So i finally got a laundry list of parts installed on my G and its just one problem after another. I had my rear brake pads replaced and now my slip/vdc comes on every day after driving for 20 minutes but fluid level is fine.

The larger issue is my exhaust setup sounds like crap while driving.

Parts:
-Stillen Headers
-HKS exhaust "Not a replica"
-Motordyne art pipes
-magnaflow crossflow

Basically if I rev the car by putting it into neutral it sounds ok but when I am driving the car I am getting a really high pitched raspy noise between 4-6k under partial throttle. Lets say 80%. It seems to go away or at least be covered up if i am 100% on throttle but that maybe due to the added engine noise with the stillen intake & motordyne spacer setup.

I havnt had time to get under my car yet as my other car is using my jackstands but I can see the torn up flex pipes were not replaced @ time of installation. Both flex pipes outter metal flex section are torn up a bit. Could this be the sole culprit?

I am getting pretty frustrated as everytime I do a nice mod for the car its 2 steps back. A $2k exhaust with another $1k+ in supporting exhaust mods shouldnt sound like this.

I am going to order flex pipe replacements now either way and have a local exhaust shop install them as the shop that originally did the work was an hour away & I would have to leave the car overnight which poses a bigger issue of getting there, back and to work the following day.

Anything else I should consider?

 

Also does anyone know what size flex pipes I should order as replacements? I would rather have the parts on hand when going to the shop than have to wait for them to order anything etc if possible.

 

HKS exhaust is 2.5" in diameter, you could order 3" so they can slip on and weld. I have the same set up you do and don't have any rasp, so it might be the flex pipe leaking. I'd use the muffler shop closest to you. Did the Magnflow X-Pipe replace the HKS crossover which is why we installed them in the first place?
Gary

 

From what I can tell they replaced the h pipe section like they were supposed to. I'll throw it on some jacks tomorrow and take a look and snap some pictures after work.

Yes I always heard good things about this combo so held out and found all the right parts over time. Hope to get it to sounding the way it should! Those flex sections need to be replaced either way so I'll start with that tomorrow.

 

You also have headers? Because they amplify the rasp.

 

Yes, stillen headers. I was messing with it on my way into work today and the rasp/leak/metal sound, sounds like its coming directly from the Y pipe area. I can floor it with 80% throttle to 4-5k and hear it really easily. It sounds like its really there the whole time but the intake/engine drowns out the sound a little if I do 100% throttle. But it does sound like its coming from that area & not the end of my exhaust system. I tested it at idle again and cannot hear the noise when rev'ing the engine, only under load.

Calling some shops to get the flex pipes replaced today & ill take a look while its on the lift.

Edit: Called some local shops and was quoted between $160-$550 to just replace the flex pipes. Talk about range of rip off. I spoke with the shop that installed it and they are gonna take a look & replace the flex pipes for me. Ill try and get them to take a test drive to verify its good. Its the only thing I can think of that would cause that within that area while only under load. Weird but we shall see

 

I was referring to Gary.
When I had headers, HFC's and the HKS exhaust I noticed some rasp at higher RPM's.

 

My HKS exhaust had some major rasp until I replaced the poor quality crossover with the x-pipe. If anyone recalls the HKS crossover had restriction issues with the pipe blocking 25% of the inside diameter. HKS only answer was to send the system back to them with a receipt proving who we purchased it from...what a joke!
Gary

 

Im taking it back into the shop today or tomorrow. Here are some pic's i snapped. I can basically re-produce the rasp or high pitched noise with throttle control in the 4-6k rpm range under partial throttle. Under full throttle sometimes its gone completely or at least drowned out. But it can be pretty loud raspy sounding from the center of the vehicle. To me it sounds more like a high pitched rattle than exhaust rasp. Especially since I can hear it coming from the area between the driver/passenger seat under the car which is where the Y pipe is & not from the end of the muffler area but we will see. The shop is gonna replace the flex sections either way & then we can go from there and see how it sounds. Exhaust sounds clean if i rev it up at idle, I can only recreate the noise under load while driving.

 

Got the flex pipes replaced but it still sounds like ***. The shop basically said it is what it is and its just the exhaust & its hard to get these cars to sound nice sometimes.

What part of the HKS exhaust has any type of internal baffles? Just the muffler portion? I can hear a distinct metal on metal rattle from the exhaust while driving if I blip the throttle from 2-3k at low speeds. Its raspy from 3k-redline majority of the time if that makes any sense. I can rev it at idle and it sounds pretty clean but under load while driving it sounds like a Honda Civic

I am considering trying to get the car on a lift at a local exhaust shop & see if they can re-produce the rattle by revving at all while we can check it out from the underside.

Thoughts?

Its pretty annoying considering I spent about $3,000 on 3 upgrades and literally each upgrade has its own problem. Ill be making others threads for those as they are non related to the exhaust.

 

There's another possibility that often gets ignored, your intake and how much airflow you're getting reflects in the sound of your exhaust! No where in your thread do you mention the type of intake you have. With headers/art pipes and a full exhaust the wimpy drop in intake won't allow enough air thru your system so it sounds good...fact! Also, has your G been tuned?
Gary

 

04 g35 automatic

Motordyne Iso Thermal plenum spacer & TB Spacer
Stillen Intake
Stillen Headers
Motordyne Art Pipes
HKS Exhaust w/magnaflow non-resonated X pipe

No tune

What is more concerning to me is the metal on metal I can hear at very low rpms when I blip the throttle. Are there baffles inside the hks mufflers? Perhaps a baffle is broken from the weld and causing this issue. I bought the exhaust, headers & art pipes used however everything was in pretty good condition besides the flex pipes from being on a lowered car.

The headers looked brand new, the exhaust and art pipes just needed some polish and they shined right up. I see what your saying about the intake but the sound its making...the amount of rasp I can hear really leads me to believe its a much larger issue such as a broken baffle or resonator within the system. It sounds like a really bad honda civic exhaust farting down the street. Sometimes when the car is first started the rasp is minimal but after its warmed up I can re-produce it quite easily and unless im at 1-2.5k rpms its pretty noticeable. I floored it the other day getting on the on ramp and passed someone once I hit the highway only to roll up my windows from being embarrassed of the sound. Shameface

I am considering making a short clip w/cell phone sometime this weekend so you can hear it yourself. Thanks for the help Gary

 

When you un-restrict the exhaust all the way to the block like that, rasp is inevitable. I highly doubt any N/A G with full bolt-ons is rasp free. OEM muffler or HFC's will help considerably. Or the more expensive route would be adding a turbo or two...

 

I get that but I also guarantee it dosnt sound like 100% rasp in most of the powerband or people would not buy these mods to begin with. Also the sound of metal bouncing inside of metal under certain rpm blips from the rear of the car indicates to me a baffle is broken somewhere & could be the culprit to begin with. There is no way in hell people are spending $2,000 on an HKS exhaust, adding another $550 for motordyne art pipes & are enjoying their car's the slightest if it sounds anything like mine at the moment.

I will check out the muffler sections this weekend if I have the time. Does anyone know if the baffle inside the mufflers can be replaced, or removed without spending an arm and a leg? Also does the center section with the 2 round silver pipes contain a baffle as well? Its hard to pin point where exactly its happening while driving only that its clear as day and I can re-product the metal bouncing effect by driving slow @ 10% throttle and blip it. Sounds like metal bouncing inside a metal can. If something is broken inside the exhaust this would "most likely is" what is making the exhaust sound like crap under full load as its just vibrating inside the exhaust.

 

Are we talking about rasp or a rattling sound? There aren't that many that go with a "full" bolt-on setup, those that do definitely experience rasp.

Just drop the back portion of the exhaust, should be easy to tell if something is loose inside of it. I'm fairly certain the only baffles are in the rear but I haven't looked at the inside of the HKS for many years.