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Old 09-09-2008, 10:53 PM   #1
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Default Wastegate signal

Where do you guys pull your wastegate signal from?

Reason I ask is that i've been pulling my signal for the external, from my compressor outlet. I can't help but think that even with my AVC-R (wich I'm getting rid of) I'm losing some boost response.

I recently went to a WG spring very very close to my target boost level, and until I switch from the EBC to a MBC I'd like to run wastegate only.

With the AVC-R set to OFF, I make less than the prescribed .8bar that the spring is rated for (according to the EBC's display) The pressure sensor for the AVC-r pulls signal from the intake manifold currently. I'd like to run wastegate only to make sure that there isn't a problem somewhere else (turbo, engine) causing me to make less than target boost with my current signal routing.

Will I get a noticeably better response with the WG signal coming from a point after my intercooler?
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Old 09-09-2008, 10:56 PM   #2
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Are you reading boost according to your enginemanagement or a gauge? I only ask because your boost values could be wrong.

I get my WG signal from the compressor outlet for my Tial. Works well with my 7 psi spring. I doubt you will get better response with the WG signal coming from after the IC. A simple inline MBC would do what you're looking to achieve though.

I like short WG lines, less chance of issues.
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Old 09-09-2008, 11:06 PM   #3
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the spool will change if you source it after the IC.
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Old 09-09-2008, 11:07 PM   #4
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Not sure what exactly you mean by "responsiveness" however I used to have an issue whereby the system would quickly come up to ful boost (~13PSI) and then MAP would gradually decrease to 10 or 11 PSI as RPMs rose.

On Abe's advice, relocating the pickup from the compressor outlet to the pipe between the I/C and the throttle body eliminated this behavior completely.


FWIW, taking the reference from the intake manifold itself strikes me as dangerous. Under certain conditions (part-throttle operation under high load) the turbo will basically be free to create as much pressure (and heat) as it possibly can.
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Old 09-09-2008, 11:15 PM   #5
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intake manifold - I've been told that you never want to let the actuator see vacuum, it can damage the diaphragm . Any thoughts?
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Old 09-11-2008, 05:44 PM   #6
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Quote:
Originally Posted by Joe Perez View Post
FWIW, taking the reference from the intake manifold itself strikes me as dangerous. Under certain conditions (part-throttle operation under high load) the turbo will basically be free to create as much pressure (and heat) as it possibly can.
But isn't that what megasquirt EBC does?
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Old 09-11-2008, 06:19 PM   #7
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Take your wg signal right off the comp discharge. This location provides the best possible system response and will reduce boost overshoot. If you want more boost than this location provides, increase your actuator preload or run an EBC.

Never, never, NEVER take the wg signal from the intake manifold. I did capitalize never. The wg actuator is NOT designed to handle vacuum. Over time, the wg diaphragm will pull out of the crimp that holds it in place in the actuator can.
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Old 09-11-2008, 06:39 PM   #8
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Okay, so, we know not to use a source from the IM. Who wants to come up with some logs of the difference between the compressor outlet and IC to TB tube?
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Old 09-11-2008, 06:53 PM   #9
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Quote:
Originally Posted by JKav View Post
Never, never, NEVER take the wg signal from the intake manifold. I did capitalize never. The wg actuator is NOT designed to handle vacuum. Over time, the wg diaphragm will pull out of the crimp that holds it in place in the actuator can.
I'm not advocating that the manifold is the best, or even a good, place to take the WG signal from, but a simple check valve would eliminate any vacuum from the signal so damage to the WG diaphram shouldn't be a consideration.

I'm re-reading Corky's book so the real answer as to the why's and why nots shouldn't be far away.
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Old 09-11-2008, 07:08 PM   #10
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Originally Posted by Thucydides View Post
I'm not advocating that the manifold is the best, or even a good, place to take the WG signal from, but a simple check valve would eliminate any vacuum from the signal so damage to the WG diaphram shouldn't be a consideration.

I'm re-reading Corky's book so the real answer as to the why's and why nots shouldn't be far away.
Now I remember why I left m.net.
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Old 09-11-2008, 09:23 PM   #11
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Quote:
Originally Posted by Maximum Boost
So, where to put the signal source?
Essentially, three choices exist for sourcing the signal: the compressor out¬let, a plenum entering the throttle bodies, and the intake manifold. Each of these has merit and problems.
The signal originating at the compressor outlet offers the best control over the wastegate with regard to its response and ability to consistently control boost to a given value.
The bad side is that torque-curve rise will suffer slightly, as this source will create the earliest possible wastegate cracking point. This early cracking point will offer some relief thermally, because the entire system will virtually never see more boost than the basic setting of the wastegate. This can be important in avoiding a quick heat soaking of the intercooler.

Fig. 12-14. Flexible wastegate vent tubes allow for extreme expansion and contraction caused by large temperature fluc¬tuations through the wastegate.

Fig. 12-15. The waste¬gate signal source can affect the system with respect to heat load and turbine response.
The intake plenum signal source will slightly improve boost response, since the turbo is free to make all the boost it can until the pressure reaches the sig¬nal source and is transmitted to the wastegate. The fact that the turbo is free to make a brief spike of boost will cause the intercooler to be hit by a greater slug of temperature. Greater temperature is always to be considered a nega-tive. For a blow-through carburetor system, where the wastegate and fuel pressure regulator must see the same signal simultaneously, the plenum sig¬nal source is best.
Sourcing the signal from the intake manifold should be considered only when turbo response is of the highest importance and the short blast of extra heat can be tolerated or ignored.
All things considered, heat should be the controlling factor. Unless unusual circumstances dictate, hook the wastegate signal to the compressor outlet and call it a day.
here is what Corky had to say...
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Old 09-11-2008, 09:28 PM   #12
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Quote:
Originally Posted by JKav View Post
Now I remember why I left m.net.
Yeah, whatever. I can't accuse you of a lack of imagination, because I've seen your ubercool LeMon's cars, but keep an open mind JKav because there are pros and cons to each location and the easiest and simplest isn't always the best even if it usually is.

So anyhow, here's what Corky's book has to say:

"The signal originating at the compressor outlet offers the best control over the wastegate" but "the torque-curve rise will suffer slightly as this source will create the earliest possible waste gate cracking point."

The intake plenum signal source will slightly improve boost response but the intercooler will be hit by a greater slug of hot air.

"The intake manifold should be considered only when the turbo response is of the greatest importance and the short blast of extra heat can be tolerated or ignored."

So boost response improves the closer you get to the intake valves, but so does the heat; the wastegate control improves the closer you are to the compressor but boost response is a bit slower.

Looks like the Brain slipped all this in just before me.

But I can definitely see why a motor built for all-out drag racing might benefit from taking the wastegate signal off of the intake manifold. The primary advantage would be that whenever the driver shifts, and because the positive boost signal drops, the wastegate will remain closed. This means when the driver gets back on the gas there's (1) a good charge of compressed fuel air mixture waiting on the other side of the throttle plate and (2) the turbo's in a position to make boost as soon as it encounters the next rush of exhaust gasses. In contrast, if the signal is taken from the compressor, when the driver shifts the surge opens the waste gate. The gate won't re-close until the pressure is dissipated and that might be the difference between winning and loosing the race.

But beyond that, and not even considering the oh-so complicated vacuum check valve to protect the wastegate actuator diaphragm, the IM source sounds like more trouble than it's worth for most driving scenarios because of the heat issue.

Last edited by Thucydides; 09-11-2008 at 10:20 PM.
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Old 09-11-2008, 09:56 PM   #13
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I use the signal source fitting provided by BEGi. Splices into the brake booster line.
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Old 09-11-2008, 10:28 PM   #14
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Quote:
Originally Posted by compy View Post
I use the signal source fitting provided by BEGi. Splices into the brake booster line.
That's interesting, because that's sourced straight off of the intake manifold, but are you sure you'd not referring to your BOV. On the BEGi turbo I've got the wastegate signal is taken off of the compressor outlet.

But if you are taking the signal from the brake booster line how's it working? And you might want to either move the signal line somewhere else or at least installing a vacuum check valve to prevent the damage to the actuator JKav's described.
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Old 09-11-2008, 11:43 PM   #15
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airbrush1, have you tried relocating the AVC-R pressure sensor signal from the intake manifold to the compressor discharge? What you're describing could simply be the pressure drop in your charge plumbing / IC. You could be losing 2 psi or so. Won't know til you measure it.

And remember that with your AVC-R (or other EBC), any wg signal source that's not the comp discharge is eroding your control authority.
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Old 09-12-2008, 10:24 AM   #16
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Quote:
Originally Posted by Thucydides View Post
That's interesting, because that's sourced straight off of the intake manifold, but are you sure you'd not referring to your BOV. On the BEGi turbo I've got the wastegate signal is taken off of the compressor outlet.

But if you are taking the signal from the brake booster line how's it working? And you might want to either move the signal line somewhere else or at least installing a vacuum check valve to prevent the damage to the actuator JKav's described.
Yeah, I misread WG for BOV.
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Old 09-12-2008, 10:34 AM   #17
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Quote:
Originally Posted by Thucydides View Post

Looks like the Brain slipped all this in just before me.

I had the ninja advantage of copying and pasting directly from the book.


I have a port I can source from the TB inlet to give it a try and log to see if I can get any actual benefit from using that location over out of the compressor
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Old 09-12-2008, 10:31 PM   #18
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Mk, well I'm going to leave it on the compressor housing..... New issue, I'll be starting a new thread also.... I burned some exhaust valves!
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Old 09-12-2008, 11:36 PM   #19
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It still seems to me the greatest turbo respnse will occur when absolutely no signal ever reaches the gate. That might suggest that the most distant source would respond the best.

Heat might be/not an issue.

All men may have been created equal, but that did not apply to wastegates.
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Old 09-12-2008, 11:41 PM   #20
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ahh! Corky Speaks!
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