Laust Pedersen

Instead of leading the “Is the k26/8 much better than the k26/6” thread further off track, I decided to start a new one, with a title better suited for the subject.

The background is listed in the referenced thread.

A few people in the other thread were asking for pictures, so here they are.

The first picture shows the finished WG with the only visible difference being the four very short stainless M3 Philips screws (with brass washers) one of which has been drilled through with a .020” to .050” bit. Finding the best size bleed hole is an iterative process and fortunately one or two of the screws are accessible with the WG installed. Too small a hole and the WG will give rising boost (as a function of rpm) and too large a hole will give a falling boost curve.
It is very important to keep the chamber behind the screws clean before assembling the WG, so nothing will block the bleed hole.
The first picture also shows the tools needed to (dis-) assemble the WG. The first and second steps in the disassembly process is removing the vacuum/pressure fitting and then remove the valve by un-screwing it. However it is very important to hold the internal nut (and diaphragm) with the smaller allen-wrench to avoid twisting a hole in the diaphragm and the same is true for the assembly.

The second picture shows all the parts. In order to fit the supplemental spring the WG top has been machined to remove an internal shield that would otherwise be in the way for the spring.
The WG housing has also been machined slightly to create a seat for the spring. Below the WG top can be seen a machined aluminum disc with very small crush lip which acts as the seal to the mating surfaces.
On top of the spring is a spacer that mates with the internals of the WG top. The thickness of the spacer determines the opening pressure of the WG. In this configuration I measured the opening pressure to 12 - 13 psi.

Laust

theedge

Very nifty, but why no Tial or dual porting the stock one? Just curious.

IanS

If there is enough exhaust leakage around the valve to pressurize the diaphragm, wouldn't that make the stock wastegate a bad candidate for a dual port conversion?

Mark-87-951

So how is this different than shimming a wastegate and does the trial and error for the bleed hole size make this too tedious or is the size you've determined going to work for others as well?

Seems quite interesting.

Rogue_Ant

The problem with shimming the wastegate is that you reduce the valves travel... reducing flow.


Rogue

eclou

Awesome work Laust

Brian 944

I think this is a great How-To...

I would like to say that IMO. It might be a good preventative thing to just purchase a new Tial 35mm or 38mm..

Technology has advanced alot in 20 Years and I am totally impressed with the Tial that I have installed in my Turbo Mazda.

Basically 70,000 Km of abusive dirving ,it has never failed to open or Spike.

tommye

Interesting idea !!!!
So, as I understand it, the difference between this and a dual-port WG is that here you have exhaust pressure acting on the back of the diaphragm instead of intake pressure. Now, exhaust pressure will be higher, and beyond the turbos efficiency range it will be much higher than the intake pressure. This would surely create a different boost profile over the rpm range.
I like the idea since it looks almost bone stock.....
What is the purpose of the 2:nd spring ? Isn't a single harder spring good enough ?
Have you actually tested the setup yet ?
I'm curious about the boost curve...
Ay idea of correct vent-hole size ?
Any risk of overheating the diaphragm ?

Cheers,
Tommy

Brian 944

I feel that this could reduce the life of the bearing.

Laust Pedersen

Theedge, it is a dual port WG. The modulated exhaust pressure controls the 2nd (bottom) port.

Mark-87-951, as previously mentioned the added spring translates (moves) the boost curve up (more than shims can do) and the bleed screw tilts the boost curve so it gets close to constant or even increasing with rpm. I would guess the average slope tuning would require trying 3 to 4 bleed screws (accessible with the WG installed).

Tommye,
Only a fraction of the exhaust pressure is used to push on the bottom of diaphragm and the fraction is controlled by the bleed-screw.
The original spring simply cannot be removed without destroying the top housing.
I have had the modified WG in my car for about a year and once dialed in it has worked flawlessly.
I too am curious about the exact boost curve and will have one once I eventually go on a dyno. However quick glimpses at the boost gauge while accelerating suggests that it holds boost “pretty well”, maybe with a very slight drop, but without a systematic verification I prefer that.
As mentioned the hole size is in the .020” to .050” range and depends on the individual WG.
I too was concerned about “burning” the diaphragm, especially since a protective shield has to be removed for the extra spring. However the new spring and the spacer provide some protection against direct flow and due to the pressure built-up, the net exhaust gas flow is actually less than in the OEM configuration and lastly it has held up for at least one year.


My main concern with this design is relying on an uncontrolled side effect of the WG namely its leakage through the valve stem-guide and especially how it would be affected by deposits and wear. However my 1-year experience has been surprisingly positive, with a very stable and repeatable behavior.

I am also fully aware of the risks involved in “playing with” a WG without boost protection. One mishap in an inattentive moment (=racetrack) and the engine is toast ... unless it can handle 40 to 50 psi of boost.

Why not go for a Tial and an electronic boost controller?
Cost, simplicity and an effort on my part to prevent my interior from looking like a 747 cockpit. I have also leaned that playing with the electronics is fun for about a month and after that all the sporadically documented wires and boxes becomes a complicating nuisance.

Laust

punchy951

Hello everibody

It is posible to have the dimension of the spring

thanks

Punchy

Luis de Prat

Laust, how has this WG been holding up since your last post? Thanks.

davepnola

Why not do this ? Less efficient ? I also closed the bleed holes and used copper washers to seal the bottom. It holds 15lbs all day long just as tial . I really believe somone could have been rebuilding these years ago for little cost and acheive just as good results than aftermarket wastegates. The materials are far superior than other wastegates I have owned, used, and seen. The only problem I see , is who could duplicate the diaphragm that wears out at it pivot points . Example :

Laust Pedersen

Luis, I gave up on the idea of having the exhaust pressure provide some clamping force. It was just too difficult to get a repeatable flow, since it depends on the exhaust contaminants, which can change the valve stem to guide clearance and even clog up the very small bleed hole.
However I still have the added spring, which works very well to generate my 25 psi boost, although without the exhaust clamping it does roll off to ~18 psi at 6000 rpm.
To combat that I finally bought an EBC (used Blitz SBC-iD), but who knows when I get time to install it.
Btw, the (cold air) “winter horses” are returning. I thought my clutch was slipping in 2nd on a dry road, when the turbo kicks in … but it’s the tires (Kumho MX, 275/40 17).

“davepnola”, What do you mean by “diaphragm pivot points”? It is sort of a rolling fold in the diaphragm when it moves. Among the maybe 10 WGs I have had my hands on I would estimate that 20% had a bad diaphragm with no age/mileage correlation. It only takes one bad disassembly attempt to rip the diaphragm, which can easily happen if the valve is screwed out without any counter torque from the top. Admitting to that would cost the mechanic about $400.
I hope you were careful de-burring and ensuring that the inside of the lower port has no protrusions, since I suspect that the diaphragm will roll at least partially onto the fitting.

Laust

blown 944

Laust, I have used the dual port method now for a bit and it works great. I tried the spring/exhaust method earlier and didn't get the same results I have now. It will run and hold great pressure and it has an absolute rock solid control to it too. No rolloff at all

For my $$ the dual port is a great modification that still retains the wastegate flow. With the turbo I'm running 25psi it does start to matter if I would get boost creep, so the flow is important IMO.

Just thought I'd pass oln some info. With a big turbo it is very easy to see the difference.

BTW thanks to both of you guys for the ideas.