Understanding Dyno Readings -- is HP "real world" HP?

[russ_watters]

The ratios listed on the wiki are gearbox ratios. The diesel will have a longer final drive than the petrol engine.

Late edit on my above post, repeated:
https://www.fleet.ford.com/truckbbas/topics/2017/2017_F-250_F-350_F-450_SD_Pickups_-_Specs.pdf
Page 63 says the gear ratios are almost identical across several engines and elsewhere that the tire options are not engine specific.

 

[xxChrisxx]

Those are the ratios for the transmission unit only. The differential will have a reduction ratio as well.

Overall ratio = gear ratio * differential ratio
diff ratios are typically 2.xx:1 - 4.xx:1.

Have a look at Page 51, under axle ratios.

 

[russ_watters]

Those are the ratios for the transmission unit only. The differential will have a reduction ratio as well.

Overall ratio = gear ratio * differential ratio
diff ratios are typically 2.xx:1 - 4.xx:1.

Have a look at Page 51, under axle ratios.

The axle ratios are 3.3-4.3:1 and it looks to me like both a gas and a diesel can be had at 4.3:1 (F-350 and F-450). Am I missing something? Can you cite specific data?

 

[russ_watters]

Hopefully this one is more straightforward:
http://nissannews.com/media_storage/downloads/TITAN-XD-Diesel-vs-V8-Gas-Specs-FINAL.pdf

Nissan Titan:
Gas: 390 hp @ 5,800 rpm, 401 ft-lb @ 4,000 rpm, redline: 6,000 rpm, Final drive ratio: 3.357
Diesel: 310 hp @ 3,200 rpm, 555 ft-lb @ 1,600 rpm, redline: 4,200 rpm, Final drive ratio: 3.916

Hopefully, "final drive ratio" is the ratio between the engine and the wheels? Or is there still another ratio I'm not seeing?

Clearly, these ratios are too close to make up for the differences. For the sake of argument, let's assume a wheel 6' in circumference. That's a redline speed of 122 mph for the gas and 73 mph for the diesel. At any particular speed and gear, the diesel will provide better power (for acceleration, towing or hill-climbing) right up to the point where it can't go any faster...and the gas can. But the gas driver can make up most of that by running in a lower gear.

 

[Moretorque]

The reason I made this thread is because Ketch said it was a real interesting hypothesis and he would get together with his drag buddies and figure it out but that was several months ago, he claims he has the answer as of the other day and will post on it.

Let me start fresh, I understand all the HP and gear lingo and that is not what I am after.

The ? is can you gear around a major lack of torque and one group says no and the other yes. This is crucial in being able to understand what a dyno is really telling for motor application.

The ship engine is just a example of extremes and the semi is in the middle.

It is my opinion and I could be wrong that a engine that makes 2300 HP at 270 RPM which equates to 44,000 thousand foot pounds of torque could accelerate 1200 hundred tons to speed which is 30 loaded semis.

Hypothetical we will say 2300 hundred HP will run 1200 hundred tons at 40 MPH on flat land.

The ? is can you drive that 1200 hundred tons to that point of 40 MPH with any 2300 HP engine and gearing.

Even the top engine builders said Nasa science and a billion $ transmission you may be able to figure out how top do it but not at all in a practical sense.

OK you ask the 2300 HP Pro Stock engine to do this task, we will give you 20 gears each gear represents 2 mph. Now I am fairly sure it would not be able to get it going of the line if you fed it a 2 MPH first gear so let's say you give the engine a head start by pushing the 1200 ton load to 20 MPH and have the Pro Stock engine kick in- in 10th gear and let it drive the 1200 tons at 20 MPH. It would be able to run it at 20 MPH but when you shifted to 11th to try and go 22 MPH it would crash because it cannot drive that load. Then you accelerate the load to 40 MPH and then let the Pro S engine take over again at 40 MPH in 20th gear and it can keep it going 40 MPH.

It's not that it lacks the power it lacks the drive coming from the crank to build RPM under such tonnage, this is what the engine builders were saying and they were saying a lot of people do not understand this so a higher torque engine is more powerful in real world use even though on paper they may look the same and you just gear for what you want.

I am saying even if average HP at RPM are similarly matched and the higher rpm turning engine is not peakier.

You need more gears on the engine with less torque and it gets to the point under heavy load to where it collapses in it's abilty to build it's RPM under load...

""""" Edit let me make a correction to this and here is where I am LOST. """"""""

Both engines the ship and the Pro Stock have 50% torque rise meaning they make the same average HP over their individual RPM operating ranges.

My brain says the Pro Stock engine would need more gears to drive the big load load if it could over the ship engine,

I am probably wrong about this but when I look at real world it just seems right to me...

 

[russ_watters]

The ? is can you gear around a major lack of torque and one group says no and the other yes. This is crucial in being able to understand what a dyno is really telling for motor application.

I would hope by now you know what the correct answer is (whether you accept it or not), and why. Can you repeat it back to me so I know you are paying attention to what you have been told? I don't want to go around in circles.

The rest of your post is more gibberish and handwaving of the same type as before. It provides you no value and I once again urge you to be more rigorous in your analysis. You are never going to have a reason to believe what the science/math tell you if you just keep throwing out meaningless numbers and gibberish phrases!

 

[RogueOne]

Yes, you can gear around low torque coming off the crankshaft, as long as it has enough horsepower to do that amount of work. All you are doing is increasing the leverage that the engine has over the load that it is trying to move.

 

[jack action]

The ? is can you gear around a major lack of torque and one group says no and the other yes.

The answer is «yes».

The ? is can you drive that 1200 hundred tons to that point of 40 MPH with any 2300 HP engine and gearing.

Yes.

Even the top engine builders said Nasa science and a billion $ transmission you may be able to figure out how top do it but not at all in a practical sense.

It wouldn't cost a billion $ to build such a transmission as there is no magic about the concept. But it is true that such a drivetrain would probably not be practical (too many gears to shift, loosing power between gears).

It's not that it lacks the power it lacks the drive coming from the crank to build RPM under such tonnage, this is what the engine builders were saying and they were saying a lot of people do not understand this so a higher torque engine is more powerful in real world use even though on paper they may look the same and you just gear for what you want.

Yes it is because it lacks power. Because the engine drops to a rpm that delivers a lot less power.

I am saying even if average HP at RPM are similarly matched and the higher rpm turning engine is not peakier.

You are maybe saying this, but you are constantly referring to examples which do not have the same average HP at RPM (Pro stock & large diesel truck engines). If they were, you wouldn't see a difference in the power delivery. Even the number of gear ratios would be the same. The only difference would be the final drive ratio.

 

[Moretorque]

Thanks for all the replies, I edited my previous post above # 35 to make it real short and sweet to my real ? and belief so for those interested please refer to it.

I am admitting I am probably wrong about this but I am real curious.

Thanks Jack for pointing out my error in above post .

Any input is welcome and thanks...

 

[RogueOne]

Here is the answer to your question:

When you move the system, you are doing work to it. If you do work to the system, you move it.
If you have an engine that is capable of making 5 horsepower, then it can do 5 horsepower worth of work to the system. If you have an enormous load, then you can move it with that 5hp engine by gearing the engine (giving it a lot of leverage) over the system. The gearing increases the amount of twisting force that is applied to the load. However, it decreases the RPM at which the twisting force is applied. So the engine is making the same horsepower and torque at the same speed as before, but that is being used to drive a gear that has a lot more twisting force over the load that you're trying to move.

You increase the twisting force being applied to the load. You decrease the speed at which the twisting force is applied. The horsepower output is unchanged by the gear ratio, aside from parasitic friction (minimal losses). The gears connect the engine to the load or object that you're trying to do work to. The engine operates at its normal speed and makes its normal amount of torque as well as its normal amount of horsepower.

Look at gears like they are levers. They give leverage. If you have a large enough lever, you can move any load by putting any amount of force on the side farthest from the fulcrum.

 

[Moretorque]

Thanks for the above post, it's my fault because I did not understand how to explain what I was looking for.

Here is an example that sums up my belief which could be wrong and according to most it is but some have said it is correct but I believe I may have misinterpreted what they told me from not giving them all the correct parameters. It is basically all things being equal does a engine that makes the power earlier have more power.

The Mack Maxidyne 238 RWHP was known to be able to push 35 tons to 62 MPH with just a 5 speed. It has a torque rise of 52% and was considered a little GEM. Underpowered by today's standards but the speed limit was lower decades ago.

You have the Mack Maxidyne that makes 238 HP at 1500 RPM and you have another engine that makes 238 HP ay 4500 RPM. We will say they both have torque rises of 52% so the power bands are identical on paper and you just cut the gear ratio by 3 for the second engine and they should be the same in real world use.

Now the Mack does have the advantage of more torque coming off the crank to get the load up and going and as stated it was mated with just a 5 speed to move 35 tons to 62 MPH. It is my belief the second engine in this comparison could not do the job near as well with a 5 speed and would need more gears to drive the load as well even though they were all laid out the same ?

This is what I am after.

It means HP is HP if I am wrong or the dyno lies and you better be able to make adjustments because something is lost in math translation...

 

[russ_watters]

Ok, that's enough. You can either accept the answer or not, but the thread is going around in circles and not getting anywhere and I won't let it keep wasting our time. Closed.