As some of you know, the addition of Berk HFC's to a stock exhaust can cause rasp, rattle and hiss noises.

First, have your exhaust system checked for leaks by an experienced tech. Gaskets should also being replaced if needed. Also make sure that exhaust components are not making contact with any of a number of heat shields. Make sure exhaust hangers are in good condition and that the exhaust system is properly aligned.

My setup: '03 coupe 5AT with JWT pop charger + Stillen air box + 5/16 Motordyne plenum spacer + Z tube + Berk HFC + 350Z HR Y-pipe + 4x22" resonator + OEM muffler

After installing the Berks with the HR y-pipe the exhaust had a deeper tone at idle. However, under load at about 3000rpms there was an horrible raspy rattling sound that drove me crazy. I was about to remove the Berks because that rasp was embarassing. While searching the forums I saw a post by DaveB describing "a metallic pinging/faint clank with some rasp under load from 2800-3500rpm's ... most often incorrectly diagnosed as a loose or broken internal exhaust part"

DaveB suggested replacing the OEM resonator or "center muffler" as described in the service manual with a larger one.

Magnaflow manufactures a glasspack model # 18146 about 30" long which is probably too long for G35 coupe but it's good reference . The resonator is a straight tube that is preforated and packed with some material that cancels certain exhaust tones. The one I used was generic, a round glasspack 4x22" from a muffler shop installed for $60. I think 22-24" will be the longest you can use without a sharp bend in exhaust tubing.

The new resonator removed about 90-95% of the rasp even at 5500rpm. The exhaust note is probably more quiet than stock at idle. Under load, the sound is nice. I can hear the sound of intake again and the muffler exhaust note still sounds like a G35.

 

Thanks for the info!


Can you post a video of the new sound now?

 

The process of adding glasspacks in place of the resonators may have quieted the exhaust but I think the real issue after installing HFCs is that the rasp comes from cramming a larger volume of exhaust thru your OE y-pipe since it only get worse at higher RPMs. If you can't afford a decent true dual exhaust you may be better off buying a 3" diameter y-pipe rather than wasting $$ on mufflers that slow down the exit of your exhaust volume.
Gary

 

That's really not the case. I've experienced this sound with my previous VQ30. It's really not dependant varying pipe sizes but rather the fact that the precats and/or the entire cat is removed. The precats/cats are effectively mufflers. The sound in quiestion is simply the sound of firing order bouncing off the walls of the exhaust piping. I spent a lot of time of money on my VQ30 trying to quell this noise and was convinced it was a loose part in a muffler resonator. I pulled the exhaust off and inspected it, checked heat shields, changed out midpipes, matched piping sizes, inspected flex sections, replaced mufflers, resonators, etc. It turns out it's just the nature of the VQ when removing muffling devices. The fix is to add some sort of additional mufflling device such as a resonator. Resonators, in general, are not power robbing devices.

As for a dual exhaust, I had the Borla TD on my sedan and it had the sound in question. It has nothing to do with the exhaust piping arrangement.

 

+1 to this. There are dynos to back this up as well.

 

I have the rasp and no hiss... I had it installed this week.. wednesday and so far the rasp/rattle is embarrassing... I don't like it.. Berk sent all new gaskets.. and i'm sure they were installed correctly.. So how do i go about getting rid of this rasp.. it's in the 2.5K to 3.5k range.. as someone state i can't even hear the intake no longer

 

I am also experiencing the same problem that everyone in here is complaining about! I was very excited to receive and install my Stillen HFC’s which made the sound deeper, but I also get the rasp over 3000 rpm. When my mechanic installed them he said that the OEM brace for the stock cats would not fit and we would have to do some custom wielding work to make them fit. So once I used my car on the weekend and heard the rasp noise I automatically thought that was the problem. After doing some research on this site I haven’t seen one person post about missing their bracket for the HFC’s. I have a full Stillen set up for my g35 sedan -Gen 3 intake, HFC’s, full Stillen cat back exhaust, and Stillen headers. I thought if stuck with the same brand for most of the parts I should have fewer problems. Not the case! If anyone knows of anything else I might be missing please let me know! Thanks in advance!

 

You may want to add a Magnaflow 11386 to your Stillen Exhaust. I does a great job at eliminating rasp on coupes with true dual exhaust systems & HFC's. It works wonders for cheaper HKS replica exhausts like mine. I can't guarantee that it will eliminate rasp on the Stillen sedan exhaust but it is an inexpensive option. An exhaust shop will have to cut & weld it in as close to the HFC's as possible.

Do a forum search for Magnaflow 11386 and you'll find tons of info and sound clip. I followed this recipe with great results. You may want to pm forum member Jairen. Hope that helps.