[Trochoidal]

Periodically it’s good to look for information about our cars and this particular communication was surprising. Most of us have read about a simple CAI not being an issue.

Can anyone explain why a CAI and/or improper warm up is a topic for piston damage?

[TheBusDriver]

I don't think that's ever happened due to an aftermarket intake and temperature in the history of the automobile.

I've NEVER heard of this.

I'd love for someone who's heard of this theory to touch on this subject.

[geaux_tigerss]

I'll take a shot.

The mass air flow sensor is a bit of a misnomer. It doesn't directly measure mass air flow (there are flow sensors that can do this but they are not practical for use in this application). The MAF sensor can measure (via pressure and temperature) the mass OF the air and it can measure velocity (speed). Multiply mass of the air, velocity, and diameter of the inlet air pipe and you get inlet air flow in mass units (or mass air flow - as opposed to volume air flow). I know this sounds kind of nit-picky, but the subtle difference is important.

Normally the inlet air pipe diameter is fixed. If you install an aftermarket intake that has a larger pipe diameter than the original did (and neglect to tune the MAF table in the ECU), the MAF sensor will UNDER report mass air flow. It will tell the ECU that you are flowing some amount of air and that it needs the corresponding amount of fuel to meet the appropriate mixture for combustion. If more air is flowing than the MAF reports this results in a lean condition which leads to more heat. Normally this isn't a big issue because the O2 sensors will detect this lean condition and add enough fuel to reach the appropriate mixture. This is what happens in closed loop combustion control (the O2 sensor "closes" the control loop).

Why is this important during warmup? Because O2 sensors have to reach a certain temperature to function correctly. For the first minute or so on a cold start (while the O2 sensors are being heated up by the exhaust gases), the combustion control circuit works in what is called open loop configuration. That means that it takes the MAF input, applies it to a lookup table in the ECU, and sets fueling as programmed. Your hypothetical change of the intake pipe diameter breaks the lookup table by causing the ECU to use a lower value for fuel than it actually should on warmup and creates a lean condition.

This probably doesn't break anything the first time it happens. However, throw a few hundred lean cycles at an engine for a minute or so at a time and it likely accelerates wear.

The same thing works in reverse. If you install an intake tube with a smaller pipe diameter without tuning you will create a rich condition on cold start.

Now on the real world. How many people actually change the inlet diameter of an intake? My guess is not many. I know my rotofab didn't. I actually tried to tune the MAF with it and ended up with roughly 1.5% change in a few areas, less in others (or basically noise). I didn't even bother changing the table.

[VinnAY]

Nothing more than telling you to not monkey with it and expect your warranty to remain in tact so they make up a far flung "reason" instead.

[Trochoidal]

Originally Posted by geaux_tigerss

I'll take a shot.

The mass air flow sensor is a bit of a misnomer. It doesn't directly measure mass air flow (there are flow sensors that can do this but they are not practical for use in this application). The MAF sensor can measure (via pressure and temperature) the mass OF the air and it can measure velocity (speed). Multiply mass of the air, velocity, and diameter of the inlet air pipe and you get inlet air flow in mass units (or mass air flow - as opposed to volume air flow). I know this sounds kind of nit-picky, but the subtle difference is important.

Normally the inlet air pipe diameter is fixed. If you install an aftermarket intake that has a larger pipe diameter than the original did (and neglect to tune the MAF table in the ECU), the MAF sensor will UNDER report mass air flow. It will tell the ECU that you are flowing some amount of air and that it needs the corresponding amount of fuel to meet the appropriate mixture for combustion. If more air is flowing than the MAF reports this results in a lean condition which leads to more heat. Normally this isn't a big issue because the O2 sensors will detect this lean condition and add enough fuel to reach the appropriate mixture. This is what happens in closed loop combustion control (the O2 sensor "closes" the control loop).

Why is this important during warmup? Because O2 sensors have to reach a certain temperature to function correctly. For the first minute or so on a cold start (while the O2 sensors are being heated up by the exhaust gases), the combustion control circuit works in what is called open loop configuration. That means that it takes the MAF input, applies it to a lookup table in the ECU, and sets fueling as programmed. Your hypothetical change of the intake pipe diameter breaks the lookup table by causing the ECU to use a lower value for fuel than it actually should on warmup and creates a lean condition.

This probably doesn't break anything the first time it happens. However, throw a few hundred lean cycles at an engine for a minute or so at a time and it likely accelerates wear.

The same thing works in reverse. If you install an intake tube with a smaller pipe diameter without tuning you will create a rich condition on cold start.

Now on the real world. How many people actually change the inlet diameter of an intake? My guess is not many. I know my rotofab didn't. I actually tried to tune the MAF with it and ended up with roughly 1.5% change in a few areas, less in others (or basically noise). I didn't even bother changing the table.

Your response is very appreciated and well written.

Like you, when I calibrated the MAF my results yielded almost an identical difference.

Thank you for the response.

[Trochoidal]

Originally Posted by VinnAY

Nothing more than telling you to not monkey with it and expect your warranty to remain in tact so they make up a far flung "reason" instead.

Exactly! Seems like a reach to me.

[Gunkk]

Don’t need NHTSA or anyone else to explain common sense.

This is no different than the knucklehead who puts his car into the wall at a race track and wants Chevy to warranty the body damage from his crappy driving.


Folks the rule is real simple: You F with it and break it, you bought it.

[Lafourche1]

Originally Posted by Gunkk

Don’t need NHTSA or anyone else to explain common sense.

This is no different than the knucklehead who puts his car into the wall at a race track and wants Chevy to warranty the body damage from his crappy driving.


Folks the rule is real simple: You F with it and break it, you bought it.

Al O said it clearly. Keep it stock. He specifically mentioned intakes.

[Whocares05050]

Originally Posted by Lafourche1

Al O said it clearly. Keep it stock. He specifically mentioned intakes.

Of course anyone on the payroll will say keep it stock...

Except chevy also sells intakes... and cams... and headers.... and new calibrations...

They must have the magic wand and not the afreemarket

Its a crock. Some intakes require a tune, some dont. This.is their "loophole" to magnuson-moss warranty act claims...