Samdeo74

I just had installed on my 2014 corvette an AFE CAI kit and TX Speed LT headers and xpipe. It connects to factory NPP axle back system. I now notice that when I accelerate to about 3k rpm and shift gears as soon as I let off gas, I'm getting a raspy/scratchy air flow sound from underneath the car. Has anyone experienced this before or have any ideas what it is? Thanks as I'm new to the forum.

FYREANT

Could be an exhaust leak. If you are able to put it up on jackstands, you can get under the car and see if there is any exhaust leaking by feeling around the connection points with your hands for air while its running.

Samdeo74

I actually just had it checked out at a local muffler shop and they checked all the joints and no apparent exhaust leak. It's definitely more pronounced inside the car then out. They thought it could be coming from the factory mufflers. Could the increased air flow to the mufflers cause this sound? It always happens right when I let off the gas pedal for about a second then goes away.

FYREANT

Nothing's impossible. Could also be that the exhaust is touching somewhere and it's causing the sound and when you let off the throttle it just happens to move the right way to make it noisy.

robert miller

But now that I have the blower on the car with the D3 radiator set up in the car. I don't hear it no more from the other. But to the OP here mine was a leak at the very back pipe to the cat back on the car. Robert

mjorgensen

Is it coming from the CAI? They tend to make more noise than the factory systems.

Samdeo74

Well I got a second opinion from another muffler shop and they again said no exhaust leak. They thought it also could be the stock mufflers. I called Tx Speed and they advised that no customers using the stock axle back NPP system have reported this issue before. It's hard to hear outside of car but inside it's very noticeable and appears to come from back half of car which I don't think would be the AFE cold air kit causing it. I'm really confused now!😳

FYREANT

Try recording the sound..

bigsapper

May be related to the AFM valves opening/closing?

Socko

I was thinking about posting on here before but decided against it. Let me at least take some cover before I post.

Most long tubes leak at the flange to the xpipe at some temperature. I would say all but I'm sure a couple people went to the trouble to resolve it or got very lucky.

If the sound is sort of the kind of gasping and very raspy on decel its probably a leak. Have someone rev it a little in the garage and listen standing and with your head by the rocker below the side mirrors. If its real loud under the car its leaking at the flange. Specifically if it comes and goes at different exhaust temps. If it only does it warm or cold.

I haven't seen the most headers on cars, but everyone i have seen there are clear signs of condensation leaking out of the header flange with soot in it.

On my c5z that had longtubes it would move from under the car to behind the car as the headers would leak less warm. Disabling DFCO removed the noise totally. As c7's also do this out the mufflers stock, thats my guess of what you could be hearing. The sound created by DFCO leaking out premuffler.

Assuming the c7 axleback uses a simmilar gasket to the c5 that i am very familiar with. The gaskets at the back had to be replaced every time i took the exhaust down cause they are 2 bolt with a gas ring they rely on some ring crush to seal. Possible what you are hearing is that as well.

black_c7

I had this happen to me when its convert to 4v in eco other than that never happened

lakemg

I have a C7 A8 with long tubes and high flow cats with NPP mufflers. If you could post a video that captures the sound that is concerning you, I would be happy to review it to see how it compares to mine.

s n v f f

Big late, hope it still help.
When Corvette does that sound after long tube headers it's not a leak, it's DFCO on decel and CFCO when shifting.
you can disable both via HP Tuner and get rid of that sound, i did, works perfectly.

mhpearlman

with your HP tuner can you also get the much desired burps and gurgles (or whatever the hell they are called) when decelerating and down shifting??

s n v f f

Absolutely, i do have pops and crackles tune on mine:

mhpearlman

2 words.......

****** AWESOME