The other day DavidZhu posted a thread asking about needing a tune after installing long tube headers. I had always been under the impression that this was this case, because of increased airflow, altered AFR, the engine running lean, etc. The physics of this explanation have always made sense to me, and I've always just taken that as the truth.

I brought this up with a buddy of mine last night, because I'm also installing headers and a tune in the near future, and he made the argument that this was just a myth. He pointed out some things that made me also question if this is just a tidbit of misinformation that has spread through forums the way misinformation tends to do (I am guilty of this myself.. reading a common sentiment on a forum, taking it as fact, and then regurgitating it elsewhere).

Anyway, his response to me was "why would increased airflow change anything?" and then went on to explain (simplified explanation): The MAF sensors are measuring how much air is coming into the engine, regardless of the headers on the other end. The wideband o2 sensors (pre-cat) are measuring the oxygen/fuel levels in the exhaust going out to detect if things are lean/rich. So just because you're flowing air through the engine at a higher efficiency, than before, your ECU still sees the data and adjusts normally. The electronics are there to support fueling regardless of restrictions or not in your exhaust.

Can someone explain why that wouldn't be the case, and why the generally accepted information about a tune being NEEDED after installing headers to prevent the engine from running lean is true?

 

I think it is more of a safety precaution than anything. From what I know our ECUs are adaptive and smart but I do think too much fluctuation will cause CELs and lean bank issues. If anything the tune is to keep your AFR's where they should be without too much guess work by the ECU. Can you run no tune with headers? Sure. Would you want to beat on your motor time and time again without a tune? Probably not.

 

I agree with your buddy to a degree as I can't recall any dyno runs with only headers (no tune) to actually show dangerous AFRs. Thing is you won't get the most out of the headers until you get it tuned.

 

It probably won't cause any damage to not have the tune but if it is catless you could get a CEL and put the car into limp mode. This is all theory as I haven't actually tried it yet but these ECU's are very adaptive so it should be okay for a little while at the minimum

 

I guess that's what I'm not understanding now. Wouldn't the AFR be kept in check anyway from the data provided by the MAF and o2 sensors if they're doing their job correctly? Why would it be beating on the motor as you say?

Sorry, lots of questions. Just trying to get a better understanding of all of this.

 

I get that decatting will throw a CEL, though that just has to do with the pre-cat and post-cat o2 sensors having no difference in readings I believe.

 

Ok, that's basically what I was trying to clarify. Necessity for a tune due to bad engine conditions vs optional tune to get the most power. Most people on the forums have argued the former.

That said, I still of course will be getting a tune, haha.

 

I'm just shooting in the dark, but could it be the electronics in the car that maybe giving codes and etc.? Especially since all the electronics are essentially tied in together; a change in parameters at one end affects another?

Older cars wouldn't have this problem because they're more mechanical than electronic(al).

I do however, believe that tunes are recommended after headers/exhaust/etc. installs to maximize the power. Anything less would mean you're limiting the potential.

 

don't think u will need a tune. but why not....


a tune will probally get more out of the header.

 

Keep in mind there are also airflow calculation parameters that will cause problems as well. example... if car can only flow 250cfm at 1000rpm, now it flows 300cfm - boom check engine light. The ecu - or ME as it's called in benz land has a series of self checks are parameters it watches and wants to see in check. For instance your throttle pedal has 2 sets of sensors in it. They move in opposite directions and it checks between the 2 to make sure they correlate like they should. Combine that with the fact the ecu programming calculations and tuning are all based off of volume-metric efficiency. This is why the engine runs so good when a sensor goes bad. Even though it's bad it knows what the engine should need to operate with what sensors it can still rely on. Whenever you modify the engine you have modified it's VE. So it's going off the original calculation which isnt accurate anymore. Even something simple like air filters changes the VE. small changes not such a big deal, Install them wrong and cause air turbulence or a leak and you get a CEL. Once again the system of self checking knowing "hey! there's no way the engine is capable of doing this". the bigger the changes to the engine are the more the calculation is off. Think of throwing a cams in a car with no tune. It will run like crap because cams have a huge effect on VE. The air fuel ratio isnt too big of a deal specially with something relatively small like headers or air filters. That can be corrected for to an extent but once again the possibility of the adaptations going out of value - self checks and tight parameters. Other things to keep in mind, shorty headers are crap for these motors. I've seen all of them for 63 motors and they are junk, marginally better than stock. Sure they do a lot with a tune because a tune does plenty on its own. All the long tubes that are worth paying for have provisions for high flow cats but not maintaining the factory ones. This is another problem. The stock ecu may not see the high flow cats effective enough in the secondary o2 sensors and cause a cel. So yes you can do it, It wont help as much as you want and may still cause problems, dont waste your money on shorties they suck.

This all applies to the 63 (m156)motor. On a purely speed density motor it is totally different and even more sensitive to changes as it has no way of knowing the volume of air other than in the tune (m113k). The 63 motor has mass air flow sensors so it can determine and adjust somewhat. speed density relies on intake manifold pressure and throttle position to determine volume of air. I could blab on and on, sorry for the long read but wanted to make sure you realize the importance of getting retuned. Older cars ecu's weren't nearly as complex. Think of how unpicky carbs are. Older ecu's were great at keeping things running but not optimally. Today's especially benz's are very nit-picky with very tight tolerances.

cliffs. Sure run headers with out a tune, you should be alright if you still have cats. will you benefit as much? no.

 

Thank you. THIS is the kind of answer I was looking for