porschefig

In the "I found my lost power thread" I asked this..
Then, I searched and found this:
If that test is right then my diverter valve is WAY GONE!!
If it's not the diverter valve....
How much boost can a k26/6 usually hold to redline?
My MBC is set to give me ~15-16 psi max in 4th gear, held by a brand new Tial 38. I get that before 3k rpms and then by red line I'm down to like 8-9 psi.

All vacuum lines are new, cycling valve deleted, venturi deleted. Just installed my 951MAX chips from Russell, and am pleased with them: I'm not so stinking rich anymore.

Keithr726

Yup sounds like your valve is done. The new OE unit is a different one than the one that originally came with our cars. Its a 993 part because the ones from our cars would fail so often. I think they're about $50. I went with the evolution motorsport billet bypass valve (same thing as diverter valve) from lindsey.

chris951

I would recommend an aftermarket valve. I use the black Forge model, it looks like stock, but is metal not plastic, and will not tear the diaphragm.

76 911s

I too use a Forge and couldn't be happier with it. I had nothing buy problems with my old Lindsey one(old style).

Zero10

I changed mine out with the OEM replacement. I run only stock boost levels (now), and was not looking to spend too much at the time. IIRC it was ~$35, and made a night and day difference to how the car drove. I previously couldn't hold over 4-5psi to redline, took me up to 8-9psi at redline (also a K26/6 like you, but mine is very very tired).

Jon Moeller

Selling my one year old 993 diverter valve for $42 shipped, if you're interested.

-Jon

formerGMguy

Try using a DV from a Audi TT w/ the 225hp 1.8T. Its only $18-20 at an Audi dealer and is usually kept in stock. Its the preferred "OEM" valve for most S4 guys with a chip (they eat stock DV's for lunch). The biturbo S4 pushes more boost than a 951 so it should work out great.

The easy way to tell if its dead is to listen for a faint "honking" sound when your on light boost. Thats the diaphragm's death rattle.

PorscheDoc

Pop the top vacuum nipple off the diverter valve and suck. If you can suck air, it is bad. Don't even have to pull it off the car to test.

porschefig

Thanks everyone!
I'll go try the honk and suck tests later today...I'm kinda tired of spending money on the car this summer; and my AC compressor is leaking now

If it's bad: I'll keep the used and the Audi DV's in mind!!

Is the consensus that my 26/6 prolly won't hold ~15 psi to redline anyways???

PorscheDoc

The audi TT valves fail at the same rate, and in the same way. I replace those all the time. If you want one that doesn't fail, then you get an Evo, forge, etc billet valve.

porschefig

Well, I can definitely suck air through it. Partly dissapointing, but on the other hand I'm glad that I'll have MORE HP soon :-)

Doc-
at the same rate as the 951 or the 993 TT diverter valves??

Everyone-
I would believe it if someone said the diverter valve on my car was stock or the first/second replacement.... The car has 120k miles and is an 86; are the billet ones worth 2-4 times the price? Shoot, if the Audi ones last as long as the one on the car right now, costs $20 AND fits perfectly....

PorscheDoc

yes, they are all valves which are virtually identical, and based of the same poor design....a thin rubber diaphragm that is under constant motion and pressure.



Here is a post I did a few months ago in the 996TT board:

This topic came up over at 6speed, so I wanted to share a bit of knowledge with you guys. You see a lot of posts recommending EvoMS billet diverter valves on the market which are replacements for the stock units. This is one of the first things we recommend doing to the car, especially if you are thinking of flashing your ECU to higher horsepower levels. Why does this matter? What makes them better than the stock units?

Here's why: The stock units contain a rubber diaphragm in them that over time will tear, causing the valve to not function properly. Porsche, VW, and Audi have been using these Bosch valves in their turbo charged cars since the early 80's, and still are using them today. Sure they use an "updated" valve, but it fails in exactly the same manner as the old valves (as well as looking the same). Typically we see these valves fail by 30k miles. In cars that run higher boost levels, the Bosch valves will fail almost immediately, because the rubber diaphragm is not designed to resist the increased pressure. It will rip and fail, and all of a sudden that $2k ECU flash that you just paid for, will seem like you got ripped off (I.E. the car will produce less boost than stock).

What are the symptoms of a failed valve? Typically you will only be able to boost a fraction of what your car should. For example, if you are normally running 1 bar of boost with a good valve, well then with a ripped valve you may only be able to produce .4 bar. This is a significant decrease in horsepower.

Here is a picture of a stock Bosch valve that I cut open and pulled apart. The red arrow points to the rubber diaphragm which will split and cause the vacuum leak. What happens, is the air is not able to push the plunger up, because it travels right through the rip. If the rip is small enough, well then a lot of air will still partially be able to push the plunger up, which is where you might still get your .4bar of boost. Basically it is like trying to blow up a balloon that has a tiny hole in it. You might be able to blow it up a little bit, but you won't get it all the way. In the case of the DV valve, it is vacuum, but the theory of air movement is the same.


And here is a picture of the Evolution Motorsports Diverter Valve. Notice the aluminum plunger, which is sealed tightly by the rubber o-rings on the side, eliminating the need for a rubber diaphragm. This virtually eliminates the valve failure. And since I know it will be asked, "Can the o-rings fail?" In theory yes, they could. In the last 2 years, I have had 1 valve come back with a bad o-ring, and this was a new valve, so I contribute that to a manufacturing defect. In contrast, last week alone, I removed 5 Bosch diverter valves that were shot from vehicles. A drastic improvement! With an Evo valve, you will also be able to run higher boost levels without fear of failure. We recommend them with all of our ECU flashes, as the boost is increased over stock levels. Replace the stock valves with billet units, and don't worry about them again!

Zero10

15psi to redline on a 26/6 is not going to happen.
Even with a new wastegate and diverter valve on a new turbo I wouldn't expect it. You're waaaaaay out on efficiency anyways. You need a bigger turbo to hold that much boost to redline in a proper fashion.

Mighty Shilling

I dig the Evo diverter valve I have. it's nice, and I get a "psht!" whenever I shift. it's quiet, but it definately happens. great product!

speedy951

My car was lacking some power the last couple days and sure enough the stock diverter valve was bad. I threw a good stock one on the car that I had from another car and now the power is back.

So that is three failed diverter valves in the last week or so. I am defintly looking at a good billet replacement.