Prodrive BCS: Myths vs Fact

There are references everywhere, from "official documentation" to a multitude of individual threads on car forums. Most are mere hints, many are guesses, some are questioning inquiries from those in true need, and some are wrong enough to destroy engines. This will explain my own conclusions.

The Prodrive BCS is a 3-port EBCS that directly replaces the stock Subaru unit.

It cannot be used without tuning, period. Doing so risks destruction of that engine.

While it has 3 ports only two are used, when plumbed properly, contrary to most instructions including 'official' information. It is necessary to understand how the boost control system works for this to make sense. You won't find that information in any digestible form that I know of, although attempts are there.

Most instructions calling for the use of all 3 ports erroneously connect one of the ports to the intake where the stock BCS is plumbed. The fact is, however, whenever the Prodrive is in one of its two states, DE-energized (zero WGDC), this port is blocked, the same condition as if that intake nipple were capped off. In the Prodrive's other state, energized (activated by the WGDC table), this port is connected to the Wastegate Actuator, again effectively capping this port (note that in this energized state the input from the turbo is blocked). Therefore, either energized or de-energized there is a) no point in a useless hose being connected to this port nor b) any reason whatsoever for the intake nipple used by the stock BCS NOT to be capped. It no longer has a function.

Plumbed properly the Prodrive is merely inserted into the loop between the turbo's compressor and the Wastegate Actuator, using the two ports that pass air when the Prodrive is dead in your hands. End of story.

There is one advantage of the stock BCS over the Prodrive, and it is significant: If the Prodrive sticks in the ENERGIZED position you will have UNCONTROLLED BOOST, potentially destroying your engine. If your stock BCS sticks open you will get the boost limitations that prompted your Prodrive purchase. Now, consider how many nay-sayers and whiners about WI cite such a catastrophic result as the reason for not using WI as opposed to all those on the Prodrive bandwagon. Interesting, eh?

I was going to include reference links here but after reviewing them found virtually all to be bogus guessing and misleading. However, the pictures below represent the Prodrive BCS. It CAN be hooked up as a 'bleeder' BCS using ports 1 and 2, but why? Your factory BCS does just fine as a bleeder device. The Raison d'etre for the Prodrive in our cars is as a blocking, or interrupt, BCS and should be hooked up one simple way using only ports 2 and 3 as noted.

In one diagram the ports are 1, 2, and 3. Three (3) is the only metal port and is the input from the turbo's nipple on the compressor. Two (2) is the normally open port connected to port 3 when the solenoid is de-energized and is connected to the Wastegate Actuator's nipple. One (1) is not used when the Prodrive is used properly as an interrupt BCS (just be sure to cap the unused nipple on the intake).

Looking at the second diagram shows an example where port #1 is 'supposed' to go to the intake. Harmless, but useless, although the Prodrive will operate as shown.

although attempts are there.

 

Most instructions calling for the use of all 3 ports erroneously connect one of the ports to the intake where the stock BCS is plumbed. The fact is, however, whenever the Prodrive is in one of its two states, DE-energized (zero WGDC), this port is blocked, the same condition as if that intake nipple were capped off. In the Prodrive's other state, energized (activated by the WGDC table), this port is connected to the Wastegate Actuator, again effectively capping this port (note that in this energized state the input from the turbo is blocked). Therefore, either energized or de-energized there is a) no point in a useless hose being connected to this port nor b) any reason whatsoever for the intake nipple used by the stock BCS NOT to be capped. It no longer has a function.

 

I'm going to have to disagree with you on this point (unless I'm mis-understanding what you are trying to say). When the solenoid is off, the actuator port is connected to "pressure source" port. When the solenoid has currently flowing through it, the actuator port is connected to the "dump" port.

Used correctly, the 3-port config reduces the actuation delays and eases the compromise made between speed of control and accuracy of control. Think of it this way, the stock bleeder system allows you to scale down the pressure seen at the actuator. Unfortunately, larger scalings need a smaller restrictor and cause the 'source impedance' (borrowing an EE term and applying it to a mechanical system) of the pressure source to increase. The actuation delay increases. With the 3 port bleeder system, you can get the scaling you want and decrease the effective source impedance driving the actuator. Without going into much control theory, I can assure you that a slower acting actuator either requires a compromise between overshoot and speed or a more complex controller. We can't modify the control algorithm, just the calibration values it uses.

Some months ago I posted a write up explaining why a 3 port can bring on boost with less of a compromise between overshoot and speed. I'm not in Toronto right now so I don't have the doc. It is probably floating around somewhere though...

Anyone wanting a quick ref should check up Ogata's work (I think the text is Modern Control Theory) or Kwong's work on discrete time non-linear control (check his notes on the "waterbed" effect).

I'm going to have to disagree with you on this point (unless I'm mis-understanding what you are trying to say). When the solenoid is off, the actuator port is connected to "pressure source" port. When the solenoid has currently flowing through it, the actuator port is connected to the "dump" port.

No disagreement, we're saying the same thing: when it is off the actuator is connected to the pressure source port and when it is energized the actuator is connected to that other port..........only that other port, the one you call the "dump" port, has no function. The actuator is a dead-end, air flow-wise. So connecting a hose to that "dump" port accomplishes nothing but use up hose. If you connect it to the intake nipple all you have done is connect a loooong cap on the nipple, better to just cap it right at the intake tube. As for the wastegate actuator being connected to an open port? Why not, you don't want any pressure on it anyway and letting it, more or less, vent to atmosphere empties it in preparation for whatever pressure is dictated by the WGDC Tables.

Some months ago I posted a write up explaining why a 3 port can bring on boost with less of a compromise between overshoot and speed. I'm not in Toronto right now so I don't have the doc. It is probably floating around somewhere though...

 

Anyone wanting a quick ref should check up Ogata's work (I think the text is Modern Control Theory) or Kwong's work on discrete time non-linear control (check his notes on the "waterbed" effect).

I love references and will get and read these. Whether I understand them or not is another issue . What I know about this subject has been accumulated over the past several months after getting StreetTuner. In the beginning I floundered but by continuously experimenting certain facts evidenced themselves. Most important was playing with different pill sizes I created and tuned for. Eventually I understood, and once that happened all the 'wrong' information started to stand out.

This Prodrive thing came up because I got it in the mail yesterday and I realized I didn't know what to do with it, so the hunt began. My original post was the result.

As soon as I am secure in the data I am going to install the AVO380LGT, AVO FP, and DW injectors sitting here. At present I am worried about only one thing, getting that intake hose onto the compressor.

lots of lube + a bent pick is the trick... the AVO inlet is bigger than stock and slightly offset so it takes a bit of fiddling

when you install the p-drive unit, you will need to make some adapters to change hose sizes. brake line brazed to a nipple fittings works pretty well.

When the pro-drive is alternating very quickly from blocking to non-blocking mode would not a small amount of air escape out the 3rd port in the transition?

I don't know how much air that would be, but wouldn't that mean there is theoretical advantage to using all 3 ports?

When the pro-drive is alternating very quickly from blocking to non-blocking mode would not a small amount of air escape out the 3rd port in the transition?

 

I don't know how much air that would be, but wouldn't that mean there is theoretical advantage to using all 3 ports?

No.

Remember, that unused port is either connected to the wastegate actuator or blocked, it is not ever connected to the pressure source so it simply cannot leak any active air. The blocking action occurs between the wastegate actuator port and the pressure source, the compressor nipple. Even the stock BCS's intake return line is more for engineering tidiness than any performance issue, the air that is returned is pre-turbo, and despite having been metered is negligible in volume.

Again, all the third port can do is vent the wastegate actuator's chamber to atmosphere. That is, unless you really want to use up some spare hose and use the actuator as a cap on the intake nipple when it isn't being capped by the BCS:).

Humor me. I am sure it is negligible.

Comp side is connected to WG actuator, it is pressurized. ECU calls for X amount of WGDC, that small little tiny bit of pressurized air (from the solenoid to the actuator) is then allowed to vent to atmosphere as the Wg actuator moves to block the comp side connection. This happens many times a second. Some air is lost.

Likely too negligible to matter, but still present, no?

As soon as I am secure in the data I am going to install the AVO380LGT, AVO FP, and DW injectors sitting here. At present I am worried about only one thing, getting that intake hose onto the compressor.

I just installed my AVO 420 last weekend, the intake hose isn't that bad, it's the oil line that was a PITA. The one they supplied was too short, and although the stock one can be modified, you have to drill out the hole in the banjo conection to get it to fit

DW injectors are going in next weekend and going to get a tune with a Prodrive BCS, I'll post up the results.

I just installed my AVO 420 last weekend, the intake hose isn't that bad, it's the oil line that was a PITA. The one they supplied was too short.

Still? Bosco had that problem with his 380 last spring.

Still? Bosco had that problem with his 380 last spring.

you are correct. it's all here http://www.legacygt.com/forums/showthread.php?t=59432&highlight=bosco%27s+install+day bosco

Please cap the 3rd port and tell me what happens While it seems to have no function, if the Prodrive operates in the same fashion as the Perrin EBCS (and I'm almost sure it does) capping the 3rd port will result in your boost diving just after spoolup. I once capped the 3rd port on a buddy's car after I installed his EBCS (ages ago) and when it was being tuned it would hit target boost then nosedive. A couple of runs later the tuner asks us what kind of boost control the car had and we told him an EBCS. His next question was: "Did you cap off the port that is supposed to be left open or plumbed back to the turbo inlet hose" DOH!

I'm not about to try and really figure out why, but from what I understand there is a small amount of air vented through the "unused" port. It is such a small amount that you can vent it to atmosphere without any ill effects or just plumb it back to the intake. Whatever you do, don't cap it.

Humor me. I am sure it is negligible.

 

Comp side is connected to WG actuator, it is pressurized. ECU calls for X amount of WGDC, that small little tiny bit of pressurized air (from the solenoid to the actuator) is then allowed to vent to atmosphere as the Wg actuator moves to block the comp side connection. This happens many times a second. Some air is lost.

 

Likely too negligible to matter, but still present, no?

That seems right to me.

Please cap the 3rd port and tell me what happens While it seems to have no function, if the Prodrive operates in the same fashion as the Perrin EBCS (and I'm almost sure it does) capping the 3rd port will result in your boost diving just after spoolup. I once capped the 3rd port on a buddy's car after I installed his EBCS (ages ago) and when it was being tuned it would hit target boost then nosedive. A couple of runs later the tuner asks us what kind of boost control the car had and we told him an EBCS. His next question was: "Did you cap off the port that is supposed to be left open or plumbed back to the turbo inlet hose" DOH!

 

I'm not about to try and really figure out why, but from what I understand there is a small amount of air vented through the "unused" port. It is such a small amount that you can vent it to atmosphere without any ill effects or just plumb it back to the intake. Whatever you do, don't cap it.

Makes sense to me, and why I will leave my third port open. As I said, it vents the acutator's containment of pressurized air, effectively resetting its state to zero. The flow of air that will emit from it will be the sum of all the actuator's pressurized air, minus its ambient volumn, left when the BCS interrupts the input from the pressure source. If that port were capped the actuator would be left pressurized, holding the waste gate, to some degree or other, partially open, draining exhaust pressure and affecting boost control.

Open, or vented through a hose to the intake, whichever, the actuactor's vented volumn of air is inconsequential to the operation of the motor. Returned to the intake nipple it reenters air being drawn into the turbo, and vented to atmosphere where it sits it reenters air being drawn into the turbo. Neither way will measurably affect anything. For those whose sensibilities are insulted by an open port, put a hose from it to the intake.

Don't insult my sensibilities.

Either way thanks for the write-up.

Still? Bosco had that problem with his 380 last spring.

Yes, still. They promised me a new oil line two months ago

Yes, still. They promised me a new oil line two months ago

they sent me a new oil line (one week) after i told them the oil line needed to be about 1.5 to 2" longer and guess what, it was the same lenght as the first one. just bend the stock hard line. bosco

Bending the stock line was the easy part, but the banjo fitting had to be drilled out by 1.0mm so that the banjo bolt would fit through it.

Making sure I had all the swarf and debris out of the pipe before installing it was worrysome.

Bending the stock line was the easy part, but the banjo fitting had to be drilled out by 1.0mm so that the banjo bolt would fit through it.

 

Making sure I had all the swarf and debris out of the pipe before installing it was worrysome.

i have the oil line they sent me and never used it if you want i can send it to you. i had no issues with bango bolt on either line maybe i'm not understanding what's going on here. bosco

Yes, still. They promised me a new oil line two months ago

Because of bosco's problems with that oil line, as well as yours and others, I've resigned myself to dealing with it like bosco did.... bend the stock pipe so the short AVO line fits. But I don't like it.

The stock oil line is shaped as it is for a reason, when the engine is shut off there is a certain amount of oil HIGHER than the turbo that drains into the bearings keeping them lubricated and fighting oil breakdown. The water operation is similar, but likely more important. To me, therefore, it is important that the oil supply line to the turbo approach from the top, not from underneath.

The banjo bolt on the 420 is larger in diameter than the stock banjo bolt. So although I could use the stock oil line, the new bolt wouldn't go through it.

The stock banjo bolt is too small for the 420 and can't be used.

I'm good with the stock line now though, but thanks for the offer.

And before Rao jumps in, yes, I did anneal the copper washers

And before Rao jumps in, yes, I did anneal the copper washers

:lol:

Bending the stock line was the easy part, but the banjo fitting had to be drilled out by 1.0mm so that the banjo bolt would fit through it.

 

Making sure I had all the swarf and debris out of the pipe before installing it was worrysome.

How did you drill that fitting out? In reading bosco's install thread he mentioned this, but it seemed it would be difficult to do correctly, centered and all. Can it be done with hand tools or did it require a drill press, etc.? I think it is the better solution, personally, for the reason I mentioned as well as keeping it stock looking.