As we all know the installation of HFC of any brand is likely to cause some rasp. I have read two different explanations on this site on why exactly this is happening.

1. Since HFCs have a larger outlet diameter than stock and are mated to the small diameter of the Y pipe inlets. This difference in diameter is causing the rasp/hiss/ping like sound.

2. The stock cats, like all stock cats are actually as muffler aswell. They muffle certain nasty raspy noises which are a by product of ALL combustion engines. Replacement of these with free flowing cats also removes the sound muffling which then causes the noise.

Personally I'm not sold on explanation 1. I have a 350Z HR Y pipe installed, the inlets are appx. 2.5inch which matches the Kinetix HFC outlet size. There is no size difference yet I'm still getting this noise. It should be noted I'm running stock coupe midpipe and stock muffler. Others have reported the same issue so this is not an anamoly. Another reason why I dont buy explanation 1 is that the noise only occurs when a lot of air is flowing through the exhaust. If 1 was the reason than wouldn't it rasp all the time?

Now I have seen other threads where people have cut out the coupe mid pipe pre muffler and replaced this with a glass pack resonator and it solves 90% of the rasp problem. My question is what If I leave the stock pre muffler in and also install a resonator along that midpipe, do you think this will silence the car too much or it will solve the rasp?

I like a lot of people are not excited about paying $$$ money for after market exhaust when our cars sound very nice from the factory. All I want is the same note and gurgle but is louder in high revs and deeper in low revs. So far I'm really close but this rasp is ruining it! Im going to exhaust shop tomorrow and installing a resonator somewhere along that midpipe but havent decieded if I want to remove that pre muffler, my gut is telling me not too.

 

i don't know alot about exhaust but you may recall i invented the infamous r-art pipes, anyway i have put resonators on ypipes and midpipes and they do wonder for rasp, check my thread for the ypipe resonator work, i did all the work myself... some pictures too if i recall... gl

 

here ya go... i did a lot of work to remove rasp from my g35 last year...

 

i will have to snap a pic of the midpipe with 200 cell count cat on it as i don't have a pic of it on my desktop here right now... but the ypipe above actually has 200 ct cat on it as well which did wonder for hfc-catypipe-350zsingleexhaust rasp reduction... i used the midpipe with cat for the oem g35 coupe exhaust with rart pipes and that did wonder as well for rasp... gl

 

Thanks for the suggestion and the pictures. Nothing beats being able to actually see what your talking about. I'm hesitant to place another cat in the system even thought that is only a 200CT so it should flow freely. I figured a resonator would work without restricting the exhaust flow. I do love the idea of welding some mounting points on the Kinetix HFCs to stop some vibration.

Other suggestions are welcome and I will report back to the forum with my results.

 

well you can run test pipes as long as you put a cat in ypipe or midpipe - which i did for a while but when i thought about selling the car i went back to stock exhaust...
anyway i have ran test pipes and hfc with and without mounting points... very little difference

hope that helps

 

My expirement did not yeild the results I was looking for. While some rasp was eliminated, 30%-50% of it is still there. At the same time this resonator quieted the car too much for my tastes. At idle the car is VERY quiet. At 70MPH freeway it is so quite you almost dont hear the exhaust at all. The resonator seemed to enhance deeper sounding notes while cancelling out the higher pitched ones for me. At the same time I seem to have lost some of that signature G/350Z sound. I'm not mad or anything this is a part of expirementation and thinking outside the box. Overall the rasp is still there but now it occurs at like 70%-80% throttle, before it started at like 50%. Back to the drawing board.

 

Your problem is your Y-pipe. The outlets for the HFC's are actually larger than the inlet of the Y-pipe. But if you get a larger diameter Y-pipe, you will also have to get a larger diameter muffler because you will have the same problem there now as well.

 

you could try a 2.5 inlet and outlet Y pipe. Only one I have seen is made by Exhaust Depot

 

Ah, I didn't know someone made one of those. Yeah, that should work also.

 

Any updates on this? Im actually in the same boat as you... What resonator did you get that did not work?

i could be wrong, but i think the stock mid muffler on the mid pipe has to be upgraded as well. i was going to do 1 glass pack 22'' resonator and replace the mid muffler with a flowmaster one.

 

I used a bottle type vibrant resonator, placed just after the mid muffler.

 

I have the same problem as you. My setup is oem exhaust manifolds, hr y pipe, kinetix hfc, coupe mid pipe, oem 05-06 muffler. I get that rattle\rasp when accelerating hard. I ordered a 2.5 to 3" y pipe to replace my HR y pipe. Want to see if the Y pipe is causing the problem.

 

Y pipe changed, rasp is still there. I have noticed, the rasp does not happen when i rev the engine in neutral. only happens under load. I believe the rasp is exhaust pulsing thru the system. The stock brick cats stop damper the pulsing. Under load the engine changes cam and ignition timing, one of these contributes to the rasp.

Only solution i see is too install a resonator.

FYI HR Y pipe inlets ARE NOT 2.5". They are 2.25. HFC outlets are not 2.5", they are 2.25.

 

XYZ pipe works a treat for this, the MD resonator module sorts out the problems.