Just wondering why a tune is so essential after you install headers and intake. I'd like to hear everybody's opinion and experiences.

From what I hear your car runs lean after you install the headers and intake and can cause the rings to get hot and burn up. All I can figure is that you are moving way more air and the fuel can't keep up until you tune the car. I just always thought these new ECUs have learning curves and would correct the A/F ratio after you put some miles on the car after install.

Just installed headers and intake on my car and it seems to be running just fine. Not idling rough or missing. Granted i have only put about 8 miles on it since install.

I'm not trying to start an argument, prove I'm right, or anything of the sorts. I would simply like to learn more.

Thanks in advance,
Milt IV

 

Installing headers especially effects the volumetric efficiency of the motor. Better flowing headers compared to the factory exhaust manifolds increases airflow and promotes scavenging thus pulling in the air/fuel mixture more efficiently. Your spark/fuel trims will need to be adjusted accordingly.

 

Thanks, that is the kind of answer I am looking for. Some reason behind the rhyme. This thread is intended to provide some FACTS about the cause and effect of installing headers/air intake.

I have done some research on this topic (on this forum only pretty much) and most of the the responses tend to be along the lines of "you don't need a tune, I know a guy that never got one and his car is fine" to "you have to get a tune or you will ruin your motor, here is a link to the mail order tuner I sell/link to my shop website." Nobody ever seems to provide any real explanation as to what happens that would cause one to need a tune.

I will be getting a tune regardless. I want these mods to produce some extra power AND I'd like the peace of mind knowing I am not running any risks.

 

OP: Check out "Joe G" post, which is the last one on this thread for more info http://forums.corvetteforum.com/c6-t...post1582036626

 

It's very simple.

Your motor is an air pump and the factory tune is set up expecting X amount of air to be ingested, combusted, and then exhausted.

The more air your bring in and expel by means of a more efficient intake or exhaust system, the more the OEM calibrations of measured air mass differ from what the tune expects to see.

The factory 02 sensors are narrowband and are only capable of measuring from 0-1 volts(a wideband has a wider range of 0-5 volts).

They are extremely accurate at measuring stoicheometric (14.68 for pure gasoline or ~14.2 for E10) but the computer relies on mathematical calculations to determine how much fuel to dump when you go into power enrichment mode(wide open throttle).

When you punch the gas, the computer stops receiving or ignores inputs from the 02 sensors(they essentially turn off) and goes into power enrichment mode and instead relies on the volumetric efficiency tables in the tune to mathematically calculate how much fuel to give the motor based upon load and rpm. The computer is no longer relying on a measured amount of fuel leftover from the combustion event as measured by the 02 sensors to make fueling adjustments, but instead is using a very complex string of mathematical calculations to determine how much extra fuel to spray to compensate for your desire to make more power(as evidenced by your pushing the gas pedal to wide open).

Hope that makes sense.

 

Very interesting. Thanks.

 

Interesting indeed. I keep reading that I won't need a tune if I do LS7 mani's/x-pipe on my LS3, but am still not convinced.

 

Technically, any time you change out a factory engineered part for one of the aftermarket variety, the OEM calibration should be redone.

 

All the above are basically correct, I am not sure what you need to be convinced of. I will try and explain it in some detail for you.
First off all of the factory calibrations are done with your engine in it's stock configuration. So the the VE table, that is the air calculation that is used from 0-4000 RPMs is based on the fact that the car has manifolds on it. So back up for a minute, the engine is an airpump, when the exhaust valve opens say for cylinder 1 and cylinder 2 just finished firing (numbers are for example, not actual firing order) and the exhaust from cylinder 2 is still present in the manifold, the only thing pushing the exhaust out of cylinder one is piston. Well the piston does not go all the way to the top of the cylinder, so when the exhaust valve closes and the intake valve opens there is still spent gases inside the cylinder. They take up space or volume, so only so much air can actually get drawn into the cylinder. This efficiency is what is in your factory calibration to put in in understandable terms. The highspeed air which is your MAF meter comes in at 4000RPMs and it tells the PCM how many g/s of air are entering the engine, the engine uses this number or frequecy(HZ) to determine the A/F. So all aspect of the calibration are effected. When you add headers, you change the dynamics of what is happening in the engine. Instead of when cylinder 1 fires and the exhaust valve opens right after cyl 2 fired. Cyl 2's exhaust has created a vacuum in cylinder 1's header tube, so when cylinder 1's exhaust valve opens the exhaust gets sucked out of the cylinder along with the piston pushing it out. So now when the intake opens there will be more fresh air and fuel in the cylinder which will make more power than before. Because of this, the calibration has to be corrected to represent what is not happening in the cylinder vs. what was happening before. Hope this explains it for you.
Justin

 

Good point Justin. Above 4k rpms, the computer relies on the MAF sensor to measure airflow instead of the VE tables. I left that part out.

 

Thanks guys, those were hugely informative & educational posts, as I'd not yet read anything definitive about the ECU not adjusting fuel in terms of changed airflow rates.

It sounds like the LS3 will run too lean(?) & should get tuned even if LS7 exhaust manifolds & h/x-pipe is the only modification.

 

It's not that the computer won't adjust the fueling for the changing airflow rates, its that it doesn't have the correct calibration for the increased flow to make the right adjustments. It will try and adjust but it won't adjust correctly as it doesn't have the data.

 

I don't think you'll have any problems with just a set of LS7 manifolds and exhaust. The ECM has a function called "fuel trims" that add or take away fuel as needed to keep the AFR at stoich in closed-loop mode, based on feedback from the oxygen sensors. They can add or subtract 25% before a code is set, so there is quite a bit of wiggle room there.

At WOT, it goes into open-loop and ignores the oxygen sensors. The good news is that the stock calibration uses the long-term fuel trims to add fuel in open-loop mode (WOT) if the ECM has been seeing positive fuel trims when in closed-loop. If the engine is always wanting to run lean because a set of headers were installed with the stock tune, it should be picked up and corrected by the short-term fuel trims, and carry over to the long-term fuel trims for open-loop startup and WOT operation.

I still think it's a much better idea to get the car properly tuned, especially if you alter the way the MAF reads the amount of air being ingested by the engine by changing the air intake. Most intakes affect the meter's accuracy --or the amount of air it is actually flowing at a given frequency. So if you change the intake, it's always a good idea to look at the MAF transer tables to make sure they're still accurate.

That's my take on it, but I'm still a rookie when it comes to tuning.

 

In a nutshell, you could bolt on a set of headers and a CAI and run with it. The PCM has adaptive capabilities that can and likely will compensate for those changes. It can compensate as much as 25% either positive or negative meaning that it can either add or subtract that amount of fuel if the sees a reported fueling error from the primary o2 sensors. Definitely you will see gains if you tune the car to optimize the mods you have done. Is it 100% necessary, no. But 3 out of 10 header installations, you will set a catalyst code or an o2 sensor code of some sort. Tuning the car for these mods will usually prevent a DTC from coming on.

When replacing a factory CAI with a performance unit, you won't change the VE of the engine, if you cam the engine then yes you have now changed the VE characteristics of the engine. What you have done is changed the CAI design which usually changes the way the MAF sees the air flow. Most CAIs uses a larger tube (thats their selling feature bigger is always better) that the MAF is mounted in. Now what happens is that the engine ingests the same amount of air but the air flow across the MAF has changed, it changed because of the larger tube. Imagine a garden hose with no nozzle, the water dribbles out because of the larger orfice, now restrict it the end of the hose and now the water rushes out at a much greater velocity. Same thing happens inside the MAF. Except now it reports a lesser than before air flow into the engine.

So now what happens is that the primary o2 sensors (they are the final control element) in the exhaust stream reports a leaner than stoich AFR, the PCM in turns sees this and adjusts the fuel trims to compensate for the leaner that setpoint AFR. If it was richer than stoich then the PCM will do the opposite. So in closing it isn't a total necessity to tune after mods, it will however optimize everything you have done.

 

StreetK, TJWong, thanks guys, you are what makes this forum so excellent & your posts are hugely helpful in addressing my lean AFR concerns.

I just bought some low-mile '08 LS7 mani's/h-pipe from another member for my '12 GS (stock LS7 intake) & will post about any sound/performance differences I notice over the stock system. I'd like to do before/after dyno runs, but up here in SLO that ain't likely.

 

Something caught my eye. The narrowband / wideband O2 sensors. So stock, our cars come with narrow band sensors? Should we move towards wideband? What to do about this, if necessary?

 

It's not necessary to do anything. 99.999% of all cars on the road have factory narrow bands. I only know of a handful of cars that come with widebands from the factory(the new 2011+ mustang GTs have 2 factory widebands ). The only reason people put wideband 02 sensors in the car is to monitor changes made to the tune as a result of aftermarket parts. When a tuner tunes the car, he watches the reading on the wideband to make sure his changes are safe in addition to them making power, improving driveability, or whatever else his goals are.

You can't put a wideband sensor in place of the narrowband because the computer does not have the capability to interpret the broader clarity in the readings and I'd imagine the car would barely run, if it would run at all. Also, a wideband is a 5 wire sensor where narrowbands are 4 wire sensors. The plugs would be different.

A narrowband sensor is not a bad thing so don't think of it as a hindrance. They are very accurate at reading stoicheometric as that is what they're designed to do. The computer is constantly adding/removing fuel to keep the 02s sensors reading the ~14.68:1 that the computer is commanding.

If you ever watch the 02 sensor voltage on a scanner, it is constantly undulating and the two readings(02 sensor for bank 1 and bank 2) chase each other like Pepe le Pew chased the foxy skunk in Looney Toons

 

I think installing a quality aftermarket wideband gauge is a good idea if doing mods. It's nice to be able to monitor AFR at full throttle, especially if the car is forced induction (blower, turbo, etc.).

The factory narrow bands are only designed to monitor AFR at light load when stoich is being commanded. Cars with factory widebands like the BMW 335i actually monitor and adjust AFR at WOT via the wideband readings. Unfortunately, the factory C6 PCMs cannot do this.

 

It may help you to understand the purpose of the four different O2 sensors. The front O2 sensors are monitoring air/fuel ratio for each bank and reporting to the ECU which is then adjusting fuel inputs.

The rear O2 sensors are also monitoring air/fuel ratio, but are behind the Cats. Therefore the rear O2 output should be flat (the Cats should burn all the O2 and fuel remnants). Occasionally, the ECU runs a Cat check right after engine start up. It is checking that the Cat output is still 0. The Cats are normally installed right up next to the cast iron exhaust manifolds. This is so they heat up to operating temp immediately and "light off".
When we add long tube headers, we relocate the Cats further down the pipe and now they take longer to light off. Thus, even when you use Cats in a long tube header car, you will occasionally get a check engine light because it did not pass the initial Cat start up check.
Tuners will turn off this report by having the ECM ignore the rear O2 sensor inputs.

 

Thank you guys for bringing some sense to this thread...