Dyno results after installing Pypes LTs

[470 GT/CS]

Don't forget 470, there's also a MAF meter at the front of the whole process telling the PCM how much air is flowing in, so it will register more MAF if there's been any flow increase. Since it knows the airflow, it can still provide the right a/f ratio.

TurboTR

I'm fully aware of the MAF, but not so much in detail about the functions it conducts.



I actually have a very interesting tuning article concerning our cars somewhere, I'm going to go find it and read it.


Here we go, this is the information in it about re-tuning for headers

Long tubes relocate the O2 sensors further downstream in the exhaust. This causes two issues. The first is, it will take the sensors longer to get hot enough to be in operating temperature range. This is because even self heating sensors rely somewhat on the heat from the gases to help heat them. The second problem is cause by the same thing as the first; the sensor is relocated down stream further. The computer knows the volume of air it has to push out of the cylinders for that air to reach the O2 sensor, so it knows that after it sprays fuel now, it can read it X amount of time later to see how accurate it was with it's predicted volume of fuel. By moving the O2 sensors further away from the motor, your increasing the volume of air between the cylinder and the sensor. Now the computer will be expecting to see a change in X time, but in fact, that change will be arriving at the sensor much later.

 

[NastyStang113]

Don't forget 470, there's also a MAF meter at the front of the whole process telling the PCM how much air is flowing in, so it will register more MAF if there's been any flow increase. Since it knows the airflow, it can still provide the right a/f ratio.

TurboTR

Oh really?

 

[turbotr]

Good article 470, all valid points.

TurboTR

 

[1fastpony]

i wouldnt let anyone in New Orleans touch my car. i made that mistake once.

Where?

 

[turbotr]

Oh really?

Well maybe we can have a good, interesting tech discussion, even in the year 2010. I'm game

I'll start off with these questions 3 (hehe)- if the hp increases because the air flow through the engine increases with the headers- how does that increased air flow sneak past the MAF then without it "seeing" it?

If the actual a/f ratio is leaning out with headers, but not because of increased MAF, how is it leaning out?

And if the MAF sees no increase in airflow, how exactly can the PCM (or tune) then compensate for a changed a/f ratio (if it just sees the same airflow as before?)

On a related note- big hp, big camshaft engines generally can't idle or run well at lower engine speeds in closed loop, either narrowband or wideband O2 control scheme (eg, FAST systems). They generally have to be run in open loop in those ranges. The a/f ratio feedback from the wb O2 will say the engine is lean, but meanwhile the exh is so rich it burns your eyes and peels the paint off the walls. So it keeps on trying to add fuel- A runaway closed loop situation based on erroneous feedback.

I assist with the engine control on a 2500+ hp Procharged BBC Camaro drag race car (gasoline only). It has a FAST XFI. We don't enable closed loop on it until about 5000 rpm (if I recall correctly).

My own street car (older car) has 160 lb inj x 6 (76 turbo + nitrous) and a 242 dur solid roller. It is able to run closed loop at idle (classic FAST system) pretty well. But the 160's are a bit too big for ~ 14:1 a/f ratio at idle, but it can get it up to about ~ 13:1. That's pretty hard on (colder) plugs on the street with C16 fuel though (lol).

Some food for thought.

TurboTR

 

[turbotr]

Long tubes relocate the O2 sensors further downstream in the exhaust. This causes two issues. The first is, it will take the sensors longer to get hot enough to be in operating temperature range. This is because even self heating sensors rely somewhat on the heat from the gases to help heat them. The second problem is cause by the same thing as the first; the sensor is relocated down stream further. The computer knows the volume of air it has to push out of the cylinders for that air to reach the O2 sensor, so it knows that after it sprays fuel now, it can read it X amount of time later to see how accurate it was with it's predicted volume of fuel. By moving the O2 sensors further away from the motor, your increasing the volume of air between the cylinder and the sensor. Now the computer will be expecting to see a change in X time, but in fact, that change will be arriving at the sensor much later.

If you're interested 470 (and it seems you're into engine tech already, good man here are some related comments. Modern engines have moved a cat or pre-cat to as near as possible to the exh ports as they physically can. The reason you quote from the article is exactly why. On an EPA emission cycle, the vast majority of pollutants collected in their big bag (and/or sniffers) occur during a cold start, before the catalysts have "lit" from sufficient heat. Thus the auto makers need the catalysts to light of as soon as possible. They can also do tricks with timing and such to help speed this process up. This is also basically what helped kill the turbo for many OEM's for most of the last few decades. The turbine increases the time until catalyst light off.

The other parameter you mention is known as transport delay or transport lag. The computer can be/is well aware of how long it takes for stuff to move through at a given running condition, based on flow rate, pipe sizes, sensor location, etc

I did some emissions research work for the US DOE and EPA back in the mid/late 90's. Mostly diesel stuff, but alot of it applies to spark ignition as well. It's all very interesting (for some of us I guess

TurboTR

 

[470 GT/CS]

That's very interesting for me too, thanks.