4BD1T Turbo Sizing and Performance Prediction.

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Originally Posted by Judo

...in steps the least technical person here. :D

How about wastegate stuck closed? Or some other wastegate flow issue. My theory being it explains high boost and fuel being OK at smaller engine loads, but big loads in high gears causes too much back pressure? Winding the fuel screw back in appears to fix it because you never have enough fuel to cause the problem.

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Maybe. But it should go extremely well at low rpm if that were the case.

I ran with a wastegate blocked, it would pull to max boost well through low rpm, then hit a wall around 2,500rpm where it wouldn't develop any more power.
At lower fuel settings it would pull well to the end.

Vern's turbine is bigger than mine, but he's intercooled which will roughly make up the difference.

Well what you explained there dougal is basically what is happening, except in the higher gears there isn't much down low.

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Originally Posted by Vern

Well what you explained there dougal is basically what is happening, except in the higher gears there isn't much down low.

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When you disconnected the wastegate arm and test drove, was there any boost?

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Originally Posted by Dougal

Maybe. But it should go extremely well at low rpm if that were the case.

I ran with a wastegate blocked, it would pull to max boost well through low rpm, then hit a wall around 2,500rpm where it wouldn't develop any more power.
At lower fuel settings it would pull well to the end.

Vern's turbine is bigger than mine, but he's intercooled which will roughly make up the difference.

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That sounds very much like what Damien is describing... Fingers crossed for an easy fix.

To suggest something else along the same lines - not blocked, but a fllow issue - perhaps just reduce the wastegate opening point. The alternative issue wategate related is that it's not opening early enough? Or it's opening, but only partial as the spring is too stiff and restricting wastegate flow?

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Originally Posted by Dougal

When you disconnected the wastegate arm and test drove, was there any boost?

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Yeah but not a lot, may have got to 10 psi on take off.

Hooked it back up now, boosting to 22. Gear change speeds are 10, 30, 70, and 98, but held it in 4th for a while and pushed it out to 110. Still no road for 5th

Q. What is the rating of the spring you have in the actuator now?

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Originally Posted by Vern

Yeah but not a lot, may have got to 10 psi on take off.

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That's a big red flag. It should be zero psi or very close to it with the wastegate open.
Is the lever free to move the flap open?

What does the wastegate open at on a bench test (use a bike or hand pump and pressure gauge).

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Originally Posted by Vern

I did think that, but would it still smoke if it had a fuel supply issue?

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Vern Could still smoke with a fuel supply problem in the lower gears but would expect bugger all when it drops off in 4th -5th

Justin its either 18 or 22. Will have to check

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Originally Posted by Dougal

That's a big red flag. It should be zero psi or very close to it with the wastegate open.
Is the lever free to move the flap open?

What does the wastegate open at on a bench test (use a bike or hand pump and pressure gauge).

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Bench test, do you think I have a pressure tester let alone a bike pump laying around.