There are several schools of thought on the necessity or for that matter the actual purpose of the BBV that is used on the 3800 Eaton Superchargers . One claim is that the valve was designed to keep supercharger noise low, the other claim is that its purpose is to limit the engine to receive only the air that it needs at cruise conditions and that the supercharger becomes overstressed if it tries to put in more air than the engine is calling for.
As for noise, Eaton did a write up on this a while back so we can assume that the BBV does suppresss some whine or noise.
As for the claim that the BBV recycles excess air under cruise conditions; I don't run a BBV and at highway speeds but my boost gauge still reads a vacuum. So does the BBV really unstress the rotors? I would say conditionally. After a WOT run you do have considerable boost, you let off the throttle and the boost needs to go somewhere so there could be some reversion but let us also not forget that the valves are still opening and closing letting the excess boost out. Under conditions of decelleration I would say that the BBV does provide some benefit but on a car that is used for car club, racing and occasiona use, I'll venture to say that you'd probably be OK without it.
This post is bound to create lots of discussion but 3800 Fiero owners seems to be thoughtful people so what say you?

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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, 3.4" Pulley, N* TB, LS1 MAF, Flotech Exhaust Autolite 104's Custom CAI 4T65eHD w. custom axles, HP Tuners VCM Suite.
87GT - 3.4L Turbocharged engine, modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

disconnected it a while back. not one problem that I have encountered.
Good info! glad to see I was on the same wave lenght.

Actually, reversion can cause problems. Probably not worth worrying about, but I know for a fact on diesel trucks, if you run a lot of boost and don't have a big enough BOV, you can get turbo "bark" under rapid deceleration from the boosted air reversing the spin direction of the turbo. Also, supposedly the BBV allows air to recerc inside the SC to increase fuel economy, but I don't buy into that claim.

my $.02

There is no discussion. GM used plastic intake gaskets instead of alum gaskets for 10+ years knowing they failed at 80k miles to save 20 cents each. You really think they would include a electronic solenoid, and a complex valve, if it wasnt required for proper operation? Intake noise is an obvious inaccuracy, because we all know the IAC valve makes a ton more noise then the blower could at idle.

Simple fact is the blower will "surge" without a BBV. Compressor maps dont show a surge line as it is inferred that a BBV is in the system. People run turbos without anti surge, and break shafts, and bend the fins on the compressor wheel, and it is a bit harder to bend the rotors in our blowers...

Just a thought here...The boost in a turbo application is created before the throttle body, and when the throttle blades shut the excess boost goes out via the blow off valve as to not damage the turbo.

In a roots blower application, the boost is created after the throttle body, so when the throttle blades close it doesn't make any difference since the boost pressure is in the intake manifold, and like the O.P. stated, the valves are still opening at low/closed throttle allowing the boost pressure to escape. Is that what the surging is? boost pressure in the combustion chamber at cruising speed?

Do I make any sense, because I just confused myself?

It surges the other way, were the motor is sucking more than the compressor/blower is outputting.

I can only speak from personal experience. I've shared my views on this before. I originally left it off of two of our cars. Later, for the hell of it, I reinstalled it. I will never take it back off again. First off, I didn't see any benefit with it off, other than cleanliness and simplicity. With the unit on, however, I did see an increase in MPG. While it might not be much, it adds up when driving halfway across the country a few times a year. I also noticed smoother engine idling, though others say they have not experienced the same result. I'm keeping mine in place if I ever do another SC swap.

If anything, you guys can take out the electric side of things and run it in "manual" mode to clean up some stuff too. The solenoid is only there to let the PCM cut boost if it feels like it (never seen it try to though).

Not to start an argument but I have run roots type superchargers like the B&M/Holley and Weiand for many years without BBV's and never had a problem. Consider that upon decelleration the valves on an engine are still continually opening and closing so it would seem a good amount of excess boost would just be blown out the exhaust I would think that if I always read a vacuum (all except for WOT), reversion would be minimal. As for the reason that GM installed it, it might be that decreased supercharger whine at low engine speeds could be the main advantage. There are guys that insist that the BBV does some good while there are others as myself that don't have one. I guess that time wil tell.

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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, 3.4" Pulley, N* TB, LS1 MAF, Flotech Exhaust Autolite 104's Custom CAI 4T65eHD w. custom axles, HP Tuners VCM Suite.
87GT - 3.4L Turbocharged engine, modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

quote Originally posted by Jncomutt: I can only speak from personal experience. I've shared my views on this before. I originally left it off of two of our cars. Later, for the hell of it, I reinstalled it. I will never take it back off again. First off, I didn't see any benefit with it off, other than cleanliness and simplicity. With the unit on, however, I did see an increase in MPG. While it might not be much, it adds up when driving halfway across the country a few times a year. I also noticed smoother engine idling, though others say they have not experienced the same result. I'm keeping mine in place if I ever do another SC swap.

This is why I leave them installed on my swaps. If you have the engine running at idle and force the BBV closed (as it would be if you removed the BBV actuator in your swap), you can definitely tell there is a load being put on the Supercharger. And this does cause the SC to draw more power from the engine. Why would you want to do this all of the time when it is not needed? Besides the MPG aspect, you need to keep in mind any time you put a load on the SC, it is producing heat. So from a performance standpoint, you would want to leave the BBV actuator installed and working just to keep the SC running as cool as possible. One could also make the argument that the increased load being put on the SC during times of normal driving could increase the wear being put on the SC vs. what it would normally see during its service life.

I also agree with DH in that you can remove the electrical aspect of the BBV system. The boost bypass solenoid is computer controlled and only commanded to reduce boost during the following conditions...

-When the transmission is in reverse gear
-When the car is nearing the top speed limiter set in the PCM programming
-During certain deceleration events (but the mechanical/vacuum aspect of BBV actuator operation does this on its own anyway)

If you leave the top half of the BBV connected to pre-SC vacuum (as it is connected stock), it will still operate as it would stock. Removing the electrical solenoid only takes the computer control away from it.

If you want to remove the BBV actuator in your swap to clean up the engine compartment, you can. But that is the ONLY benefit you will gain from this "mod". It DOES NOT increase performance of the SC or engine in any way by removing the BBV actuator.

-ryan

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5+ years on this same swap -- NO engine or transmission failures...

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

quote Originally posted by Dennis LaGrua: Not to start an argument but I have run roots type superchargers like the B&M/Holley and Weiand for many years without BBV's and never had a problem. Consider that upon decelleration the valves on an engine are still continually opening and closing so it would seem a good amount of excess boost would just be blown out the exhaust I would think that if I always read a vacuum (all except for WOT), reversion would be minimal. As for the reason that GM installed it, it might be that decreased supercharger whine at low engine speeds could be the main advantage. There are guys that insist that the BBV does some good while there are others as myself that don't have one. I guess that time wil tell.

Just get one from the junkyard and make up your own mind, Dennis. They're cheap and you can take it off if you don't like it. I don't understand why someone who has been running roots type superchargers for many years would even ask this question that has been debated a thousand times on this forum.

quote Originally posted by darkhorizon: There is no discussion. GM used plastic intake gaskets instead of alum gaskets for 10+ years knowing they failed at 80k miles to save 20 cents each. You really think they would include a electronic solenoid, and a complex valve, if it wasnt required for proper operation? Intake noise is an obvious inaccuracy, because we all know the IAC valve makes a ton more noise then the blower could at idle. Simple fact is the blower will "surge" without a BBV. Compressor maps dont show a surge line as it is inferred that a BBV is in the system. People run turbos without anti surge, and break shafts, and bend the fins on the compressor wheel, and it is a bit harder to bend the rotors in our blowers...

look at how much effort GM put into the ZR1 to quiet down the supercharger then it will make sense.

as for compressor surge, the turbo is still spinning at a high rate of speed and still has a wide open suction side. which is why it needs a BOV to release the pressure while the turbo decelerates. you cant compare this to our TB restricted setup.