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?

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.

the spool will change if you source it after the IC.

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.

intake manifold - I've been told that you never want to let the actuator see vacuum, it can damage the diaphragm . Any thoughts?

But isn't that what megasquirt EBC does?

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.

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?

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.

here is what Corky had to say...

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.

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.

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.

Yeah, I misread WG for BOV.

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

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!

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.

ahh! Corky Speaks!

...cryptically...

ebc ftw

Yeah, he's like that dude who retired from the FED, Alan Greenspan. Greenspan would say something nobody could understand but that they could all interpret anyway they wanted and billions would be made and lost on the world markets.

In Corky's case, that's just how engineers talk. I think it means, "the info's out there, here's some more, figure out what works for your situation."

Flogging a dead horse...

Compressor outlet: tightest control, but boost at throttle plate will fall off at high RPM because there is no measurement/compensation for pressure drop across the I/C. Worth considering a way to modestly reduce the effective boost at high RPM as a cap to the maximum stress on the engine.

Plenum: slightly looser (and possibly less stable) boost control, but maintains constant boost at the throttle plate across entire RPM range.

Intake Manifold: Maximum responsiveness when opening the throttle, but lousy on a) throttle linearity and b) heat/efficiency at partial throttle because the compressor output may climb very much higher than the target boost level. Example: a) boost target of 15 psi, b) engine at partial throttle with 3 psi boost in the intake manifold, requires c) 25 psi pressure in the plenum side of the throttle late resulting in d) huge backpressure on the exhaust side of the engine, but e) the still the wastegate remains closed -- trying to build even more boost -- because the WG signal is still 12psi below the boost target.

M.

Good thread!

Many DSMs tap into the BOV line, which itself is sourced from the intake manifold. I've been running this setup myself for the better part of 6-7 years now. With a ball-spring MBC hooked up in the signal line, is there still a risk to the wastegate actuator canister?

http://www.slowboyracing.com/downloa...ller-cheat.jpg

That seems like a really bad idea to me....

The wastegate/mbc should have their own dedicated vacuum source.