[otaner142]

So im going to go straight forward to this question that its bugging me a lot !
Lets take for the sake of this example a simple upgrade to your car, lets say a high flow filter system that will increase some HP allowing more air to the engine.

-If i introduce more air into the engine that means that i am changing the compression ratio.
-A bad compression ratio leads to engine failure (long or short term i dont know but i does)in this case it would be a lean mixture.
-The ECU of the car most likely will not compensate for this engine upgrade meaning that it will read the air intake ratio as if no upgrade was done (which is bad).
-If you want to compensate the extra air (that is eventually going to the engine much faster thanks to the upgrade intake system) you need extra fuel, the fuel system is designed to inject fuel at a certain rate and speed. Chances are that you need to reprogram the fuel system to get the right ratio.
-will the engine hold this new compression ratio ?

I might be wrong in some points but why would anyone want to modify a cars engine if so many things will go wrong if not professionally tunned ? and even so you might still face some other issues.

 

[XJman]

So im going to go straight forward to this question that its bugging me a lot !
Lets take for the sake of this example a simple upgrade to your car, lets say a high flow filter system that will increase some HP allowing more air to the engine.

-If i introduce more air into the engine that means that i am changing the compression ratio.
-A bad compression ratio leads to engine failure (long or short term i dont know but i does)in this case it would be a lean mixture.
-The ECU of the car most likely will not compensate for this engine upgrade meaning that it will read the air intake ratio as if no upgrade was done (which is bad).
-If you want to compensate the extra air (that is eventually going to the engine much faster thanks to the upgrade intake system) you need extra fuel, the fuel system is designed to inject fuel at a certain rate and speed. Chances are that you need to reprogram the fuel system to get the right ratio.
-will the engine hold this new compression ratio ?

I might be wrong in some points but why would anyone want to modify a cars engine if so many things will go wrong if not professionally tunned ? and even so you might still face some other issues.

1. No
2. No
3. Yes
4. Maybe, usually only timing or changing to higher or lower flow.
5. Compression ratio is static no matter how much air is introduced.

6. Even the best built engine can fail. It’s all in the name of fun

 

[otaner142]

ok thanks ! but how come introducing more air in the mixture doesnt give you a lean misture ? question 2

 

[XJman]

It doesn’t change your compression ratio.

 

[otaner142]

well compression ratio remains the same but the Stoichiometric ratio does changes.

 

[XJman]

well compression ratio remains the same but the Stoichiometric ratio does changes.

Your afr will change with the addition or subtraction of air and fuel, yes.

However that is easily accounted for with tuning.

 

[otaner142]

ok , then i must ensure that its a good tunning shop the one doing the job !

 

[otaner142]

hooo.... by the way i also noted that people love to change their rims... that also has an effect in electronics such as abs systems in most cars.
-So many issues... i would just do something else to the car rather than going through so much pain

 

[XJman]

Exactly.

Depending on your vehicle and mods you may need other supporting modifications like injectors and a pump, but for the most part a tuner will tell you what you need when you start to buy everything.

 

[otaner142]

yup i was thinking the same, injectors and pump. Yet people lower their engine (car ) life without proper tunning thinking that a simple air system wont do anything but good.... we got to adress this to everyone out there lol !

 

[zax]

Based on what I've read in your post, you have a VERY rudimentary understanding of how the internal combustion engine works.

I don't think I need to beat the horse here about compression ratio, but the ECU determines the mixture of air/fuel based on the MAF sensor voltage. There is a table in the ECU that correlates the voltage to the expected air mass ingestion rate. When this correlation is disrupted, then problems occur. The ECU has closed-loop fueling functions to modify the correlation for altitude, temperature, and fuel ethanol content.

You should know that you are barely scratching the surface of how an engine works and I would highly recommend that you learn A LOT more before modifying your vehicle. I know that most people don't follow my advice, but my $0.02.

 

[otaner142]

well you are proving me right . if there is a disruption of the air&fuel mixture then the ecu will go crazy if it cant compute the new mixture. I am not auto engineer, im just an airframe mechanic...

 

[zax]

if there is a disruption of the air&fuel mixture then the ecu will go crazy if it cant compute the new mixture.

The correct answer is somewhere between "wrong" and "that's a supreme oversimplification."

You don't need to be a practiced engineer to have the drive to learn...

 

[XJman]

I’m a strong back so I’ll try to give some answers in terms I get.

For your tire and wheel question the only time I’ve seen any issues with abs, traction control, or stability management systems is where guys slap on giant tires on their trucks and SUV’s. They are adding several inches in diameter and width and in cases over 100lbs a corner.

Your engine is an air pump. If it says it’s a 2l engine that means that the total displacement of each cylinder adds up to around 2l. Your compression ratio is the difference in volume between bdc and tdc. It is typically static and doesn’t change regardless of how much air is in the cylinder. If you add forced induction and add another bar of pressure in the system the compression ratio remains the same however the air will be denser allowing more fuel to be burnt. It also increases cylinder pressures and temperatures and can lead to knock. If anything is off.

If you have a 4 cylinder 2l generically your engine will pull in about .5l in each cylinder on the intake stroke. We will assume this is what you get at 1 bar of pressure. This amount will change depending on several factors but that’s the gist. Forced induction at say add another 1 bar of pressure so you’ll have 2 bar of pressure in the engine effectively doubling the .5l of air in each cylinder.


The maf sensor tells the ecu how much air has passed so it has then knowledge to inject the correct amount of fuel to get the target afr. Your engine is only going to pull so much air so fast. Many times factory air boxes can deliver far more air than the engine will require and are effectively useless stock. However they can skew the reading of the calibrated maf sensor and tell the engine the wrong amount of air has passed this can lead to rich or lean conditions. However many lean toward the lean side to try and squeeze out power from an intake that otherwise isn’t providing more air than the factory’s intake provided.

I’m on my phone and as mentioned before a string back with a weak mind so this is grossly simplistic but it should get you on the path to understanding

 

[otaner142]

thank you so much ! my mind is more clear now !