Boost solenoid bypass.. .

I was just talking to a fellow tuner who will help me tune my 3800SC-III with Gen V in the spring… we got to talking about the boost solenoid bypass.. I told him I was just going to weld it shut and forget about it. He made a good point for keeping it… I want to run it by others on here to get a better picture..

I will have a 5 speed F23. He suggest we just tweak and tune the boost solenoid instead of removing it. The reason being, when you let off the gas quickly, The SC is still pushing boost but the injectors are backing off. You are leaning out momentarily and can cause detonation. He suggests tuning the boost solenoid to go full on at less than 5% throttle. (giving you a small margin of error for TPS out of calibration due to temps etc..). This would cut boost during a shift or any time you let off the gas. It might also be kinder to my seals.

What do you think?

No one?

I guess it is a tough one to figure out.

Patience, Grasshopper, its only been 5 hours.....

I'll bite.

There are two things being discussed here so I want to make sure everyone understands the difference.

1) Boost solenoid.

2) Boost bypass valve Actuator (BBVA).

The boost solenoid is controlled by the PCM. Its only function is to cut off boost level (by feeding boost pressure to the actuator's bottom port) when the PCM wants it to. The conditions the PCM "wants it to cut boost" is when the transmission is in reverse gear, you are decelerating, or you are nearing the top speed limiter (and maybe some other conditions which we have yet to discover). In any case, this solenoid is NOT a means of REGULATING boost pressure. It is just a means of cutting it as much as possible.

The boost bypass valve actuator can function normally without the boost solenoid being connected to it. All that is needed is a single vacuum line connection to the top of the actuator to a port on the blower housing that only sees vacuum (no boost). When the throttle is closed enough for the engine to produce vacuum, vacuum will be present in the blower housing above the blower roots and this vacuum will act on the bypass valve actuator to open the bypass valve, preventing boost pressure from being made by the supercharger. This reduces operational load of the supercharger on the engine which saves fuel and reduces internal supercharger temperatures (since air is not being compressed needlessly).

In all the swaps I've done, I've removed the boost SOLENOID but I've left the bypass actuator installed and functioning - working off the vacuum port only. There's NO reason to remove the actuator unless your goal is cleaning up the look of the supercharger. Removing the actuator and blocking the bypass valve closed does NOT improve performance and can actually cost you both in performance and fuel economy because the blower will be working 100% of the time, trying to make boost, when it's not needed (which costs engine power and heats up the blower).

I've heard the argument made for years that removing the BBVA and blocking the valve closed improves performance because this supposedly allows boost to be built earlier with lower throttle position. The truth of the matter is this doesn't actually improve performance at all, but all it may do is let boost build with lower throttle position which could be accomplished by simply reworking the throttle linkage cam on the throttle body. But what's the point of that? You aren't actually getting any HP/TQ gains out of the engine. And, like I said earlier, all you are doing is just working the blower 100% of the time which costs fuel economy and does nothing but heat up the blower.

Having the BBVA present and functioning (even if only by vacuum) will give you full boost capability the moment the throttle is opened enough to drop pre-blower (manifold) vacuum levels to 0 which will usually be achieved before you even reach 100% throttle opening.

-ryan

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OVERKILL IS UNDERRATED

Custom GM OBD1 & OBD2 Tuning | Engine Conversions & more | www.gmtuners.com

Any pics of what we are talking about?

Hey Darth!

Thanks for the info!

I'm just a bit skeptical about the vacuum presence behind the throttle plate... In my opinion (I have to test this with a gauge) there should be vacuum there 90% of the time, only at 90%+ throttle opening would the vacuum drop enough to potentially release the BBV..

The whole point of having a throttle plate is to restrict air flow to the engine. That means there is suction, that means there is vacuum..

Does anyone know how much vacuum is required for the BBV to engage? I'm guessing not much.. :\

What about a vacuum regulator? Is there such a thing?

quote Originally posted by Darth Fiero: I'll bite. There are two things being discussed here so I want to make sure everyone understands the difference. 1) Boost solenoid. 2) Boost bypass valve Actuator (BBVA). The boost solenoid is controlled by the PCM. Its only function is to cut off boost level (by feeding boost pressure to the actuator's bottom port) when the PCM wants it to. The conditions the PCM "wants it to cut boost" is when the transmission is in reverse gear, you are decelerating, or you are nearing the top speed limiter (and maybe some other conditions which we have yet to discover). In any case, this solenoid is NOT a means of REGULATING boost pressure. It is just a means of cutting it as much as possible. The boost bypass valve actuator can function normally without the boost solenoid being connected to it. All that is needed is a single vacuum line connection to the top of the actuator to a port on the blower housing that only sees vacuum (no boost). When the throttle is closed enough for the engine to produce vacuum, vacuum will be present in the blower housing above the blower roots and this vacuum will act on the bypass valve actuator to open the bypass valve, preventing boost pressure from being made by the supercharger. This reduces operational load of the supercharger on the engine which saves fuel and reduces internal supercharger temperatures (since air is not being compressed needlessly). In all the swaps I've done, I've removed the boost SOLENOID but I've left the bypass actuator installed and functioning - working off the vacuum port only. There's NO reason to remove the actuator unless your goal is cleaning up the look of the supercharger. Removing the actuator and blocking the bypass valve closed does NOT improve performance and can actually cost you both in performance and fuel economy because the blower will be working 100% of the time, trying to make boost, when it's not needed (which costs engine power and heats up the blower). I've heard the argument made for years that removing the BBVA and blocking the valve closed improves performance because this supposedly allows boost to be built earlier with lower throttle position. The truth of the matter is this doesn't actually improve performance at all, but all it may do is let boost build with lower throttle position which could be accomplished by simply reworking the throttle linkage cam on the throttle body. But what's the point of that? You aren't actually getting any HP/TQ gains out of the engine. And, like I said earlier, all you are doing is just working the blower 100% of the time which costs fuel economy and does nothing but heat up the blower. Having the BBVA present and functioning (even if only by vacuum) will give you full boost capability the moment the throttle is opened enough to drop pre-blower (manifold) vacuum levels to 0 which will usually be achieved before you even reach 100% throttle opening. -ryan

[This message has been edited by Purple86GT (edited 02-21-2013).]

quote Originally posted by Purple86GT: Hey Darth! Thanks for the info! I'm just a bit skeptical about the vacuum presence behind the throttle plate... In my opinion (I have to test this with a gauge) there should be vacuum there 90% of the time, only at 90%+ throttle opening would the vacuum drop enough to potentially release the BBV.. The whole point of having a throttle plate is to restrict air flow to the engine. That means there is suction, that means there is vacuum.. Does anyone know how much vacuum is required for the BBV to engage? I'm guessing not much.. :\ What about a vacuum regulator? Is there such a thing?

I think the BBVA closes the BBV before the vacuum level drops to 0.

The manifold vacuum behind the throttle blade drops to 0 at different throttle openings depending on engine load and RPM.

But who cares? At 100% throttle, the BBV is closed and you're getting 100% boost level. What difference does it make at other throttle positions? If you want full boost, give it full throttle.

Let me put it another way: If you removed the BBVA and blocked the BBV so it was closed full time, you aren't going to get full boost level with a partially open throttle because it is going to cause a restriction until it is open far enough to give the blower all the air flow it wants.

All that BBVA system does is takes the working load off the supercharger when its not needed. That's it (unless you leave it under PCM control via the solenoid and the PCM commands a no boost condition).

Ryan, do you have pic of this so i can gear mine up the way you mentioned when i get to that point? Am i right by saying i can run a vac line from one of the 3 nipples on the plastic port on top of the blower to the bypass actuator and it will work as stated?

troy

BBV delete for 3 years. No ill effects but slightly more supercharger noise at idle, 27 hwy mpg. You decide.

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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Powerlog manifold, Northstar TB, LS1 MAF, 3" Flotech Afterburner Exhaust, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

quote Originally posted by Dennis LaGrua: BBV delete for 3 years. No ill effects but slightly more supercharger noise at idle, 27 hwy mpg. You decide.

I've had customers get over 30mpg hwy fuel economy with the BBVA still hooked up....

[This message has been edited by Darth Fiero (edited 02-22-2013).]

With the throttle plate closed (and BBV closed as well) does the lower intake manifold see vacuum? If it does, would it not be better to attach the BBV vacuum feed there?

My concern is the SC upper vacuum port seems to be a place where you would see vacuum all the time EXCEPT MAYBE during full throttle. That charger is sucking air and any resistance from the throttle plate would cause a vacuum between the TB and supercharger.

quote Originally posted by Purple86GT: With the throttle plate closed (and BBV closed as well) does the lower intake manifold see vacuum? If it does, would it not be better to attach the BBV vacuum feed there?

Yes. The lower intake manifold vacuum port sees both vacuum and boost. But NO, you don't want to hook the top port of the BBVA to this because it was not designed to see boost on this port. And even if you did hook it up, it wouldn't make ANY difference in the max power output of the engine.

quote My concern is the SC upper vacuum port seems to be a place where you would see vacuum all the time EXCEPT MAYBE during full throttle. That charger is sucking air and any resistance from the throttle plate would cause a vacuum between the TB and supercharger.

The BBVA closes the BBV before vacuum levels reach 0. I don't have the exact vacuum level it closes at because I don't have a blower sitting here on my bench I can test. I can tell you there is a spring inside the BBVA that normally holds the BBV closed and it takes a certain amount of vacuum to overcome this spring pressure to open the BBV.

I guess I don't understand why anyone would be concerned about the BBV closing EARLIER relative to throttle position. It is going to close before you reach WOT and it will be closed when you reach WOT which will give you full boost.

Who cares what it is doing at part throttle? Do you race down a dragstrip at part throttle? Do you run your car on a dyno at part throttle? At full throttle, it will be closed and you'll have full boost potential. So why the concern otherwise?

YOU AREN'T GAINING ANY PERFORMANCE BY REMOVING THE BBVA AND BLOCKING THE BBV CLOSED FULL-TIME - PERIOD. The only reason why anyone would have for doing this is to simply clean up the look of the blower. That's it.

[This message has been edited by Darth Fiero (edited 02-22-2013).]

quote Originally posted by Darth Fiero: I've already told you that the BBVA closes the BBV before vacuum levels reach 0. I don't have the exact vacuum level because I don't have a blower sitting here on my bench I can test. I guess I don't understand why you are so concerned about the BBV closing EARLIER. It is going to close before you reach WOT and it will be closed when you reach WOT which will give you full boost. Who cares what it is doing at part throttle? Do you race down a dragstrip at part throttle? Do you run your car on a dyno at part throttle? At full throttle, it will be closed and you'll have full boost potential. So why the concern otherwise? YOU AREN'T GAINING ANY PERFORMANCE BY REMOVING THE BBVA AND BLOCKING THE BBV CLOSED FULL-TIME - PERIOD. The only reason why anyone would have for doing this is to simply clean up the look of the blower. That's it.

Engine efficiency. No I don't drive WOT all the time, but I want to have some boost all through the throttle curve. The engine has lower compression than the NA counterpart. To remain efficient it needs to see boost..

quote Originally posted by Purple86GT: Engine efficiency. No I don't drive WOT all the time, but I want to have some boost all through the throttle curve. The engine has lower compression than the NA counterpart. To remain efficient it needs to see boost..

The blower is nothing but an air pump. With the throttle closed enough to build vacuum, all the blower is doing at that point is trying to draw in more air than can flow thru the partially closed throttle. All this does is MAKES THE SUPERCHARGER WORK WHICH DRAWS POWER FROM THE ENGINE VIA THE SUPERCHARGER BELT.

GM designed the BBV to allow air to bypass the supercharger roots in order to take the load off of the supercharger which reduces engine load. The main benefit of having a functioning BBV and BBVA system is increased fuel economy. That's why they put it on there.

Taking it off does NOTHING to increase WOT performance and the result will DECREASE fuel economy.

[This message has been edited by Darth Fiero (edited 02-22-2013).]

I had my blower setup as darth recommends. No solenoid, vacuum line from top of blower to top of actuator, bottom port open. Boost would come in at ~25-30% throttle depending on load. I think your over thinking this. Keep the vacuum line hooked up for economy and to keep blower cooler. If you watch the actuator, and blip the throttle open in park, it will close the bypass extremely fast. I can't see any measurable gain in keeping it closed all the time. You won't lean out when you close the throttle either. With the throttle closed, very little air can enter the blower, no air, can't lean out, it will also go to vacuum right away, no boost.

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10.263 @ 134.44MPH - 1.49 60'
Billet 6262 Precision turbo, PT1001 intercooler, ST1 cam, 130lb springs, comp pushrods, HV3, ARP Rod bolts, otherwise stock L36.


Old M90 XP Cam time -
11.425 @115.60
1.543 60'

quote Originally posted by Darth Fiero: I've had customers get over 30mpg hwy fuel economy with the BBVA still hooked up....

Yes but probably not on a 3800SC with a 4T65eHD auto, and a genV supercharger, with a 3.4" pulley. I do not believe that running the BBV will really change gas mileage much. I'll give you that a .5 mpg improvement ,might be possible but you aren't getting 30 HWY MPG with my setup.
------------------
" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Powerlog manifold, Northstar TB, LS1 MAF, 3" Flotech Afterburner Exhaust, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

[This message has been edited by Dennis LaGrua (edited 02-22-2013).]

quote Originally posted by Dennis LaGrua: Yes but probably not on a 3800SC with a 4T65eHD auto, and a genV supercharger, with a 3.4" pulley.

Actually yes, I've had customers with identical setups get over 30 mpg hwy.

quote I do not believe that running the BBV will really change gas mileage much. I'll give you that a .5 mpg improvement ,might be possible but you aren't getting 30 HWY MPG with my setup.

You can believe what you want. What I've discussed in this thread about the benefits of having a working BBV system was, in part, based on documentation I've read that was published by GM explaining why the BBV system was added. Their own documentation explained the fuel economy gains that were a benefit to having that system on there and functioning.

You know, you could always reinstall your BBVA and see if you pick up any fuel economy having it. I bet you would. How much is the question. But even if it was only 0.5 mpg, at over $4/gal for premium unleaded, wouldn't it be worth the long-term savings?

[This message has been edited by Darth Fiero (edited 02-22-2013).]

Whoa! Guys! let's not get worked up on this, it's a discussion to see if the BBV idea can be improved on.

What about using the solenoid and actually tuning the BBV? Any benefit?

Thanks for the detailed explanation of the BBV system.

I'm sure I'm not the only one who did not have a full understanding of the system.

quote Originally posted by Purple86GT: What about using the solenoid and actually tuning the BBV? Any benefit?

Tuning it to do what? Use it for boost control? I suppose with the right controller and perhaps a different type of solenoid, you could do that with it. But to what end? The supercharger puts out a fixed amount of air (volume/boost) for a given RPM, so there's really no worry about boost "running away" on this type of supercharger like it would on a turbo application. There's no reason to lower the boost level unless you get a tank of crap gasoline - in which case you could just hook up a boost line directly to the lower port on the BBVA which would cause it to keep boost levels to a minimum (perhaps 1 psi or so). But regulate it down? That's difficult to do with this setup. Much easier to just change out the SC pulley to the size (boost level) you need.

Now I will say I've had family and friends who owned L67 powered cars that wanted to be able to run crap 87 octane fuel in them and they asked me what they could do to their engines to get away with this (all of these were stock applications) without damaging the engine. I told them they could unplug their boost solenoids (the PCM cuts power to the solenoid to cut boost) which would have the affect of routing any boost to the bottom port of the BBVA at all times (if boost tried to build). Since it takes a small amount of boost to overcome spring pressure within the BBVA, some has to build before it can open the BBVA and prevent the boost level from climbing. You could probably safely run 87 octane in one of these engines if the boost level wasn't allowed to go any higher than 1 or 2 psi.

Due to the SC engine's lower static compression ratio, it should get slightly better fuel economy running 87 octane than it does on premium grades. But where's the fun in not being able to use the boost?

[This message has been edited by Darth Fiero (edited 02-23-2013).]

Ryan, looking at these photos, do I have this hooked up according to the way you set these up? Also, in the first pic, what do i do with the 2 outlets on the silver port. And in the second pic, concerning the black port on the top, the small outlet gets plugged i think, but what do i do with the larger port?

quote Originally posted by fieroaddicted: Ryan, looking at these photos, do I have this hooked up according to the way you set these up? Also, in the first pic, what do i do with the 2 outlets on the silver port. And in the second pic, concerning the black port on the top, the small outlet gets plugged i think, but what do i do with the larger port?

You have the BBVA connected properly in the 1st picture.

The silver vacuum tree sees both boost and vacuum. What you have there is an early design M90 blower (1996-97). GM deleted that metal vacuum tree (you painted silver) in 1998-up applications. You can hook a boost/vacuum gauge up to this port if you have one. The fuel pressure regulator and/or MAP sensor can also be connected to these ports.

In the 2nd picture showing the top vacuum tree, the small port you have open there can be plugged or you can connect it to your EVAP purge solenoid (if you are using one). The largest port was for the vacuum brake booster. But if you have a large open vac port on the throttle body, you can connect the Fiero brake booster vac line to this port and just plug the big one on top of the blower housing.

quote The silver vacuum tree sees both boost and vacuum. What you have there is an early design M90 blower (1996-97). GM deleted that metal vacuum tree (you painted silver) in 1998-up applications. You can hook a boost/vacuum gauge up to this port if you have one. The fuel pressure regulator and/or MAP sensor can also be connected to these ports.

Yes, i do have a vac/boost gauge so i will hook it up there instead of "Teeing" off the front port of the intake plenum. I will then hook the fuel reg up to the other port. Thanks
troy

You can also flip the black vacuum block around so the big port points forward, easier to connect to brake booster that way.

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10.263 @ 134.44MPH - 1.49 60'
Billet 6262 Precision turbo, PT1001 intercooler, ST1 cam, 130lb springs, comp pushrods, HV3, ARP Rod bolts, otherwise stock L36.


Old M90 XP Cam time -
11.425 @115.60
1.543 60'

quote You can also flip the black vacuum block around so the big port points forward, easier to connect to brake booster that way.

good point thanks!