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Old 09-05-2006, 12:06 AM   #1
project92SC2
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Default Basic Engine Operations

This topic is posted to explain why faster intake speeds on a naturally aspirated engines will not efficiently help.

Note to administrators and moderators: please maket this a sticky in the main tech or FAQ section.

Basic Engine Operation 101:

An engine is an air pump. It sucks air in via the intake system, compresses it, combusts the compressed air, and pushes it out the exhaust system, thus, creating power that is transferred through the transmission gears, to the wheels, therefore moving our lazy butts because we're too lazy to walk.

Most people want to go faster, therefore they modify their engines to make more power to the wheels so they go WHEEEE!! until their eyes push into their brains causing head trauma.

The basis of going faster is less restriction to the intake and exhaust systems. A larger-than-stock exhaust system would make less back-pressure on the engine, making it easier to remove exhaust from the combustion chamber, thus making it possible for more power to the wheels. To add more power, you would want less restriction on the intake as well, which here comes the larger aftermarket intakes.

Also to make more power, an engine can only fit so much air into the cylinders. There are 2 ways of adding more air to the cylinders. Colder air is denser, so this is why the cold air intake was invented. For every degree 15*F cooler the intake charge is, you are able to add an estimated 5 cubic inches of air compared to a normal intake temperature that is heated from the engine bay heat. This helps greatly in engine operation, but benefits mainly from having the larger-than-stock exhaust, because their is more air in the cylinders after combustion than the stock exhaust was designed for. You're still getting more power, but it's taking a little more power to push the exhaust out.

Ram-Air intakes operate in the same way. They are basically a shorter CAI, making it easier, and faster for the engine to get colder air, but again, as I can explain this, your naturally aspirated engine cannot pump air any faster than it was designed, so there is a limit to how much air goes in to the cylinders. Here's where forced induction steps in.

Forced induction basically increases air speed. They in turn, when increasing intake speed, compress the air from pressure build up behind closed valves. There are two ways of doing this. One, a supercharger. A supercharger operated on the power of the engine. In 2 stroke engines, it operates off of a permanent gear setup, on 4 stroke engines, it operates off of a belt sytem from the crankshaft. Thus, using horsepower to make horsepower. Not so efficient huh? Luckily, the second way is better, but takes a bit more tuning to do. The second way of increasing intake speed is a turbocharger. A turbocharger operates of of the engine's exhaust. It uses a turbine on one side that is connected through a shaft to the intake impeller on the other side. Thus, using very little, if any engine horsepower. The reason further tuning is needed with a turbocharger, is so that the air/fuel mixture isn't too lean. The leaner your mixture gets, the better the chance of detonation.

Typically, when running either mode of forced induction, you'll want to run more fuel to the engine to deter detonation. Detonation is the term used for when the a/f mixture ignites prematurely and causes major engine trouble. (i.e. shattered pistons/ heads, broken rods...etc.....)
Fuel isn't a power additive. Gasoline and Diesel are used to deter detonation. The octane level in gasoline determines the pressure level required for ignition without heat. The higher the octane level, the better chance you stand in detering detonation. The cetane level in diesel does the same, but is usually kept at a standard, because all diesels run at about the same pressures.

When you want to make more power without going forced induction and spending hundreds to thousands of dollars, then timing adjustments can be made. The typical way to do this, is the guessing game. You'll want to advance your intake timing, opening your intake valves sooner, and retard your exhaust timing, opening your exhaust valves later. (doing both is only able to be done on a DOHC engine unless you have a custom cam made with those adjustments.) This will allow more air into your combustion chamber, and aid in pushing the combusted exhaust out, thus creating more power.



All and all, there is not a possible way to effectively increase intake "speed" without going forced induction.

Nitrous is a different story. People think it is a big power add-on because it is more combustible. Not at all true. It is a big power adder because Nitrous is sent through at a VERY VERY cold temperature, somewhere around -150*F or lower. This allows the air inside to condense, thus, effectively helping the larger intake system. This type of power add-on definitely requires proper tuning to operate correctly, otherwise, it is an easy way to blow an engine. Beginners should not do this modification alone, have someone experience there to help you. Nitrous Oxide can be very fun, but when not properly used, can be very dangerous.



With either forced induction, or nitrous oxide injection, you'll want to run colder spark plugs, and extra fuel. Why? Because I said so..... jfwy. It's to deter our best friend...... detonation. Cooler spark plugs don't have a cooler spark, they just dissapate heat quicker, so it's not so on the incoming air. Extra fuel is to make sure the engine doesn't run lean, and you end up with a knock, also requred that you run higher octane / cetane levels depending on your engine. (gas/diesel) Also, before doing either to a stock engine, make sure you have your cylinder head(s) serviced. Have all carbon build-ups cleaned out of your combustion chamber and have it polished. Have your exhaust ports cleaned and polished. Have your intake ports cleaned and honed. This makes it so the intake has better turbulence to mix the air and fuel. The polishing of the exhaust ports and combustion chamber makes for smoother flow, and less carbon build-up. Carbon build-up can retain heat in the combustion chamber, which could also lead to detonation.

For safety reasons, you should have your vehicle fully inspected and repaired for all safety equipment (brakes, tires, suspension and steering, electrical) before modifying your car. Make sure your engine is not burning oil, or running hot. Check everything head to toe on your car. If you take shortcuts, it will come back to bite you, and it will cost you more in the long run if you wait to fix it.

I hope this post helps those who are just starting. Enjoy.

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Old 09-05-2006, 09:31 AM   #2
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Default Re: Basic Engine Operations

This is not S-Series specific....it is general....

Please learn to post in the proper area..

...
It's not easy being Green(SC2). (IntelliTXT SUCKS)
I refuse to be a Lemming!!

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Old 09-05-2006, 04:32 PM   #3
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Default Re: Basic Engine Operations

Quote:
Originally Posted by GreenSC2
This is not S-Series specific....it is general....

Please learn to post in the proper area..

I couldn't find it. Please have someone move it there, and make it a sticky.
This applies to ALL engines.

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Old 09-05-2006, 04:33 PM   #4
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Default Re: Basic Engine Operations

Quote:
Originally Posted by project92SC2
...Forced induction basically increases air speed...
Sheesh. 25 posts and Mr. uber-poster is asking the mods to make this a sticky...

By the way, spell check is your friend, and forced induction increases air volume, not speed.

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Old 09-05-2006, 04:44 PM   #5
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Default Re: Basic Engine Operations

Quote:
Originally Posted by Saturn-Eh!
Sheesh. 25 posts and Mr. uber-poster is asking the mods to make this a sticky...

By the way, spell check is your friend, and forced induction increases air volume, not speed.
Noted, I missed that. It both increases volume and speed.

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Old 09-05-2006, 07:26 PM   #6
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Default Re: Basic Engine Operations

Quote:
Originally Posted by project92SC2
Noted, I missed that. It both increases volume and speed.
The forced induction method increases volume alone. The size of the intake tract determines the speed of the intake charge. Smaller intake increases velocity & larger intake decreases velocity.

You should also mention ignition timing as a method of of increasing horsepower in a naturally aspirated engine (not just cam timing) coupled with an appropriate increase in octane to once again prevent detonation...

Sorry to come across somewhat snide, but you need to a) Search (your post topic has been covered here before) and b) build up a somewhat larger post count before telling mods to turn your post into a sticky...

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Old 09-05-2006, 10:01 PM   #7
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Default Re: Basic Engine Operations

Quote:
Sorry to come across somewhat snide, but you need to a) Search (your post topic has been covered here before) and b) build up a somewhat larger post count before telling mods to turn your post into a sticky...
Thats true! You come here and start flamming members that you have history with but he has more post count than you. Im sorry but when you come a new forum you dont start flamming a member(s)!!

Matt

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Old 09-06-2006, 01:15 AM   #8
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Default Re: Basic Engine Operations

I'm not going to argue with you guys. It's not worth it. Sorry, don't tell me forced induction doesn't increase intake speed, I've worked with it too much, it doesn't matter how big of a post count you have.

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Old 09-06-2006, 03:57 AM   #9
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Default Re: Basic Engine Operations

Quote:
Originally Posted by project92SC2
The octane level in gasoline determines the pressure level required for ignition without heat. The higher the octane level, the better chance you stand in detering detonation. The cetane level in diesel does the same, but is usually kept at a standard, because all diesels run at about the same pressures.
Gasoline octane and diesel cetane ratings are inversely related. Straight chain hydrocarbons are easy to ignite and have low octane / high cetane ratings (n-heptane is the 0 for the octane scale, n-hexadecane is the 100 standard for the cetane scale). Branched chain hydrocarbons are difficult to ignite and have high octane / low cetane ratings (2,2,4-trimethylpentane (iso-octane) is the 100 standard for the octane scale while 2,2,4,4,6,8,8-heptamethylnonane is the low standard (15) for the cetane scale. Preignition / detonation are bad for spark ignition engines but rapid ignition following injection is good for a diesel.

Quote:
Originally Posted by project92SC2
You'll want to advance your intake timing, opening your intake valves sooner, and retard your exhaust timing, opening your exhaust valves later. (doing both is only able to be done on a DOHC engine unless you have a custom cam made with those adjustments.) This will allow more air into your combustion chamber, and aid in pushing the combusted exhaust out, thus creating more power.
Sure, you can modify your cams and sacrifice the low end to get more power over 4000 RPM, but do you really want to? This was a popular mod for a 3-cylinder Geo Metro where the gearing keeps the engine over 3000 RPM most of the time, but saturns are geared much taller.

Quote:
Originally Posted by project92SC2
Nitrous is a different story. People think it is a big power add-on because it is more combustible. Not at all true. It is a big power adder because Nitrous is sent through at a VERY VERY cold temperature, somewhere around -150*F or lower. This allows the air inside to condense, thus, effectively helping the larger intake system.
Yes, N2O is pretty darn cold after it transforms from a liquid in the tank to a gas in your intake, but it's nowhere near cold enough to condense air (which boils at -190C). The big deal with N2O is that it decomposes into N2 and O2 during combustion, and it is 33% oxygen while the air is only 21%. 50% more O2 + low temperature intake = double power.

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Old 09-06-2006, 07:03 AM   #10
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Default Re: Basic Engine Operations

Excellent post "project92SC2". It was very informative.
"Jeesh" give the guy a break, people. Mentioning spell check..c'mon, that's just stupid.
I'd have to agree with most of what you stated. Don't listen to these fools project92SC2..These people (not everyone) only wished they had knowledge that you have.

I do have one question for your theory project92SC2. Why do people get more power on colder low altitude days?

Last edited by 10W30; 09-06-2006 at 07:10 AM..

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Old 09-06-2006, 07:35 AM   #11
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Default Re: Basic Engine Operations

Quote:
Originally Posted by 10W30
..Why do people get more power on colder low altitude days?
Density altitude. Humidity also plays a role. Denser air means more oxygen in a given volume which means you can burn more fuel.

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Old 09-06-2006, 07:43 AM   #12
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Default Re: Basic Engine Operations

Quote:
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Density altitude. Humidity also plays a role. Denser air means more oxygen in a given volume which means you can burn more fuel.
Yes....I understand denser air means more oxygen.
My question is "WHY does it give you more power"?
Why do you get more power while colder air is pouring into the combustion chamber and more fuel is burning?

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Old 09-06-2006, 08:42 AM   #13
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Default Re: Basic Engine Operations

Quote:
Originally Posted by Gerry Proctor
Density altitude. Humidity also plays a role. Denser air means more oxygen in a given volume which means you can burn more fuel.

Not exactly. A cooler denser mixture has a greater expandtion ratio and it is expanding gass that drive the piston down and convert it to work in the form of torque and RPM with can them be converted to HP. Humidity can also increase the expansion in the combustion chamber to a pint as it can alter flame speed and increase effective expandtion ratio. We can split hairs even further in that tempature and himidty effect octane requirements as well and there fow can effect engine time and with low octane fuel the difference in performance level on hot and cold days can be amplified by need to retard spark more on hot days with 87 octane. What does all this mean? there is a lot more science to engine operation than meets the eye.

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Old 09-06-2006, 10:00 AM   #14
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Default Re: Basic Engine Operations

Quote:
Originally Posted by 10W30
I do have one question for your theory project92SC2. Why do people get more power on colder low altitude days?
Thanks for the defense.

The issue with cold low-altitude area, is because the air is denser, and your can can operate at a higher volumetric efficiency than in a hot high-altitude area. For a normal day, you'll be running around 75%-80% volumetric efficiency, because well..... N/A engines just aren't that efficient, that's why we modify them.

You already stated you know colder air is denser, well the issue with lower altitude is that the air is already denser at sea level than it is in say.......... Tenessee or Colorado ( hehe....Colorado.....der.....)
Anything above sea level has less atmosphere weighing down on it. That's why someone like me could weigh 230lbs in South Carolina (I was at Ft. Jackson for Basic Training) and come back home to Michiganand weigh 205lbs. (also lost a few more pounds.)

Sea level atmospheric pressure, is 14.7psi on around a good 70*F day (my temperature could be wrong, but it's close) and when you cool it, its weighs more. It also changes density with the humidity level. You can have a car out in the middle of Arizona running 300whp, bring it to Florida in the summer and notice about a 20hp increase due to the denser air, which contains more water vapor, which makes it much denser. This is why some people in dry areas run what is known as "water-injection." It increases compression, but directly injecting water (about 1 drop per cylinder MAX) is not the safest way to run the engine. It is actually risking more harm to the engine than running Nitrous if you don't know what you're doing, because there is a risk of hydro-lock.

Let's face it, colder air weighs more, because it is denser, and I can build my Saturn up to 250whp here, and it would run about 260whp in Florida on a cool day due to a heavier atmospheric pressure. Weather also affects this, being in a high-pressure or low-pressre zone. This is cars show less performance in bad weather.

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Old 09-06-2006, 10:05 AM   #15
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Default Re: Basic Engine Operations

Quote:
Originally Posted by 97coupe
Not exactly. A cooler denser mixture has a greater expandtion ratio and it is expanding gass that drive the piston down and convert it to work in the form of torque and RPM with can them be converted to HP. Humidity can also increase the expansion in the combustion chamber to a pint as it can alter flame speed and increase effective expandtion ratio. We can split hairs even further in that tempature and himidty effect octane requirements as well and there fow can effect engine time and with low octane fuel the difference in performance level on hot and cold days can be amplified by need to retard spark more on hot days with 87 octane. What does all this mean? there is a lot more science to engine operation than meets the eye.
Not really. Unless your running insane cylinder pressures, there is no reason to mess with spark in a different air-density or temperature area. Engine operation remains the same, performance changes slightly. The only thing you would want to do with the car running high-cylinder pressure is go to a higher octane level, or add a bit more fuel to keep it from leaning out.

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Old 09-06-2006, 10:05 AM   #16
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Default Re: Basic Engine Operations

Quote:
Originally Posted by 97coupe
Not exactly. A cooler denser mixture has a greater expandtion ratio and it is expanding gass that drive the piston down and convert it to work in the form of torque and RPM with can them be converted to HP. ...
Thank you. I know nothing about how engines work or how to make horsepower. You've filled a great void in my knowledge.

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Old 09-06-2006, 10:14 AM   #17
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Quote:
Originally Posted by project92SC2
Not really. Unless your running insane cylinder pressures, there is no reason to mess with spark in a different air-density or temperature area. Engine operation remains the same, performance changes slightly. The only thing you would want to do with the car running high-cylinder pressure is go to a higher octane level, or add a bit more fuel to keep it from leaning out.

double post see below

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Old 09-06-2006, 10:16 AM   #18
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Quote:
Originally Posted by project92SC2
Not really. Unless your running insane cylinder pressures, there is no reason to mess with spark in a different air-density or temperature area. Engine operation remains the same, performance changes slightly. The only thing you would want to do with the car running high-cylinder pressure is go to a higher octane level, or add a bit more fuel to keep it from leaning out.

See that is where you are mistaken because with a modern hi compression engine limping allong on 87 octane on a hot verse a cold day, you are indeed constantly messing with the spark because if you have a fixed curve like the old days and set curve for a cool day with 87, it would rattle and knock to beat the band on hot day. The knock sensor hides you true octane requirements at the expense of MPG and performance at times but there are those that believe 87 is the best no matter what because it is the cheapest too and if it is not knocking it is because it is the best gas, not because the knock sensor is stealing your MPG and power silently.

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Old 09-06-2006, 10:23 AM   #19
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Default Re: Basic Engine Operations

Quote:
Originally Posted by 97coupe
See that is where you are mistaken because with a modern hi compression engine limping allong on 87 octane on a hot verse a cold day, you are indeed constantly messing with the spark because if you have a fixed curve like the old days and set curve for a cool day with 87, it would rattle and knock to beat the band on hot day. The knock sensor hides you true octane requirements at the expense of MPG and performance at times but there are those that believe 87 is the best no matter what because it is the cheapest too and if it is not knocking it is because it is the best gas, not because the knock sensor is stealing your MPG and power silently.
Dude, that is why they made such advanced stock engine computers today. It controls it, and it worries about it, so you don't have to. Unless you're rurnning a full standalone engine management system, you don't have to worry about it. Of course you're going to get worse MPG on some days, and better on others. This is EARTH. We ****ed up the weather pattern, so the weather doesn't remain the same everywhere as it used to. Thus, quit your complaining. I do know what I'm talking about. Don't tell me I'm wrong, I didn't say you were wrong, I said NOT REALLY. I'm not mistaken, again, I know what I'm talking about.

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Old 09-06-2006, 02:36 PM   #20
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Default Re: Basic Engine Operations

Quote:
Originally Posted by project92SC2
Anything above sea level has less atmosphere weighing down on it. That's why someone like me could weigh 230lbs in South Carolina (I was at Ft. Jackson for Basic Training) and come back home to Michiganand weigh 205lbs. (also lost a few more pounds.)
The atmospheric pressure effect is due to buoyancy and is very small (less than a pound difference between sea level and vacuum) and opposite in sign (you are lighter at sea level).

Quote:
Originally Posted by project92SC2
Sea level atmospheric pressure, is 14.7psi on around a good 70*F day (my temperature could be wrong, but it's close) and when you cool it, its weighs more. It also changes density with the humidity level. You can have a car out in the middle of Arizona running 300whp, bring it to Florida in the summer and notice about a 20hp increase due to the denser air, which contains more water vapor, which makes it much denser. This is why some people in dry areas run what is known as "water-injection." It increases compression, but directly injecting water (about 1 drop per cylinder MAX) is not the safest way to run the engine. It is actually risking more harm to the engine than running Nitrous if you don't know what you're doing, because there is a risk of hydro-lock.
Sea level pressure is always near 14.7 psi (101.3 kPa) regardless of temperature. Extreme ranges are between about 90 kPa (eye of large hurricane) and about 105 kPa (strong high pressure system). Temperature does affect density though, so cold air is more dense than warmer air at the same pressure.

Water vapor does NOT make air denser. It actually displaces oxygen so high humidity air has less oxygen per unit volume than low humidity air at the same temperature and pressure. Water vapor is less dense than oxygen or nitrogen, which accounts for "dry line" thunderstorms (humid air is forced up and over dry air, triggering cumulonimbus cloud formation). More power in Florida than Arizona is strictly an altitude effect, the humidity is working against you.

Water injection will help cool the intake air by evaporation and thus help prevent preignition / detonation and allow you to run higher compression and/or more advanced ignition timing (= more power). Also, if the water enters the cylinders in the liquid phase, it does not displace nearly as much oxygen as it would in the vapor phase.

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