Problem holding boost at 20psi - MY350Z.COM Forums



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Old 07-18-2016, 09:55 AM   #1
2one8
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Default Problem holding boost at 20psi

VQ35DE
8.8 Wisco pistons
Eagle rods
ACL bearings
ARP L19 studs
Cometic head gasket
JW valve springs, otherwise factory heads
MD plenum spacer
Powerlabs single turbo kit (first version)
Garrett GT3582R turbo, new CHRA
Tial MV-R 44mm WG, 17lb spring combo brand new springs
HKS EVC-S controller
Uprev GT MAF
equal length headers, 3" turbo back, Tomei Expreme Ti
Tuned on Uprev

484hp/475ft lbs on 93 octane
515hp/505ft lbs on 110/93 mix

I am at 20psi by 3700 RPM, but around 4700 it will steadily drop to 16-17psi. We have leak tested to 22psi and everything held, no leaks and no lift. WG diaphragm is good, no exhaust leaks. Originally tuned on manual controller and when the boost would drop it would get very choppy and fluctuate, so we went with the HKS controller. This smoothed it out, but it will still drop. Because of this drop we get fight detonation at high RPM.

My questions are these:

I'm told the GT3582R should be big enough to achieve 600hp on this motor. I'm currently ~500rwhp, could the turbo be getting maxed already? I'm seeing conflicting information on this turbo and the capabilities. If so I'm looking to change to Precision 6266. I've tried to do all the calculations on what I need for a turbo but that ish goes right over my head, or I'm just thinking too hard about it.

The WG is right off the passenger side header, would moving it downstream closer to the turbo help? Possibly need a new WG? The diaphragm looks good.
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Old 07-18-2016, 11:13 AM   #2
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dang it, didn't realize I clicked the 370 forum... mods please move to 350 turbo tech
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Old 07-18-2016, 01:20 PM   #3
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Quote:
Originally Posted by 2one8 View Post
This smoothed it out, but it will still drop. Because of this drop we get fight detonation at high RPM.

that doesn't sound right.
Sounds like its time to get a real tuner.

What is the duty cycle of the boost control solenoid when it starts losing boost?
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Old 07-20-2016, 05:54 AM   #4
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Default high back pressure

You are experiencing severe back pressure on the hot side of the turbo due to the inlet pipe and ar housing. The wastegate is having a difficult time maintaining a constant level due to the high pressure being placed on it. Also, You are just blowing hot air past ~16 lbs boost with that setup. Yoyu could try an open wastegate dump to quickly remove some of the air going through the turbo and/or a larger 1.06 ar housing to allow a little more flow through the turbo. These changes will net you some more power but will not get you to 600whp. The 6266 will make more power but it will be a small step up and may or may not get you to 600whp without having to use racegas or e85. If you use an alternative fuel source you will hit 600whp with the gt35r turbo with the 1.06 ar housing. the gt35r on a dynojet with the .82 housing may get you to very low 500 range, the 1.06 housing will get you to 525-550, the 1.06 housing with race gas or e85 will net you 0ver 600whp. A couple of guys state that they achievd 600whp with the 6266 ,on pump gas,with the vband housing but I have not seen a dyno yet.

Last edited by james12345pt; 07-20-2016 at 06:02 AM.
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Old 07-20-2016, 09:28 AM   #5
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Quote:
Originally Posted by james12345pt View Post
You are experiencing severe back pressure on the hot side of the turbo due to the inlet pipe and ar housing. The wastegate is having a difficult time maintaining a constant level due to the high pressure being placed on it. Also, You are just blowing hot air past ~16 lbs boost with that setup. Yoyu could try an open wastegate dump to quickly remove some of the air going through the turbo and/or a larger 1.06 ar housing to allow a little more flow through the turbo. These changes will net you some more power but will not get you to 600whp. The 6266 will make more power but it will be a small step up and may or may not get you to 600whp without having to use racegas or e85. If you use an alternative fuel source you will hit 600whp with the gt35r turbo with the 1.06 ar housing. the gt35r on a dynojet with the .82 housing may get you to very low 500 range, the 1.06 housing will get you to 525-550, the 1.06 housing with race gas or e85 will net you 0ver 600whp. A couple of guys state that they achievd 600whp with the 6266 ,on pump gas,with the vband housing but I have not seen a dyno yet.

Excellent info thanks. I did find another guy having the same problem as me, and there was talk about going to the 1.06 housing in that thread also, or moving to a T4 housing.

I do have open dump wastegate. I did this same time I installed the EBC, and the tune after those installs did get me another 20ish peak which is where I'm at currently. I wasn't sure if this was due to the EBC smoothing out the boost, different atmospheric conditions, or just a fluke.

So next question, would running a 6266 T3 .82 have the same problem? I'm familiar with what everything means, just not familiar with how each one effects response and flow.

GT35 T3 1.06 4 bolt
GT35 T4 .63, .82, 1.06 vband
6266 T3 .82 4 bolt
6266 T3 .82 vband
6266 T4 .58, .68, .81, or .96 vband

If I can get 550 on pump gas I'll be happy, and then can run separate maps for race gas for the days I want to have more fun. I also am looking into Haltech with flex for next year and have the option to run E85. Only problem is E85 has limited availability here and I do take longer trips with this car, so I'd like the ability to run pump. I'd like to not run the turbo at its limits on pump though.
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Old 07-21-2016, 09:25 AM   #6
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I believe that it will take the 6266 with the T4 inlet to get to the 600whp mark on 93 oct. This will require a inlet pipe with T4 mount and the first section of the downpipe to be widened to 3.5 inches. Powerlab carries an vband inlet and outlet section for the 6266 but the vband band inlet is only the same flow as the t3 inlet. I don't know if the larger turbo will help if there is still a restrictive hotside flow.
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Old 03-08-2017, 03:53 PM   #7
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Im late but another good post , i am looking into the powerlab GT37 kit on a built motor on my 07 rev up and wanted to run higher compression or at least stock OEM compression 10.6:1 id be real happy to get 550 or even 480 ish . Good thread
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