Wilbert350 Posted May 24, 2018 Share Posted May 24, 2018 (edited) Hi all, I recently fitted resonated decats, and the state my OEM Y pipe was in, I'm surprised it didn't start blowing sooner! Anyway it started hissing LOUDLY from a flexi and the car felt pretty sluggish. My solution was to get a Stillen Y Pipe - fitted it (along with new gaskets and some silicon hi-temp gasket juice) and now, well it sounds a hell of a lot better! That VQ engine sounds much more like it should. However from around 1500rpm to 2200 as you get going, there's still a faint hiss. It's only audible from the rear of the car - actually from the exhaust tips as demonstrated when I had a mate rev it and we checked for the source. If you check some of the other forums, there's loads of posts about how HFC's will cause a 'notorious' VQ hiss, which only some systems solve. I'm wondering if maybe resonated decats behave in the same way? I have a fairly young scorpion back box which is in great condition, so struggle to believe it's ruptured, especially as the faint hissing seems to be coming from the tips. As you can imagine, with just over £1k worth of exhaust parts now, it's pretty frustrating to hear cheap noises like that. Additionally; the decats don't have brackets to fix the OEM cat bracket, and the Stillen is, of course, a solid unit with no flexis. Anyone got anything? Cheers, Wilbert Edited May 24, 2018 by Wilbert350 Quote Link to comment Share on other sites More sharing options...
Ekona Posted May 24, 2018 Share Posted May 24, 2018 Hang on, first you say you fitted decats then you mention HFCs then it's back to decats again: What have you actually got on right now? Quote Link to comment Share on other sites More sharing options...
Wilbert350 Posted May 24, 2018 Author Share Posted May 24, 2018 1 minute ago, Ekona said: Hang on, first you say you fitted decats then you mention HFCs then it's back to decats again: What have you actually got on right now? Apologies, edited for clarification. Not sure if maybe the resonated decats behave similarly? I have resonated decats. Quote Link to comment Share on other sites More sharing options...
Ekona Posted May 24, 2018 Share Posted May 24, 2018 Go back to OEM cats and see if the noise is still there. That way you'll know if it's the decats or the backbox. Quote Link to comment Share on other sites More sharing options...
Wilbert350 Posted May 24, 2018 Author Share Posted May 24, 2018 Is there any other leak test? I don't mean to seem dismissive but it seems like a laborious way to test it especially as I have just spent the last two weekends doing all of the various fitting jobs to get it sounding better... Quote Link to comment Share on other sites More sharing options...
Ekona Posted May 24, 2018 Share Posted May 24, 2018 Get under there whilst the exhaust is nice and toasty, then get a mate to rev the engine whilst physically looking for leaks is the only other way. With no flexis in the system I reckon you've got a joint or two not sealking properly as there's no give, and tbh with no flexis on there that's going to crack at the weakest joint in a matter of weeks. Quote Link to comment Share on other sites More sharing options...
Wilbert350 Posted May 24, 2018 Author Share Posted May 24, 2018 Okay I'll have a go doing that. They're fresh gaskets too. I have bought the Stillen at the recommendation of Chris & Bob at Tarmacsportz, they say that they sell far more Stillen than anything like Cobra or Scorpion Y-Pipes, and never receive complaints about them cracking or breaking. Surely that's not a common issue? Quote Link to comment Share on other sites More sharing options...
Ekona Posted May 24, 2018 Share Posted May 24, 2018 Might not crack there, could well go somewhere else. With no flexi joint in the system there's nothing to take up the slack, so could crack anywhere from nice and easy at the backbox joint to PITA at the manifold. That's the reason why every OEM setup (and 95% of aftermarket ones) have flexi joints in them. Quote Link to comment Share on other sites More sharing options...
Wilbert350 Posted May 24, 2018 Author Share Posted May 24, 2018 Is there a precaution all these people buying Stillen have taken that I need to then? Seems surprising so many are sold if it's such a concern, especially as hardly any decats or HFC's feature brackets to use the OEM bracket. Quote Link to comment Share on other sites More sharing options...
Ekona Posted May 25, 2018 Share Posted May 25, 2018 No idea tbh. It’s more common sense than anything else: I’m no aware of any specific Stillen or 350Z issues, but with no ability to soak up lateral movement then where else is the shock supposed to go other than the weakest point? But one step at a time, get the leak fixed first. Quote Link to comment Share on other sites More sharing options...
Ekona Posted May 25, 2018 Share Posted May 25, 2018 If indeed it is a leak, might just be a random noise that your particular setup is making. Quote Link to comment Share on other sites More sharing options...
Wilbert350 Posted May 25, 2018 Author Share Posted May 25, 2018 Thanks Ekona, yeah, that would be a shame but I suppose would make me feel better. Like I said My350Z.com and a few other have loads of posts about hissing HFC's, and a few of decats... I'd be puzzled if it was also just the system because each pipe thickness is 2.5" matched - although it goes from resonated decat to straight through Y Pipe, back to resonated Scorpion... We shall see. Quote Link to comment Share on other sites More sharing options...
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