Technical Why horsepower and torque curves cross at 5252RPM

Baring some factor outside the parameters you mentioned, The vehicle should be going the same speed with either engine. If both are turning exactly 7000 rpms and using the same gearing, then the result should be the same no matter the power of the engine. In real life, seldom are things exactly repeatable when racing, so there could be some variation when comparing results. This is simply a gearing question if both are turning the same rpms.

Exactly right. Now.......thats a more real world comparison. Again, if someone picks a target rpm.........then the ONLY variable is Torque. Find a way to increase Torque and you increase the "result"
400tq x 4500 rpm = 1,800,000
375tq x 5500 rpm = 2,062,500 344tq x 6000 rpm = 2,062,500 295tq x 7000=2,062,500
376tq x 5500 rpm = 2,068,000
400 tq x 5500 rpm = 2,200,000

Whatever modification someone makes to an engine to improve its volumetric efficiency.......comp ratio,lift, duration,fuel ratio, etc........it must increase the torque at that rpm to increase the result (HP)

Exactly Right !
No matter what rpm the engine is operating at (above peak torque or not). Even though the torque available at a higher rpm may/will be less than peak torque .......the number of combustion cycles will raise the power output because its using the available torque more times per minute.

 

Bingo- running it out a little past peak lets you pick up the next gear at a stronger point, with the available gearing, and you gain overall. The gear ratios in that Maxitorque transmissions were very carefully matched to the Maxidyne engine. It worked, I have driven them- and the sound was incredible at WOT at 1200 RPM peak torque. They also worked up a Maxidyne V8 engine with a similar torque curve that worked the same way. Car, tractor, truck whatever, basics of torque and HP are the same- torque does the work, HP is a mathematical tool to measure the work done, and why the curves cross at 5252- pure math

 

So, the same RPM is it? That means we can build a 400HP @ 7000RPM engine and go the exact same speed.

To me, it's like those desk toys with the 5 ball bearings. If the same angle is used from a single ball with twice the weight, does it move 1 ball or 2? Is an internal combustion multi cylinder engine as linear in output as an electric? Each cylinder is punched harder. If that means nothing, why? Brain food...

 

I think that's over simplified, but the way you're wording it makes it a simple gearing equation. 7000 rpms is 7000 rpms; the amount of horsepower the engine is capable of is not part of that equation. IF the lower HP motor can pull the load at the same RPMs, than all else being equal, the speed would also be the same. Right?

 

In order to get results from a hypothetical situation, you need to give all the factors involved. Highlanders example left too many open ended parameters.

If both engines could turn 7000 rpm , at 7000 rpm the speed of the car would be exactly the same, if all other factors were the same( wind, traction, etc.). Now, you may need the extra horsepower to turn that 7000 rpm, in which case the 750 horsepower engine would be faster.


Bones

 

When I was working as an estimator/ project manager, this Commiefornia crap came up, and I sold off a lot of stuff for the company, much going to Mexico and El Salvador- but some got "modified" to get us in the 2500hp and under category. A solution for a lot of stuff? Adjust the HP, by turning down the governor. There was a big emphasis on "under 50HP". I had to sell three fairly new tow-behind air compressors, as turning down the governer doesn't work well on them. The new ones we bought had proudly displayed on the back "49HP". Some of the engine manufacturers like Deere put up charts on their sites that showed you what RPM to set the engines down to that gave you 49HP, and they would be legal then
https://ww2.arb.ca.gov/resources/documents/road-fleet-average-calculators

 

This is 286 HP at work- at about 1200 RPM. Torque rise AKA "bellarin' louder"

 

I don't know what load you are placing on your engine or how it is geared. You say you can make either engine turn 7000 rpms under whatever load you have. If your 400 HP engine can reach 7000 rpms under the exact same load, you will be going the same speed. The question is at what point do you have an engine that can't reach 7,000 rpms under that load. A 2,000 HP engine will also go the same speed at 7,000 rpms and the same gear/load. I'm not sure what you are trying to get at, but it seems pretty simple to me.

 

Your scenario said that one engine was rated at 400hp and the other was rated at 750hp. Both ratings were measured at 7000rpm. That figure has little to do with what final rpm will be achieved at terminal velocity, or exactly how quickly it will get there.

Forget the 7000rpm figure. It is only there to state where the engine makes the peak hp output. It is meaningless from that point on if all other things remain the same.

The 750hp rated engine has more torque available, simple as that. It will accelerate to terminal velocity quicker because each piston fire is giving a bigger punch to the crank. It will also get to a higher final speed because it will have the power to get to a higher final rpm rate.

What you are missing is that the final rpm rate of either engine has absolutely nothing to do with the 7000rpm figure used to calculate the peak horsepower. The determining factor will be power vs load.

 

Look just like our old D-9 Dozer!




Bones

 

That should be the slightly later 320 HP version- with the dual air cleaners

 

Thanks, she was a workhorse on the ranch!





Bones

 

I guess I have a hard time accepting that a 4 cycle engine makes work exactly like a 60 cycle electric motor. The only thing they have in common is turning rotational energy into work. My thing is how that work is done and what effect it can have on the outcome. Sure we can bend and twist and shoot for a specific star. MPH is an excellent metric of how, or how much, power is made. Change nothing in your drag car except power. Convertor, gear, launch, tires, temp, track conditions, barometer, all the same. Add a bigger carb or whatever for more power and your terminal RPMs are the same but you get there quicker (ET) and you go faster (MPH). Now you can tell me I'm full of shit or I don't know how to read a tach or I wanted it to be that way so bad I was seeing things. Sorry dearly beloved, this old fat fuck has been there, done that, even DO have some T Shirts. Got me thinking, what if I'd done that on the salt or Maxton? Why did this happen? How much more power? I tested a Da Vinci 1200-something CFM Dominator on my race motor vs my regular ol 1050. I went quicker and faster at the same RPM and shift points. Not a lot, but notable. Almost a tenth, 2 MPH faster. This was a car I made hundreds of passes in. I didn't miss things, it was all habit, muscle memory, 2nd nature. The improvement while notable was moot. I was bracket racing. Was not worth the $650 he wanted (1995). My initial thought was I'd run out of gear because of the increased CFM, more power, blah-blah-blah. Through the traps exactly 7600, as always. Ok, I'm in the dunk tank so throw the balls and tell me...what? 1/4 mile don't count? Wrong dynamic? Too short to consider the possibility?

4 cycles vs 60 (not accounting for companion cylinders or cyl count). I believe the same thing might happen in a speed trials car and why I think that. Just like the desk toy mentioned above. I may have never thought this had I not made the change/improvement back then in my racecar. Next...?

 

Not being disrespectful, but if you were still getting EXACTLY the same 7600rpm across the line, you can't have been going 2mph faster. Not physically possible if all other things remain EXACTLY constant. I agree that the elapsed time of the run could have been quicker by a tenth, but only because you got to the 7600rpm earlier due to the power increase. Sounds to me that the terminal maximum rpm that your engine could achieve was 7600rpm. Or the finish line revs were actually a little more, maybe an extra 100 or so rpm, to get the extra 2mph.

Or, as you would know, very slight and unnoticeable variances in other areas (traction/air temperature/relative humidity/etc) can give noticeable variations in ET and mph. You won't be able to physically feel the change in these things, but the computer timing will show up the effects.

And, torque works the same way in any rotating motor/engine, whether it is electric or internal combustion. The torque is simply a function of the force and the 'moment' (think lever arm length, or the distance from the rotational centre that the force is applied). It works exactly the same way in either situation.

 

I hope this isn't taken as an argument. It's a theoretical discussion among interested parties, and this car life doesn't get any better.

There are math equations that help measure work over time and can give us power output based on results. I'd be lying if I said I remember how much extra power it made to 2 MPH faster at the end. And ok not a full 2, like 1.86 (close enough for coffee talk). That lone event began this, because how, why, I wonder, etc. Maybe it is because 1/4 mi is a short distance. Maybe in 10.41 seconds isn't enough time to register why may or may not happen. From launch to the traps it worked harder and produced a result. Where else would/could this result show up is the seed that was planted, and if here yes, but why not in a longer measure? My only conclusion was work cycles. Like I said before, I may be full of shit and have been told as much.

 

I believe that you believe what you are saying. I think you have presented your thoughts/beliefs in a respectful and objective way. No personal attacks and well done. I think thats the best way when people have different viewpoints. You don't have to agree with me and vice versa......but we can still respect what is said in an honest difference of opinion.

Let me ask you this, since you like to use electic motors for comparison.

If you have 4electric motors using different combinations of voltage and phase and they all drive the same gear box on a machine. The gearbox has minimal resistance because it is a light duty fan that is being driven, and the gear ratio is a simple 2 to 1.
The motors are : 1/2 HP Single Phase 120 Volts 1725 RPMs
2 HP Single Phase 240 Volts 1725 RPMs
5 HP Single Phase 240 Volts 1725 RPMs
10 HP Three Phase 440 Volts 1725 RPMs

My question is, since the gearbox and fan have minimal load resistance, how many rpms will the fan be turning with each motor?

Now, going back to your example with the drag car. There may be a difference at the end of the track because the acceleration rate is different and you are essentially "passing thru" 7000 rpm rather than operating a vehicle at a steady state at 7000 rpm. We both have opinions, and I respect your experience. We all can learn from differing viewpoints.

 

Excellent thought. All cycled or holding at 1725, but what is different between each. The higher powered motor will essentially work "easier" and create less latent heat to do the work. The 1/2 HP will be hot to the touch doing the work. The 5 will be much less, run cooler, and although not cheaper to run will certainly not use excess energy. But electric is linear power delivery. The difference might only be seen at the meter because the work is an established target. The lights might dim running the 1/2 or 2 HP and maybe not at all with the higher variants. 440 3ph, pennies. In those examples we could ask more work of each one with excess ability. Run 2 fans.

I would have to dig up and sort time slips then find which one was which, etc. Then I'd have to find my book with the power calculations to see what I actually produced. I remember it because back then it sparked this thought, and like most felt that X gear with Y motor using Z convertor and trans driving 3645# to given speed is a max of A mph. I went from about 124 MPH (123.8, 124.2, 124.1, etc) almost all the time to just a blip under 126, I think 125.8 was the best number.
A more dramatic change came when I reduced weight by almost 100#, went to a bigger cam and had the trans freshened up. The weight reduction and a 200 RPM higher shift point gave me a drop in ET of .1 (a car length) and an increase in speed of 129.86. Same gear, convertor, even tires. Same asshole at the helm too Same RPM at the finish line because a shorter shift would have me "run out of motor" in the traps. 7600 was edgy but safe, 7800 felt like borrowed time, which short-shifting would do. That was a lot of changes and the end result was essentially measured acceleration, and while it almost played to this big question the rate of rise was faster as a whole. From a several hundred round average in the mid to low 10.40s at 124 I went 10.32 at 129.86. I have to add that I used to be consumed with barometer, temp and humidity readings because the goal was consistency. It became such second nature that by test pass 2 I knew what I'd get. Good ol Detroit Dragway was super consistent condition wise. If I could have dialed by 60' times or MPH I'd have been unbeatable
Anyways, the end result of the electrics is measured linear energy delivery. And frankly thinking through this again it seems the only logical or mechanical reason is the change in how the power is delivered. There is no other answer, for me that is. We can't feel or even always hear the cyclical energy pulses of an internal combustion engine. The increased energy of each pulse does a measure of extra work. It can (might) be seen or measured as MPH to us car guys.

 

Ok, take note, the PULSES FROM THE PIPES.
Eyes instead of words? Is this why?

 

You have lost me a bit. I'm going to need more explanation of your theory.
But thanks for the video of the Lamattini family "Carrot Kings" top fueler. Great footage of an Australian car I see perform quite often.......

 

Every pipe shows an explosion (energy) that forces the piston.