New to the forum, So I got a 5th gen camaro SS L99 engine, previous owner did dod and vvt delete and a bigger cam the car was tuned but with stock exh manifolds and cats, now I want to install long tubes but I don’t know if I should get a tune or run the current tune, I can take care of turning off O2 sensors but would it affect air fuel ratio?

 

A tune is recommended after headers, good chance it will be leaner in many areas of the maf curve.

 

Zackly: headers increase the flow of air through the engine compared to manifolds, therefore the fueling curves are almost always wrong, usually in the direction of not enough fuel.

Cats by themselves don't affect tune or engine performance much these days in all but the most "every last HP" kind of situations. Not like the pellet-bed crap from the early 70s. No good reason not to run them if the rest of your situation calls for them.

 

Wouldn't the MAF and O2 sensors correct for differences in airflow, within reason?

 

The trims will add fuel but it's such a bandaid that is very noticeable when the exact setup has had the proper fueling tuned-in.
It will feel sluggish in comparison to a wideband tune (or narrowband o2 trim tuned for mild to medium load areas).

Trims will go to 0% at full throttle once power enrichment is triggered at higher load and rpm.
​​​If your tune still has Long Term Fuel Trims enabled, and if the fuel trims prior to power enrichment were positive (ecu needing to add in fuel), you get a hail mary of fuel added in once you go into that open loop no feedback zone (power enrichment).

It's just a guess of what you may need at a much higher MAF frequency, again just a guessing bandaid.
PE is where fueling targets change from the typical 14.x afr range target to a more suitable higher load afr such as mid 12s (for most NA setups).

As you can see the learning that does happen is minimal for any gains and is nowhere near optimal, just there to get you from point A to B until recalibration.

Some setups stock are so rich (95% of 2011 trucks I've tuned) that you have a bit of safety pillow as you start off. However this vehicle was already tuned, it's impossible to know where it's currently at until the sensor data is scanned.

Some fuel economy and power will be unlocked once fuel is added where it's lean. This will make happier fueling at higher loads and allow you to run more ignition timing that a leaner mix wouldn't previously allow, win win win.

 

Sorry for the long reply, I felt I had to mention all that in there to properly explain this scenario. Yes there are some specifics I left out otherwise it would be even longer haha. Hope this helps someone.

 

Thank you for the thorough explanation! Also good to know stock truck tunes lean to the rich by a fair margin. I've heard that about Gen III's in older trucks too.
Another question (sorry if I'm hijacking!)-
When I decide to go thru my LM7 if/when it gets tired (200k and going strong) I want to make incremental upgrades like a good multiangle valve job, get the valve pockets/bowls blended, and mill the heads along with a .040 gasket to achieve 10:1 compression and get quench in line.
I would then cap it off with a very mild but larger-than-stock cam like a 200/204, .553/.553, 114LSA truck cam. WHEW!
How far "off the ranch", tune-wise, would all these minor mods take things?
What I'm worried about is, here in Commiefornia CARB is threatening to check bitsums (any disturbance in the Force..) in the ECM for variations from stock. Tuning would disturb this, right?
I know ZIP about that end of things. Hoping the rich stock tune will be enough to cover my butt here
Thanks in advance!

 

Not a problem, glad to help when I have a sec.
I can promise that even with a mild cam like that, plus headwork, the higher load portions of the Maf/VE/VVE(depending on the year) will be at least a few % on the leaner end. Unless you have a factory freak 😁

Probably safe enough in the short term but without a doubt, an eventual tune will only make more efficiency. You may just get by untuned but I would never suggest it longterm without at least datalogging after the cam swap.

You may actually be a tad rich though in the 2000 rpm and lower load ranges after that cam.
Basically as the cam's duration increases, it shifts the power range/curve up, although that's common knowledge on here, what it does to the tune is sometimes not mentioned.

The larger the cam over stock, typically the richer it is at low rpms before the tune. Less efficieny= less fuel required as the engine isn't pumping air as well down low.

2010s I've tuned were fairly tuned stock or on the lean side (positive fuel trims when reading trims where the iat sensor isn't seeing heatsoak).
So it's hit or miss on the factory fueling calibration and what your year truck may have gotten. You would have to adjust the fueling tables more likely than not. Also may need to bump the idle.

Sadly if they don't allow that then that is horrible news. I do understand if they didn't allow tune changes related to disabled cat codes and tests.
Warm up the engine, start recording a scan/datalog after a 15 minute drive. Add in a few dead stops and to the speed limit again without being aggressive on the throttle, that will tell you mostly what's going on before or after the cam swap.

 

The Cam Motion cam mentioned above would compare/contrast to the stock one (191/190, .457/.466, 114 LSA).
The C.M. cam is also available with .501/.501 lift rather than the .553/.553 shown above. Would that ease things a bit?
The overlap is -26 degrees compared to -37.5 for the stocker.
IVC is 29.5 (stock) and 31 for the aftermarket one.
Needless to say, it will idle like a stocker with -26 overlap. NO loping or uneven idle at all.
I have heard of people putting in the LQ9 cam (196/207, .467/.479, 116 LSA) without tuning. Neither this nor the C.M. cam mentioned are huge leaps above stock, but enough to gain torque throughout the rpm band.
Thanks again for your advice!

 

The lift may contribute a bit to needing more fuel. However if your state doesn't allow any tune changes whatsoever, this is small enough of a spec to try out without a tune.

After the cam swap you should have it datalogged to see what the fuel trims are like. If they're in the positives, then I'd simply buy a used spare ecu and have the tune done on there (aim for the same year and transmission type, the tuner should be able to change any other parameters to suit your displacement and injectors). Then reinstall the old/current ecu when it's time for an inspection.

 

Yeah, I'm not sure that will take place, especially if testers will have to invest very much for that capability. As it is now, they do a visual and plug into the OBDII to check for codes. THAT lets you do all I mentioned as long as no codes are thrown.
I saw something yesterday that seems implausible-
An engine rebuilder is offering CARB-legal 5.3 with Comp cam that has CARB exemption (210/218, .570/.541,118LSA). It is claimed to have about 385-400 HP, PLUS they say NO TUNE required! I find that VERY hard to believe. That much cam and no tune? Right....
Thanks again for your input!

 

Yes I doubt it doesn't need a tune as I agree that seems like a wild claim. Unless magically that 118 LSA changes everything. Most cammed LS setups I've tuned have LSA ranging from 106 to 114, perhaps the 118 does some voodoo haha.

If stock lope and no codes is all that they check for, your spec of cam will probably do the trick but I'd keep the stock airbox and maf to ensure as little tuning is needed as possible.
100% stock trucks I've tuned whether a 1999 4.8 or 2018 5.3, always were lean in the maf curve from any aftermarket "cold air intake". Keeping the stock intake tract sounds like the best option in your state.

 

Yep with the new rules leaking in to the various smog laws,,, Piggyback control is going to be the norm, my understanding is the only holdup on rollout has been collecting the ECU data for all the models of cars. OBD1 isn't in play but OBD2 vehicles will be. Going to have to fool that factory ECU into thinking everything is OK.. We have sort of a early version of this testing and its 100% dependent on the data it gets from the OBD2 test port. You cant have disconnected you battery recently it causes you to fail. (It needs all the test items reported in as good and that takes a couple hundred miles on some cars..

 

The airbox is OEM with a dry permanent AEM element. The tube is Airaid but legal. Plus, I have a Walker low restriction cat-back. Not sure any of it helped, but it sounds good...
Yeah, what I did note about that cam is the similarity to the stock LS3 (204/211,.550/.525,117LSA) to keep valve events "in the neighborhood". I agree, the wide LSA might get it in the clear there.