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Scooby![color=red]As written by NJHK on cobaltss.net and can also be viewed on ecotecforum.com
The most common misconceptions, the concerns and the state of mind of tuners
This is by no means saying what my opinion is the end all and say all to car tuning but it's something to think about or even something to question if you feel to. Hopefully this will raise some discussion either on the forum boards or in real life.
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1. A engines limitation with forced induction is determined by how much "boost" it can hold
This is incorrect. A engines limitation is more in a phsyical basis as far as parts holding up to stress.
"Boost" is nothing but air pressure that is above atmospheric pressure. It's less about how much pressure you're creating and more about the amount of air (CFM) being compressed per pound of air pressure (PSI).
2. Backpressure is something you need
First understand that your engine is a big air pump. It ingests oxygen (or maybe even is forced fed oxygen) and expels wastes. The most important part to also understand is that velocity of air traveling plays effect in both parts. If you don't understand what velocity is:
Quote:
In physics, velocity is defined as the rate of change of displacement or the rate of displacement. It is a vector physical quantity, both speed and direction are required to define it.
When talking about your exhaust system, increasing the diameter of your exhaust system or even increasing the primaries on your manifold/header, it effects the velocity of the exhaust leaving your engine. If it doesn't make much sense to you, think of it like this:
Take a straw that is 3 centimeters in diameter and blow into it. The air from your lungs is now traveling through your mouth and into a closed area at a certain rate of speed. When it reaches into the straw, what determines the speed is the force of the air travel in this inclosed space. Now take a straw that is 6 centimeters in diameter and the same length. Lets also assume that the air leaving your lungs and traveling through your mouth is going at the same speed/velocity. With having a larger diameter straw, this is going to change how fast air will travel through the straw...hence change the velocity of the air.
Using the example above, your lungs is the engine, your mouth is the ports on the cylinder head(s) and the straw is your exhaust system.
Now that you understand what velocity is, understand what backpressure is.
Backpressure is exactly that, air (or in this case exhaust waste) traveling back torwards the engine. Now most of us understand that it's about how fast the exhaust gets out of the motor and the exhaust system. If there is a force of air traveling out of engine into one direction, backpressure would be a force of air attempting to travel in the opposite direction.
Backpressure is caused by restriction, whether it be a crimp in the exhaust system, for example, a crush bent pipe:
or it be because of a very small diametered exhaust system (including primaries on the manifold/header).
The most important thing to understand in the cases of having an engine that is naturally aspirated or supercharged (turbocharged engines don't run off this method post-turbocharger) is that when you increase the diameter, you are getting rid of backpressure...yes but you are at the same time effecting the velocity of air traveling out of your exhaust system. It's basically taking the good with the bad.
Why is exhaust velocity important? Exhaust velocity does have a direct relation to your powerband and where it is located which is why it's very important for you to pick the proper size exhaust system in the first place. The wrong size can effect your powerband in the negative way (well, negative to you as the user of the vehicle). The slower the velocity, the later in the RPM Band your powerband will be moved to. If off extremely, it will make the performance of your engine very peaky or at worst, make you lose power.
Overall, everything should be considered and it is important to think about exhaust velocity...not backpressure. I would also suggest reading up on scavenging effects.
3. Higher Octane means more power
Higher Rated Octane Gasoline alone will NOT gain you power. The octane rating in relation to your engine is all referring the resistance to detonation (knock). Detonation is a uncontrolled explosion in your combustion chamber (not like a normal controlled igniting of fuel).
Higher Octane also has nothing to do with flame speed.
Now being that high octane fuel more resistant to detonation occuring, you can yield power gains by advancing ignition timing or even possibly running at a leaner air to fuel ratio (of course this depends on the application and the condition of the engine or setup you're running).
4. You shouldn't or can't boost a high compression (static) engine
This isn't true and there is nothing wrong with doing so if you of course know what you are doing from the beginning.
The reason people say this is because naturally, higher compressioned pistons (taller), experience higher combustion chamber temperatures than lower compressioned pistons (shorter). If you were to "boost" a naturally aspirated engine that is (for example sake) 10.5:1 compression, nothing different will occur than if you had 8.5:1 compression pistons.
The pros of boosting a higher compressioned engine is that less air is required from your compressor to yield X HP/TQ than if you had a lower compressioned engine. Why? High compressioned engines compress the air/fuel mixture tighter which also allows for a better air/fuel mixture burn which would yield a stronger ignition on the top of the piston, which creates force to turn the crankshaft and create more power.
With less boost pressure required, it is also more likely that you will be staying in the efficiency range of your compressor, which means a less likely of you creating excess heat and raising your IATs (Intake Air Temperature).
The con: Excessively High Combustion Chamber Temperatures
Yes, that is bad but it's all about countermeasuring it and doing things to a degree. There are many of ways to counteract excess heat:
1. Running a richer fuel mixture
2. "Colder" spark plugs
3. Retarding ignition timing
4. Running Higher Octane
5. Running Meth/Water Injection
6. Better (more efficient) Intercooling
These are the more general ways of doing so.
#4 is usually a big concern because of course, not everyone has access to Octane Fuel higher than 93 Rating but to also run into another misconception that you will NEED higher octane fuel...that's also incorrect because the other 5 options I listed can help to achieve the same goal.
5. A "larger" profile camshaft will always gain you power
Just like how I explained exhaust velocity, it works the same way going into the engine. With camshafts it's all about drawing air into the combustion chamber at a certain point of the Intake Stroke and for how long the camshafts keep valves open. The piston going downwards on the intake stroke is what causes air to get "sucked" into the combustion chamber.
Usually a "larger" profile means that they are changing the characteristics of the lobes/cam profile to increase the lift and duration.
Camshafts do nothing more than determine where your powerband is going to be located by how long it's going to keep the valves open for and how far the valve will get pushed down.
Now remember that RPMs = Revolutions Per Minute. The more revolutions made, the more intake strokes there will be. At lower RPMs, of course, there will be less intake strokes made and meaning less air will be ingested or even needed. Having a high duration camshaft (non-vvt motor) means that it's having the same duration no matter what RPM you're having. If you had less duration, this means that the camshaft will have the valve open for a less period of time which will creating a stronger velocity pull of air throughout the intake system and intake ports on the cylinder head. The higher duration, the weaker velocity pull at lower RPMs BUT the possibility of you drawing in more air with the increase of revolutions of the engine.
If you have a "larger" profile camshaft and you plan to have a engine that has a lot of engine revolutions, you're capable of drawing in more air in the higher RPM band because you are having more intake strokes occuring in a minute.
Camshafts also determine how broad or peaky your RPM band can be & the amount of valve overlap you're creating (Example: DOHC) as well as where your powerband is located.
Overall, it's not a guarantee that you WILL gain power. It could cause such a shift in your powerband that you could be slower than you were before.
6. Tuning Misconception: "My engines air/fuel ratio was good but my engine still blew"
There are more factors that play into how long your engine lasts for than Air to Fuel Ratio. Monitoring the follow are key as well:
1. EGTs (Exhaust Gas Temperatures)
2. Knock Sensor
3. IATs (Intake Air Temperatures)
Assuming you have a proper fueling system and a engine setup that was working fine in the first place, monitoring these 3 things are also important.
Your EGTs are a direct relation to how hot your combustion chamber is getting. Think of it as if you're cooking something in your oven, if you burn something, it will smoke and may reflect the temperature of the item burning.
Your Knock sensor listens for any abnormal "explosions" in your combustion chamber, which is also known as detonation. When it "hears" something abnormal, it senses it and sends a signal to your computer which in relation, your computer starts to retard ignition timing as a safety countermeasure. Your computer also reads the signal and translates it by "degrees of knock". If you are reading anything other than 0 degrees of knocking that is a problem and you should start to figure out why this is occuring and how to fix the issue.
Your IATs are the starting point and can be what may be causing a issue. Some vehicles have more than 1 IAT sensor on the intake side. On vehicles with forced induction, they can have a pre and post IAT sensor to see the temperature of the air coming into the compressor and then the temperature after the compressor. If you are capable of monitoring this, I'd suggest doing so because it can have direct relation to how hot your combustion chamber is getting...if your IATs are excessive, so will your combustion chamber temperatures.
There are other things you can look out for but these are the most common things that a tuner can check up on before having a blown engine BESIDES their air to fuel ratios. This is of course assuming that everything else was setup properly and parts were sufficient for the job at hand.
7. Increasing my rev limiter will gain me more power
Yes and No. If you have a stock vehicle and you increase your rev limiter, it won't yield you any MORE power. You would actually start to see a drop off in power.
Why? There are many reasons why but typically the most important reasons are that your valvetrain or compressor (in stock form) or both aren't capable of keeping up a steady and higher airflow demand to for the increased engine revolutions.
8. I was going to tune with a air/fuel gauge with my stock O2 sensor
Doing this is actually useless when it comes to fuel tuning for performance.
Why? Most automakers produce vehicles with atleast 1 O2 Sensor that is the primary O2 sensor for determining fuel consumption during idle and cruising speeds...basically for gas mileage. The chemically ideal stoich air/fuel mixture is 14.68 air/fuel ratio which is basically what these sensors are capable of reading accurately around. These are called narrowband O2 sensors. If you were to install a air/fuel gauge to pick-up your narrowband O2 sensor, you'll basically get a light show during cruising speeds and in higher throttle positions, it will probably peg in one because it's not capable of knowing how rich or lean you are actually running. Just like the name, it's range of reading is just that, narrow. For all it knows you could be running 9 a/f or 12 a/f.
What should you use? You should get a wideband O2 sensor. It has a much broader range of reading your air/fuel mixture in your exhaust stream (I believe as rich as low 9s to 20+ a/f). This is something that you wouldn't replace your stock O2 sensor with because your computer wouldn't be able to understand the signal voltage referencing from the wideband sensor. Companies sell them with a unit that will translate it to you in a number form and it is seperate from your stock computer. There are standalone computers (if you were that far into engine management systems) that will allow you to use a wideband O2 sensor that it can reference to and you can tune with and it can reference to...but that's another topic in itself.
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My concern is basically about the state of mind of tuners when it comes to modifying.
When tuning your vehicle, it is most important to understand that a engine is a very controlled item and when you start to modify, it is up to you to keep up that controlled type of environment. If you don't catastrophic things will occur and your pockets will hurt.
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Originally Posted by subachad
