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Old 08-30-2011, 05:20 PM   #1
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Default Who says you can't have EBC at >2x mech. boost?

I've a 5 psi can, and after a 6speed install, recently raised boost from 10 to 15 psi. No prob. I think the key is to have a proper open loop table, and proper PID. AEM has no 'D', so I built a circuit to add D.

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Old 08-30-2011, 05:48 PM   #2
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I'm amazed that the internal spring on your actuator is able to keep the flapper closed during boost rise. That afaik is the typical mechanical issue with IWG and boost control that is much higher than the actuator's rating. And the reason I had to add a helper spring to my IWG setup.
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Old 08-30-2011, 05:56 PM   #3
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my 7psi spring is holding 15psi perfectly flat...EBC is required towards to the top end.
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Old 08-30-2011, 07:04 PM   #4
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Quote:
Originally Posted by m2cupcar View Post
I'm amazed that the internal spring on your actuator is able to keep the flapper closed during boost rise. That afaik is the typical mechanical issue with IWG and boost control that is much higher than the actuator's rating. And the reason I had to add a helper spring to my IWG setup.
That is why I looked for a can with a large diameter. Such a can would require a stronger spring for a given wastegate opening pressure.
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Old 09-06-2011, 11:46 AM   #5
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my 3.8 psi EWG was holding 8 psi perfectly flat.
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Old 09-06-2011, 12:00 PM   #6
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My issue was on a small canned 7psi OE actuator @14psi. The helper improved spool dramatically- and this was post EBC tuning.
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Old 09-06-2011, 12:13 PM   #7
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Jason, you mean 3x not 2x.

I assume no:

boost spike
boost oscillation
boost sag?
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Old 09-10-2011, 03:01 PM   #8
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The "common wisdom" is that you can't have boost >2x can boost, because it'll overshoot or sag or oscillate. I have 3x and with just one round of tuning I have no spikes no oscillations, and very little sag (undershoot, actually) which I haven't bothered to tune out yet.

I attribute the performance to having a real 'D' and a "linearizer" circuit. (AEM doesn't have 'D' and I added a circuit to implement it)

I looked into the math and a 3way solenoid can indeed theoretically cause issues when running something like 3x can boost. A 2 way solenoid with a properly sized bleeder won't. The problem with a 3way is that as duty cycles go very high (>65% or so), the resulting boost becomes very sensitive to duty cycle. e.g.:

duty boost
40% 8 psi
50% 10 psi
60% 13 psi
70% 18 psi
80% 26 psi

That is, the effect of the 3way is highly nonlinear at very high duty cycles. This can cause oscillation at high boost. The solution, is to use a 2way solenoid, or what I did, which was to linearize it (like a lookup table to compress teh duty cycle) I built it into my D circuit. I didn't expect it to work very well but it did.

BTW 2 way solenoids have more control response lag than a 3way, and require 'D' even more so than 3 ways. This is because 2 way solenoids require a restrictor in the boost feed (sense) line.

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Old 09-10-2011, 03:20 PM   #9
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Quote:
Originally Posted by y8s View Post
my 3.8 psi EWG was holding 8 psi perfectly flat.
The "common wisdom" refers to IWG's, which are more nonlinear than EWG's.
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Old 09-10-2011, 03:24 PM   #10
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The log shows 4 WOT events. The first 3 are at ~5500 RPM, the 4th is at ~3800 RPM.

I tried stabbing the throttle at 5500 RPM because that would normally show bad overshoot. The 'D' arrests the overshoot significantly (< 1 psi) but then there's a slight undershoot. Without the 'D' circuit, at just 10 psi target, I could get 5 psi of overshoot. In the above log the worst undershoot is 10 kPa (where the cursor is)

When I stab the throttle at 3800 RPM there is no overshoot and no undershoot and the boost is pretty darn flat.
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Old 09-14-2011, 09:51 AM   #11
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OK soo....you're going to sell this to us other AEM users?
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Old 09-14-2011, 11:43 AM   #12
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Quote:
Originally Posted by TurboTim View Post
OK soo....you're going to sell this to us other AEM users?
please do...with dummy instructions... I overshoot to 19-20psi before settling at 15.
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Old 09-14-2011, 12:06 PM   #13
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My boost safety cut is 2psi over my target haha. It hits it every now and then when snapping on the throttle at torque peak rpm.
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Old 09-19-2011, 03:58 PM   #14
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I will build another proto for a friend to see how well it works on another setup, then decide what to do afterwards. I posted the schematic in another thread.
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Old 09-19-2011, 04:36 PM   #15
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Sounds good. Which solenoid are you using? GM? DIYAutotune's? Other?
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Old 09-19-2011, 04:53 PM   #16
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Gm
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