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Stock GSX turbo screech over 16 PSI

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raptoranderson

Proven Member
195
21
Sep 24, 2015
Graham, North_Carolina
Just installed a GFB G-Force II electronic boost controller and an Innovate LC-2 wideband O2 sensor. Whilst driving around I decided I would do some tuning with the electronic boost controller to see how it all worked and to see if it actually made a difference (P.S. it does!)

I got up to around 16 PSI and tuned it back down to 14.5 PSI just to be safe until I actually map the car and see how the engine is running with additional boost. But whilst tuning and under high boost (plus 16 or so PSI) the turbo began to screech. Loudly. Or at least something began to screech. It wasn't a whistling noise like a boost like or a sucking noise like a vacuum leak, it was a screeching/ shrieking noise. My initial thought was that it was the turbo overboosting and so I immediately reduced the boost controller duty cycle and didn't dare push it any further.

I'm very hesistant to crank up the boost and repeat the noise for you all to hear, but surely I can't be the only one who has come across this phenomenon. It's a stock '98 GSX with a stock T25 turbo.
 
Check turbo for shaft play and do a boost leak test. Also if you can post a video of the sound it could help. T25's don't like being turned up much. I had mine at 18psi and it didn't last long haha. But also had around 180-200k miles on it haha.
 
Thanks for the quick responses! :D

I replaced the stock bov with a recirculated Greddy Type S BOV because I know for a fact that my stock bov leaked over 3 PSI -.- I'll inspect the turbo and see if there's any shaft play, but a boost leak wouldn't be overly surprising ..... I drove the car for another 10 or so miles after the noise occurred and it boosted and drove just fine. I'll see if I can replicate the sound and I'll post it here. It's definitely a brain teaser .... :hmm:

Turbo only has 78,500 miles on it btw. So does the whole car ROFL
 
I just took the car out for another drive to tune the boost controller a little more and the noise came back under high boost. I went under the engine bay and checked all of the connections and it turns out the noise was the boost control solenoid bleeding air which was hitting the overflow bottle and causing the screeching/ whistling noise ROFL

I'll confirm my findings over the next few days on my daily commute just to be sure, but I'm confident that was the source of the noise!
 
I bought a bone-stock 97 GSX with 68K original miles a while ago and when I pulled the oil pan to do a balance shaft elimination there were pieces of a T25 thrust plate in the oil pan. So lack of use apparently doesn't defeat the fact that the T25 is a terrible turbocharger on DSM's.

Pull the intake and check for in/out shaft movement if the noise persists....if there is shaft movement, replace or upgrade the turbo.
 
So lack of use apparently doesn't defeat the fact that the T25 is a terrible turbocharger on DSM's.

Just since I managed to lure you here and you mentioned not liking the T25, do you have any preference or priority over using a 20G as opposed to an FP68HTA or an FP Green, or vice versa? :hmm:
 
Just since I managed to lure you here and you mentioned not liking the T25, do you have any preference or priority over using a 20G as opposed to an FP68HTA or an FP Green, or vice versa? :hmm:
For a correct response...
What are your goals, what are you trying to do with the car? Autox, street, strip, power goals, etc...
Providing a little more info will help our turbo guru steer you in the right direction. :thumb:
 
It's going to be a daily driver of sorts, maybe go to a couple track days. I'm looking to 400hp out of the car and have it be something that has good response and power throughout the whole rev range, ideally running up to but not over 25 PSI.

It's definitely not going to be doing any autocross or drag racing events ROFL but something that's fun to drive and fast. Because the T25 maxes out wayyy too quickly, in my car it starts hitting boost taper around 4250 rpm in 4th and 5th :toobad:
 
do you have any preference or priority over using a 20G as opposed to an FP68HTA or an FP Green, or vice versa? :hmm:
They're all MHI-based turbos, although the FP models are 100% aftermarket at this point- think of the 68HTA like a billet 18G and the Green like a billet 20G because that's almost exactly what the compressor specs are. So whatever you think would fit your requirement for spool, airflow, fitment, etc....don't be lured by the "this guy made 500whp with a 68HTA" threads that people will link you- it's by no means a 500whp turbo. The people who make 500whp with a 68HTA would make 465whp with an Evo III 16G because their car has a fully-built engine, aluminum driveshaft, 8lb flywheel, lightweight brakes, etc...so their results are irrelevant.
 
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