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Old 07-08-2015, 08:59 AM   #1
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Default Boost control - by ECU or externally?

Hi All -

I remember reading this thread - https://www.miataturbo.net/diy-turbo...eed-ebc-47532/
years ago, and amending my setup to suit.

I currently run a Gizzmo EBC, on my Greddy'd car. I'm installing a standalone, and the advice from the ECU suppliers is 'use our boost control'.

Fine. Except - using the engine ECU to control boost means using the ECU's MAP sensor. I.E. the sensor measuring the manifold - after the throttle plate. That's right place to measure what's going into your engine, but surely not the right place to measure what your turbo is outputting.

Surely this puts you into the situation described on that thread ^ where on a long part throttle drag, your turbo is working crazy to force air past a tiny throttle opening, creating loads of heat and pain?

So why would it seem to be preferential, as everyone with MS or other standalone seems to think, to have your ECU doing your boost control?

(On the basis you only have 1 MAP sensor on your ECU, I'm sure there may be some that have thought about that).
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Old 07-08-2015, 10:17 AM   #2
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Using the aftermarket ECU to control the boost allows additional features & safety not provided by an external EBC. Using the map sensor covers the car's entire tune from idle to redline (all conditions). For example, you can tune the aftermarket ecu to hold it's EBC until a certain pressure or condition is met then start making adjustments (more fuel to comp for additional positive air being added).

Short answer: It can be tuned out to prevent what you're talking about.
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Old 07-08-2015, 10:23 AM   #3
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That would be why the boost tables use throttle position and rpm to determine duty cycle for your EBC valve. For low TPS positions where you are really restricting flow you should be at a duty cycle that allows the wastegate to open as it would without EBC and limit boost to wastegate spring pressure. The wastegate itself is still operated by the same reference pressure (before throttle body), the EBC just restricts boost pressure seen at the wastegate diaphram to allow for boost levels above wastegate spring pressure.
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Old 07-08-2015, 10:53 AM   #4
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boost before and after the throttle plate are the same.


youre over thinking this by tenfold.
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Old 07-08-2015, 02:43 PM   #5
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Honest question.

Why when I had my reference hooked up after the TB on partial throttle I would smell gear oil? But once I changed it the right way before the TB it went away? I have an old non water cooled unit.

My mind thinks because the turbo has to work much harder to get that wastegate pressure. Thinking 7psi spring, the pressure before the TB at part throttle is 15psi but after being crammed into a small opening it's at 7psi.

But I'm wrong if you say it's the same before and after so back to my original question.
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Old 07-08-2015, 03:03 PM   #6
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the difference pre/post TB is only so the wastegate doesn't see vacuum.
the difference pre/post IC is to factor in pressure drop.
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Old 07-08-2015, 03:14 PM   #7
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I would be surprised to find the pressure to be the same on both sides of the throttle plate on a turbocharged car unless it was allowing enough throttle opening to satisfy the needs of the engine. If the pressure is the same on both sides then the throttle has ceased to meter the air and must be allowing all that is necessary to balance pressure on both sides. If it is restricting the air at all, then there is necessarily a pressure differential by design.
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Old 07-08-2015, 03:40 PM   #8
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youre over thinking this by tenfold.
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Old 07-08-2015, 03:44 PM   #9
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I believe that the concern comes with part-throttle operation.

This can, of course, be tuned with a 2D (RPM vs. TPS) map. I can be tuned well, or it can be tuned poorly.
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Old 07-08-2015, 05:33 PM   #10
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The anti boost sag thread fixes a common boost curve shape that most people don't want.

With ecu controlled boost you can have ANY boost curve shape you desire, and a different one at any throttle position (or gear, or mph, or... Etc)

Brain is wrong in this case BTW. Completely wrong. But he is right in saying that you should stop thinking, and run ecu ebc.
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