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drmatera's Avatar
 
Join Date: Aug 2009
Location: Nicholson, Ga
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Wastegates for dummies

ok, I know what the job of a wastegate is and how it operates. But mine is doing something weird and I just wanted to see if anybody has come across the problem


Turbo- Bullseye S262 (600hp capable)

The gate in question is an XS Power 46mm (Tial knock-off). Boost control is handled electronically by MS2. I can set a boost target by RPM so that should enable me to add or subtract boost as the engine revs thru it's range.

Problem - On the street and the dyno this is what happens. In 3rd gear Boost hits it's peak (20psi) by 3500rpm, stays there till about 4000rpm then starts to decline gradually to 15.5psi by 5500rpm and stays there till I lift (5800-6100rpm). So I raise the boost target from 4000rpm-up and get no response. I have been told the spring in these gates are inferior and when they get hot they get weak and overpowered by the exhaust pressure and open more than commanded which causes the boost to drop.

There are no leaks in the intercooler piping or exhaust. It made 388rwhp last night on a dynojet. I was really hoping to make 20psi all the way and smash the 400rwhp barrier but this boost issue keeps foiling my plans.

Anybody fighting WG issues?

Old 09-03-2010, 09:19 AM
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Don't know if it would help but Tial springs fit into those wastegates.

You could take the waste gate's pressure line off and slowly take it up to 5000 rpms without boost and get on it gradually while watching the mechanical boost gauge to see if the boost goes as high as you want for a second or 2 as long as it doesn't approach going way too high if there is such a thing with the E85 gas and MS EFI you're using.
Old 09-03-2010, 09:30 AM
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Jim, I have tried it with the line off. It hits overboost quickly. Since I sell Tial stuff I just finished installing another spring so base boost pressure should be 18psi. I'll find out tonight
Old 09-03-2010, 10:36 AM
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How are you controlling the boost on the wastegate with the device you mentioned?
If it is like other boost controllers that use pressure supplied to the vent side of the wastegate housing to provide more force than the spring is set to go off at then I dont think the spring is the issue.
The spring in this type of arrangement should be set to go off at a lower boost then desired and then the pressure supplied to the normally vented side of the wastegate varies to make up the differential to control the boost.
I would suggest making sure the pressure going to the vented side is being controlled properly because it should be self compensating. Meaning that even if the spring were getting weak at higher engine rpm the boost pressure on the vent side would increase via the contoller to maintain your 20psi set point.
Without seeing your system in detail though it is hard for me to say accurately but this is my experience from how other systems seem to work.
Did you try it in 4th gear to see what happens? Maybe the turbo is running out of capacity or you are not getting enuff load on the engine to generate the boost where you expect.
Just ideas.
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Old 09-03-2010, 11:06 AM
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I should have mentioned that before.

The controller solenoid is on the boost line going to the bottom port of the gate. The vent port is open. So the controller solenoid is just bleeding off boost signal. I have considered routing it the way you mentioned and if this spring change doesn't work thats my next move.

Funny you mention 4th gear. The other night I made a 3rd - 4th gear run down the highway. In 4th I noticed a pulsing noise coming from the wastegate dump. That is what got me thinking about the gate.

I believe the turbo is plenty capable.
Old 09-03-2010, 11:39 AM
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It's possible then back pressure in the exhaust overpowers the spring even with boost controller running 100% duty cycle and venting all the boost pressure signal. That is possible with small turbo hot side and weak WG spring. I assume you have a "pill" restrictor in your line?
If that is the case, conecting the controller signal to the vent side of the waste gate should cure it (with reprograming your ECM).
Old 09-07-2010, 10:21 AM
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Jerz, I agree with that. I ended up adding an additional spring and now with the controller off i'm seeing a solid 17psi . I haven't got back on the dyno to play with the boost controller but hope to soon
Old 09-07-2010, 10:42 AM
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Could it be that you bleeder solenoid that you seem to be managing with your MS cannot bleed enough air on high RPM, try two solenoids in paraller or a bigger solenoid. Which one are you using BTW?

Another issue could be the programming on the MS, naybe the duty cycle is not fast enough.
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Old 09-07-2010, 11:24 AM
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the duty cycle issue is a good point, i'll look into that

The solenoid is commonly used for boost controllers and should be able to flow enough

Old 09-07-2010, 12:23 PM
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