Help with wastegate needed - Tial
08-29-2003, 12:45 PM
#16
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I think your issue may be pretty simple actually. I could be wrong, but it seems to me that taking your gauge reading from the wastegate signal line with a "T" is why you're seeing higher pressures than you expected (1.4 vs. .8 bar).
The pressure in the signal line should be the maximum that the turbo can make, 1.4, 1.6, whatever. The pressure in this signal line that goes from the intake system somewhere after the turbo, usually near the "in" side of the I/C, is what acts against the side of the diaphragm opposite the spring in the wastegate. The spring opposes this pressure sent from the signal line, post turbo, to a degree that preserves whatever boost (exhuast gas flow) you select, be it .8, .9, 1.0 bar etc...
The accuracy of your gauge reading relative to what the actual boost the motor is recieving really depends upon where the signal line is attached on the intake system.
Usually it's in the traditional place, from a port on the "in" side of the intercooler.
Sometimes however, guys will move the signal line a little further down the line, to the point of attaching it to the intake manifold. This lets the turbo spool up considerably more before the wastegate begins to recieve a boost signal, thus opening and bleeding off boost, enhancing the response of the turbo, but creating more of a pressure spike and a considerable heat soaking of the intercooler.
If your signal line is fed from a point near the turbo outlet- I/C inlet, in a configuration similar to factory, and your boost gauge is "T"'d in here, you're getting a false reading. The intake manifold and ports are not seeing the level of boost indicated by the gauge, because the wastegate is opening and mitigating the pressure spike before it travels through the intercooler, throttle body and intake plenum.
The best place to attach the boost gauge hose is somewhere on the intake plenum, preferably as near the intake port as possible.
Now, first I would verify that the diaphragm in your stock wastegate is good, it's easy enough to do and it's probably worth replacing anyway since you just did other major work, kind of like icing on the cake.
Then, I think if you move your boost gauge attachment point your issues will probably disappear.
It's worth a try before buying new, expensive, possibly unnecessary (but cool looking) parts.
A good book on turbo theory that dummies (like me) can comprehend is Corky Bell's "Maximum Boost".
The pressure in the signal line should be the maximum that the turbo can make, 1.4, 1.6, whatever. The pressure in this signal line that goes from the intake system somewhere after the turbo, usually near the "in" side of the I/C, is what acts against the side of the diaphragm opposite the spring in the wastegate. The spring opposes this pressure sent from the signal line, post turbo, to a degree that preserves whatever boost (exhuast gas flow) you select, be it .8, .9, 1.0 bar etc...
The accuracy of your gauge reading relative to what the actual boost the motor is recieving really depends upon where the signal line is attached on the intake system.
Usually it's in the traditional place, from a port on the "in" side of the intercooler.
Sometimes however, guys will move the signal line a little further down the line, to the point of attaching it to the intake manifold. This lets the turbo spool up considerably more before the wastegate begins to recieve a boost signal, thus opening and bleeding off boost, enhancing the response of the turbo, but creating more of a pressure spike and a considerable heat soaking of the intercooler.
If your signal line is fed from a point near the turbo outlet- I/C inlet, in a configuration similar to factory, and your boost gauge is "T"'d in here, you're getting a false reading. The intake manifold and ports are not seeing the level of boost indicated by the gauge, because the wastegate is opening and mitigating the pressure spike before it travels through the intercooler, throttle body and intake plenum.
The best place to attach the boost gauge hose is somewhere on the intake plenum, preferably as near the intake port as possible.
Now, first I would verify that the diaphragm in your stock wastegate is good, it's easy enough to do and it's probably worth replacing anyway since you just did other major work, kind of like icing on the cake.
Then, I think if you move your boost gauge attachment point your issues will probably disappear.
It's worth a try before buying new, expensive, possibly unnecessary (but cool looking) parts.
A good book on turbo theory that dummies (like me) can comprehend is Corky Bell's "Maximum Boost".
08-29-2003, 01:53 PM
#17
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Randy,
I'm using a Kokeln IC and sensing the boost signal from an area to the rear if the IC. It is near the feed to the BOV, which the 964 turbo style. So the signal is within inches(distance-wise) of the manifold. The wastegate was working before this failure occured. As a matter of habit, I routinely "exercise" the wastegate to blow out any condensation in the valve area.
Believe me, I do not want to buy a new wastegate, the factory unit has served me well (60K miles), but it is time to replace a piece of equipment that, in time, is going to be more and more difficult to get parts for. The stock WG's are known to bleed off pressure before the specified pressure is reached. That's why I have decided to go the EBC/Tial route. It's a more predictable solution.
I'm using a Kokeln IC and sensing the boost signal from an area to the rear if the IC. It is near the feed to the BOV, which the 964 turbo style. So the signal is within inches(distance-wise) of the manifold. The wastegate was working before this failure occured. As a matter of habit, I routinely "exercise" the wastegate to blow out any condensation in the valve area.
Believe me, I do not want to buy a new wastegate, the factory unit has served me well (60K miles), but it is time to replace a piece of equipment that, in time, is going to be more and more difficult to get parts for. The stock WG's are known to bleed off pressure before the specified pressure is reached. That's why I have decided to go the EBC/Tial route. It's a more predictable solution.
08-29-2003, 04:28 PM
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Do note that the Tial WG presure ratings are not accurate for our aplication!
I have a .7 bar and it does not open till near .9 bar.
I emailed Tial about this and they said they designed them to work in aplications where there is more exaust presure gererated than our 930 after market exausts supply.
A WG's rating is a combnation of the seat presure generated by the valve's spring and the "counteracting" exaust presure generated agenst the valve. For example the spring might be set to hold 1.2 bar of presure with the expectation of the exaust presure will be pushing back at .2 bar giving one a 1 bar rating for the WG. Because of this you really can not test when a WG opens buy using compressed air and a guage.
Thus, don't buy a 1 bar Tial WG and think it will open at 1 bar. More like 1.1 or 1.2 bar. I have been told that a .9 bar Tial will pull up to 1.1 bar.
Interms of boost control operation, the Tials are designed to work best with an electronic boost controller as they have a smaller volume and smaller pistion so they act faster to input. However, not the best choice for a mechanical boost control system.
---
If interested, I have a stock WG that was working fine when I removed it. It opens at .9 to .92 bar. $50 plus shiping.
Keith@Acquisitionpartners.com
I have a .7 bar and it does not open till near .9 bar.
I emailed Tial about this and they said they designed them to work in aplications where there is more exaust presure gererated than our 930 after market exausts supply.
A WG's rating is a combnation of the seat presure generated by the valve's spring and the "counteracting" exaust presure generated agenst the valve. For example the spring might be set to hold 1.2 bar of presure with the expectation of the exaust presure will be pushing back at .2 bar giving one a 1 bar rating for the WG. Because of this you really can not test when a WG opens buy using compressed air and a guage.
Thus, don't buy a 1 bar Tial WG and think it will open at 1 bar. More like 1.1 or 1.2 bar. I have been told that a .9 bar Tial will pull up to 1.1 bar.
Interms of boost control operation, the Tials are designed to work best with an electronic boost controller as they have a smaller volume and smaller pistion so they act faster to input. However, not the best choice for a mechanical boost control system.
---
If interested, I have a stock WG that was working fine when I removed it. It opens at .9 to .92 bar. $50 plus shiping.
Keith@Acquisitionpartners.com
