PorscheDoc

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!

blacknight

Good info, but can't seem to find it on your site to purchase!

ebaker

PorschePhd, what kind of grease do you use to lubricate the pistons in the evo DV's?

BMo

Great info indeed. Thanks for sharing Doc, you're an asset for the forums.

PorscheDoc

They are lubricated and assembled when new, but for the rings, any silicone lubricant will work just fine.

I'll see if I can where the link went, lol.......

PorscheDoc

Hmmm for some reason the website has had things shifted around. I don't like posting prices of things on forums, but since the website is funky, normal price is $139 a valve. Rennlist members get them for $119 a valve. Easiest way to order is to give the guys a shout at the shop (913.310.9927) and tell them you want the "rennlist special," and they will take care of you....or you can ask for me, it doesn't matter

Garey Cooper

Just a comment based upon my experience. My stock diverter valves went bad within the first 3K miles I had on the car which itself was stock at the time. This was before there was much knowledge of which valves to use (sorry Doc, at the time I wasn't aware of your services!). I used Diverter Valves by another company, I WILL NOT steal this thread 'cause it's a public service by the "Doc". After about four years in service they did need to be re-lubricated...I think a Red Line light grease was used.

But, as the Doc says whatever replacement valve you go with....get 'er done.

PorscheDoc

Wise words

wross996tt

I agree that they need to be done, but I think it is also fair to let folks know there are other makes out there and I think some are better than EVO (Forge for example). Hope Idon't **** people off, but this is about equal sharing....I have no relationship with any provider, just a user.

PorscheDoc

You make a good point.

Can you explain what makes a Forge valve better than an Evo valve?

Garey Cooper

All of the aftermarket DV's I've seen have a piston contolling the flow countered by a spring. There may be choices of which spring you use which will control the point at which the piston begins to move. There are various schemes of sealing, o-rings, etc. but they all share these characteristics so far as I know. The plus point to some is the orientation of the vacuum nipple. Mine are co-axial to the piston travel which means they stick straight up from the top of the DV.......it makes for a tight bend of the vacuum line. Others put the vacuum line at a 90 degree angle from the piston travel or the barrel of the DV. Still others allow a radial motion of the top of the DV to locate the vacuum line where it is most convenient for re-assembly into the car.

I'd REALLY be hard pressed to say one has significant performance advantages over another......perhaps by varying the sping tension against the piston you might chance the blow-off characteristics...but so far as I know it's more a question of does it work now and will it work for a long time from now that is the major question. You can fine tune nearly all of them for the spring relief point.

MK19

Here are a couple of observations from a long time aerospace valve designer;

1)Clearly, from a design and expeience point of view, a piston type valve will be more durable than a diaphram design. Especially if the diapharam is overloaded. High temps don't help. But on the flip side (physics is all trade offs),
2) a diaphram valve is inherently lower in sliding friction than a piston/o'ring design, and thus more sensitive to small pressure changes. Note too, that friction equates to what engineers call hysterisis; or a tendancy to stay put, wheather staying open, or staying closed (ie resisting a change of state).
3) a plastic diaphram/piston design is clearliy lighter or lower in mass than a metal part....and thus, far more responsive (faster acting, remember F=MA, where A is acceleration(speed, time), and M is Mass(weight) and in this case F, or force is directly related to differential pressure across the valve) and more sensitive to rapid pressure changes.
4) so, when you put 2) and 3) together, a diaphram design is a far more sensitive (read accurate to design pressure characteristics) in it's dynamic mode....albeit less robust (especially if the plastic body fails....not noted here). This is why the designer would pick a diaphram design over a piston design.
5) additionally, the diaphram design is relitively insensitive to changes in friction....unlike o'rings that are highly sensitive to lubrication and contamination.

All of that conceptual analysis doesn't meam much if they work better in experience..and you cannot detect any performance impact.

However, as I understand it, this valve is intended to contain boost overshoot and thus protect a lot of other stuff ( heard of pressurized intake hoses blowing off of fittings??....a result of a slow control of boost overshoot and resulting pressure spikes??.....)

Just a few thought to consider.....no reflection on any of the products or opinions expressed above.
Mike

Kevin

Actually the primary design purpose it to protect the turbocharger.. Having a turbocharger that is turning in excess of 160K and then you pull your foot off the throttle.. The throttle-body slams shut.. Your turbocharger needs to keep spinning. Without a bypass valve the charge air will hit the closed blade.

wross996tt

In response:
1. Forges are serviceable. Both the piston and the o-rings are easily replaced should the need arise.
2. Adjustable spring set.
3. Recommended by my tuner.
4. Advised by another member after finding materials in their DVs.
When our cars are modified, the response from these valves is fine...the problem is blowing apart the stock POS.