[torchred]

I have heard many responses over the years, with the most common being i can install headers without a tune and only negative being i wont gain as much power as with a tune. Is this correct for the C7, or are there issues with the engine running lean? As for V4 mode, will the backpressure loss affect anything?

 

[Dasyatis]

Since the computer has a built in learning mode that constantly adjusts as you drive, no tune will be compensated to keep the mixture correct. Of course for maximum benefit (power etc) a tune would be needed.

 

[spaceaholic]

I believe that for longtubes a tune is required or you will throw a CEL

 

[mjw930]

Since the computer has a built in learning mode that constantly adjusts as you drive, no tune will be compensated to keep the mixture correct. Of course for maximum benefit (power etc) a tune would be needed.

It does but learning is only capable to move a certain percentage off the baseline and if the mod is great enough it could max out it's ability to adjust. It also only adjusts in closed loop and under many situations such as WOT it goes into open loop and depends on the base map more. Ideally a new tune to update the base settings is always advisable then the learning can deal with fine details.

 

[torchred]

Yea this is what i was figuring. Maybe my best bet is to go with a "double Helix x-pipe" ,instead of the headers, to remove the last two resonators before the mufflers. For now im just interested in the sound...NPP is fine, but a little more of a throaty note would be nice!

 

[J.R]

Since the computer has a built in learning mode that constantly adjusts as you drive, no tune will be compensated to keep the mixture correct. Of course for maximum benefit (power etc) a tune would be needed.

That is not correct and I see the damage all the time when Corvette owners finally come to me to clean the mess up

The PCM is not designed nor does GM's adaptive strategy care about a perfect tune.
The main purpose of PCM is to abide by EPA and smog output.
Error codes (DTC) have a wide operating window and the engine can be as much as 13% too lean before that lean code even trips and as much as -13% rich
for those DTCs to trip

Corvettes for some time come with short tube headers. Going to long tube for its total costs gain little

Common sense is the CATs and the O2 sensors were designed to be in certain exhaust temps and distances.
Long tube forces those functions to be moved further downstream where the temps are cooler which effects those functions and causes
different or even false AFR readings.

As it is if owner cares is that long tube headers are illegal as moving those smog devices is illegal.

From the PCM adjustments, it will not make large adjustments to fueling needs, add the E10 gas which leans AFR even more and the worst case
is owners are being suckered to either/and rid the CATs or the rear 02 sensors.
Consider the CATs alone the PCM has a over temp protection to prevent CATs from burning out so when PCM senses that it pumps in excess fuel to cool them down
Now moving or removing the CATs and PCM still acts if CATs are where GM put them even if the CATs or the crappy so called high flow CATs are installed
( which is also illegal)

Now you have the 4 02 sensors and the downstream movement or the rear ones ripped out and the stock GM tune not only cannot adjust properly but DTCs are tripping and not only will not go away but prevents the built in ON-board smog tests from being in a completed/passed state.

Now add most headers sold are "canned" headers made for C5s are even been sold as C6 or C7 designs and in many cases then cause a loss of low end torque.
Add the heat issues from long tubes and the total is a MUST of PCM being properly tuned ( and not the junk tunes where tuner hides the issues by simply turning off the DTCs to hide the problems from you)

Vendors claim high performance gains of their LT headers but the games is a tune is done which is what really made the gains and not the headers,.

Remember yes you could drive the car without a tune but you also could drive a 4 banger engine and that is not what a Corvette is about and in long term the incorrect tune will cause more fuel use, higher temps and more carbon built up on piston and valve tops and in most cases the wrong sparkplugs are used for LT headers.
Let's face it a Corvette owner can spend about $2,000 in total for LT headers and in fact lose backpressure and proper exhaust flow to reduce torque and
if not installed correctly with proper exhaust gaskets ( common fault I see) induce exhaust leaks which effects 02 sensor feedback to PCM.

 

[torchred]

That is not correct and I see the damage all the time when Corvette owners finally come to me to clean the mess up

The PCM is not designed nor does GM's adaptive strategy care about a perfect tune.
The main purpose of PCM is to abide by EPA and smog output.
Error codes (DTC) have a wide operating window and the engine can be as much as 13% too lean before that lean code even trips and as much as -13% rich
for those DTCs to trip

Corvettes for some time come with short tube headers. Going to long tube for its total costs gain little

Common sense is the CATs and the O2 sensors were designed to be in certain exhaust temps and distances.
Long tube forces those functions to be moved further downstream where the temps are cooler which effects those functions and causes
different or even false AFR readings.

As it is if owner cares is that long tube headers are illegal as moving those smog devices is illegal.

From the PCM adjustments, it will not make large adjustments to fueling needs, add the E10 gas which leans AFR even more and the worst case
is owners are being suckered to either/and rid the CATs or the rear 02 sensors.
Consider the CATs alone the PCM has a over temp protection to prevent CATs from burning out so when PCM senses that it pumps in excess fuel to cool them down
Now moving or removing the CATs and PCM still acts if CATs are where GM put them even if the CATs or the crappy so called high flow CATs are installed
( which is also illegal)

Now you have the 4 02 sensors and the downstream movement or the rear ones ripped out and the stock GM tune not only cannot adjust properly but DTCs are tripping and not only will not go away but prevents the built in ON-board smog tests from being in a completed/passed state.

Now add most headers sold are "canned" headers made for C5s are even been sold as C6 or C7 designs and in many cases then cause a loss of low end torque.
Add the heat issues from long tubes and the total is a MUST of PCM being properly tuned ( and not the junk tunes where tuner hides the issues by simply turning off the DTCs to hide the problems from you)

Vendors claim high performance gains of their LT headers but the games is a tune is done which is what really made the gains and not the headers,.

Remember yes you could drive the car without a tune but you also could drive a 4 banger engine and that is not what a Corvette is about and in long term the incorrect tune will cause more fuel use, higher temps and more carbon built up on piston and valve tops and in most cases the wrong sparkplugs are used for LT headers.
Let's face it a Corvette owner can spend about $2,000 in total for LT headers and in fact lose backpressure and proper exhaust flow to reduce torque and
if not installed correctly with proper exhaust gaskets ( common fault I see) induce exhaust leaks which effects 02 sensor feedback to PCM.

Wow! all that goes on with just the exhaust huh? i just knew the basics like loss of backpressure, lowered lowend responce, etc. I had no clue the cats were cooled and fuel ratios could be off by 13%, this is good stuff! So from what i gathered in your post, my best bet is to leave the long tubes off and not mess with the tune. Im assuming that the x pipe is still ok to change, considering its after the cats and sensors? I remember removing those last two extra resonators on my camaro made a big difference, so should do the same for the LT1

 

[J.R]

Think of it this way
the C6 Z06 began with a short tube type of header and with a tune puts out about 570 flywheel HP from 505 HP

Now the C6 ZR1 with a tune puts out about 660ish flywheel HP and uses the same exhaust manifold design so clearly the stock GM design is not
limiting performance of the C7 LT1 and assume the same exhaust setup for the new 640 HP C7 Z06

You could use that money more wisely for other things while not having to deal with the federal EPA issues LT headers bring about.

As to X-pipe, keep the differences apart as to a H-pipe, a "canned" X-pipe and a true X-pipe design and placement

If canned type and just putting in further downstream will balance the sound and not effect tuning
but if installed closer to collector will enhance low end torque and extract exhaust out of cylinders better
Though if C7 is like late C6s they already have GM X-pipe in proper placement.

You could spend big bucks for LT header and end up losing low end torque if primaries and total length are incorrect for the cylinder volume and just have minor exhaust sound.
As to O2 sensors, GM designs the total powertrain with set specs so it is clear if O2s are selected to match the quad hardware drivers of the PCM for a set amount of exhaust temperature and lets say that is about 900 degrees yet by the time it gets to muffler the temp is down under 200 degrees you can see that even if the LT header requires the 02s moved 1 foot downstream what the temp drop is which effects then what 02 feedback to PCM is that effect PCM commanding fuel injector pulsewidth ON time

Lastly do not forget that the C7 now deals with ethanol in gas and the 02 sensors play a better part in PCM knowing when E10 or E15 gas is used that leans the AFR up to being too lean so again placement of 02s is important.

 

[Dasyatis]

It does but learning is only capable to move a certain percentage off the baseline and if the mod is great enough it could max out it's ability to adjust. It also only adjusts in closed loop and under many situations such as WOT it goes into open loop and depends on the base map more. Ideally a new tune to update the base settings is always advisable then the learning can deal with fine details.

That is not correct and I see the damage all the time when Corvette owners finally come to me to clean the mess up

The PCM is not designed nor does GM's adaptive strategy care about a perfect tune.
The main purpose of PCM is to abide by EPA and smog output.
Error codes (DTC) have a wide operating window and the engine can be as much as 13% too lean before that lean code even trips and as much as -13% rich
for those DTCs to trip

Corvettes for some time come with short tube headers. Going to long tube for its total costs gain little

Common sense is the CATs and the O2 sensors were designed to be in certain exhaust temps and distances.
Long tube forces those functions to be moved further downstream where the temps are cooler which effects those functions and causes
different or even false AFR readings.

As it is if owner cares is that long tube headers are illegal as moving those smog devices is illegal.

From the PCM adjustments, it will not make large adjustments to fueling needs, add the E10 gas which leans AFR even more and the worst case
is owners are being suckered to either/and rid the CATs or the rear 02 sensors.
Consider the CATs alone the PCM has a over temp protection to prevent CATs from burning out so when PCM senses that it pumps in excess fuel to cool them down
Now moving or removing the CATs and PCM still acts if CATs are where GM put them even if the CATs or the crappy so called high flow CATs are installed
( which is also illegal)

Now you have the 4 02 sensors and the downstream movement or the rear ones ripped out and the stock GM tune not only cannot adjust properly but DTCs are tripping and not only will not go away but prevents the built in ON-board smog tests from being in a completed/passed state.

Now add most headers sold are "canned" headers made for C5s are even been sold as C6 or C7 designs and in many cases then cause a loss of low end torque.
Add the heat issues from long tubes and the total is a MUST of PCM being properly tuned ( and not the junk tunes where tuner hides the issues by simply turning off the DTCs to hide the problems from you)

Vendors claim high performance gains of their LT headers but the games is a tune is done which is what really made the gains and not the headers,.

Remember yes you could drive the car without a tune but you also could drive a 4 banger engine and that is not what a Corvette is about and in long term the incorrect tune will cause more fuel use, higher temps and more carbon built up on piston and valve tops and in most cases the wrong sparkplugs are used for LT headers.
Let's face it a Corvette owner can spend about $2,000 in total for LT headers and in fact lose backpressure and proper exhaust flow to reduce torque and
if not installed correctly with proper exhaust gaskets ( common fault I see) induce exhaust leaks which effects 02 sensor feedback to PCM.

Thanks for the clarification. Sorry if I wasn't detailed enough as I wasn't trying to imply anything close to perfection, just that some compensation will occur.