Rasp...coming from what part of my 370Z's exhaust?
 

Hi all, I have Stillen G3 long tube intakes, stock headers, Berk HFCs, and the Stillen CBE.

When the car/engine is cold I have lots of rasp at low revs, which goes away after the car is warm.

When the car/engine is warm or cold, I have lots of rasp under heavy load from acceleration.

It's starting to get annoying, as the rasp wasn't there when the parts were first installed. Anyone know if the rasp is coming from the HFCs? Or is it coming from the CBE?

If the HFCs are the culprit, will I eliminate rasp by switching to test pipes? Will the exhaust get louder (remember, Berk HFCs currently, not stock cats), even at cruising speeds?

Finally, some with exhaust plus HFCs/test pipes say there's an "air fart" noise on overrun (letting off throttle after accelerating), would this be even louder with test pipes than HFCs?

Thanks in advance!

Test pipes would be even more raspy. Chances are the rasp will go away if you revert back to the stock cats.

However there's a chance you've developed a leak somewhere.

HFCs would be my bet

m4a1mustang, why would test pipes create more rasp?

Also, can anyone answer my other questions as well?

Thanks...

i've had the Stillen CBE installed for a while now. Just installed the HFC and now i have a rasp. Although IMO it sounds great. So to answer your question, it's a very good bet it's your HFC.

Definitely the HFC's; test pipes will sound as bad or worse.

Options are to live with it, replace OEM cats, or get resonated test pipes/HFC's.

Could you explain why resonated test pipes will eliminate rasp? Is this their purpose? Do resonated test pipes work as well as resonated HFCs? What brands should I consider?

So to maximize power and minimize rasp, my order of preference should be:

1) Resonated test pipes (less rasp, more power?)
2) Resonated HFCs (less rasp, no difference in power?)
3) Different HFCs (maintain power, hope for less rasp)
4) OEM cats (least rasp/least power/quietest)
5) Test pipes (most power/most rasp/loudest)

?

I look forward to your advice! Thanks in advance...
Marcus

Shouldn't affect power, but the resonators are supposed to cancel out the vibrations making the rasp sound.

Bump for more opinions...

^^^ check all your flanges and your gaskets to be sure they're no broken welds or a bad seals. Another thing is make sure that your pipes are not rubbing up against anything (heat shields) this could be mistaken for rasp. use some exhaust crack joint and crack sealant. The gaskets that come with the exhaust are not very good, you should get them from napa/autozone along with grade A bolts, nuts and washers probably from home depot. if not a bad seal, broken weld or head shields touching your exhaust then you COULD have a faulty HFC. You can see if they will take it back and get another one. The HFC should create minimal rasp if any. I hope this help and GL

I have been dealing with this issue for a while! I have had the rasp since I put test pipes on. I just recently put on the Stillen CBE and the rasp is crazy loud now. I did some throttle manipulation a couple months back to combat the back pressure, it worked great but my gas mileage went to **** and I was getting some weird side effects with throttle response and a lot of backfire.

I am really beginning to believe it is the resonators; not by their design but by the exhaust design. Your stock cats are doing a really good job at creating a "buffer" to a stable atmosphere. Removing them seems to be creating a high flow which in general is good. From the point at which the exhaust splits all the way back to the exhaust tips seems to be the issue...in this case pressure differences. Just like when you crack a window on the freeway and everyones ears explode, it seems the pipes are fighting each other. I have spent hours trying to figure this out, I am getting a clear sound coming straight from the resonators when I use a stethoscope...no where else!

I am really starting to believe '10Anamoly 's theory with using a pipe to bridge atmospheres...check it out if you already havent read it.


http://www.the370z.com/intake-exhaus...rks-great.html

Bottom line, this issue is driving me MAD!

Straighter the pipe the more rasp.
Also, it will depend on where your resonators, mufflers, and cats/hfc/TP are. Depending on where each is located and the distance & size will adjust if you have or increase rasp.

I think it's definitely coming from you CBE. A friend of mine has the Agency Power CBE paired with the Berk HFCs and has ZERO rasp. It is a very deep tone.

I put my cats back on today, sound is BEAUTIFUL! Looks like I have some Berk test pipes for sale...I don't think im going back until the turbo kit.

i know what you mean...i have HFC's and sometimes contemplate putting the stock cats back on. i hate the rasp