[Blk16SS]

Originally Posted by oldman

should be a sticky

I'm in need of a tune. After installing my K&N cai kit, I'm getting just a touch and I mean a touch of part throttle jitters... If your cruising along in tour or sport mode, and you touch the throttle just barely, you can feel some A/F inconsistencies. In track mode its not as apparent but its still there.
EFITuning to the rescue real soon....

[PRAY]

Here are three graphs that were mentioned. I spread them up so you can see the fuel as well. No tuning was done between any of these runs. Each graph is basically back to back i.e. same day/same dyno minutes apart.

This is the M6 cars max gains. Stock to with the ported IM/TB.



This is my car stock tuned to just swapping to the ported IM/TB.



This is my car back to back with the Rotofab. This test has been done three times on my car at different stages.



I hope this helps settle some of the questions.

[gdgraph]

General rule of thumb for exhaust is that cat backs and anything less (axle backs) are safe to run without a tune. Exception is if you increase the diameter significantly. If you go to headers that's when you'd need a tune because you don't have enough back pressure on the stock tune. With an intake, you generally want to tune it so you get the right A/F ratio. There are some CAIs out there that say they are "safe" to run on stock tune but the car doesn't run great and you don't really benefit from power so not sure why you'd want to spend money on it and then not tune. Exhaust I can see because you'd do it for the sound. With any other performance mod I can't see why you wouldn't wanna tune it because you've prob voided the warranty in most cases so why wouldn't you want the max power you can get (exhaust being exception because maybe the car is just too quiet stock)... just my two cents.

[Lemosine]

But is there honestly any proof that headers with no tune will drastically cause changes to the A/F Ratio. I thought the ECU is designed to learn and adjust to changes like that to where the car can safely run. Only problem is that you don't technically get the full potential. I know this is different, but how when it is cold (I could have this backwards) The ECU adjust everything so that it is not running too lean, When it is really hot it keeps it from running too rich. I also thought that now days engines if you do not really have any back pressure it is not dangerous for car where as I believe older motors it was dangerous/bad for the engines. I had an LS2 GTO that had full exhaust with kooks long tubes. It ran without a tune for 4 years, I never had 1 issue just a CEL for no cats. Sold her and they took it to a dyno, told me it made 368 WHP untuned. Of course now it is a fully built monster. I would want to see visual proof comparing stock A/F ratio to a untuned car with headers, that has had time for the ECU to learn.

[Whitemaro6]

I too had a ls2 GTO with otrcai, fast 102, and slp long tubes no cats and the car ran great at 399 wrhp. NO TUNE for 5 years

[gdgraph]

Headers drastically reduces back pressure, that's why you'd want to tune, to re-calibrate the timing. If you do headers your warranty is gone, so what's the point of not getting the tune... you won't see significant power gains and would probably throw a CEL for the reduced back pressure loss.

Originally Posted by Lemosine

But is there honestly any proof that headers with no tune will drastically cause changes to the A/F Ratio. I thought the ECU is designed to learn and adjust to changes like that to where the car can safely run. Only problem is that you don't technically get the full potential. I know this is different, but how when it is cold (I could have this backwards) The ECU adjust everything so that it is not running too lean, When it is really hot it keeps it from running too rich. I also thought that now days engines if you do not really have any back pressure it is not dangerous for car where as I believe older motors it was dangerous/bad for the engines. I had an LS2 GTO that had full exhaust with kooks long tubes. It ran without a tune for 4 years, I never had 1 issue just a CEL for no cats. Sold her and they took it to a dyno, told me it made 368 WHP untuned. Of course now it is a fully built monster. I would want to see visual proof comparing stock A/F ratio to a untuned car with headers, that has had time for the ECU to learn.

[Fraxum]

Originally Posted by gdgraph

Headers drastically reduces back pressure, that's why you'd want to tune, to re-calibrate the timing. If you do headers your warranty is gone, so what's the point of not getting the tune... you won't see significant power gains and would probably throw a CEL for the reduced back pressure loss.

Recalibrate the timing?

I disagree about power, with LTs you will see most of the gain without a tune and while you will get CELs its because you moved the rear O2s too far downstream. So one of the main benefits of the tune is suppressing those CELs.

I am not necessarily recommending doing LTs with out a tune. But I have done it and picked up 3-4 tenths in the 1/4, drag raced often, read and turned the CELs off often, and drove the SS as a DD for about 2 years. Never lost my warranty, then put it back to stock, and got top trade in $$ for my SS. Although I did get dinged for needing rear tires.

[Ryephile]

I just want to clarify that I was mistaken earlier about the ECU's fueling strategy. It runs a pair of narrowbands, one per bank, and operates in open loop fuel at WOT. This means it's unable to self-tune it's fueling at WOT, only at part throttle where it's targeting Lambda = 1.

It does appear GM's charge air calculations are quality enough to get away with not using widebands. The lack of full time closed loop however does mean it's key to not mess with the MAF scaling, and big changes in VE will need a full VE recalibration by the tuner. This explains why some airboxes that replace the MAF tube mess up fueling and others don't.

[gdgraph]

Nope, that's wrong, CEL is caused from the increase in pipe diameter (There are LT set ups that don't change O2 sensor configuration by much). I have even seen cars throw codes from a cat back when you increase pipe diameter too much from stock (those CELs have absolutely nothing to do with O2 sensors at all because you are not touching those sensors). Same issue when you do headers, you are increasing flow of exhaust which messes up A/F ratio which all boils down to timing (engine timing that is). Tuning will fix all of that by optimizing the engine valve timing to get the proper A/F ratio & valve timing necessary for the entire power band.

I never said you can't get power gains from LT without a tune, I am just saying it is not optimized without a tune. The engine needs to be calibrated so you don't run too rich and so that you have the proper back pressure. Increasing flow in the exhaust changes all of that. When the GM engineers designed the car they had the engine calibrated to function with the stock pipe diameters, changing any of that messes with that. It's not drastic, but I it's not optimal. You'll still see power gains, but you'll get even more if you get a proper tune and you engine will run with the proper A/F ratio.

Originally Posted by Fraxum

Recalibrate the timing?

I disagree about power, with LTs you will see most of the gain without a tune and while you will get CELs its because you moved the rear O2s too far downstream. So one of the main benefits of the tune is suppressing those CELs.

I am not necessarily recommending doing LTs with out a tune. But I have done it and picked up 3-4 tenths in the 1/4, drag raced often, read and turned the CELs off often, and drove the SS as a DD for about 2 years. Never lost my warranty, then put it back to stock, and got top trade in $$ for my SS. Although I did get dinged for needing rear tires.

[Lemosine]

Pretty much exactly what we were saying but in greater detail. Wont be a drastic change that will destroy your engine because it is running at an extreme lean or rich level. Your just not receiving the full potential. I myself have never seen a CEL for back pressure. I think open headers would cause a CEL like that being that it would be huge loss in it. I was specifically told at a GM house 1 hour away from me, tell me I wont void my warranty at all unless I make changes to the Computer. He said these engines are built solid now days and I should be fine, of course if you do get a CEL due to back pressure yes you are screwed. But Im not recommending to run with no tune, but just stating I have ran without one and everything was fine.

Originally Posted by gdgraph

Nope, that's wrong, CEL is caused from the increase in pipe diameter (There are LT set ups that don't change O2 sensor configuration by much). I have even seen cars throw codes from a cat back when you increase pipe diameter too much from stock (those CELs have absolutely nothing to do with O2 sensors at all because you are not touching those sensors). Same issue when you do headers, you are increasing flow of exhaust which messes up A/F ratio which all boils down to timing (engine timing that is). Tuning will fix all of that by optimizing the engine valve timing to get the proper A/F ratio & valve timing necessary for the entire power band.

I never said you can't get power gains from LT without a tune, I am just saying it is not optimized without a tune. The engine needs to be calibrated so you don't run too rich and so that you have the proper back pressure. Increasing flow in the exhaust changes all of that. When the GM engineers designed the car they had the engine calibrated to function with the stock pipe diameters, changing any of that messes with that. It's not drastic, but I it's not optimal. You'll still see power gains, but you'll get even more if you get a proper tune and you engine will run with the proper A/F ratio.

[gdgraph]

Completely agree with you here. The point I am trying to make is that it's not optimal to do headers without a tune, running your car too lean or too rich for it's lifetime is not ideal from efficiency/performance perspective.

Dealerships are so inconsistent, if you have a dealer that says you may do headers without voiding your warranty you're lucky, mine won't and I am sure many others won't, again dealers are very inconsistent when it comes to that.

I have witnessed a few cars that just increased exhaust size by too much and it caused a CEL, reverting to stock fixed the CEL, so the car ultimately needed a tune (to change the variable timing to bring A/F ratios and compression ratios back to proper limits) and that fixed everything.

All and all people can do whatever they want / whatever they can afford. For me as an engineer, I personally will be getting a tune when I do my headers, it's both optimal for the car and will also give me best performance. Also I am not looking at one mod, more air out also benefits with more air in so doing an intake/TB/manifold with the headers gives you a complete system which will get you overall better gains as a package (rather than one component by itself).

Originally Posted by Lemosine

Pretty much exactly what we were saying but in greater detail. Wont be a drastic change that will destroy your engine because it is running at an extreme lean or rich level. Your just not receiving the full potential. I myself have never seen a CEL for back pressure. I think open headers would cause a CEL like that being that it would be huge loss in it. I was specifically told at a GM house 1 hour away from me, tell me I wont void my warranty at all unless I make changes to the Computer. He said these engines are built solid now days and I should be fine, of course if you do get a CEL due to back pressure yes you are screwed. But Im not recommending to run with no tune, but just stating I have ran without one and everything was fine.

[Fraxum]

Originally Posted by gdgraph

Nope, that's wrong, CEL is caused from the increase in pipe diameter (There are LT set ups that don't change O2 sensor configuration by much). I have even seen cars throw codes from a cat back when you increase pipe diameter too much from stock (those CELs have absolutely nothing to do with O2 sensors at all because you are not touching those sensors). Same issue when you do headers, you are increasing flow of exhaust which messes up A/F ratio which all boils down to timing (engine timing that is). Tuning will fix all of that by optimizing the engine valve timing to get the proper A/F ratio & valve timing necessary for the entire power band.

I never said you can't get power gains from LT without a tune, I am just saying it is not optimized without a tune. The engine needs to be calibrated so you don't run too rich and so that you have the proper back pressure. Increasing flow in the exhaust changes all of that. When the GM engineers designed the car they had the engine calibrated to function with the stock pipe diameters, changing any of that messes with that. It's not drastic, but I it's not optimal. You'll still see power gains, but you'll get even more if you get a proper tune and you engine will run with the proper A/F ratio.

The 5th gen I mentioned was with the same diameter tubing post cats 2.5". We willl just have to agree to disagree. I am not saying other conditions will not throw codes. But are they dangerous to the health of the motor? That seemed to be the OPs question. From what I understand from others more knowledgable than me exhaust changes are easier for the car to keep at the more ideal A/F ratios. Intake changes can be more disruptive.

And LTs on the CA6 LT1 by themseves are worth around 15 rwhp tuned or not. Remember we are starting with stock manifolds that are pretty much shorties. Or why did Chevy bother building them when moving the LT1 from the Corvette to the Camaro? The standard cats flow pretty well so removing them or replacing them does not seem like much of a HP adder on the LT1.

[gdgraph]

True, I think we are all saying the same thing, there's just some slight disagreement over what's better. I personally do not like the idea of running headers or an increased pipe diameter without a tune to change the variable engine timing to get proper A/F ratios and ultimately proper compresion ration. Running a little rich may not hurt the car short term, but it's not great for the lifetime of the car because it ultimately adds extra forces & stresses that the car was not designed to handle.

I believe both the intake & exhaust both change A/F ratios, maybe it's true that an intake is more drastic, not really sure (would have to see the flow calcs to weigh in on that). Going back to OP's original question, I'd agree with you that it won't kill the car, but I would say that over the lifetime of the engine it isn't making things any better by running a little rich.

Some people may have run a car it's entire life with headers and no tune and may never have any issues but there are so many variables. If you are racing your car more frequently maybe you will see issues because you are applying greater stresses in non optimal conditions.

In the end I'd recommend a tune... eventually just because it is more optimal for the engine and gives better performance. Great discussion though, we are being very thorough!

Originally Posted by Fraxum

The 5th gen I mentioned was with the same diameter tubing post cats 2.5". We willl just have to agree to disagree. I am not saying other conditions will not throw codes. But are they dangerous to the health of the motor? That seemed to be the OPs question. From what I understand from others more knowledgable than me exhaust changes are easier for the car to keep at the more ideal A/F ratios. Intake changes can be more disruptive.

And LTs on the CA6 LT1 by themseves are worth around 15 rwhp tuned or not. Remember we are starting with stock manifolds that are pretty much shorties. Or why did Chevy bother building them when moving the LT1 from the Corvette to the Camaro? The standard cats flow pretty well so removing them or replacing them does not seem like much of a HP adder on the LT1.

[Abdulisraddd]

Ok so I'm picking up my ported stock im/tb tomorrow and already had rotofab and 2nd cat delete in stock tune (the rotofab gave me 14hp and 10tq). My questions is how much hp will I roughly gain when adding the ported stuff with out a tune. And how much more power can I squeeze out if I do get it tuned. Thanks I'm still in the learning process . I'll dyno my car after the ported stuff is installed and post my results untuned .


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