# Horse Power Gas vs Diesel vs Electric



## Duncan (Dec 8, 2008)

Sunking said:


> Pardon me if this sounds silly question coming from an Electrical Engineer, but there is something I always wondered about and never asked or looked too deeply. It relates to HP in the three engine/motors. Goes something like this.
> 
> If you have a vehicle with a 100 hp gas engine and replace it with either a diesel of electric; to get like performance they will be smaller or less hp Example a 80 hp electric motor Or as the cliche goes: Torque wins races, and horsepower sells cars.
> 
> ...


Hi Sunking
As far as diesel is concerned there are two aspects
(1) - Your comment about peak/continuous is true diesels tend to be rated as a continuous power gas(petrol) as peak
But that is not why you can replace a 120Hp petrol engine with an 80Hp diesel

(2) The power is delivered at a more "usable" rpm range
A petrol engine will need to be buzzing at 5000rpm to deliver its power
A diesel will deliver most of its power at more like 3000rpm

As an example (from long ago) - in the 80's ford made Transit vans
The diesel had 55hp - the petrol 100hp

But in top gear at 60mph the diesel had 20% more torque

If you revved the nuts off the petrol it was faster

If you drove it the way most people did the diesel had more torque available so felt faster

The electric motor case is similar - power available when you want it is simply worth more than power available only if you go down a couple of gears


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## Hollie Maea (Dec 9, 2009)

Sunking said:


> Or as the cliche goes: Torque wins races, and horsepower sells cars.


That cliche is total BS. Torque can be sacrificed for RPMs, and vice versa, with gears. If your vehicle "doesn't have enough torque" and you can't fix it with gears, it just has too small of an engine. 

A truck with a 300 hp rotary engine that lacks torque but can spin up to 20,000 RPM would tow a truck just as well as a 300 hp diesel, if you geared the hell out of it.

What matters a lot more is the width of the torque band. If your engine has a very narrow torque band, it will feel like it lacks torque because you keep falling off the peak. In this regards, electric motors excel, due to their wide and flat torque band.

That's why I have an EV grin in my tupperware car even though it only has one gear and a 35 hp motor.


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## Duncan (Dec 8, 2008)

_A truck with a 300 hp rotary engine that lacks torque but can spin up to 20,000 RPM would tow a truck just as well as a 300 hp diesel, if you geared the hell out of it.

_It would - IF people drove like that

The reason the diesel feels better is that people don't (unless they are racing) drive at those revs

Most people keep their engines running at 2000 - 3000rpm

If they habitually kept their engines at 4000 - 5000rpm then the gas engine would be noticeably more powerful


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## steelneck (Apr 19, 2013)

Electric = Instant torque.

Petrol = What, me? The engine says. Wait a minute, i just have to wake up, stretch a bit and then rev up first..

Diesel = Somewhere in between.

Yes, 100kW mechanical power is 100kW no matter how it is produced. But look at the RPM curve, it is just produced within a quite narrow band. A high performance petrol two-stroker is the worst example, almost dead up to 6000 RPM but has insane amounts of torque at 8000 and over revs at 10. Nervous.

If you instead power (kW) measure the amount of energy (kWh) over the time one gear is used, then you can see why 80 kW electric can win over 100 kW petrol. If you start at 2000 RPM and accelerate up to 5000, the electric motor will output the same torque all the way, but the petrol engine will be weak in the beginning, be at its best at 4000 and after that start do decline. The average over the whole RPM window will be higher for the EM, even if its top is a bit lower.


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## lithiumlogic (Aug 24, 2011)

steelneck said:


> If you instead power (kW) measure the amount of energy (kWh) over the time one gear is used, then you can see why 80 kW electric can win over 100 kW petrol. If you start at 2000 RPM and accelerate up to 5000, the electric motor will output the same torque all the way, but the petrol engine will be weak in the beginning, be at its best at 4000 and after that start do decline. The average over the whole RPM window will be higher for the EM, even if its top is a bit lower.


That's a factor which applies when accelerating all out in a race, or when attempting to keep up with traffic in a low power:weight ratio vehicle like a bus, van or truck.

For everyday driving there is also the "mother in law" factor. If family members are occupying the passenger seats, you cannot access most of the HP of an internal combustion engine without drawing disapproval. If yours are anything like mine, more than half throttle and more than 2500prm bring accusations of "driving like a maniac" even though we're 10mph under the speed limit and have following cars sitting 6 inches from your bumper. 

With an electric motor you can use 100% pedal and rpms that give rated power and they'll have no cues that you are doing so.


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## Sunking (Aug 10, 2009)

Duncan said:


> As far as diesel is concerned there are two aspects
> (1) - Your comment about peak/continuous is true diesels tend to be rated as a continuous power gas(petrol) as peak
> But that is not why you can replace a 120Hp petrol engine with an 80Hp diesel
> 
> ...


Do you mean wider Power Band over a wider Bandwidth of RPM's?

I know diesels torque is somewhat similar to electric AC Induction Motors where torque tends to be somewhat flat from idle up to 2400 to 3000 RPM? 

Not sure that clicks with me yet. A diesel power band would be roughly a bandwidth of 2000 RPM say 500 to 2500 RPM, where a gas engine would say be 5000 to 9000 RPM. That tells me the gearing ratios would just be different.


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## dougingraham (Jul 26, 2011)

Sunking said:


> Do you mean wider Power Band over a wider Bandwidth of RPM's?


A Netgain WarP 9 is almost flat from 0 to 4000 rpm if you feed it 150 volts. That goes up to 5000 rpm if you feed it 170 volts and almost 6000 rpm if you feed it 190 volts (at 1000 amps). 



Sunking said:


> I know diesels torque is somewhat similar to electric AC Induction Motors where torque tends to be somewhat flat from idle up to 2400 to 3000 RPM?


There is a lot of difference between 0 rpm and idle.



Sunking said:


> Not sure that clicks with me yet. A diesel power band would be roughly a bandwidth of 2000 RPM say 500 to 2500 RPM, where a gas engine would say be 5000 to 9000 RPM. That tells me the gearing ratios would just be different.


But the torque varies across that band with ICE of both varieties. You need to go drive an EV to understand the difference. It should be easy to test drive a Leaf or Volt.


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## Duncan (Dec 8, 2008)

_Not sure that clicks with me yet. A diesel power band would be roughly a bandwidth of 2000 RPM say 500 to 2500 RPM, where a gas engine would say be 5000 to 9000 RPM. That tells me the gearing ratios would just be different._

Yes - BUT
In a car or van you select the gearing(gear) (and most people change early)

In the transit I exampled if you left it in gear until 5000+rpm the petrol was faster

If (as most people do) you use first to get started - shift into second immediately,
third by about 20mph and top (fourth) by 30mph then the diesel will feel a lot stronger

It's not the best way but its the way people drive (enforced by the "mother in law" factor)


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## piotrsko (Dec 9, 2007)

Uh, diesels don't turn that fast generally. Max torque is around 1700. The gassed conversion types can run to 3000, but the power efficiency kinda drops off a cliff. A 1200 hP stationary Waukesha runs at 100 to 300 ish rpm. Red line for a Cummins is 2000


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## Duncan (Dec 8, 2008)

piotrsko said:


> Uh, diesels don't turn that fast generally. Max torque is around 1700. The gassed conversion types can run to 3000, but the power efficiency kinda drops off a cliff. A 1200 hP stationary Waukesha runs at 100 to 300 ish rpm. Red line for a Cummins is 2000


*Red line for a Cummins is 2000*

Where the hell did you get that???

The ones I used to work with went up to about 4500rpm

I was the Quality Manager (Engine Test) for the Darlington Engine Plant from 1990 to 1997

I suspect (I'm damn sure) that the modern ones will rev even higher as we were limited primarily by the fuel system pressures and those have gone up from about 1200Bar to over 2400Bar

Even the big engines that we worked with (Wartsilla) (Up to 700MegaWatt) revved to about 1500rpm


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## Sunking (Aug 10, 2009)

piotrsko said:


> Red line for a Cummins is 2000


I have a Dodge Ram 2500 with a Cummins Turbo Charged Diesel and red line on it is 3300 RPM

While that might be true for some diesels the engines made for small light weight passenger vehicles use Turbo Chargers and that allows manufactures to shorten the stroke length a bit, and thus higher RPM's. At least I think that is how it works and what I have read.


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## Sunking (Aug 10, 2009)

dougingraham said:


> But the torque varies across that band with ICE of both varieties. You need to go drive an EV to understand the difference. It should be easy to test drive a Leaf or Volt.


I have driven EV's like a Telsa Roadster and thus why I am asking what am I missing. It you were to rip out Telsa's motor and replace with a gas engine would have to be higher horsepower to achieve the same acceleration and speed.


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## major (Apr 4, 2008)

Sunking said:


> I have driven EV's like a Telsa Roadster and thus why I am asking what am I missing. It you were to rip out Telsa's motor and replace with a gas engine would have to be higher horsepower to achieve the same acceleration and speed.


No, it would have to produce the same power (and/or torque) to achieve the same acceleration and speed (assuming the vehicle mass was unaltered).

Power is power and torque is torque regardless of how it is produced (or converted). The difficulty you folks have is with the way different engines (or motors) are rated. Also the different power (or torque) vs speed characteristic of these different engines (or motors) means simple substitution of one for another having the the same "rated power" will not yield equivalent performance.


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## Sunking (Aug 10, 2009)

major said:


> Power is power and torque is torque regardless of how it is produced (or converted). The difficulty you folks have is with the way different engines (or motors) are rated.


Yes Major that was what I was driving at and the crux of my question. Only thing that makes sense to me is GAS engines are rated for Peak and diesels and electric are rated Continuous. I don't know if that is correct or not and why I am asking. 

An example I am familiar with is a golf carts. One in particular is the EZ-GO RXV which uses a BLDC motor with a 230 amp controller with 48 volt battery produces 5.5 hp. Remove the RPM limiter in the controller and change out the differential gear to 8:1 ratio and you have a 36 mph cart that was limited to 19.2 mph. Same model with a gas engine is rated 14 hp and if you disable the governor best you get is 25-30 mph and risk burning up the engine. 

Where I live there re around 600 golf carts of all makes and models. If you drag race the two above modified models the electric version has a higher rate of acceleration and a higher top speed on a motor rated roughly 1/3 the HP. The only thing I do not know is on the electric version is the PEAK HP with the 230 amp controller as the manufacture does not publish the motor specs. At face value 48 volts x 230 amps = 11 Kw or roughly 14 HP input power. Efficiency unknown but guessing 80% puts it roughly at 11 hp Peak.

Anyway Major this revolves around me selecting a motor to convert a DC golf Cart to AC. The more research I do the more convinced I am the HPEV AC-9 motor looks like the ticket to get a 35+ mph vehicle with a curb weight of roughly 700 pounds. The AC-9 @ 48 volts is a 10 HP continuous motor and with a 650 amp controller peaks @ 27 hp @ 2200 rpm and decays down to 10 hp continuous @ 6000 rpm. If I have figure the ratios out 35 mph should be at 4000 RPM. What I am still trying to figure out is how much torque is needed to maintain 4000 RPM. My gut feeling is th eAC-9 has more than enough torque to maintain 4000 RPM and some left over for hills. Then again I could be all wet.


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## major (Apr 4, 2008)

Yes, that is what I've been telling you. The guys at Thunderstruck or HPEVS should verify this. The AC-9 was designed to be the high performance AC golf cart motor. If you intend to use it with the larger Curtis, 550A or higher, I'd spend the extra few bucks and get the AC-15. I'd also get a good set of Lithium batteries for it with BMS and good charger. Why screw around and regret it later?


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## Hollie Maea (Dec 9, 2009)

Sunking said:


> Only thing that makes sense to me is GAS engines are rated for Peak and diesels and electric are rated Continuous.


Keep in mind that in the ICE world, "peak power" means a different thing than in the electric world. For an electric motor, "peak power" is the maximum power you can get for a short amount of time. For an ICE, "peak power" is the maximum power you can get out of the engine at a specific RPM. That will generally be the power you get at an RPM slightly higher than the peak torque RPM. But that's a single point on the torque/RPM curve, and tells you nothing about what torque you can get at other RPMs (spoiler alert: much less). The "driving experience" is all about what torque you can get at the wheels over a wide range of speeds. So that's a direct function of the torque curve and the gear reduction. "Peak power" of an ICE doesn't really tell you a lot about that, but in general the fact that torque falls off strongly in both directions from the peak is why an electric motor with the same power rating will probably have a more desirable "driving experience".


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## Sunking (Aug 10, 2009)

major said:


> Yes, that is what I've been telling you. The guys at Thunderstruck or HPEVS should verify this. The AC-9 was designed to be the high performance AC golf cart motor. If you intend to use it with the larger Curtis, 550A or higher, I'd spend the extra few bucks and get the AC-15. I'd also get a good set of Lithium batteries for it with BMS and good charger. Why screw around and regret it later?


Well I already got the battery, a new set of GBS 16S 4 x 4 100AH Block. Being that is roughly 48 volts eliminates the AC-15 unless I add another 4S Block. Pretty confident the AC-9 will do what I want.

Only thing I am not convinced of is if a BMS is really necessary for my application. I will not be operating to get every precious mile out of the vehicle meaning I do not need to charge to 100%, nor discharge all the way down to 20%. More like the 80 to 30% range. With that said I think all that is necessary is an occasional voltage check and bottom balance as required on weaker cells. At most on a day is 27 holes of golf plus round-trip from house is roughly 10 to 11 miles per day. Rough calculations of 200wh/mile works out to 45 to 50 AH on a 100 AH battery. I spent more on the batteries than I had planned, so I have a little time to make up my mind on motors. My other major expense is BRAKES. Hopefully front wheel wet disc brakes is all I will need as REGEN will supplement on the rear tires, and REGEN may be enough alone most of the time. 

Good charger is no problem for this ole telecom train driver, I got tons of 48 volt 100 amp reciters to choose from. All of them extremely easy to modify for lithium algorithm, all I need is a tweak tool to spin the 10-turn pots to the correct voltage and float at 90% SOC and terminate when current tapers down to a couple of amps. All it will ber used for is golf of course, and neighborhood transportation. I live in a gated community with a private lake and golf course called Lake Kiowa Texas. Roads are private so I don't have to deal with license, just comply with 35 mph speed limit. There are only a handful of carts around here that can do 35. All of them the modified EZGO RXV's.

Want to hear something funny? The EZGO RXV does not have BRAKES. Its all REGEN and a Resistor if battery is full. Only brake it has is a Motor Brake used only for parking. Now what is funny EZGO make a LSV called the 2Five. It is the exact same cart, street legal, different gear ratio 8:1 to obtain 35 mph, and controller RPM raised up to 6000 RPM which is 35 mph. The other difference is it has 4-wheel drum brakes and no resistor. Still has REGEN, just no resistor and real brakes added.


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## major (Apr 4, 2008)

Sunking said:


> Being that is roughly 48 volts eliminates the AC-15 unless I add another 4S Block.


What does this mean? The AC-15 runs great at 48V (even at a bit lower).


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## Karter2 (Nov 17, 2011)

Sunking said:


> . A diesel power band would be roughly a bandwidth of 2000 RPM say 500 to 2500 RPM, where a gas engine would say be 5000 to 9000 RPM. .


 You need to be more realistic and compare actual current motor specs.
Modern diesels as used in road cars ,..VW, Audi, BMW etc run much higher rpm with peak power at 4000 + rpm (max torque 2-3000rpm) and will "run" easily up to 5+k rpm. and output 200+ bhp from 2 litres.
Also, there are very few Gas engines in cars that rev over 6 k rpm, with most also peaking between 4-5 k rpm.Again 200 bhp is a typical figure for a 2 litre gas motor.
so there is not a huge difference in reality, other than the diesel normally has more torque at lower rpm and a wider power band.


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## Sunking (Aug 10, 2009)

major said:


> What does this mean? The AC-15 runs great at 48V (even at a bit lower).


 Well as I look at the power graph for the AC-15 only shows 72 and 96 volts which I assumed were the operating voltage range.

Is that not correct? If I am mistaken where would I found the 48 volt specs?

Edit Note:

Correct me if I am wrong but I think the AC-9 and AC-15 are the same motor. Only difference is AC-9 just uses a 48 volt controller? However the AC-15 does not have the right drive shaft with a C Face, I need 19 spline for DANA differential. Is any of this correct?


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## major (Apr 4, 2008)

They changed the web site a bunch. Used to have 48V info on the AC-15 and different mechanical drawings of which I thought had a version to mount to the GC axle. Oh well. 

We've run the AC-15/Curtis 1238-6501 in competition go-karts for several years at a nominal 45V. Runs great. They had 48V curves 4 yrs ago when we started and we did a lot of bench testing and tuning against those.

I thought the AC-15 was a longer core motor than the AC-9 or AC-12. And thereby was a higher torque motor and would provide higher average power before reaching thermal limits.

I still think you should talk with HPEVS or Thunderstruck and get the real story. If they have the AC-15 available with the GC mount, get it over the AC-9. For the extra inch and few pounds of motor, you'll enjoy the torque


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