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Chatter sound from turbos near 3k rpm?
I'm getting a strange chatter / vibration sound that seams to be coming from the turbos. The sound is similar to a thick piece of paper hitting a fan blade. It lasts about 2 seconds when it happens, it's loud, and occurs about 50% of the time in 1st or 2nd gear between 2500 and 3000 rpms. I have also reproduced it while parked in neutral and revving, but it's not consistent. I've only had the car a few months, but it's made this sound the entire time.
The car has 99 spec sequential twins, highflow cat / air-pump, full supporting mods for ~330whp twins setup (ignition, fuel, cooling, etc), PFC. The car is running fine otherwise, although I am getting a boost drop off around 6500 rpms that I haven't been able to solve (~14psi down to 10psi from 6500 to 7500 rpms). It may be related, but who knows. Has anyone had this problem or have any ideas what it could be? Thanks! |
This?
♫Fluttering Wastegates♫...muttering monster. |
First thing I would do is pull off the compressor inlet pipes and feel how much shaft play the turbos have. If play is excessive, the compressor wheels could be contacting the housings. The biggest reason why the 93-95 and 99 turbos fail is running higher than stock boost. They have outdated 270 degree thrust bearings and small shafts which cannot withstand the loads of elevated boost for long. If the turbos feel tight I would start looking for a leaking charge relief valve or other hose in the vicinity. Does the car boost fine otherwise?
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Originally Posted by IRPerformance
(Post 12189351)
First thing I would do is pull off the compressor inlet pipes and feel how much shaft play the turbos have. If play is excessive, the compressor wheels could be contacting the housings. The biggest reason why the 93-95 and 99 turbos fail is running higher than stock boost. They have outdated 270 degree thrust bearings and small shafts which cannot withstand the loads of elevated boost for long. If the turbos feel tight I would start looking for a leaking charge relief valve or other hose in the vicinity. Does the car boost fine otherwise?
The turbos seem to build boost fine, transition fine, and and not make any noises other that what i described. No oil leaks either. But, there's a significant drop off of boost after 6.5 k rpms. It drops from 13-14lbs down to 10 almost instantly. |
You should be able to hold 13-14lbs past 6500. Could be something leaking or in the boost control setup/tune.
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Originally Posted by IRPerformance
(Post 12189420)
You should be able to hold 13-14lbs past 6500. Could be something leaking or in the boost control setup/tune.
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I can't help but wonder if it's not airpump related. Try unplugging the electrical connector to the airpump that engages the clutch and see if the sound is still there?
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Originally Posted by ArmitageGVR4
(Post 12189715)
I can't help but wonder if it's not airpump related. Try unplugging the electrical connector to the airpump that engages the clutch and see if the sound is still there?
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I took a look at the turbos more closely; I don't like what I'm seeing, but I'm also not sure what's normal with these suckers. My last 3 FDs had single turbos. Please let me know what you think.
Primary turbo: -- No Oil -- No in/out shaft play -- Some side-to-side shaft play. Not sure what's normal, but the blades touch the housing when pressed. There's some marking on the tips of the blades, but no chips. There's some marks on the inner housing surface as well. Secondary turbo: -- Oil on the compressor housing, doesn't appear to be coming from the inlet or drain pipe. Appears to be coming from the back of the housing where it mates to the body. -- No in/out shaft play -- Some side-to-side shaft play, same concerns as primary. Primary turbo Pics (note marks on blade and inner housing surface marks) - https://cimg0.ibsrv.net/gimg/www.rx7...378dbdff72.jpg Secondary turbo pics (note the oil leak, possible blade wear, and inner housing markings) - https://cimg2.ibsrv.net/gimg/www.rx7...5f938f060f.jpghttps://cimg3.ibsrv.net/gimg/www.rx7...7a36a74dd6.jpghttps://cimg5.ibsrv.net/gimg/www.rx7...0412b1976b.jpg |
Some side to side shaft play is normal but the wheel should not come in contact with the housing.
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Agree with Mike, compressor wheel should not be contacting housing, which might be the sound you are hearing. I'd stop driving the car to see if the turbos can be salvaged with a rebuild. Hopefully the clearance/wear isn't too far off nominal.
Originally Posted by silverTRD
(Post 12190562)
Some side to side shaft play is normal but the wheel should not come in contact with the housing.
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Thanks guys... I agree, they are shot. I started pulling them tonight, got through the DP, and now letting the turbo nuts soak in pb blaster overnight. I'll get them off tomorrow and inspect them more closely.
... Going with a set of BNRs. |
Pulled the turbos and again confirmed the excessive shaft play (both turbos hit the housing liner). I don't know the history of the car, but it's high boost setting was 1 bar. I suspect that has something to do with it.
The good news is that the hotside looks great, so they should make a great set of bnrs. https://cimg9.ibsrv.net/gimg/www.rx7...4707fc3fce.jpg https://cimg2.ibsrv.net/gimg/www.rx7...6ce7c2eaff.jpg Also noticed that someone used some orange RTV to mate the comp housing on the primary turbo. Seems like a pretty stupid idea to me - a small it of RTV hitting a turbine at 100k + rpm would not go well... https://cimg4.ibsrv.net/gimg/www.rx7...f84ee56db5.jpg |
Quick update -
Got the bnrs in this weekend and there's no more chattering sound. So, I'm guessing that the chatter I saw on the comp housings was to blame. |
Sorry I saw this late but the compressor wheel scraping the side of the abradable coated compressor housing is a GOOD THING. Matter of fact it is the entire point behind the N3G1 "99" turbos and why they spool faster. The newer they are the more they bind up, when brand new you can hardly turn them.
Also 1 Bar is stock boost pressure for N3G1's. Not saying these turbos were not bad for another reason but the conventional wisdom posted above does not in any way apply to these turbos. |
Originally Posted by laujesse
(Post 12208013)
Sorry I saw this late but the compressor wheel scraping the side of the abradable coated compressor housing is a GOOD THING. Matter of fact it is the entire point behind the N3G1 "99" turbos and why they spool faster. The newer they are the more they bind up, when brand new you can hardly turn them.
Also 1 Bar is stock boost pressure for N3G1's. Not saying these turbos were not bad for another reason but the conventional wisdom posted above does not in any way apply to these turbos. Regardless how they feel new, the blades shouldn't touch anything while spinning. The lining may reduce the clearance and improve efficiency, but I doubt that its meant to make any contract with the blades. Also, it's my understanding that these turbos are built for 11-12 psi at most. Sustained 1 bar of boost on 99 twins will likely burn them out, specifically the bearings. Given the shaft play and oil leakage from the compressor, I suspect that's exactly what happened. |
Those turbos have definitely been opened by someone, there are white alignment marks on the turbine housings, some yellow paint on the primary, and that mystery orange RTV.
The 99s do have nylon abradeable seals around the compressor wheels, they are designed to be slightly oversized and the spinning compressor wheel rubs into the nylon, making for a near-perfect fit and improving efficiency. The aluminum compressor wheel will easily eat into the nylon. That said, I don't think it touching slightly or anything is necessarily the root of the problem, it's the fact that someone in the past has pulled these turbos apart and didn't reassemble them properly. Could also be some loose orange RTV in there making the noise. Most likely those turbos could be saved, it would be worth sending them to Bryan at BNR to go through them and clean/assemble/test them. Could be a good set of turbos for someone. Dale |
Thanks for chiming in. I'll concede that they are designed to rub, but it just to defies common sense to me. Having anything touch a compressor blade at 100k + rpms and sending nylon shavings into the intake track just seems nuts to me. That being said, there was a few mm of clearance on this set, and the shaft play was enough to touch the walls easily. Also, the marks were not symmetric. Between the play, the oil, the noise, the lack of boost above 7k, and the rtv, these suckers were shot. In the end, I can only conclude that the sound was exactly what it sounded like; the compressor blades hitting. I used the turbos as a core for my bnrs since the hotside components were in perfect shape. |
A few pics of the bnrs (hard lines got bent shipping, but they straightened out no prob) -
https://cimg3.ibsrv.net/gimg/www.rx7...274507892c.jpg https://cimg4.ibsrv.net/gimg/www.rx7...d0525903a8.jpg https://cimg7.ibsrv.net/gimg/www.rx7...60b33b7d5b.jpg https://cimg9.ibsrv.net/gimg/www.rx7...9847da7d0b.jpg |
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Originally Posted by moehler
(Post 12208023)
Thanks for the input, but I find both of these statements hard to believe.
Regardless how they feel new, the blades shouldn't touch anything while spinning. The lining may reduce the clearance and improve efficiency, but I doubt that its meant to make any contract with the blades. Also, it's my understanding that these turbos are built for 11-12 psi at most. Sustained 1 bar of boost on 99 twins will likely burn them out, specifically the bearings. Given the shaft play and oil leakage from the compressor, I suspect that's exactly what happened. It is a statement of fact not a debatable opinion. To qualify that statement I have sold over 100 of these N3G1 turbos on this forum over the years, several of them new, and personally ran them in 4 separate FD's since 2004. Like Dale said your specific primary turbo looks very questionable for several reasons none of which are the rubbing. |
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