CO951

I forgot to mention that I have run shims with a mostly stock setup for years. Adding the shims and changing the amount of shim never changed the max boost above the stock. Which is exactly the way it should be, because nothing was changed with the stock boost control.

TurboTommy

Boost is controlled by a combination of spring strength and boost controller. Why would aftermarket wastegates like a Tial, for example, come with different springs. Under your theory it wouldn't matter what spring one uses, because the boost controller does everything. What you're saying doesn't make sense; think about it.
If you have a boost controller set a certain way, and then do nothing else but add a shim or change to a stiffer spring, your boost will go up by roughly the resting spring strength (depending on other factors).

I have no idea why you wouldn't experience boost increase with a shim. Years ago I had the weltmeister chip set and a wastegate shim came with the kit. My boost increased a good 3 psi with no change in boost controller (stock cycling valve).

CO951

Like I said before the spring effects the pressure it takes to open the wg valve. Since the valve maybe slower to open it could possiblely briefly shoot past the max setting of the controller. Or if you have too much shim the valve can't open enough to dump enough to keep it from over boosting. It is possible that a very simple bleed valve boost controller could see a slight increase in boost from a shim, but the question was about the stock boost control.
I have also previously run the Welt chips and they are the only chip I know of that made a change in the KLR that allows it to boost up to the physical maximum of the boost sensor in the KLR. In my '89 that was an increase of 1 or 2 psi and would probably be 3psi in your car. I have tested this many times with other DME chips. Any time I put the Welt KLR in I yould see that slight boost gain and it would go away when I took it out. The shims were in through all of this. That boost gain had nothing to do with the shims.
With the stock boost control if it starts to open the wg valve and the boost level continues to go beyond the setting, it will continue to send more and more pressure to the wg to open it more until it maintains the set boost. Sprint rate has no effect on it.
I don't really know the Tial wg, but I assume the reason it has different springs is the same as why we would shim the stock. The spring pressure must be less than your max boost or it will be the only thing effecting when the wg opens, but having the spring pressure too far below the boost level makes it harder to keep the valve closed. But again, everything I have talking about is related to the stock system which I understand very well because on my engineering degree, study of the sytem and experimentation with the system.
So again, when installed properly in a stock system, shims only help build boost quicker.
I just looked at Lindsey's shims http://www.lindseyracing.com/LR/Part...EGATESHIM.html and the say it helps with high RPM boost drop, too, but they don't mention increasing boost.

TurboTommy

That's the only thing you said which is correct.

You believe what you want.
Maybe re-evaluate your knowledge of the system and your engineering degree.

mahoney944

Wastegate shimming is old school any how. Dual port for the win.

And your both correct in part. Shimming a WG causes a reduction in boost lag and higher boost. Because shimming essentially raises the spring side net pressure, the WG stays shut longer which allows the turbo to spool faster. However, once the turbo starts building boost, it has to work harder to open the wg because the shim in place. This results in the turbo making higher boost. Just in time for the bone stock setup to enter over boost protection.

Yabo

Ok.. I will remove my lindsey boost enhancer valve and see if the shims + chips had any effects on the boost pressure that builds. A little difficult when I don't have a real boost gauge (just the one on the instrument cluster)

CO951

Tommy, just because you have turbo in your self selected name doesn't make you and expert. I have give tons of details and sources to support what I am saying and all you have done is insult me and say I was wrong. I have not said one insulting thing about you about your ignorance of this exact situation and you inability to provide anything to support your opinion.

I didn't post on here to get in an arguement with you. I posted to give an answer to a question on something that I understand very well. I am not going to contiune trying to convince you. I'll let Yabo and anyone else who reads this decide who is more credible. Someone who can't provide any details to support his argument and can't have a debate without resulting to insults or someone who has politely stated the merits of his position.

Good luck to all involved!

TurboTommy

CO951;
it's human nature sometimes when one gets fixated on an idea, that we end up not being open to contradictory information. It's happened to me.
Your perceived insults from me are not going to feel as bad to you as you feeling silly after you threw around "engineering degree" and your "understanding of the system"; and then you find out your tunnel vision was mis-guided.
And, I have no idea how you got fixated on the idea that spring strength has little consequence on ultimate max boost (that's what you're sayin', right).
And, I don't know how possibly anybody could provide you details (or proof) over a keyboard, here. All we can do is a discussion (that's all you did).
Maybe, call around. Ask wastegate suppliers why different springs. Call Lindsay (the only reason they didn't list as "possible benefits" is because it's just so obvious that max boost increase is the main purpose, that they neglected to even mention it).
And yes, of course, it just goes hand in hand that other side effects of a stiffer spring is faster boost building and less boost drop off at higher RPM.

I am sorry if I came across as insulting. You deserve better.

67King

Jeez, guys, lighten up. Look, if it weren't for the cycling valve, shimming the wastegate would ABSOLUTELY change the boost level. Without the cycling valve, which by any other name is what we call an electronic boost controller, the wastegate will open at about 3 PSI. Which is why when your KLR puts you in limp home mode, that's all you get. I should know, I tried running around with the BMW club in March that way, as I had a bad wire on my knock sensor.

You shim the spring, and that opening rate may be somewhere around 4 PSI. I don't know quantitatively. But as it is, it is already pre-loaded (or else it would open at 0.000000000001 PSI).

But overall, the electronic valve decides when to let the signal get to the wastegate. And unless that happens markedly lower than at 12PSI or whatever the factory setting is, the difference made by the shim won't have any notable impact.

As for why Tials come with multiple springs......many applications do not have boost controllers, manual, ecelctronic, or otherwise. Many just run a hose right to the wastegate. But for those that do, having a closely matched springs will probably make a manual controller a little more precise.

So, under a "typical" scenario, a shim would increase total boost. When you have a valve that completely shuts off the signal to a wastegate and its opening pressure is several factors higher than the uncontrolled wastegate's opening pressure, then the shim won't really increase max boost level.

TurboTommy

67king;

Had a tial with a 7psi spring with boost controller set to achieve 14 psi boost;
changed to tial 10 psi spring (their rating system), kept the boost controller at the exact same setting,; achieved 18 - 19 psi boost.

Another 951, 11 -12 psi stock boost with CV etc; did nothing else but added a shim to the wastegate, achieved 14 -15 psi boost.

End of story.

Many more examples I could list during almost 20 years and three 944 turbos of ownership, which rendered the same conclusions regarding this topic.

The world's gone mad; you guys believe what you want.

Oddjob

There is some misunderstanding or more credit being given to the stock CV control system than it deserves. Its not a true closed loop feedback electronic boost control system. There is some limited feedback to the KLR, maybe. But the boost curve is mostly controlled by a set duty cycle mapped on the KLR chip. The duty cycle is just a open/close sequence for the CV, which is just a solenoid diverter valve, that either is open to the WG diaphragm or open to a return line back to the intake boot, depending on the position of the solenoid piston/plunger.

You can change the KLR chip mapping to run more boost, but this is seldom done by aftermarket tuners. Most aftermarket chips use a mechanical means of increasing boost. One of the older methods is to use a restriction in the line to the CV or WG, e.g. the APE jetted banjo bolt. This reduces air flow and therefore pressure in the WG diaphragm for a given KLR/CV chip duty cycle.

You can also use shims in the WG. This puts preload on the WG spring, so a little higher diaphragm pressure is needed to open the WG, and the max valve lift is reduced.

Both these methods will increase boost on a 944T still using the stock CV control system. If you still have the stock factory DME chip, it will likely hit overboost protection on 26/6 car. The 26/8 cars (Turbo S DME/KLR) seemed to have a little higher limit before overboost protection kicks in.

ibkevin

Looking back, I would rather re-chip and shim the valve.

Less moving stuff to go wrong.

reno808

Wait why not just put in a Tial wastegate??

Willard Bridgham 3

What you need to know is the spring formula, F=KX

F=force
K= spring constant
X= distance the spring is compressed

If the spring is compressed, the force increases.