IPF Bypass Valve Spring

[MagnumForceGB]

Decided to create a new thread for this experiment I'm going to do, put a stiffer spring the bypass valve. Our stock Evolution Motorsports bypass valve is actually real good, but will open up at -5 in/hg and be fully open at -7 in/hg. I've upgraded to a Lindsey Racing spring that starts at -15 in/hg and fully opens at -20 in/hg. I'm hoping this will fix the LTFT issues that I have, at high vacuum my LTFT's are perfect, but when I get around the -12 to -5 range my LTFT's run extreme positive, meaning more air is getting in than the MAF detects. This could be caused by the air going through the bypass.

Instead of me writing a bunch of stuff, here is a piece from this site:
http://www.lindseyracing.com/hptalk/1207.htm (Go down to the area called "Shop Talk") This is based off Turbo's.

In this issue we are going to discuss Bypass Valves. Sometimes they are called Blow Off Valves, Recirculation Valves, Pop Off valves and probably a few other names. This discussion is focused on the two different valves we currently sell. We are also going to touch slightly on turbos, but only in the sense of how they fit into the Bypass Valve picture.

First things first. We want to stress that on the 944 Turbo, we need to run a valve that connects back into the system or air intake in front of the turbocharger like the factory valve did. Not one that dumps or blows to atmosphere under the hood. If you're running an Engine Management System or device using a MAP (Manifold Pressure) sensor, versus a MAF (Mass Air Flow) or stock AFM (Air Flow Meter), then you can dump to atmosphere, but aside from that, it should connect back in. A loop from the charge pipe to the turbo inlet like you see below.

Over the last 6 or 7 years, we have carried a few different valves. Today, we sell the EVO or Evolution Motorsports Valve (left) and the Champion Motorsports Valve (right).

When we first sold the Champion valve, there were two versions. A diaphragm and a non-diaphragm unit. They no longer offer the diaphragm unit for unknown reasons so we only sell their non-diaphragm part. So both the Champion and the EVO pieces are without diaphragms and this discussion is limited to these two valves we currently sell.
The difference between diaphragm and non-diaphragm should be explained. The diaphragm style uses a rubber diaphragm between the main body of the valve and the lid or top where the vacuum fitting connects. The diaphragm is pinched between the body and lid. This diaphragm makes an air tight seal allowing the top of the chamber to either hold vacuum or boost pressure. The center of the diaphragm protrudes down into the piston and the spring is placed inside. This allows the piston to travel up and down and maintain a seal. The non-diaphragm type valve instead has a grove (in some cases two) machined into the piston bore where a large diameter rubber o-ring is placed. This o-ring sticks up slightly from the bore so when the piston is placed in the bore, it contacts the piston and makes the seal. This o-ring helps achieve the air tight seal without a diaphragm. There is also an o-ring sealing the lid to the body.

Both of these types of valves house a spring. This spring sits on top of the piston and holds the valve in a normally closed position. Pictured below is a typical non-diaphragm valve.

Worth mentioning here is these valves without a diaphragm need a little lubrication from time to time. Remove the top and remove the spring and valve. Clean off the old grease or lube from both the bore and piston. Then re-apply some new lubricant. We like to use a lightweight grease. Something really slippery that doesn't feel like it has a lot of drag.
There are two forces that actuate the valve. These are Vacuum and Boost Pressure. The valve is connected to a vacuum hose that is connected to the intake manifold plenum (between the throttle body and the intake runners). If it's not, you need to correct it or the valve will never operate properly. So whatever the pressure is in the intake manifold plenum , we have the same pressure in the top chamber of the Bypass Valve. When the engine is under boost (positive pressure), this pressure in conjunction with the spring holds the valve closed. When not in boost, and under vacuum, negative pressure pulls or sucks the valve open working against the spring. The rate or strength of this spring can have an effect on when the valve is open with relation to how much vacuum you're pulling.

We have all watched our boost gauge while driving around. When idling, you have vacuum. When driving on the highway at a sustained speed, you have vacuum. When you lift the throttle and decelerate such as when coming to a stop, you have vacuum. In all these conditions, the amount of vacuum can vary. If on the highway, and the grade of the road is going up and down slightly, you can have higher or lower vacuum because the engine loading changes. Larger cam profiles typically mean lower engine vacuum in all of these conditions. Thus the vacuum varies from engine set-up to load conditions.

When you depress the throttle and start to load the engine, the vacuum lowers to zero then transitions to positive pressure or what we all know as boost. How much boost doesn't really matter in this discussion. Just understand that it's not vacuum any longer and the force on the valve through the vacuum line connected to it is now pressure and this holds the valve closed. The spring is aiding this pressure in holding the valve closed.
The primary function of the bypass valve is to release or bleed off the pressure when you lift the throttle and close the throttle blade in the throttle body. Your turbo can be spinning in excess of 100,000 RPM and it's pumping the air through the intercooler, past the throttle body and into the cylinders. All of a sudden you close the throttle body or in effect have slammed the door on the passageway to the cylinders. This can be hard on the turbocharger. Some more than others, and some not affected by it.
When the turbo is spinning at these extreme RPMs and you close the throttle, this backing up of the air can try to force the shaft in the turbo laterally or sideways and permit contact of the wheels to the housings. This damage can quickly cause the demise of a turbo. So the bypass valve system is designed to open a venting hole to allow this pressure somewhere to go. In the 944 Turbo, and probably most applications, the pressure escapes and returns back into the turbocharger's inlet plumbing and is compressed once again. Thus the name recirculation valve.
The bearing in the turbo resisting this sideways movement is a thrust bearing. On the K26 turbos from KKK that come stock in the 944 Turbo, they have 270 degrees of contact area. Think of it as a pie with 1/4 of it eaten or missing. Our Super and Sport Turbos and probably most other Garrett turbos out there have a full 360 degree bearing. What makes them different is whether or not this 360 degree bearing is bolted in place.
Both KKK and Garrett produce the turbo with a spring washer holding the bearing in place. In order for it to be bolted in, it would be a secondary operation performed by the aftermarket turbo builder such as ours. This spring washer can compress with the sideways force caused by not bypassing the air and allows the contact. If the bearing is bolted in, the shaft cannot move and there is little to no chance of resulting damage.
If you have a Lindsey Racing Sport or Super Series Turbo, then you have no worries since they are all bolted in. Fact is, you don't need to run a bypass valve if you don't want to with one of our turbos. We would argue that the main reason Porsche has one on the 944 Turbo is to prevent this damaging sideways shaft movement. If you have a Garrett Twin Ball Bearing Turbo, such as our new line, those are every bit and then some as durable as a 360 bolted in.

We have tried removing the Bypass Valve altogether on the 951 with our set-ups and the results are not favorable. The problem is that the car does not return to idle quickly. That last 1000 to 1500 RPM back to idle can take a few seconds vs. a fraction of a second. This means that the deceleration of the engine is slower and you cannot use this to engine brake like normal. Strange enough, even though the Bypass Valve is removed, the resulting sound of the air backing up into the turbo's compressor housing sounds identical to still having one.

When tuning the car with a Piggy Back fuel controller coupled to a MAF Meter, this inconsistent opening and closing or position of the Bypass Valve can affect the state of tune. If you're going up a slight grade, then down, the air fuel ratio can be switching from rich to lean from your desired target ratio. When bypassing, the amount of air entering the meter is not the same as when it's not bypassing. It's a slight difference, but enough to aggravate tuning. In some cases making the car buck or miss when transitioning from open to closed or vise versa.

The EVO valve has two areas needing improvement. The spring is of a rate that allows the valve to start to open at 4 to 5 inches of vacuum, and is wide open at 7. Second area is that the spring is not precision ground flat on the ends. This allows the valve or piston to tip and possibly bind up or drag once opened and the centering tip of the piston comes out of the corresponding alignment bore on the valve's body.

The Champion Motorsports valve starts to open at 6 to 7 inches of vacuum and is full open by 9 or 10. That's with the stiffest supplied spring in their kit (comes with three springs and two shims). Each shim increases the amount of vacuum required to open it by about 1. So with the stiffest spring, and both shims, you're full open at 11 to 12 inches of vacuum.
If you watch your vacuum gauge while driving, you will see your vacuum run the gambit from 0 to about 15 inches with the exception of full deceleration where the vacuum goes way up to 20 or even more. The air fuel ratio in this condition doesn't matter since the injectors are turned off anyway and the boost went away and the engine is coasting down.
We want to point out that this early opening of these two valves may be fine when running an AFM. But we have found that on MAF set-ups, it's not so good, or it can certainly be improved.

So we decided that a new spring was needed. One that would start to open at 15 inches of vacuum, and fully open at about 19-20. So the only time the Bypass Valve will open is when you lift the throttle under full boost and the vacuum surges past 15 inches. This is when the backpressure is there and when the bypass valve is needed. The rest of the time it will remain closed. This makes tuning of the car easier since this open and closed variable is eliminated.

Since both valves have similar internal dimensions, we were able to make one spring that fits both valves thus we get the same results with each.
We also feel this will help with "tip in" of boost since the valve would already be closed. A stock valve or one with a weak spring would be normally be open just before you go full throttle. So you bypass a little air before it closes and building of boost. This new spring may not work for everybody. But it has proven successful on our projects and cars we tune in house. We feel this new spring should be used on turbos with a bolted in 360 bearing or a Twin Ball Bearing turbo set-up with a MAF. The AFM doesn't seem to mind the bypassing and that's how Porsche had it set up based on their other components. It may prove ideal for AFM cars as well. Get one and give it a try if you're still running an AFM and an EVO or Champion Valve.

Our stock spring vs Lindsey Spring:
http://www.lindseyracing.com/LR/Pors...LR-BOV-RS.html

[blackTT600]

Very interesting

[MagnumForceGB]

Should have reset the ECU, car bucks a little and in park as soon as it goes under 15 vacuum the engine runs rich. Trims looked better though cruising, will keep playing with it since it is a cheap mod.

[MagnumForceGB]

Definitely needs adjustment, in park the car wants to hover right around 15, so it starts trying stall out every time the valve starts opening, so the throttle opens up, removes some vacuum and the valve closes and no idle problem till it hits again.

[MagnumForceGB]

Car stalled for the first time since December, don't know if it was because the valve was closed or open. Tonight I'm going to pull the vacuum line off the valve and see how it idles. If it stalls then the spring is too stiff and the stock spring is best.

The stiffer spring seems to make the throttle respond better, but there is probably 0 track gain from this. Nice cheap experiment though.

[MagnumForceGB]

No go on this, if the bypass valve is closed at idle the engine tries to stall out. Since the bypass valve opens up at -15 in/hg and idle wants to be at -12 to -17 in/hg with the stiffer spring it won't work. The stock spring does open up at -5 in/hg, maybe getting one to open up at -10 in/hg might work but for the gains, not worth it stalling. It helped build boost a little faster because it didn't have to wait for the boost pressure to enter the intake manifold to push back on the valve to seal it up.

[Ventmaster]

Nice work and a very interesting FYI. Thanks!

And BTW- what light grease are we gonna lube with for future cleaning?

[MagnumForceGB]

Probably just bearing grease, I have royal purple grease from all the suspension work.

Didn't work out, but some of this information might be FAQ worthy.

[gutterball]

My bypass valvue Flutters when open. J&M Motorsports is replacing it with a larger Bypass valvue.