I think you'd have more luck fixing this by having a muffler shop put the stock transmission bracket back on. The pieces to weld onto your test pipes are still on your stock cats. I'm going to try this too once I get a chance to take my car over to a muffler shop. I really believe this bracket will either fix the problem or help it a lot.

If you have this done, please report your results. I'll do the same.

 

yes please report i am very curious also i get a bbq smell fom my exhaust now i know its because i have no cats but do i have anythig to worry about like runnig dangerously lean ro anything like that thaknk you!

 

your engine definitely runs leaner w/ test pipes...but only a wideband o2 will tell you by how much. Removing cats always makes your car stink when it's running...I wouldn't spend too much time inhaling that crap.

 

its it harmful to run lean? eventual;y i will be getting the ecu tuned and possible if this sound doesnt go away opting forhi flows or a different brand of resonated pipes

 

it's harmful to run lean to a point where the engine begins detonating. You could check out your a/f ratio on a wideband to be sure you're running safely.

If the rattle annoys you so much why don't you try getting the stock bracket welded on?

 

well im ditching my old test pipes with reson for some kinetixs whihc supposely retain stock brace well see how it works

i dont have a widebacnd sensro are there any sotrys of a NA z running dangerously lean

 

that's cool. Let us know if those have the same problems after you got them installed!

You can get a wideband run done on a dyno if you want. Every Z will run at a different a/f ratio given mods, fuel quality, temperatures, etc.... Too many factors to take into account.

 

This thread has lasted a while but we still haven't found a solution for the strange noises. I personally experience more of the hiss than the rattle (but I also hear a rattle sometimes-for example: when I cut the ignition.)



Some test pipes retain the brackets so that might solve the rattling sound but probably doesn't have much to do with the hissing/snake/blow-off valve type noises.

I was just wondering: are the high-flow cat people experiencing the same (or similar) hissing noises with their 350zs?


Thanks.

 

I would agree that my decel noise is more of a hiss than a rattle. I was calling it a rattle since other people were, but I believe we're hearing the same sound.

The rattle you hear when u cut the ignition is more likely the vibration of the driveshaft (it is on my z anyway).

 

yeah ont he decel i get a hiss and then a when acceleratining aroudn 2.5 3 k i get a rattle inside supposivly the hiss is common even with HFC's

i should have the pipes (kinetixs) on in a week or so ill definetly keep ou updated

thanks for all the replys

 

thanks buddy...we look forward to your update

 

i like the whisp on accell... sounds like a turbo spoolin' .... the rattling snake thing is annoying... but you can learn to play the throttle to get it to stop

 

I had the same noise!!! Just got my Z last month and just Installed a Top Speed Exhaust with Test Pipes. And I drove it when it decelerated it vibrated. We discovered the pipes without the bracket cause a pipe to rattle against a peice of the car. Instead of welding the bracket on, just did a little west coast customs ******** and welded something to the pipe to keep it up high enough to cause it to not rattle. Now I just have a freakin loud exhaust!

-David

 

hm. Your problem might be a different one than ours. Are you sure that the rattling was caused by your exhaust hitting the body? Perhaps it was just the lack of a bracket to dampen the vibrations? I'm not doubting you; just trying to gather more helpful information. My system is definitely not hitting any part of the body.

I'm starting to believe the "rattle snake" hiss on decel is just more rasp as the exhaust gas pushes through the test pipes. If this is true, welding resonators in place should cure this.

 

not the body but a part of the undercarriage of the car. If you threw your car on a lift you'd see what I'm talking about. And if you have after market test pipes then yes it definately hits this peice without the stock bracket. The stock bracket can be tapped into the pipes or you can do a custom weld to hold it up from hitting that peice

 

I've been under my car literally hundreds of times. No part of my exhaust system hits anything at all. I had it on the lift a few times as well to look over with a muffler shop...nothing comes close to hitting anything. I'd be curious to find out which part was hitting on your car... The usual suspect is the black "M" shaped boomerang connected to the underside in front of our LSD. Mine used to hit this, but it caused rattling/clanging noises and not the imfamous test pipe hiss on deceleration

 

I have the infamous "hissing" sound on my G35 coupe as well. I recently put on RT cats with my Borla exhaust. I never heard this hissing sound before I had the RT cats (and just the borla alone). The previous owner who I bought my Borla exhaust from had helix test pipes and the infiniti tech (who installed the cats) was familiar with the hissing noise. He told me it was air resonance due to the higher flowing cat and that you'd just have to live with it or put in more resonators on your exhaust.

I can live with the hissing noise so long as I know it's not an exhaust leak.

 

thanks for the information buddy. I believe another set of resonators inline might do the trick as well...

 

I have a Borla true dual exhaust and the Megan Racing resonated test pipes. There is no rasp! I immediately noticed a whisp sound after installing them. I rev up to 3k rpms and let off. When it gets to like 2300 rpms I hear it. I also hear it above 3k rpms under heavy acceleration and full load. I have welded in the eyelets and installed the stock bracket. It didn't help. I ended up disconnecting my exhaust and still heard it. It's something inside the resonators that are rattling around making that noise. Maybe the screening material? Megan Racing sent me another set, free of charge, but I haven't put them on yet. This set is probably going to do the same thing. Save yourselves alot of time and ditch the idea of welding pieces on to fit the stock bracket. It just doesn't work. I've already did it and it had no effect whatsoever. If you're going to do anything, disconnect the exhaust from the test pipes. I assure you'll still hear it.

 

thx for the info. Please let us know how those new megan pipes work for you. Mine are straight through helixes so there's nothing to rattle inside. I think the sounds are just air flow resonating the thin test pipe walls. Adding resonators will likely cure both the rasp and the hiss I have. I'm just afraid my car will become super muffled (i have a borla exhaust)