Jfrahm

I'm a little confused by the wastegate operation on the 951. I understand there is a spring on the wastegate that can get weak, and prevent me from getting full boost. However I also understand that the KLR has an absolute pressure sensor that is used to control the wastegate. It seems to me that if there is a spring controlling the wastegate it would work on relative pressure, but if the KLR is programmed to control the wastegate by absolute pressure would it not have to work around that spring somehow?

Thanks for any insights,
-Joel.

nine-44

I beleive the WG spring is set about 7psi, the KLR reads the boost level and either diverts the signal pressure to or away from the WG to control the boost. This is my understanding, not the official explanation. It does use the cycling valve to do this.

Jfrahm

I see. And so the weaker the spring gets, the sooner the wastegate opens. The spring sets a base pressure, and the KLR adjusts the pressure signal line to the wastegate to raise it, dumping excess pressure somewhere?

Thanks!
-Joel.

Andy

The story according to this Andy...

The wastegate spring provides a fairly large force to keep the wastegate closed. The cycling valve controlled by the KLR diverts boost pressure to the wastegate diaphram to overcome this spring pressure. In a stock configuration the CV can overcome the spring to only allow 4psi which is the default setting if the CV loose power or the overboost protection is triggered. And generally the KLR/CV starts opening the WG a small amount above 4psi to gently roll-on the boost for a milder driving behavior.

A good spring without outside intervention can provide over 22-23psi and mine in it's weaked and shimmed state will still provide 17-18psi (it probably starts to open at 12-13psi.) So yes they do get weak overtime because of all the heat cycles. Now I have heard conflicting reports from reputable souces about the KLR's ability to overcome spring weakness, I am inclided to believe it can modify the CV frequency to account for a weakening but I'm sure others will disagree. It's really a moot point because you should replace it anyway with an EBC or MBC for better performance and more consistant boost levels.

Danno

"And so the weaker the spring gets, the sooner the wastegate opens. The spring sets a base pressure, and the KLR adjusts the pressure signal line to the wastegate to raise it, dumping excess pressure somewhere?"

Yes, by default most of the pressure headed down to the CV goes straight to the wastegate, opening it early and giving you no boost. This is a failsafe method in case something goes wrong. Then the KLR is controlling the CV, it causes the CV to divert pressure away from the wastegate (returns to intake pipe in front of turbo). This raises boost by closing the wastegate. As boost builds in the mid-range and hits the max range, the KLR signals the CV to send pressure to the wastegate just enough to keep boost at the max-boost setting.

Now what you're alluding to and almost grasping is the concept of closed-loop feedback control of which is NONE in the KLR/CV combination. The KLR just sends out a fixed pre-programmed, duty-cycle curve optimzed to yield 11-12psi max-boost on a stock turbo with stock wastegate. It doesn't even monitor what the resultant boost will be and it doesn't re-adjust its duty-cycle signal to actually hit the desired boost.

So if you have a weaker-than-stock wastegate spring, you'll end up with a lower-stand-stock boost-curve (from the same KLR duty-cyle curve). Conversely, if you shim your wastegate spring or get an aftermarket wastegate, then you'll end up with more boost than stock; the KLR doesn't care. Really what the pressure-line going down to the KLR does, is it lets the KLR drive the stock boost-gauge on the dash and that's it.

Jfrahm

Thanks again,
Another question: If you remove all the boost controls and rely on the spring, is your boost limited by absolute pressure + boost or boost over ambient?

-Joel.

Danno

It depends upon how you measure boost, absolute or differential. The stock wastegate will always open with a 4-5psi additional pressure over atmospheric (bottom of diaphragm is vented to atmosphere). Using a spring-only regulation method would yield you 4-5psi of boost. However, the regulation isn't linear.

Using an aftermarket wastegate with stiffer spring to open at say... 13 or 15psi will make it harder to open the wastegate, thus more boost. But, it will also cause some boost-spikes due to the time-lag.

When the turbo is coming into its max-boost and most efficient range, around 3000-4000rpm, boost can build from 10psi to 25psi very, very quickly. You want to open the wastegate to dump the excess boost at 15psi. Let's say you have a spring set up to open at 15psi, by the time boost hits 15psi, travels down the long hose to the wastegate, build up pressure in the diaphragm (due to is volume), the actual pressure in the manifold may have reached 20psi. The wastegate finally opens and dumps boost back down but it will overshoot 15psi and dump to 14-13psi. At which point the wastegate closes and builds boost in the turbo back up again and at 15-16psi starts to pressurize the wastegate, which starts to open...

This mechanical feedback loop is slow and the resultant boost-curve looks like a sine-wave with the first wave as an overboost spike. What you really want for maximum performance is an electronic controller with some fuzzy logic and learning capability.

Andy

Joel,

I think Dan misunderstood your question. I think you meant if you disconnect the boost line from the wastegate what controls the max boost that the wastegate will allow, right? Technically in that case max boost pressure is really a byproduct of the exhaust backpressure working against the spring. In my case, it yeilds a nice, consistant curve. Spoolup is identical as when I had an LBE inline, it probably starts cracking open at 13psi and it maxs at 17-18 (stays above 16 from 3500-5000rpms) and tapers to 14 at redline which I attribute to the increasing backpressure of my #6 exhaust housing. If my wastegate could keep the 17-18psi to redline, I'd be at 300 rwhp, instead I'm limited to 280.

Anyway I don't recommend you go try this because you don't know how strong your spring is. I know of a guy in Florida who runs his track car the same way it it maxs out a 22-23 psi and he's running a bigger Garrett turbo! I found about mine while on the dyno 2 years ago when I couldn't get the LBE/KLR/CV to give me an acceptable curve. Take care.

toddk911

Noticed my gauge is reading only 12 psi, but stock guage seems to read 15.

Is stock guage off? Leak to after market guage?

If not, then time for new wastegate? As LBE is now almost turned all the way closed, also due to by passed CV. Maybe LBE spring is going bad?

Andy

Factory guage is notoriously inaccurate. You probably do not have leak just in the line to the aftermarket guage, but check the connections anyway. You may have a leak somewhere else but that would be a pretty big leak and it should be showing less vacuum at idle too. Assuming you have no intake leaks, it might be possible that your wastegate can't hold more than that. Try shimming it with washers as Danno has shown and see if that helps. I wouldn't want to guess on the reliability of the LBE but it should last longer than that. You might want to check your turbo too, the leading edges of my old one where all chewed up like it sucked something in, the limited my bone stock hp to 155 rwhp... Good luck.

Jfrahm

Thanks for the replies,
I'm not planning on removing the vacuum line from the wastegate, but rather to understand the whole system better by breaking it down in to smaller parts that I can understand. I think a simple spring-loaded wastegate would be a good starting point. With a spring loaded wastegate (no vacuum or pressure control line, or the line disconnected) I would suppose you get a boost level that is equal to atmosphereic plus the pressure needed to overcome your spring? Then you add vacuum or pressure to the diaphram thingy to make the wastegate easier/harder to understand?
(or in the case of a dual port, you can add your force to either side of the diaphram?)

-Joel.

adrial

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Danno:
<strong>
This mechanical feedback loop is slow and the resultant boost-curve looks like a sine-wave with the first wave as an overboost spike. What you really want for maximum performance is an electronic controller with some fuzzy logic and learning capability.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">How accurate a boost gauge would be required to measure this sine curve?

Are you saying that without an EBC (KLR included as a form of EBC), just running an MBC will yield a large overboost spike? Or is that only when running on only the wastegate spring, with no other form of boost control?

thanks,
Adrial

Andy

Joel,

The early 930's used a spring only for the wastegate control, and they have several different springs available depending on what kind of boost they want to run.

And yes you are right about the diaphram, our wastegates are single chamber only meaning the boost pressure can only be applied to one side forcing the valve open early. A dual chamber has the ability to have boost pressure diverted to either side and forcing it open or closed.

Watch out, you're on the vurge of being addicted to boost knowledge...

Danno

"How accurate a boost gauge would be required to measure this sine curve?"

Something accurate to 0.25psi that can be datalogged. Most gauges have 1psi accuracy with mechanical dampening (friction or fluid-filled) and don't show the fluttering action of mechanical boost-controls. One way to datalog is with an AVC-R hooked up, but using a manual controller. Or you can datalog MAP pressure with an EFI system. The initial boost-spike is larger with a check-valve type of controller compared to a pressure-regulator partly because the boost builds quicker.

Here's some past articles I wrote up on boost-regulation and wastegate control. You have to remember that boost-pressure is NOT the same as exhaust-pressure; one MUST incorporate the boost-pressure coming out of the turbo in the boost-regulation mechanism:

<a href="http://forums.rennlist.com/cgi-bin/rennforums/ultimatebb.cgi?ubb=get_topic&f=15&t=010253" target="_blank">LBE intalled, getting weird readings </a>
<a href="http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic&f=18&t=002698" target="_blank">Europroducts chip set with LBE. Are shims required?</a>

On dual-port wastegate configurations, I'll have to draw up some pictures...

Jfrahm

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Andy:
<strong>Joel,
Watch out, you're on the vurge of being addicted to boost knowledge... </strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Yes, I really would like to understand it. I'm still not clear on ambient and absolute pressure... I live at 5300' so if I don't have some sort of absolute system that measures the mass of the air going in, I may end up with boost+ambient and not get sea level performance, I think.

-Joel.