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Getting over my head in physics


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I have been attempting to answer, what I thought was a simple question, and have been swallowed by internet caves of information. The question is "Is more gasoline required to create more horsepower." Now, I thought this would be easy to confirm, gasoline has a specific energy (1 gallon of finished motor gasoline (containing about 10% fuel ethanol by volume) = 120,286 Btu) Note: I did not find an official site that contained energy listings for higher octane or "regular" gasoline.

At first, I thought the answer would be "sometimes" with factors such as: engine compression, engine injection vs. carb, weight, engine efficiency, etc. etc. But, quickly learned that aside from specialty vehicles or prototypes, the differences in engine horsepower and gasoline consumption stay in a basic range. An engine can be operated only so lean, before it grenades, while a turbo charger and/or high compression and/or a supercharger can provide more horsepower without additional fuel, dramatic increases will dramatically shorten engine life. 

 

I will spare, all the energy conversions, extraneous factors, e.g. aerodynamics, vehicle weight, rolling resistance, altitude. Suffice, that I believe the original hypothesis holds, all other factors being equal, an engine producing more horsepower will require more gasoline. A fuel injected engine, a turbo charged engine or a super charged engine can increase horsepower derived from gasoline, by increasing engine  efficiency.(I was unable to find exact data on the efficiency increase, relative to fuel consumption with the addition of injection or forced induction.)

 

I did find a published study that demonstrated a seven horsepower gain, through timing advance on the Z24.The Z24 has been the engine behind this research. All other parameters being equal, will a fuel injected Z24, creating around 100 horsepower, consume less gasoline (better mpg) than a KA24E creating around 200 horsepower. If the same turbo is added to both engines, will there be disparity in fuel consumption vs. horsepower gained?

 

 

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2 hours ago, frankendat said:

 An engine can be operated only so lean, before it grenades, while a turbo charger and/or high compression and/or a supercharger can provide more horsepower without additional fuel, dramatic increases will dramatically shorten engine life. 

 

This is wrong. A forced induction moves more air into the combustion chamber so if no additional fuel is added it will, by your first sustenance go lean and grenade. If more air is added more gas must also be added to this air and more power is the result.

 

Higher compression is not in the same class as  forced induction. Higher compression compared to the lower compression of the same amount of air and gas increases the efficiency of the engine. This is because a smaller combustion chamber (all other things equal) has a smaller surface area. A smaller surface area means there is less heat absorbed into the surrounding metal and the cooling system. More heat means there is more expansion of the burning gasses, more pressure in the combustion chamber, more pressure to push down on the piston and do work. (this is one of the reasons that diesels with 2 1/2 times the compression of a gasoline engine are so scary efficient.) Having said this there are limits to compressing gas without having it self ignite. Higher octane does not mean the gas has more energy in it, or more explosive. Octane simply makes it harder to light compressed gas and air. It becomes less sensitive to auto ignition, thus you can run it in a more efficient high compression engine and get more out of it.

 

 

Quote

 

I will spare, all the energy conversions, extraneous factors, e.g. aerodynamics, vehicle weight, rolling resistance, altitude. Suffice, that I believe the original hypothesis holds, all other factors being equal, an engine producing more horsepower will require more gasoline. A fuel injected engine, a turbo charged engine or a super charged engine can increase horsepower derived from gasoline, by increasing engine  efficiency.(I was unable to find exact data on the efficiency increase, relative to fuel consumption with the addition of injection or forced induction.)

 

Fuel injection

More efficient because the fuel is atomized by being injected under pressure just before the intake valve or better yet direct injected into the combustion chamber where a carburetor uses intake vacuum to basically suck fuel through a straw. The engine has to work (loss) to suck the fuel in.

 

Turbo charged

Keep in mind that as soon as you boost you increase fuel consumption. But at cruise speeds a tiny amount of boost can overcome the losses for the engine having to work to pull the intake air in through a carburetor and all the intake bends and plumbing, and the intake valve. But as soon as you start pushing in more air than the engine would normally draw in itself more gas will be added.

 

Super charger

As a super charger is a huge parasitic air pump you will never get back what you put into it. Even at light throttle. Don't forget, the exhaust energy running the turbo is basically waste and free. 

 

 

So does more fuel make more power.... Yes if you add more air with a forced induction like a turbo or SC, otherwise you are just running richer.

 

Can you make more power with the same amount of fuel...... yes by increasing the efficiency of the engine such as increasing the compression ratio. You can also coat the combustion chamber and piston tops with a ceramic coating that resist heat transfer keeping it in the combustion chamber doing work. Exotic engine oils reduce friction, such as synthetic. EFI rather than carburetors. Lower restriction exhaust.

 

Quote

 

I did find a published study that demonstrated a seven horsepower gain, through timing advance on the Z24.The Z24 has been the engine behind this research. All other parameters being equal, will a fuel injected Z24, creating around 100 horsepower, consume less gasoline (better mpg) than a KA24E creating around 200 horsepower. If the same turbo is added to both engines, will there be disparity in fuel consumption vs. horsepower gained?

 

 

 

I don't recommend advancing the timing above factory. There must be more to this 7hp gain. The Z24 is very efficient and had dual plugs allowing a very small ignition advance. The piston should be at around 170 ATDC and just starting to accelerate down the cylinder. This is the most efficient position for the hot expanding gasses to reach maximum pressure. Too late and the expanding gases will be chasing the rapidly accelerating piston down the bore. Too soon and the piston, rod, and crank shaft are closer to a vertical stack that can't be pushed down on. Advancing the timing will result in a power loss as

 

All things equal a 200hp KA24E will be using twice as much fuel as a 100hp Z24.

 

If you add a turbo and cram 14.5 PSI (1 Barr) into both engines (basically doubling the amount of air and fuel) the Z24 will make 200 hp and the KA24E, 400hp

 

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Maybe you should look at it another way, you don't get something for nothing.  Potential energy in equals potential power out minus all the inefficiencies, heat, wear and probably a few others.  So sure it takes more gas to make more power but the bigger the engine the less efficient it becomes and no two engines are created equal.

A theoretically perfect engine will produce X amount of power whilst consuming Y amount of fuel, scale up the engine by 5 times and it would produce 5 times the power at the cost of 5 times the fuel but in the real world it is all about efficiency.

 

Just off the top of my head I think an average internal combustion engine is only about 20% efficient so there's lots of room for improvement and the difference between any 2 engines is within that 80% waste.

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7 minutes ago, grannyknot said:

Maybe you should look at it another way, you don't get something for nothing.

 

Truest statement in the world.

 

 

7 minutes ago, grannyknot said:

 

 

 

Just off the top of my head I think an average internal combustion engine is only about 20% efficient so there's lots of room for improvement and the difference between any 2 engines is within that 80% waste.

 

20% is at the low end but some reach 35%. I would assume our Datsuns are at the low end. There was a Mercedes that uses captured exhaust heat (most of the 65%-80% heat energy wasted anyway) to boil water for a 12 hp steam engine connected to the driveshaft. Perhaps 7% efficient so added to the 25%????  That's not bad. Just a way of extracting more work from the heat energy.

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2 hours ago, datzenmike said:

 

This is wrong. A forced induction moves more air into the combustion chamber so if no additional fuel is added it will, by your first sustenance go lean and grenade. If more air is added more gas must also be added to this air and more power is the result.

 

Higher compression is not in the same class as  forced induction. Higher compression compared to the lower compression of the same amount of air and gas increases the efficiency of the engine. This is because a smaller combustion chamber (all other things equal) has a smaller surface area. A smaller surface area means there is less heat absorbed into the surrounding metal and the cooling system. More heat means there is more expansion of the burning gasses, more pressure in the combustion chamber, more pressure to push down on the piston and do work. (this is one of the reasons that diesels with 2 1/2 times the compression of a gasoline engine are so scary efficient.) Having said this there are limits to compressing gas without having it self ignite. Higher octane does not mean the gas has more energy in it, or more explosive. Octane simply makes it harder to light compressed gas and air. It becomes less sensitive to auto ignition, thus you can run it in a more efficient high compression engine and get more out of it.

 

 

 

Fuel injection

More efficient because the fuel is atomized by being injected under pressure just before the intake valve or better yet direct injected into the combustion chamber where a carburetor uses intake vacuum to basically suck fuel through a straw. The engine has to work (loss) to suck the fuel in.

 

Turbo charged

Keep in mind that as soon as you boost you increase fuel consumption. But at cruise speeds a tiny amount of boost can overcome the losses for the engine having to work to pull the intake air in through a carburetor and all the intake bends and plumbing, and the intake valve. But as soon as you start pushing in more air than the engine would normally draw in itself more gas will be added.

 

Super charger

As a super charger is a huge parasitic air pump you will never get back what you put into it. Even at light throttle. Don't forget, the exhaust energy running the turbo is basically waste and free. 

 

 

So does more fuel make more power.... Yes if you add more air with a forced induction like a turbo or SC, otherwise you are just running richer.

 

Can you make more power with the same amount of fuel...... yes by increasing the efficiency of the engine such as increasing the compression ratio. You can also coat the combustion chamber and piston tops with a ceramic coating that resist heat transfer keeping it in the combustion chamber doing work. Exotic engine oils reduce friction, such as synthetic. EFI rather than carburetors. Lower restriction exhaust.

 

 

I don't recommend advancing the timing above factory. There must be more to this 7hp gain. The Z24 is very efficient and had dual plugs allowing a very small ignition advance. The piston should be at around 170 ATDC and just starting to accelerate down the cylinder. This is the most efficient position for the hot expanding gasses to reach maximum pressure. Too late and the expanding gases will be chasing the rapidly accelerating piston down the bore. Too soon and the piston, rod, and crank shaft are closer to a vertical stack that can't be pushed down on. Advancing the timing will result in a power loss as

 

All things equal a 200hp KA24E will be using twice as much fuel as a 100hp Z24.

 

If you add a turbo and cram 14.5 PSI (1 Barr) into both engines (basically doubling the amount of air and fuel) the Z24 will make 200 hp and the KA24E, 400hp

 

 

I attached the study that researched the advance timing to increase engine  efficiency. It is filled with equations that are beyond my understanding, perhaps  you could decipher the reasoning behind the increased horsepower.  There are published works that claim a low boost turbo, which remains engaged throughout the RPM range will increase  mpg. Is a 14.5 psi a large turbo?

Additionally, and to confirm my hypotheses, the Z24 will provide better mpg than a KA24E--correct?

Z24 performance mods.pdf

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The engine was simulated numerically. A real engine in the real world wasn't used. These friggin scientists probably think that with 9 women they could produce a baby in 30 days. I guess it's there but couldn't find the timing they claim and the claim is theoretical not measured.

 

The cam timing specs are nowhere near the ones in my '84 FSM.

 

Also it says the power output per cylinder for the Z24 was 137Kw..... 137,000 watts which is over 183 hp or 734hp for the entire engine.

 

49 minutes ago, frankendat said:

 

I attached the study that researched the advance timing to increase engine  efficiency. It is filled with equations that are beyond my understanding, perhaps  you could decipher the reasoning behind the increased horsepower.  There are published works that claim a low boost turbo, which remains engaged throughout the RPM range will increase  mpg. Is a 14.5 psi a large turbo?

Additionally, and to confirm my hypotheses, the Z24 will provide better mpg than a KA24E--correct?

Z24 performance mods.pdf 537.75 kB · 0 downloads

 

Numbers can say anything as this was not proven on an actual engine. It was a simulation. I still don't understand the 137Kw power output. Should be more like 18Kw-20Kw.

 

 

Both engines are 2.4 liters but the KA will be far more efficient as it's EFI controlled with O2 feedback for more uniform mixtures. There's' a CAS so the timing is adjusted many times a second, (by the EFI) it has a far more efficient head with individual tuned length runners.

 

Carburetors are stuck with what ever jet was put in them that will more or less cover your needs. Mixture can only be adjusted by changing them. They are 'good enough' but don't adjust themselves. The Z24 distributor timing is vacuum and or mechanical and set and non adjustable. It's again... good enough.

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3 hours ago, datzenmike said:

The engine was simulated numerically. A real engine in the real world wasn't used. These friggin scientists probably think that with 9 women they could produce a baby in 30 days. I guess it's there but couldn't find the timing they claim and the claim is theoretical not measured.

 

The cam timing specs are nowhere near the ones in my '84 FSM.

 

Also it says the power output per cylinder for the Z24 was 137Kw..... 137,000 watts which is over 183 hp or 734hp for the entire engine.

 

 

Numbers can say anything as this was not proven on an actual engine. It was a simulation. I still don't understand the 137Kw power output. Should be more like 18Kw-20Kw.

 

 

Both engines are 2.4 liters but the KA will be far more efficient as it's EFI controlled with O2 feedback for more uniform mixtures. There's' a CAS so the timing is adjusted many times a second, (by the EFI) it has a far more efficient head with individual tuned length runners.

 

Carburetors are stuck with what ever jet was put in them that will more or less cover your needs. Mixture can only be adjusted by changing them. They are 'good enough' but don't adjust themselves. The Z24 distributor timing is vacuum and or mechanical and set and non adjustable. It's again... good enough.

 

It is true, I am plagued with difficulty accepting "good enough". The author of that paper listed an email for questions and comments. The paper is from 2010, but I sent an email, questioning the 137 number. I will keep this thread updated, if contact is achieved or new developments on timing are discovered.

Thank you

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IIRC there are 746 watts in a HP. I remember this from high school. There is a metric HP designated as PS rather than HP which is 735 watts (had to look this up)

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this is above my pay grade but more fuel more air more horsepower 

more efficient even more horsepower 

BLAH BLAH BLAH DATSUN LOL

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I haven't had time to read it all but a quick skim of his calcs shows he is using over 90% volumetric efficiency which is not going to happen. Best case for that cylinder head would be 80%. That would significantly reduce his numbers. 

 

Boost pressure isn't necessarily a direct relationship to turbo size. An increase in boost indicates the engines inability to consume all the air it is being provided. At cruise for better mpg how much boost your engine can have would depend on how lean it can run. Because eventually more boost means more fuel. There is balance.

 

There is a relation ship between boost pressure and exhaust pressure in the manifold before the turbine, more exhaust pressure equals more drive power, but it also means the boost pressure needs to be able to overcome the exhaust pressure at valve overlap to fill the cylinder properly, or have minimal overlap, or reduce turbo back pressure which increases lag. More balance. 

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Also the 137kw could have been a mistake by old mate. He could have read 137kw instead of 137hp on the engine specs, based all his calcs off that. Being all theoretical paper even if he picked it up later he wouldn't change it after all that work. 🤔

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