ZPower

Alright, in talking to a buddy of mine the other day, I'm curious as to the following:

1) How is heat related to an engine's power output? Basically why is it that if it's 95 degrees outside vs. 30 degrees your car doesn't make as much HP (or does it)? It is anything to do with the motor itself, the air intake temp (heat soak), or else?

2) I watched a show on nitrous oxide on IIRC Spike TV once, and they basically asked the question of where exactly does the extra HP come from. According to what I remember, most comes from combustion but some also comes from the cooling effect of nitrous oxide. Was I dreaming that day, or does nitrous oxide really cool off the manifolds (or whatever part) and does that produce power?

3) Why does the HP and TQ curves on a dyno always cross at 52xxRPM? Is this always the case?

My buddy studies mechanical engineering and I was telling him how guys on the track ice their turbos/superchargers, sometimes the motor itself, to prevent overheating and to prevent HP loss (so I thought). He says heat should not make the motor lose power. He also doesn't believe the HP and TQ curves always cross at the exact same RPM. Oh, and cold air vs. hot air on the intake shouldn't make significant power increase, just like headers. Now, he's actually a bright guy, just not into cars and motors are not his "expertise", he's just thinking about efficiency, which apparently increases with heat, though the downside is wear also increases with heat. And I'm an electronics guy and never really got into mechanics. So anyway, any help is appreciated. Thanks.

LanceG33

I'm no expert but I do know that cooler air compresses more quickly than hot air so there is an advantage to cooler engine parts.

The two great enemies of the automobile are:

1) heat
2) friction

mdracer76

iTrader: (1)

Cooler air is more DENSE... thus has more oxygen to be combusted.

N2O ... Nitrous breaks down in the combustion chamber to form 2 oxygen molecules. having nitrous on my Z as well... I think that the cooling effect is negligible.

As far as question #3…. Not sure … I have never noticed that the HP and torque converge always at 52xx rpm… Is this in reference to the Z? or to all cars.

As far as your buddy.. he’s not .. Entirely wrong.. I think that the best thing you can do for your car is to keep the intake charge cold.. And the exhaust as hot as possible. Wrapping your equal length headers with a heat locking tape will help keep under hood heat temps down… while keeping your exhaust gasses as hot as possible…. Which is ideal.

Kruzr

It's not the oxygen content of more dense air that gives you more horsepower, it is the additional weight of the air itself. An internal combustion engine is a mass machine. The engine output is proportional to the mass being pushed through the engine. More pounds of air mean more pounds of fuel are needed to combust the additional air. Therefore, more pounds of combustion gases are pushing the pistons up and down. This additional energy has to go out in either heat or work. More work goes to the crank therefore more HP is produced.

Nitrous is an oxidant. More fuel must be burned to combust it. More fuel means more combustion gasses again. The cooling effect helps the efficiency but not that much.

ZPower

Good stuff. I did a quick search and found:

(TQ*RPM)/5250 = HP

If you make RPM = 5250, then TQ = HP at that point in RPMs. I'm not sure where it comes from though. One of these days I'll make some time and try to find it in a technical text edition.

Risk

The tourque and HP curves are entirely relative to the motor in question......take a big deisel motor for instance, most of those dont even rev to 5000rpms, but are rather designed to get weight moving by making the most amount of tourque (which has to do with gearing also) straight from idle.

As far as N20 goes, the above posters are correct. In laymans terms, it acts as a substance which allows much more air to fit in the same space (cylinder) and thereby raises compression on the compression stroke. Old school motors that wanted to make good use of N20 were set up to run rich as hell while not on the juice.

drift350

the breakdown is this...

TQ is force, or work.

HP is force/work over time, which is what the equation extrapolates from a torque reading.


because of this, any torque reading will equal the equivalent horsepower at 5250rpm on any motor.

drift350

an internal combustion motor is basically an air pump. colder intake is air is more dense... colder molecules are less excited and move less. think water and ice... water moves, ice does not as the molecules are moving very little or not at all. if the molecules move, friction occurs and heat is generated. cold air allows for more oxygen (and other molecules) molecules to be packed into a smaller area, creating increased density as the molecules do not need as much room to move compared to hot air. increased oxygen as an oxidizing agent that fuels the combustion creates a larger consumption of gasoline, creating a more powerful explosion in the combustion chamber.

the sudden heating and expansion of the gas when fuel is burned pushes the piston downward to put the crank in motion. so more air/fuel mixture, the bigger the bang, and more power results.

as for heat soak, energy is wasted in the form of heat due to friction. expanded molecules bump each other and create friction, resulting in heat. this wasted energy, if harnessed, will increase the eifficency of an internal combustion motor.

nope. NO2 is an oxidizer. 2/3 of Nitrogen Dioxide is OXYGEN. this increased oxygen content, which is 1/3 more than what occurs on avg in the atmosphere is what provides increased combustion and cylinder pressures when ignited with the proper amount of fuel. NO2 systems require more fuel. essentially, it's like having a larger displacement motor... you can take in and combust the same amount of fuel and air in a smaller motor as what would occur normally in a larger displacement motor. only in this form, the O2 concentration is extremely dense to fit into a smaller combustion chamber. being cold is only a necessary factor to keep larger amounts of NO2 in a smaller space as the density increases when temperature drops due to less molecular movement (refer to #1).

yes. like as said before:

(Tq * RPM) / 5252 = HP

so if you insert any value for Tq, and set the RPM value at 5252, HP and Tq will be equivalent... therefore any value for Tq qill be equal to HP when the RPM is at 5252.

heat does not cause a loss in power... heat IS lost power. heat is the byproduct of friction, friction is lost power.

HP and Tq HAS to be equal at 5252 as per that equation... simple mathematics.

icing a forced induction's intercooling system helps create denser air, allowing more oxygen molecules to be packed into a smaller area. oxygen is the required oxidixer for combustion.

headers allow for more efficient evacuation of combusted/expanded gases... if the burnt gases are stuck int he combustion chamber, fresh unburned gases cant get in... get it?


your friend needs to drop mechanical engineering if he's having problems with internal combustion motors.

Neo105

When you heat nitrous oxide to about 300 degrees C (~570 C), it splits into oxygen and nitrogen. So the injection of nitrous oxide into an engine means that more oxygen is available during combustion. Because you have more oxygen, you can also inject more fuel, allowing the same engine to produce more power.

Nitrous oxide has another effect that improves performance even more. When it vaporizes, nitrous oxide provides a significant cooling effect on the intake air. When you reduce the intake air temperature, you increase the air's density, and this provides even more oxygen inside the cylinder.

ZPower

This must be what I vaguely remember from the tv show.

Drift350, from your response to this one, it doesn't look as if you agree?

Do you by any chance know where the 5250/5252 comes from?

Again, his area of concentration is not internal combustion motors. And he does understand why allowing more volume of air at the intake and freeing up the exhaust would produce more power. Our argument was not about that. Our argument was the temperature effects and what caused them (with the engine as the primary focus). Even though heat is wasted energy (unless heat is the intended output), his argument was that as long as the engine's cooling system keeps it in the op temp, changes in ambient temp will not change its output with respect to the engine temp, and he is right - it's not the delta ambient temp vs. constant motor temp that affects power output, it is the change in air density at the air intake due to lower ambient temps. My argument was just that I simply didn't know exactly why, but that it did affect the output of an engine (I just never bothered with it, just something I knew as a rule of thumb from being a car enthusiast).

We were actually pretty sure it had to be air density, but we just wanted to make sure. I figured it would be easy and fun to ask these questions here, as neither one of us has a lot of time (and will after a full day's work) to search the web or a textbook. We just like to get into arguments during lunch, and this was one of them.

drift350

the cooling effect is a byproduct of having to compress a significant quantity of NO2 into a cylinder. if it were at room temperature, the cylinder would hold a lot less NO2.

basically, the cooling effect is secondary... mainly because as NO2 being an oxidizer with ~66% oxygen content, it's the high oxygen content that gives you the majority of the power... being cold just allows it to be more densly packed.

think of NO2 chemically as i had stated before... Nitrogen Dioxide. 2 oxygen atoms per 1 nitrogen atom bonded into a molecule. when at combustion temps, the nitrogen is split from the oxygen molecule, producing the increased amount of oxygen to be combusted.

on a side note, since the motor is releasing nitrogen when burning NO2, you can smell it... like a whiff of lawn fertilizer. so if you're out racing, you'll be able to smell it if you're careful to see if the guy next to you (or in front of you if he's winning ) is squeezing.



horsepower is defined as 550ft/lbs per second... i.e. 1hp = 550ft.lbs/sec.

to extrapolate that into engine terms, it must be divided by engine speed, which is 0.10472 radians per second. 550 divided by 0.10472rad/sec = 5252.

therefore, 5252 is the divisor when calculating horsepower based on torque multiplied by engine rpm.




it's more of a chemical engineering ideal where temperature of an oxidizing agent increases the density of the agent. constant motor temp has little to do with the operating efficiency as it is only a result of operating efficency or inefficency. the ambient temp is critical only in the aspect that it affects the fuel compound itself... colder=denser=more oxygen per cubic centimetre.

if the motor were more efficient, the operating temp would be lower due to decreased friction and loss of power int he form of heat.

i'm sure you see the correlation i'm making here, so i'll stop.