine with 440 hp at 5800 rpm and a peak torque of 465 lb ft at 3400 rpm was stuck in a f350 with a rear end gear ratio of 7.1:1 it could be expected to pull identical to a 440 hp Powerstroke diesel installed a similar truck with 3.55 gears.
I would agree only if the gasoline engine was turbo charged or if they are only operated at sea level.
440 HP at the flywheel is 440 HP at the flywheel. If the gearing allows an engine to make that much, it doesn't matter. HP is a measure of work being done.myredracer wrote:
The guy in the video seems like a kid fresh out of mechanical engineering school regurgitating his book learning. :) Kinda like I would have been at that age. He actually has a decent video on why engines don't need exhaust back pressure.wilber1 wrote:
I believe it was actually Fiat that developed the first DOHC engine in 1912 followed by Peugot in 1913 and Alfa in 1914. I think it was Fiat that was also the first or one of the first to use belt driven overhead cams.
Overhead cams go back before WW1. A 1912 Peugeot race car which won the French Grand Prix was the first DOHC engine. Several WW1 aircraft engines used overhead cams.
Could be. I know the Fiat 124 Spyder that came out in 66 had belt driven DHOC's.4x4ord wrote:
Torque and horsepower ratings together help to explain the power curve of an engine They are both valuable numbers.
If a gasoline engine with 440 hp at 5800 rpm and a peak torque of 465 lb ft at 3400 rpm was stuck in a f350 with a rear end gear ratio of 7.1:1 it could be expected to pull identical to a 440 hp Powerstroke diesel installed a similar truck with 3.55 gears.
I would agree only if the gasoline engine was turbo charged or if they are only operated at sea level.- Torque is force. Horsepower is a calculation: Torque x RPM divided by 5250.
A motor that makes 500 ft/lbs at 4000 RPM will have twice the HP number of a motor that makes 500 ft/lbs at 2000 RPM.
You could build a giant engine that made one million ft/lbs of torque at 10 RPM. It would only be 190 HP.
Let’s say you have to remove a very tight bolt. You put a wrench on it and apply torque. If the bolt isn’t moving, you are still applying torque but no horsepower, since there has to be RPM (the bolt has to be turning) to measure any horsepower.
Torque is how hard you pull on the wrench.
Here’s another analogy. If you’re riding a 10-speed bike at 10 MPH, you could be in 1st gear pedaling lightly but very fast to create the total power needed to cruise at 10 MPH.
You could also be In 10th gear, pedaling really hard but very slowly to create the power to cruise the bike at 10 MPH.
The former would use less torque and more RPM at the pedal crank, the latter would use more torque at less RPM, and both created the same result, the horsepower to move the bike along at 10 MPH. - Think of horsepower as a water pump. One 400 horsepower motor will pump the same as any other 400 horsepower motor, regardless of the fuel. One might be screaming, one might last forever, one might cost ten times what the other does, but they will all pump the same amount of water during the test. By definition, that is what horsepower is. The water pump has no way of knowing what kind of fuel is in the engine. (I know that some horsepower ratings are/were jacked up by auto manufacturers) I am only talking about real 400 horsepower engines regardless of what is in the tank.
- The guy in the video seems like a kid fresh out of mechanical engineering school regurgitating his book learning. :) Kinda like I would have been at that age. He actually has a decent video on why engines don't need exhaust back pressure.
wilber1 wrote:
I believe it was actually Fiat that developed the first DOHC engine in 1912 followed by Peugot in 1913 and Alfa in 1914. I think it was Fiat that was also the first or one of the first to use belt driven overhead cams.
Overhead cams go back before WW1. A 1912 Peugeot race car which won the French Grand Prix was the first DOHC engine. Several WW1 aircraft engines used overhead cams. 4x4ord wrote:
If a gasoline engine with 440 hp at 5800 rpm and a peak torque of 465 lb ft at 3400 rpm was stuck in a f350 with a rear end gear ratio of 7.1:1 it could be expected to pull identical to a 440 hp Powerstroke diesel installed a similar truck with 3.55 gears.
Of course the transmission couldn't be allowed to select the proper gear for your example to be valid.- Torque and horsepower ratings together help to explain the power curve of an engine They are both valuable numbers.
If a gasoline engine with 440 hp at 5800 rpm and a peak torque of 465 lb ft at 3400 rpm was stuck in a f350 with a rear end gear ratio of 7.1:1 it could be expected to pull identical to a 440 hp Powerstroke diesel installed a similar truck with 3.55 gears.
