C7 exhaust

[David123]

So after my recent c7 purchase I have spent literally a week watching exhaust videos and reading forum . If anyone can answer the following questions I would be grateful -

1) I am now reading that replacing my oem x pipe and secondary cats with an aftermarket replacement x pipe can cause a loss in power if the car isn’t re tuned ?
2) I have watched numerous videos on axle back after market exhausts …. Some just delete the whole npp valve system which is fine .. but what confused me is that some aftermarket exhausts delete the AFM (air fuel mixture sensors) that are situated before the muffler .. surely this upsets the running of the car ?

any recommendation re aftermarket exhausts without having to retune the car ? Thanks

 

[Chevrolet]

What are you looking for? More/different noise, more power or both? Guess you have been looking at videos of mainly Borla, Corsa. Flowmaster etc exhausts?

Did you see this one? I am guessing this will apply to UK spec cars too? I know several guys up in Notts with UK spec C7s, but they are all autos and none of them have gone for aftermarket exhausts or tried the below.

 

[teamzr1]

So after my recent c7 purchase I have spent literally a week watching exhaust videos and reading forum . If anyone can answer the following questions I would be grateful -

1) I am now reading that replacing my oem x pipe and secondary cats with an aftermarket replacement x pipe can cause a loss in power if the car isn’t re tuned ?
2) I have watched numerous videos on axle back after market exhausts …. Some just delete the whole npp valve system which is fine .. but what confused me is that some aftermarket exhausts delete the AFM (air fuel mixture sensors) that are situated before the muffler .. surely this upsets the running of the car ?

any recommendation re aftermarket exhausts without having to retune the car ? Thanks

As I mentioned in another post, doing a CAT back only changes the sound and no performance gains
Changing from a H pipe to X-pipe in mid-pipes only balances the sound left/right

People are known to spend $2,000 to $4,000 in thinking there is a performance gain to have a midlife crisis after all the costs and
zero gains

Next is the stock NPP valves

If the C7 has 8 speed auto tranny, there are another 2 NPP valves (4 total) closer to the engine and are needed for more back pressure when the AFM kicks in
AFM is what commands via the PCM going from 8 to four cylinders mode and back

If having the manual 7 speed tranny only has 2 NPP valves by mufflers and PCM commands the butterflies wide open when doing WOT

Yes, owners ask me when I tune the PCM to turn off AFM, but that is more for people want 8 cylinders all the time
Vendors who sell high cost CAT backs, some replace the stock NPPs with theirs and are not exact to stock ones
and can cause error codes to trip, and you have to solve that with tuning, so be sure the seller in writing says their NPPs will not trip DTCs

If installing a CAT back with no NPPs then either have to buy and install NPP simulators so DTCs do not trip or turn off those DTCs

In the end if all you want is exhaust sound change is replacing stock mufflers, fewer costs and less hassle

 

[David123]

I have looked at all the Borla , Cora’s and other makes .. not looking for power just increased noise and better tone

So now even more confused .. I thought the oem exhaust has an x pipe connected to the secondary mufflers ?

My question remains .. if I delete the oem secondary cats and stock x pipe and replace with and after market x pipe .. will this reduce power so I need to retune the car ?

Also on the axle back rear set ups some delete the afm sensors .. surely this affects running hugely ? Thanks for your help

 

[teamzr1]

Why spend money to replace the stock X-pipe with another when there would be no difference at all ?

No such thing as AFM sensors, you mean the NPP exhaust valves and if a manual tranny as I stated there
is just 2 of them mounted right before the mufflers, and they are for a bit more sound and performance at WOT

If auto tranny then there are 2 more NPPs (4 total) up front and are used when AFM is commanded to switch from/to 8 to 4 cylinders

There is no performance loss or issues when removing the rear CATs as long as also not deleting the rear oxygen sensors

 

[scazman]

I have looked at all the Borla , Cora’s and other makes .. not looking for power just increased noise and better tone

So now even more confused .. I thought the oem exhaust has an x pipe connected to the secondary mufflers ?

My question remains .. if I delete the oem secondary cats and stock x pipe and replace with and after market x pipe .. will this reduce power so I need to retune the car ?

Also on the axle back rear set ups some delete the afm sensors .. surely this affects running hugely ? Thanks for your help

David.
Email me at scazmanathotmail.com (replace the at in the middle with @ ) and I'll let you know my findings with the AWE system I have.
Jon

 

[David123]

Thanks

 

[Chevrolet]

So now even more confused .. 1) I thought the oem exhaust has an x pipe connected to the secondary mufflers ?

My question remains .. 2) if I delete the oem secondary cats and stock x pipe and replace with and after market x pipe .. will this reduce power so I need to retune the car ?

1) Correct. Fitting an aftermarket one is replacing/removing the factory x pipe and secondary mufflers
2) No. Presume you have not read that anywhere and non of the YouTube videos mention that.

 

[Chevrolet]

Also on the axle back rear set ups some delete the afm sensors .. surely this affects running hugely ?

Where did you see/read that? "Team ZR1 is saying above there are "no afm sensors." AFM= Active Fuel Mangement is where the car goes into fuel saving/emissions reducing V4 mode. UK spec autos only run in V4 in "Eco mode" The car is in Eco mode when you start it up, so everyone including me switches it immediately to Tour, Sport or Track as required to run in V8 all the time. I've looked at another thread. That says UK spec manuals also only run in AFM V4 when in "Eco" mode. So if you don't drive in Eco, you will be getting the full V8 blast thru any aftermarket x pipe and/or axle back mufflers. If you want to be "really noisy" there are US YouTube videos of the "Muffler Delete".

Think the above is correct, If anyone else knows better?

 

[teamzr1]

DOD/AFM is solely controlled by the PCM as it controls the lifters, timing, etc as when commanding AFM on and off along
with other factors as I show below is the tunings settings in the PCM calibration
As I mentioned the loading and unloading of load and torque when AFM kicks on/off GM needed the 2 extra NPP valves for the ill of A8
as to sound and exhaust back pressure

There is nothing any exhaust makeup would have as to some sensor in exhaust to command AFM on or off

Displacement on Demand

DoD Enable ERT 45 Sec.
DoD Disable Vehicle Speed 5 MPH
DoD Disable Vehicle Speed Hysteresis 1 MPH
DoD Enable Vehicle Speed - in P/N 5 MPH
DoD Enable ECT 36 Deg. C
DoD Enable ECT Hysteresis 4 Deg. C
DoD Disable_RPM 3200 RPM
DoD Disable TPS 50 %TPS
DoD Disable TPS Hysteresis 2.5 %TPS
DoD Disable Brake Vacuum 0 kPa
DoD Enable Brake Vacuum 0 kPa
DoD Disable Low Oil Pressure 25 psi
DoD Disable High Oil Pressure 68.2 psi
DoD Disable Low Oil Temp 18 Deg. C
DoD Disable High Oil Temp 130 Deg. C
DoD Disable Low Ignition Voltage 1 11 volts
DoD Disable Low Ignition Voltage 2 11 volts
DoD Disable Low Ignition Voltage Hyst. 0 volts
DoD Re-enable RPM 3100 RPM
DoD Low RPM Limit Hysteresis 475 RPM
DoD High RPM Limit Hysteresis 200 RPM
Min. DoD Off Time 3 Sec.
DoD Fuel Cutoff Enable Delay 3 Sec.
DoD Delta Vacuum Test Enable Time 480 Sec.
DoD Max. Time 600 Sec.
DoD Disable Pos. Delta Vacuum 5 kPa
DoD Disable Neg. Delta Vacuum -5 kPa
DoD Min. Re-enable Time 60 Sec.
DoD Disable Oil Aeration RPM 3100 RPM
DoD Disable Oil Aeration Time 5 Sec.
DoD Disable Oil Aeration Reset RPM 3000 RPM
DoD Disable Oil Aeration Reset Time 50 Sec.

 

[David123]

So I was never very good at school and reading ! So my manual Uk car will run on 4 cyl in eco mode ? It reverts to eco for every start .. can I stop this ?

As to exhausts and afm sensors .. I have watched videos of stock cars .. the afm s are situated in the exhaust between the x pipe and rear mufflers .. I believe just before the exhaust goes over the rear axle . I fear when these are deleted the cars over fuel ..

Next issue is there appears to be nowhere in the states that now sells an x pipe which includes a secondary cat delete .. due to new regs .. without this there’s no point in the exercise

 

[Chevrolet]

So I was never very good at school and reading ! 1) So my manual Uk car will run on 4 cyl in eco mode ? It reverts to eco for every start .. can I stop this ?

2) As to exhausts and afm sensors .. I have watched videos of stock cars .. the afm s are situated in the exhaust between the x pipe and rear mufflers .. I believe just before the exhaust goes over the rear axle . I fear when these are deleted the cars over fuel ..

3) Next issue is there appears to be nowhere in the states that now sells an x pipe which includes a secondary cat delete .. due to new regs .. without this there’s no point in the exercise

1) Just turn the drive mode button to Touring, Sport or Track as you wish, to stay in V8 all the time. What I don't know is if you are in Eco mode and you step on the gas hard, will it go into V8 and then go back to V4. or stays in V4 all the time? You can test that if you drive in Eco, as instrument display will tell you if its running V4 or V8.
2) Lets see the video. No mention of "AFM sensors" in here:

3) Not surprised. CarGuy11 in the video above descibed it as an "off road" x pipe I think?

 

[teamzr1]

So I was never very good at school and reading ! So my manual Uk car will run on 4 cyl in eco mode ? It reverts to eco for every start .. can I stop this ?

As to exhausts and afm sensors .. I have watched videos of stock cars .. the afm s are situated in the exhaust between the x pipe and rear mufflers .. I believe just before the exhaust goes over the rear axle . I fear when these are deleted the cars over fuel ..

Next issue is there appears to be nowhere in the states that now sells an x pipe which includes a secondary cat delete .. due to new regs .. without this there’s no point in the exercise

There is 2 ways to turn the damn AFM off so that it never goes to 4 cylinders mode

1. Here is Amazon in the UK

Amazon.co.uk : afm

This is an AFM defeat module that as long as it is connected to the diag port under the dash, it prevents AFM being used
At any time you can unplug that and AFM functions as normal

select one of those that says for your vehicle

2. Tuning the PCM controller as I do and turn AFM off so the PCM thinks AFM does not exist so never command AFM at all

In either way your C7 will finally feel it has some balls as a sports car and fuel mileage will not change very much
and engine will sound smoother

 

[Pinhead]

I have turned DOD off with efi live on my 2014 USA spec car
It's so much better you used to get a jerk like a gear shift when it went in and out which I guess was the torque converter unlocking and locking again to smooth the transition

Question for team zr1
Is there anything to be gained power wise on a stock stingray in the tune
No aftermarket parts at all
I have noticed keith (eurovettes) claim a big hp increase but I find it difficult to believe more than let's say 10 or 15 hp is available

 

[teamzr1]

I have turned DOD off with efi live on my 2014 USA spec car
It's so much better you used to get a jerk like a gear shift when it went in and out which I guess was the torque converter unlocking and locking again to smooth the transition

Question for team zr1
Is there anything to be gained power wise on a stock stingray in the tune
No aftermarket parts at all
I have noticed keith (eurovettes) claim a big hp increase but I find it difficult to believe more than let's say 10 or 15 hp is available

That is what causing the problem with the A8 as engine going in and out of AFM which effects torque ramping lower when AFM is on and then torque going back up when AFM turns off, that loading/unloading has an effect on the torque converter at what RPMs if locks and unlocks

As I mentioned, when I am doing custom tunes I ask the owners if they want me to turn off DOD or AFM
or reduce when it comes on

I did the tune remotely you mentioned,
GM uses an 80% design rule, so their calibration limits HP/Tq by 20% of the ability of design of the engine and tranny
so common to see with tuning 30 plus HP gains at flywheel and I redo the torque curve so from the lower end to mid-engine loads
the torque is much better, and I reduce how much torque is reduced via the torque management function in the calibration has
and also tune the TCM for A8 to allow more torque

 

[Pinhead]

That is what causing the problem with the A8 as engine going in and out of AFM which effects torque ramping lower when AFM is on and then torque going back up when AFM turns off, that loading/unloading has an effect on the torque converter at what RPMs if locks and unlocks

As I mentioned, when I am doing custom tunes I ask the owners if they want me to turn off DOD or AFM
or reduce when it comes on

I did the tune remotely you mentioned,
GM uses an 80% design rule, so their calibration limits HP/Tq by 20% of the ability of design of the engine and tranny
so common to see with tuning 30 plus HP gains at flywheel and I redo the torque curve so from the lower end to mid-engine loads
the torque is much better, and I reduce how much torque is reduced via the torque management function in the calibration has
and also tune the TCM for A8 to allow more torque

Keith is claiming 517hp from 465 factory
That's 53hp certainly more than the 30+hp you mentioned
Has the power been verified I would be very tempted if gains like that are possible with no detriment to drivability

 

[Roscobbc]

Keith is claiming 517hp from 465 factory
That's 53hp certainly more than the 30+hp you mentioned
Has the power been verified I would be very tempted if gains like that are possible with no detriment to drivability

Or to insurance perhaps?

 

[teamzr1]

Here is part of recorded OBD2 scanner data on a testrun they did after I tuned it
so all this is what the PCM reported via OBD2
Numbers in art better as the weather was only 58 F degrees, so good for making power and speed to 130 MPH
Being this was over 1 1/2 years ago, I cannot recall if 2014 C7 was totally stock or not

As to health long term I have tuned Corvettes 20 plus years ago, including my own
One friend who has a 2002 Z06 then I tuned back in 2003 and still has the tune in it and engine now has
over 270,000 miles on the LS6 and even passes Ca smog tests
Many others I keep in touch with I tuned many years ago from stock to all types of boost, CAMs, ported, stroked, etc engines

 

[Pinhead]

Seems I have derailed this thread and maybe better starting a new thread on tuning
In the image above it shows what I would consider a lot of KR
My only tuning experience was my own heads and cam 99 camaro with efi live
It went well when I had finished running 11.6
I have forgotten much of what I learnt but do remember chasing knock on launch and cured it with a catch can
I am guessing that a little oil was accumulating in the intake manifold and got consumed just as I went wot
Here is my old car with a couple of mates
all basically the same mods but with subtle differences like cam and stall etc
Mine although not the most aggressive cam or stall had a slight edge on the other 2

 

[Chevrolet]

Seems I have derailed this thread and maybe better starting a new thread on tuning

I have forgotten much of what I learnt but do remember chasing knock on launch and cured it with a catch can

Start a new one then? Why don't you phone Keith and ask him about his/let us know? Think we are talking a "remap" here? If you do a search on C7 Corvette LT1 remap, including on YouTube, think its correct to say that there is virtually nothing there? This company in London claims to add 20 bhp to your C7, but I wouldn't be going there:

🥇 Catalog - Tested and Safe Files for Tuning | TC Performance

An extensive database of ECU tuning files ➦ A large selection of cars. Intuitive navigation ➦ Select brand, model, generation and engine and find a file!

www.tc-performance.com

Might be worth talking to TopCats Racing? But see on their website they are talking LS1 engines?

ECU Engine Tuning – Topcats Racing

topcatsracing.com

The "lads" in Notts I know with LT1 C7s and Camaros have put "catch cans" on theirs.