Automotive Can a High RPM Gas Engine Move a Heavy Load Like a Low RPM Diesel?

[Moretorque]

No you guys got it and especially CJI and all of you all so thanks a million, no he is right the engine builders are wrong. Actually I understood it better before I got lost searching to understand it better by listening to info that was wrong. You have to have a setup for what you are doing and have the right gear set for your app.

The dyno does not lie, I have a couple more ?'s but let me go over all this so I understand it correctly before I ask. Again thank you.

If you throw enough spaghetti against the wall enough will stick for a good meal, so thanks for taking the time.

 

[jack action]

I have noticed on my CR 500 and I weigh 320 it stomped my CRF 450 bad in getting me going all things being pretty much equal and the CRF 450 has a way broader power curve and same HP pretty much on a dyno but the CRF 450 peaked at about 9 grand vs 5600 for the CR 500. It will kill a CRF 450 on hill climbs just google CR 500 hill climb and it has a way narrower power curve but makes like 50% more torque.

Not according to these power curves:

​

Not only does the CR500 can achieve 20% more power than the CRF450R, it can produce more than 44 hp from 4600 to 7250 rpm, a ratio of 1.58. The CRF450R can stay above 44 hp (without ever reaching the power of the CR500) from 7750 to 11 000 rpm, a ratio of 1.42. So the CR500 power band is not only wider, it also have a higher average power rating in its power band.

 

[Moretorque]

Not according to these power curves:

​

Not only does the CR500 can achieve 20% more power than the CRF450R, it can produce more than 44 hp from 4600 to 7250 rpm, a ratio of 1.58. The CRF450R can stay above 44 hp (without ever reaching the power of the CR500) from 7750 to 11 000 rpm, a ratio of 1.42. So the CR500 power band is not only wider, it also have a higher average power rating in its power band.

I am talking modified, go look them up. Guy's are getting 60 to 75 RWHP out of them with no problem with mods and they really do work good. The one thing about a 2 stroke over a 4 stroke they build power faster. In the sand a 2 stroke hydro plains on the sand much quicker and gets going on top of it, a dyno does not show this.

There getting over 100 out of the new CR 500 big bore kits, A Cr 500 motor in a modern chassis with over 100 HP at 225 pounds tagged for getting around anywhere set up would destroy practically any other vehicle made.

Jump over curbs going 50 or 60, cut through the neighbors back yard then jump the creek to hit the road behind the house in a 9 second package.

If you have the balls.

 

[Moretorque]

Now I will talk to some builders because I understand it better and see what they say it means in the real world in apps.

I always believed the dyno did not lie and actually understood this to a pretty good degree until people starting saying no it is not like that in the real world then I got really really lost but understand it much better now. They have the engine operating out of it's zone and not set up right and do not understand this but overall now that I understand it better it makes it obvious why a good diesel not the new ones for the most part are the way to go for pulling.

Thanks.

 

[jack action]

@Moretorque:

I don't follow your argumentation. We're telling you only how much power produced counts. You come back with this CR500 vs CRF450 real life example where you state:

all things being pretty much equal and the CRF 450 has a way broader power curve and same HP pretty much on a dyno

(...)

It will kill a CRF 450 on hill climbs just google CR 500 hill climb and it has a way narrower power curve but makes like 50% more torque.

So I show you evidence that a stock CR500 has more HP (and a not-so-narrow power curve) than a stock CRF450 and you come back by telling us that the CR500 is modified, maybe up to 100 hp, i.e. twice as much power as the CR450?!? I've been doing a little search and even if you used a modified CRF450, the most powerful modified bike I've found had 60 hp.

At this point, you are just proving what we're explaining to you. You really need to understand that we are not working against what the engine builders say, we are just explaining it better than they can. Believe us, this «power theory thingy» we're talking about has been established for a few hundred years now and it's the reason why we have airplanes that can break the speed of sound, why we have turbines generating electricity for millions of people, and why men were able to walk on the moon. Believe us, it works and the combustion engine of a car/truck/motorcycle is not an exception to this concept.

 

[Moretorque]

The CRF will do better than 60, guy's use them in go karts making quite a bit more. There very expensive however. My modified CRF 450 was about the same as the stock CR 500. The CR 500 peak is around 5600 hundred or 5700 RPM like a diesel truck narrow and that usually is the way 2 smokes are. The CRF's that are built up to around 55 plus have way more over rev and pull over a longer range but not near the torque however.

When you ride a CR 500 it is odd the light guy's say the power band is way to short with no top end and the heavy guy's say the CRF 450 does not pull them right on hills. This is why you will find the CR 500 is real popular with big guy's and smaller guy's will tell you it is to narrow power for them. The CRF with mild mods make the same peak HP as a CR 500, there are a lot of them out there.

I agree with what is being said the dyno does not lie but talking how it equates to seat of the pants is all in real world.

 

[Ketch22]

I really like this statement. As we have explored already it is more about having the appropriate drivetrain as an entire package and that matching the use. On another forum a while back I was part of a thread looking at performance mods. I made the comment that unless you can actually deliver the power where the customer uses it you are not really a Tuner but just a builder. This drew tremendous distain as it was an affront to some peoples sensibilities.

The big picture is that there are large numbers of variables. Case in point you can get great performance for you on your bike. If you gave it to me and I went out with my 195 lbs riding aggressive enduro type stuff. I would possibly come back and say "your bikes OK but not great" It is all about the fit within the variables.

 

[Moretorque]

It's all in setup for what you are doing. Thanks for getting me straight on this everybody who took time. You can make anything work if HP is there for what you need to do but some power types work better for certain apps than others depending on what you are doing.

 

[Moretorque]

iT's all in setup for what you are doing. Thanks for getting me straight on this everybody who took time. you can make anything work if HP is there for what you need to do but some power types work better for certa than others depending on what you are doing.

@Moretorque:

I don't follow your argumentation. We're telling you only how much power produced counts. You come back with this CR500 vs CRF450 real life example where you state:
So I show you evidence that a stock CR500 has more HP (and a not-so-narrow power curve) than a stock CRF450 and you come back by telling us that the CR500 is modified, maybe up to 100 hp, i.e. twice as much power as the CR450?!? I've been doing a little search and even if you used a modified CRF450, the most powerful modified bike I've found had 60 hp.

At this point, you are just proving what we're explaining to you. You really need to understand that we are not working against what the engine builders say, we are just explaining it better than they can. Believe us, this «power theory thingy» we're talking about has been established for a few hundred years now and it's the reason why we have airplanes that can break the speed of sound, why we have turbines generating electricity for millions of people, and why men were able to walk on the moon. Believe us, it works and the combustion engine of a car/truck/motorcycle is not an exception to this concept.

Why are diesels so slow, I saw videos with a 1400 HP diesel funny cars only able to muster a 9 second 1/4 mile.

 

[jack action]

Why are diesels so slow, I saw videos with a 1400 HP diesel funny cars only able to muster a 9 second 1/4 mile.

It's hard to answer you because I just don't know where you take your numbers. This http://www.bankspower.com/magazines/show/599-the-worlds-quickest-diesel-pickup-breaks-new-ground. This top fuel with 1800 hp is in the 6-second.

http://www.bankspower.com/magazines/show/609-Marine-animal is even more interesting, as we have a weight (817 kg) and it has the same 1300 hp engine as the previous funny car. http://www.bankspower.com/topdieseldragster/overview2/ (The video in the previous link seems to indicate 7.17 s). If you put 1950 lb (= 817 kg + 150 lb driver) and 1300 hp into a simple ET calculator, you get 6.6187 sec. Note that these calculators don't care about torque or whether it is diesel or gas: Power and weight is all you need for an amazingly close approximation.

So I did a little search for you 9-sec, 1400 hp funny car and I found this one. We don't know the weight of the car and even if we assume the 1400 hp is exact, it is probably a standardized value. And if you look carefully at the description, the run was done at Bandimere speedway, which is in Morrison, Colorado (elevation 5764 ft) at 79°F. This means that the actual power is only 77.9% of the standardized value or 1090 hp. But I admit that even with this number, it should be faster than that ... unless it weighs 4500 lb ... unless that 1400 hp claim is exaggerated!

 

[Moretorque]

Thanks for taking the time, because they are long stroke don't they take a little more time to wind up to make power. Can they be a touch slower in this regard ?

So not being able to turn the RPM limits them in power, I take it the compression is why they do not spin a lot ?

 

[Moretorque]

I am realizing seat of the pants is just that seat of the pants and the real #'s do not lie, before I got into this I actually understood it pretty good but went by what people were saying in the real world and thought I was not seeing something in the math that was not there.

Here is the next ? , is it possible the backstop of all this is in maintaining the HP under heavy load once it is built up is the fact on a bench when you take a low RPM motor vs a higher RPM motor of same HP value with no transmission and put a brake on it to stop it from spinning it will be harder to stop the motor that has more torque over RPM to make the HP ?

 

[jack action]

Thanks for taking the time, because they are long stroke don't they take a little more time to wind up to make power. Can they be a touch slower in this regard ?

It's a good point that you are bringing the stroke. The reality is that the piston goes at the exact same speed in the low-rpm engine or the high-rpm engine. The longer stroke gives a mechanical advantage that gives a higher torque, but the rpm is reduced. So increasing the stroke of an engine doesn't increase its power, it acts more like an «internal» gear set. Read about mean piston speed to learn more.

So not being able to turn the RPM limits them in power, I take it the compression is why they do not spin a lot ?

If you want to create a high compression engine, you will have to lower the deck clearance (see figure below). A lower deck clearance creates thermal losses and the fuel mixture is harder to fully burn. But if you increase the stroke (or reduce the bore) while increasing the compression ratio, you will regain your deck clearance (it's a simple geometry exercise). If you reduce the bore, you will need to increase the number of pistons to keep the same bore area such that the power output is the same, which is very complicated. The preferred method is to increase the stroke, but it will lead to lower the rpm if you want to keep the same mean piston speed (which is more of a limiting factor than the engine rpm). Since the mean piston speed and bore area are the same, the power output is also - theoretically - the same (there are other effects to take into account, but those are very important and fundamental).

Here is the next ? , is it possible the backstop of all this is in maintaining the HP under heavy load once it is built up is the fact on a bench when you take a low RPM motor vs a higher RPM motor of same HP value with no transmission and put a brake on it to stop it from spinning it will be harder to stop the motor that has more torque over RPM to make the HP ?

First, there is no «backstop of all this is in maintaining the HP under heavy load»: Once you have the HP, you have it. Maybe you had less HP in lower rpms and that made it more difficult to reach the rpm you are actually in, but once you are there, there's no quality grading in the HP you have. If you have enough HP to hold, it will hold. Naturally, assuming the power is properly adapted for the given load, i.e. set to the appropriate torque and rpm.

The second part of your question is also of interest. «Will it be harder to stop?» It all depends what you mean by «harder». This is where the difference between the concept of «torque» and «power» is important. Assume you are stopping your motors with a friction brake, i.e. by converting the mechanical energy into heat.

The friction brake must be able to handle the torque applied to it. If one motor has a greater torque, higher stresses will be applied to the part and they could failed if they are not strong enough. In that sense, the higher torque engine will be harder to stop.

The friction brake must be able to remove the energy from the rotating motor, either by absorbing it (its temperature increases) or by transferring it (to the surrounding air or a coolant). The amount of energy going out of the engine in a given period of time must be the same that is going in the friction brake in that same period of time. So the engine power must be equal to the braking power. Since the power is the same for both motor, the brake power required will be the same in both cases.

Here is an example to help visualize. Two workers have a job to do: moving one stack of brick a certain distance within a certain time. The first worker is not very strong but is very fast and takes one brick at a time, running the distance many times to move all the bricks in the given time. The second worker cannot run fast but is very strong. So he takes the whole stack of bricks and travel the entire distance once, at a very slow pace such that it takes him the same time as the first worker. Both workers have done the same work, in the same period of time, thus have the same power. But one was stronger and the other was faster and because of the way they are «build», they couldn't exchange places as they would of failed to do the job if they've tried the other worker's method.

 

[Moretorque]

So basically it's all in set up but for pulling heavy the diesel because how efficient it is by not turning much RPM is the clear choice and you do not need a lot of MPH but pulling efficiency.

Thanks..

 

[cjl]

So basically it's all in set up but for pulling heavy the diesel because how efficient it is by not turning much RPM is the clear choice and you do not need a lot of MPH but pulling efficiency.

Thanks..

The diesel is the clear choice for pulling heavy because large diesel engines are very reliable, last a long time, and are more efficient than high power gas engines. In terms of actual pulling capability (if set up correctly), all that really matters is the horsepower and powerband.

 

[cjl]

@cjl

I tried to read between the lines with @Moretorque to understand what he means and what he's referring to, rather than analyze every single word he said.

What I think he's referring to is the small highly-boosted engines vs large displacement engines. It's not really about diesel vs gas. Your Corvette engine is not a good reference in this case, as it can be considered as a truck engine fitted within a car (I mean 7.0L ! C'mon, that is huge!).

It's a sports car engine, through and through (look at the redline and power peak), definitely not a truck engine. It is definitely a big engine though, designed for smooth power throughout the rev range.

Here's a dyno sheet I retrieved from the web that is claimed to be from a 1999 Honda Civic with a turbocharged 1.8 L:

​

If you look at the run with 503 hp and 334 lb.ft, the 75% of peak torque rpm range is 5200-8500 rpm (a ratio of 1.6).

That's a highly tuned modified engine though, clearly made for bragging rights and high peak power output (not for useful power). No car manufacturer would deliver an engine like that from the factory, since the usable power band is too small.

So from that point of view, he is right, even with your criteria (I personally prefer qualifying useful rpm range by the power curve rather than the torque curve, since engine torque is irrelevant to acceleration as you and I stated). With two engines with the same peak power, the one with the highest power in the lower rpms should accelerate faster (Even though he used the terminology «diesel» and «gas», I considered he meant a generalization for a «wide power band» vs «narrow power band»).

He was comparing diesel trucks to gas trucks earlier though, and a gas truck would often use a large displacement V8 or V10. Also, as I said, in many (I would even say most) cases, gas engines have a wider power band than diesel. Looking at a modified 1.8L turbo engine isn't necessarily a great example either - for comparison, look at this 360hp factory turbocharged 2.0L engine from Mercedes:

This shows the difference between a tuned engine and a factory engine - a lot of people who modify their engine just put a giant turbo on and look for high peak horsepower, with little concern for powerband, while an engine designed for a particular power from the factory will have a much broader and more usable range (look at the peak torque range on that engine - nearly full torque from just over 2000RPM all the way up to 6000 or so). As for the rest of your post, it's hard to say what anyone's intention is at any time online, so I won't bother trying to do a detailed response. I just wanted to respond to your claim here that small engines (and gas engines in general) don't have wide powerbands and that the LS7 is a truck engine.

 

[Moretorque]

So you are saying a Indy Car motor can power a Semi but what would the gear set be like to keep it chugging happily without falling off the pipe ?

 

[cjl]

So you are saying a Indy Car motor can power a Semi but what would the gear set be like to keep it chugging happily without falling off the pipe ?

An indy car motor could easily power a semi faster than its normal speed. It could probably pull it at 85-90mph, given the horsepower (550-700, compared to 200-400 for a normal semi). I can't find a torque curve online, but assuming that it's making 600hp at 12000RPM (the rev limit), it would probably chug happily along at 55-65mph at 8 or 9 thousand rpm or so, and it should climb shallow hills nicely at 60+mph at 12krpm. Assuming that 60mph on flat ground takes 200hp for an 80klb semi (which seems pessimistic to me - I'd expect the actual power requirement to be lower), it should be able to climb a 3% grade at 60mph at 12krpm.

(Of course, there's no guarantee how long it would last spinning at 8000-12000RPM all day long under a heavy load, since they're only really designed to run a few hours at a time, unlike truck engines which run for months between services. It'd also need a large amount of cooling, since it is less efficient than a truck engine so it makes more heat for the same power output).

 

[Moretorque]

Thanks CJL but what would the gear set be like, I mean would it need more than the standard setup, would a air shifter help a lot under that kind of load ? I know going 240 MPH in a Indy car is like pulling 80 grand at 80 for a semi load wise ?

 

[cjl]

You wouldn't need an air shifter or anything (what is an air shifter anyways?). You'd just set it up so that you would wind it up to 10k or so in first (going all of 5mph or something like that), then shift into second which would be turning something like 7krpm at that same 5mph, wind that up to 10 or 12k at 8 or 9mph, then shift into third (which should be at 7k or so at 8 or 9mph), wind that up to 10 or 12k at 13mph or something like that, and keep repeating that sequence until you're at 55 or 60 in 10th gear or so. You could have gears set up such that the top speed in each gear went something like this:

1st: 4mph
2nd: 6mph
3rd: 9mph
4th: 13mph
5th: 19mph
6th: 28mph
7th: 35mph
8th: 48mph
9th: 68mph
10th: 85mphThat would probably work pretty well, and wouldn't require a really broad powerband either, since each gear only covers about a factor of 1.5 in speed. You could do it with fewer gears, but fewer gears means less overlap in usable speed between gears, which means you'd pretty much need to wind it all the way to redline in every gear.

(It'd also sound pretty ridiculous when accelerating, since you'd hear a racecar engine screaming to 12krpm in a big truck as it slowly lumbered up to highway speed, shifting 5 or 6 times before 20mph)

 

[SteamKing]

You wouldn't need an air shifter or anything (what is an air shifter anyways?).

Air shifters use pneumatics to actually shift the gears in the transmission, without using a manual shift mechanism. The gear changes can be done much quicker, and the driver doesn't have to take his hands off the steering wheel to shift (it's like using paddle shifters).

http://www.racegadgets.com/airshifter.htm

 

[Moretorque]

Thanks,

 

[Moretorque]

This is actually an interesting thing here, motors builders are telling me what is on paper is wrong and it is not like this in the real world. Like I posted about the Mack with only a 5 speed and 237 HP moving a 70000 pound load with no problem and that is a real setup. You can look it up with drive reviews. The real world consensus is you will never be able to maintain the RPM on a car motor under such a load to keep the 237 HP pulling that kind of weight.

I was told the torque is what allows you to maintain and build the HP under such a load and that the HP is your peak MPH in real world use, I will research this further. Thanks for the education on the #'s and math on this subject and on my end it all adds up but top engine builders have told me no.

 

[insightful]

The real world consensus is you will never be able to maintain the RPM on a car motor under such a load to keep the 237 HP pulling that kind of weight.

What if the "car motor" had 15 speeds to work with?

 

[Moretorque]

Then yaa but what do I know and what the people say here is right and I am not arguing that but the latest guy to tell me no was Roland Stuart face to face and he is crew chief on the Spider mans top fuel bike. Not only him but other builders as well who build unlimited tractors in both diesel and gas multi configurations.

Until one of these engine builders take the time to break it down and explain why in like real math the math guy's are right because the #'s do not lie. Thanks for everybody's time here to explain it and just trying to get the engine builders on the same page.

 

[cjl]

This is actually an interesting thing here, motors builders are telling me what is on paper is wrong and it is not like this in the real world. Like I posted about the Mack with only a 5 speed and 237 HP moving a 70000 pound load with no problem and that is a real setup. You can look it up with drive reviews. The real world consensus is you will never be able to maintain the RPM on a car motor under such a load to keep the 237 HP pulling that kind of weight.

If the motor is putting out 237 horsepower, it's putting out 237 horsepower. There's nothing particularly special about whether it's doing that at 1600RPM (like a truck engine) or 6500RPM (like a car engine), both will be able to do the same amount of work in the same period of time (since that's the definition of power). If it takes 237hp to move the truck at 70mph, then the car engine will maintain 6500RPM just as easily as the truck engine will maintain 1600, assuming they're both geared to hit those RPMs at 70mph.

Also, I'd be skeptical about 237hp and a 5 speed moving a 70klb load "no problem" - sure, it'll move it on flat ground OK, but it'll be awfully slow up hills, and the gearing will probably leave something to be desired compared to a more modern truck with a 10, 13, or 18 speed.

I was told the torque is what allows you to maintain and build the HP under such a load and that the HP is your peak MPH in real world use, I will research this further. Thanks for the education on the #'s and math on this subject and on my end it all adds up but top engine builders have told me no.

Horsepower tells you rate of acceleration under a given load, and also determines top speed. Torque on the other hand doesn't tell you much about the performance of the vehicle, just about what kind of gearing you'll need.

 

[Ketch22]

Thanks for sharing Rolands comments. I would caution just a little about the anonymous character of the interwebs, There is so far nothing to say that you are not already talking to real world engine builders. I personally am against playing that card in either direction.

Bear in mind that Roland is partially correct. If you had a fictional engine that was a diesel. For round numbers let's look at 1000 FtLbs of torque at 2000 RPM This delivers approximately 380 Hp. Carried to the road via a transmission with a 4-1 ratio this would then be 500 RPM with 4,000 FtLbs. This same engine makes 1000 FTLbs of torque at it's limit of 2500 RPM or roughly 476 Hp.

Compare this to a Petrol engine also fictional. This one delivers 280 FtLbs of torque at 7000 RPM approximately 373 Hp. In the same vehicle this now requires a 14-1 ratio to achieve 500 shaft RPM. Bringing the delivered torque to 3920 FtLbs. The same engine makes 280 FtLbs of torque at it's limit of 10,000 RPM, roughly 533 Hp.

The true side is that if it takes 3,400 FtLbs of torque to maintain equilibrium, greater than that number will accelerate the vehicle. Given the Diesel producing 4,000 and the Petrol producing 3,920 the Diesel will in fact provide more acceleration than the Petrol.

However, The Diesel will soon be overcome. As it jumps forward (for a bit) the endpoint of that engine is at 2,500 RPM which has seen a decline in Hp delivered and the actual shaft power of now 625 RPM and 4,000 FtLbs. or roughly flat acceleration for 20% of the range. Followed by falling of for ( name your own reason for redline)
The Petrol Engine will be slightly slower but at the endpoint of 10,000 RPM there will still be an increase in Hp (due to the revolution count) The actual shaft power will show at 710 RPM and 3,920 FtLbs. Translated as roughly flat acceleration but covering 30% of the range. The Petrol engine will by virtue of it's increased RPM (think total power) catch and overtake the Diesel. This will happen at each transmission equivalent ratio and actuality the added 10% will accumulate due to shifting time and other gains.

The instant acceleration of the diesel does not overcome the ideal that greater power happens at a place where the diesel is starting to run out of lungs while the Petrol is still gaining.

 

[Ketch22]

Oops, I just realized that I got distracted while I was composing yesterday. The missing paragraph in my reply regarding the two engines is the end of where that benefit from Petrol engines raises it's head.

With the additional 10% of RPM brought into the design of the drivetrain. Let's shift our Petrol engine to maintain a 20% range so as to match the Diesel. This now brings the Engine speed to 8000 RPM. Adjusting reduction ratio to maintain 500 RPM shaft speed now shifts from 14-1 to 16-1. The resultant power delivered to the shaft would be 4,480 FtLbs at the same RPM. We have shifted from the Petrol engine (measured at the tailshaft) being at an 80 FtLb deficit to it being at a 480 FtLb advantage.

It is as you can see all in the application engineering not so directly with the engine itself. If as in this example the effort required is lower than what can be produced [3,400 FtLbs required and both engines producing more] the petrol engine can catch up and pass the Diesel. If the parameter falls into a range between the engines [ for this example let's say 3,950 FtLbs required] the diesel would continue to accelerate for a little bit more while the Petrol engine slowly fell on it's face.

 

[Moretorque]

Thanks for keeping this thread alive and all the help. I am still studying the subject. It seems as though twisting force at the crank beats spinning more RPM in being more powerful in the real world when making more power and maintaining it under load. The dyno does lie ?

 

[cjl]

Thanks for keeping this thread alive and all the help. I am still studying the subject. It seems as though twisting force at the crank beats spinning more RPM in being more powerful in the real world when making more power and maintaining it under load. The dyno does lie ?

Nope. Both are important, and the dyno doesn't lie (assuming you read it correctly). Of course, that's been said many times throughout this thread...