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Old 14th March 2012, 12:50 PM   #1 (permalink)
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Turbo(?) noise on full boost with Y pipe

I've just had a GTC resonated y pipe fitted to a stock MY11 GTR and plan to drive round with it for a few weeks to make sure I like it before getting a stage 1 remap.

The major difference I've noticed that when full boost is reached there's a raspy sort of turbo noise that can be heard with the windows up. I'm not sure if it's some sort of waste valve, but it doesn't sounds like a exhaust note.

Could the standard map be dumping more excess boost pressure now that the turbos are breathing more easily. Has anyone noticed a noise like that? Would it disappear with a map that allowed higher boost?

I didn't noticed the sound when I was taken for a drive in a stage 2 car at Litchfields.

I'm looking for improved exhaust sound quality when driving rather than more power. At the moment, on balance I think I'll be going back to the stock Y pipe due to the greater sense of refinement and lack of drone around 75 mph.
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Old 14th March 2012, 12:58 PM   #2 (permalink)
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I'd check it was not hitting the aluminum cross brace. Mine did when i first fitted and it gives a rasping sound

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Originally Posted by computergeek View Post
I've just had a GTC resonated y pipe fitted to a stock MY11 GTR and plan to drive round with it for a few weeks to make sure I like it before getting a stage 1 remap.

The major difference I've noticed that when full boost is reached there's a raspy sort of turbo noise that can be heard with the windows up. I'm not sure if it's some sort of waste valve, but it doesn't sounds like a exhaust note.

Could the standard map be dumping more excess boost pressure now that the turbos are breathing more easily. Has anyone noticed a noise like that? Would it disappear with a map that allowed higher boost?

I didn't noticed the sound when I was taken for a drive in a stage 2 car at Litchfields.



I'm looking for improved exhaust sound quality when driving rather than more power. At the moment, on balance I think I'll be going back to the stock Y pipe due to the greater sense of refinement and lack of drone around 75 mph.
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Old 14th March 2012, 12:58 PM   #3 (permalink)
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I run a Miltek resonated y-pipe and don't hear the noise you described. I can hear the turbos winning from in the cabin, I wouldn't call it a raspy sound.

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Old 14th March 2012, 01:05 PM   #4 (permalink)
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I run a Miltek resonated y-pipe and don't hear the noise you described. I can hear the turbos winning from in the cabin, I wouldn't call it a raspy sound.

Anders
Anders,

It's not the jet turbine like sound that you hear when you open the throttle in sixth on the motorway. That's a great sound.

It's more like the sound I've heard temporarily in turbo diesel and petrol cars when you lift off the accelerator pedal after accelerating. Except, it keeps going as long as the car is on full boost.
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Old 14th March 2012, 01:27 PM   #5 (permalink)
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I'd check it was not hitting the aluminum cross brace. Mine did when i first fitted and it gives a rasping sound
There's tons of space around the cross brace and there's no hint of the sound on anything less than full boost.

The guys at Dragon who fitted it think I'm now hearing the waste gate noise that would have been muffled by the stock y pipe.

I'm probably just over fussy about mechanical sounds, but to my ear at the moment the y pipe is not an overall improvement in sound quality from the drivers seat.

I'll give it a few more days before deciding though.
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Old 14th March 2012, 01:28 PM   #6 (permalink)
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Here's a picture of the cross brace:

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Old 14th March 2012, 01:35 PM   #7 (permalink)
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Check from the other side it's on the left it hits
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Old 14th March 2012, 01:49 PM   #8 (permalink)
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Check from the other side it's on the left it hits
Thanks for the tip

It looks fine on the cross brace from the left too, but I really need to get the car on a lift to check:

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Old 14th March 2012, 03:58 PM   #9 (permalink)
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Just driven it again. A better description rather than raspy would be a a high pitched shrill that becomes quite dominant on top of the normal engine/exhaust noise at full boost. It sounds like it is coming from under the bonnet.
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Old 14th March 2012, 04:28 PM   #10 (permalink)
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Try driving at 6500rpm with no boost ie 3rd gear on the motorway without accelerating and see if you still hear it, if you're generating no boost at 6500 the wastegate will be fully open.

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Old 14th March 2012, 04:34 PM   #11 (permalink)
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Try driving at 6500rpm with no boost ie 3rd gear on the motorway without accelerating and see if you still hear it, if you're generating no boost at 6500 the wastegate will be fully open.

Anders
Yes, I'll try that.

The noise didn't seem to be RPM dependent and only appeared when the Boost guage reached it's maximum setting (15psi I think).
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Old 14th March 2012, 05:50 PM   #12 (permalink)
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Not that cross brace there is one further bacl where the Y turns into I. Thats where it can hit. I do hope thats all it is as simple to fix


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Thanks for the tip

It looks fine on the cross brace from the left too, but I really need to get the car on a lift to check:

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Old 14th March 2012, 06:31 PM   #13 (permalink)
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Not that cross brace there is one further bacl where the Y turns into I. Thats where it can hit. I do hope thats all it is as simple to fix
Unfortunately, it doesn't look like that either:

View from left:


and from right:



I'll see if I can get it on a lift tomorrow and have a proper look
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Old 14th March 2012, 06:52 PM   #14 (permalink)
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suggest go back to your local GT-R shop Ross Dragon to inspect

if your on a stock map you won't be seeing 15psi
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Old 14th March 2012, 08:53 PM   #15 (permalink)
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suggest go back to your local GT-R shop Ross Dragon to inspect

if your on a stock map you won't be seeing 15psi
My boost gauge definitely shows 15 psi peak on a stock map MY11. That's about 1 bar. Isn't that the standard boost pressure?

I've driven it some more tonight with the window down. It doesn't seem like a vibration type noise. It really just sounds like louder turbo noise. Not a smooth whine but more like the sort of thing from a waste gate. Would the y pipe make the turbos louder than before?

I never really looked at the peak boost in the past. Presumably, the y pipe shouldn't make any difference as the ECU would adjust it anyway.

Anders - tried driving at 6500 rpm without accelerating and the noise is not there. Only when the boost pressure comes up.
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Old 14th March 2012, 10:34 PM   #16 (permalink)
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My car hits about 15 psi, that's normal.

I recon next step would be to swap the oem y-pipe back on, you'll need to do this before taking it in to the HPC anyway. If the sound goes, may be there's a fault in the resonated exhaust section?

If the sounds still there after oem y-pipe is back on, small chance one of the turbos has gone.

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Old 14th March 2012, 11:06 PM   #17 (permalink)
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Originally Posted by Anders_R35 View Post
My car hits about 15 psi, that's normal.

I recon next step would be to swap the oem y-pipe back on, you'll need to do this before taking it in to the HPC anyway. If the sound goes, may be there's a fault in the resonated exhaust section?

If the sounds still there after oem y-pipe is back on, small chance one of the turbos has gone.

Anders
Thanks for confirming the 15 psi.

I agree putting the oem y-pipe back on would be a sensible next step to see if the sound goes away.
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Old 15th March 2012, 05:08 PM   #18 (permalink)
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Had it checked out by Dragon and nothing was wrong with the y pipe or fitting. It was the turbo waste gate that I could hear.

I've got the stock y pipe back on and I'm loving it. I didn't realise how much I like the original sound. The GTC y pipe had a lower pitched roar with the higher frequency turbo noise over the top.

The stock y pipe doesn't have really have any low pitched sound when pushed - it's just a smooth jet engine type noise at full throttle. The waste gate noise may stil be there but if so it's masked by other whooshing noises instead.

I guess it's just a matter of taste. However, I must admit the GTC y pipe did sound amazing to anyone outside the car. Even my wife remarked at how good it sounded when I pulled away.

The downside is that that I won't be getting any power mods unless I find something that's close to the stock sound or better.

Sorry Kazutoshi Mizuno - I'll never question your judgment again!
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Old 15th March 2012, 06:11 PM   #19 (permalink)
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Glad to hear that's sorted. Dragon is good guy

When removing cats you won't find a y-pipe which sounds as quiet as the oem, unless you also change the rear cat back for an exhaust with very large packed mufflers. Many people really like the oem sound

sorry your correct about 14-15psi, i didn't know you have a MY11
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Old 15th March 2012, 06:26 PM   #20 (permalink)
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Glad to hear that's sorted. Dragon is good guy

When removing cats you won't find a y-pipe which sounds as quiet as the oem, unless you also change the rear cat back for an exhaust with very large packed mufflers. Many people really like the oem sound

sorry your correct about 14-15psi, i didn't know you have a MY11
Yes, the guys at Dragon are great and very knowledgeable about GTRs.

I don't think the sound level was the problem for me. I think the stock y pipe generates a whooshing sound as the exhaust gases go through the secondary cats. The GTC pipe lacked that sound making the turbo sound more prominent.

Are there any tuning options that allow the stock y pipe to stay in place? Or is it too restrictive?
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