Wastegate for BOV

[BOT_ROCKET]

Hey all. I've been looking into what BOV I want to use when I build my intake, and I keep coming up with new questions. I don't really like the thought of having the BOV open under normal driving conditions, so a sequential seems to be out. I like the Tial valve, but it seems like there is a very fine line when it comes to spring pressure. Too much and you get surge/slow operation, too little and it will stay open too often. It seems to me like it would work better if it weren't controlled strictly by vacuum.

Then it occurred to me that the Tial wastegate I got from Steelblu has ports to operate off both boost and vacuum.

So here is my question: can I run a line from the manifold to the top of the wastegate and a line from the charge pipe to the bottom of the wastegate? In theory that would allow for a lighter spring, say 3-5 psi, so the valve only opens when there is a 3-5 psi difference across the throttle. I imagine that would make for a very fast and reliable response, and should still hold whatever boost you throw at it.

The only thing I can think might be a problem is if it would cause any tuning discrepencies, ie: commanded tip/map.

I assume if I were right this would be a far more popular mod, so what am I missing?

Here's a pic to illustrate what I mean. I added the AJP overboost mod in the drawing, too.

[MiWiAu]

Just to clarify, the boost regulator gate ("BOV" as it's called in your diagram) is controlled by boost, not vacuum. Both the charge pipe reference (blue) and an IM reference (red) would be POSITIVE pressure when under boost, not vacuum.
In the standard setup, the boost ref is hooked up to a bottom port, which pressurizes the diaphragm under boost and opens the valve.

After tuning (both with springs and desired TIP), my boost regulator is not open under normal driving conditions, only when pressure spikes during WOT upshifts or downshifts, otherwise it is closed

Frankly, I think you're overcomplicating it. In the standard setup, you just need a boost reference, the spring is sized based off your desired boost, and AJP can fine tune the opening of the gate by changing desired TIP.

IMO, by hooking it up the way you show in your diagram (PS, I like how you used a nuclear power plant, lol), you potentially severely limit your tuning options. The lightest spring in the Tial kit is 4.35 PSI, which may be too strong based on the differential between MAP and TIP. You have no kit options to step down, and the next step up is nearly 1.5 PSI. Additionally, there are additional connection points which increase the likelihood for leaks in the long run.

Good on you for thinking through some alternate setup options. I guess in the grand scheme of things, I just don't see any benefits to hooking it up the way you proposed as compared to a "standard" setup.




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[derfdog15]

My concern would be the Gate (BOV) opening during acceleration or while trying to build boost, and bleeding boost off.

A BOV stays open at idle/vacuum and closes when in boost, once you get out of boost it opens and relieves the pressure. A wastegate on the other hand is closed at vacuum/building boost, and opens when there is too much boost. As such I would stick to using a wastegate for the regulator mod, and a typical BOV for the BOV. TiAL with a -8PSI spring works very well.

[BOT_ROCKET]

Just to clarify, the boost regulator gate ("BOV" as it's called in your diagram) is controlled by boost, not vacuum. Both the charge pipe reference (blue) and an IM reference (red) would be POSITIVE pressure when under boost, not vacuum.
In the standard setup, the boost ref is hooked up to a bottom port, which pressurizes the diaphragm under boost and opens the valve.

After tuning (both with springs and desired TIP), my boost regulator is not open under normal driving conditions, only when pressure spikes during WOT upshifts or downshifts, otherwise it is closed

Frankly, I think you're overcomplicating it. In the standard setup, you just need a boost reference, the spring is sized based off your desired boost, and AJP can fine tune the opening of the gate by changing desired TIP.

IMO, by hooking it up the way you show in your diagram (PS, I like how you used a nuclear power plant, lol), you potentially severely limit your tuning options. The lightest spring in the Tial kit is 4.35 PSI, which may be too strong based on the differential between MAP and TIP. You have no kit options to step down, and the next step up is nearly 1.5 PSI. Additionally, there are additional connection points which increase the likelihood for leaks in the long run.

Good on you for thinking through some alternate setup options. I guess in the grand scheme of things, I just don't see any benefits to hooking it up the way you proposed as compared to a "standard" setup.




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I think you misunderstood my intent. The valve labeled "BOV" in my diagram is the blow off valve which is controlled by vacuum traditionally. The boost regulator (the one that controls turbo speed) is not in the diagram. I would be leaving the stock wastegate to control boost via tuning. The only difference between my idea and a traditional BOV is that instead of having the manifold hooked to the top port and the bottom open to atmosphere, it would have the top port hooked to the manifold and bottom port hooked to the charge pipe. That way when you slam the throttle shut, you have vacuum on top and boost on bottom. When the throttle is open, you have boost on top and bottom with spring pressure keeping the valve closed.

In any case, I figured out why the light spring wouldn't work. In a traditional BOV, the boost on top is what is keeping the valve closed, not the spring, so if you put boost on bottom, the spring is not enough to hold it shut under boost. The spring is there to counter vacuum at idle, it is not supposed to be able to counter boost. I didn't take into account the fact that the top of the valve is still open to atmosphere so the spring would have to be able to hold the boost pressure.

I'm not giving up on this, though. There has to be a way to keep the valve closed at all times that it isn't venting pressure, without causing surge.

What would happen if I mounted a duplicate of the over-boost valve, but put the manifold reference on top and charge pipe reference on bottom. Basically the same as my original idea, but with a heavier spring that was just enough to hold boost. I *think* it could use a lighter spring than the over-boost valve, since it doesn't have to counter boost both under the valve itself and under the diaphram. Both ports under boost=valve closed, top port under vac/bottom port under boost=valve open, both ports under vac=valve closed. I just worry this might not respond fast enough with a heavier spring. I might try this since I already have the parts to test it.

My concern would be the Gate (BOV) opening during acceleration or while trying to build boost, and bleeding boost off.

A BOV stays open at idle/vacuum and closes when in boost, once you get out of boost it opens and relieves the pressure. A wastegate on the other hand is closed at vacuum/building boost, and opens when there is too much boost. As such I would stick to using a wastegate for the regulator mod, and a typical BOV for the BOV. TiAL with a -8PSI spring works very well.

With the light spring in my original idea it would bleed boost. I think it might work with a heavier spring, though.

A spring type BOV is supposed to be closed at idle and normal driving, only opening to release pressure when you close the throttle. A sequential BOV as I understand it is open at all times under vacuum.

[MiWiAu]

I think you misunderstood my intent.

I think you're right, lol. And it still to early in the morning for my brain to be working, so I'll have to check in on this a little later.


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[derfdog15]

My concern would be the Gate (BOV) opening during acceleration or while trying to build boost, and bleeding boost off.

A BOV stays open at idle/vacuum and closes when in boost, once you get out of boost it opens and relieves the pressure. A wastegate on the other hand is closed at vacuum/building boost, and opens when there is too much boost. As such I would stick to using a wastegate for the regulator mod, and a typical BOV for the BOV. TiAL with a -8PSI spring works very well.

With the light spring in my original idea it would bleed boost. I think it might work with a heavier spring, though.

A spring type BOV is supposed to be closed at idle and normal driving, only opening to release pressure when you close the throttle. A sequential BOV as I understand it is open at all times under vacuum.

I know the TiAL Q that I use (and a few others use) is open at idle/no load (I can hear air exiting when I open the hood at idle). There is only one port on the traditional style BoV, on top, for a boost reference. I have not seen a BOV with a secondary reference. I run the TiALQ to replace stock BOVs, and a MV-S wastegate for my regulator mod. Like I said, a wastegate is meant to hold boost, so if you replaced BOVs with the gate you would have issues, since they are functionally opposite, which is how I understood the original question.

My TiAL has caused NO issue at all, on the -8psi spring, no surge, etc. Car drives like stock, except with a nice whoosh, and of course a lot more power due to the AJP Tune.