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Old 06-18-2011, 09:48 PM   #1
Austinw88
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Default Wastegate?

Ok I have a 87 turbo supra, I was wondering whats the stock wastegate spings at? I've been reading and seen some people say the stock wastegate will let you go up to about 12psi but im not sure.
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Old 06-19-2011, 02:53 AM   #2
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Stock is in the 6.7lb neighborhood.
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Old 06-19-2011, 03:04 AM   #3
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Stock is in the 6.7lb neighborhood.
Thanks for the reply man, me and my buddy just got it and were new at this so we were wanting to know. it had a boost controller on it and we didnt know what we could boost it too safely.
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Old 06-20-2011, 01:45 AM   #4
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Toyota service manual states the WG should open at 7.4 PSI.
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Old 06-20-2011, 03:34 AM   #5
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The signal pressure required for the stock actuator to open partially or fully varies. As it ages it'll open at lower pressures and it'll start opening earlier. It's one of the more common reasons a person will assume a perfectly good turbo is shot. Yes, the actuator should move its full range (approx 1/2") with 7.4psi supplied... BUT it starts moving before that; how much before affects how quickly you'll come to full boost at WOT and there's still the possibility that the spring is weak and the gate is now fuly opening at just 5psi. Naturally, if the diaphragm is leaking it won't open until the boost is higher than expected. So, to simplify: A weak waste gate actuator spring means it may take a long time to reach full boost or may result in a drastic reduction of boost altogether. A leaking WGA diaphragm may result in excessive boost levels.

At any rate... I'm not sure this is what Austin is asking... The stock waste gate actuator won't let you go any further than the amount of pressure required to compress the internal spring (typically in the 6ish psi range on old, stock units).

There are two other questions which both seem more relevant:

1) What is the maximum pressure that the stock waste gate actuator can take before it gets damaged?

2) What is the maximum boost you can push before you outflow the built in waste gate and start having issues with over-boost/boost-creeping.

As you're not going to efficiently flow enough from a stock CT-26 for #2 to even be a concern I'll assume you're actually asking #1... The answer: Toyota specifies that the waste gate actuator diagram should never receive more than ~11psi. With an old unit you can take a couple more psi off that limit for safe continuous operation (say, 9 psi). If you're running on an old waste gate and want to increase your boost pressure it would be wise to run a bleed type type control valve versus a ball type. These bleed pressure before it ever sees the WGA. So (for example... and overly simplified) with 14psi in the manifold, a bleed of 8psi between the turbo and WGA the WGA still only sees 6psi.; Almost all electronic boost controllers operate as an electronically modulated bleed valve. With manual boost controllers the more sophisticated ones often include both a ball valve (preset for between 8 and 10psi) and a bleed valve (which you adjust to reach your target pressure).
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Old 06-20-2011, 09:53 PM   #6
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Quote:
Originally Posted by cre View Post
The signal pressure required for the stock actuator to open partially or fully varies. As it ages it'll open at lower pressures and it'll start opening earlier. It's one of the more common reasons a person will assume a perfectly good turbo is shot. Yes, the actuator should move its full range (approx 1/2") with 7.4psi supplied... BUT it starts moving before that; how much before affects how quickly you'll come to full boost at WOT and there's still the possibility that the spring is weak and the gate is now fuly opening at just 5psi. Naturally, if the diaphragm is leaking it won't open until the boost is higher than expected. So, to simplify: A weak waste gate actuator spring means it may take a long time to reach full boost or may result in a drastic reduction of boost altogether. A leaking WGA diaphragm may result in excessive boost levels.

At any rate... I'm not sure this is what Austin is asking... The stock waste gate actuator won't let you go any further than the amount of pressure required to compress the internal spring (typically in the 6ish psi range on old, stock units).

There are two other questions which both seem more relevant:

1) What is the maximum pressure that the stock waste gate actuator can take before it gets damaged?

2) What is the maximum boost you can push before you outflow the built in waste gate and start having issues with over-boost/boost-creeping.

As you're not going to efficiently flow enough from a stock CT-26 for #2 to even be a concern I'll assume you're actually asking #1... The answer: Toyota specifies that the waste gate actuator diagram should never receive more than ~11psi. With an old unit you can take a couple more psi off that limit for safe continuous operation (say, 9 psi). If you're running on an old waste gate and want to increase your boost pressure it would be wise to run a bleed type type control valve versus a ball type. These bleed pressure before it ever sees the WGA. So (for example... and overly simplified) with 14psi in the manifold, a bleed of 8psi between the turbo and WGA the WGA still only sees 6psi.; Almost all electronic boost controllers operate as an electronically modulated bleed valve. With manual boost controllers the more sophisticated ones often include both a ball valve (preset for between 8 and 10psi) and a bleed valve (which you adjust to reach your target pressure).
That helps alot, Thanks for the info. I was just asking how much because we turned the boost up a little and hit 6 psi and i think we hit fuel cut at 4500 in second only, but not sure if its fuel cut or something else so we turned it down a little and stayed at about 5psi. we just wanted to go as high as we could safely.
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Old 06-20-2011, 10:04 PM   #7
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The limit you're hitting isn't caused by the waste gate.... not precisely. You should be able to flow upward of 13 - 15psi before hitting fuel cut. If it's cutting out as low as 5 or 6psi something is wrong. Check for leaks in the intake plumbing, fouled spark plugs and check for diagnostic error codes (most likely either AFM related, abnormal turbo pressure, lean conditions or knock).

What boost gauge are you using and where is it connected? You should be hitting at least 5psi without a boost controller, even on a weak waste gate actuator.
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Old 06-21-2011, 02:59 AM   #8
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Quote:
Originally Posted by cre View Post
The limit you're hitting isn't caused by the waste gate.... not precisely. You should be able to flow upward of 13 - 15psi before hitting fuel cut. If it's cutting out as low as 5 or 6psi something is wrong. Check for leaks in the intake plumbing, fouled spark plugs and check for diagnostic error codes (most likely either AFM related, abnormal turbo pressure, lean conditions or knock).

What boost gauge are you using and where is it connected? You should be hitting at least 5psi without a boost controller, even on a weak waste gate actuator.
We have both the stock boost gauge and aftermarket gauge hooked up, its tapped into a line that goes to the boost pressure sensor.

Last edited by Austinw88; 06-21-2011 at 03:07 AM.
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