BOV or BPV ?

[1996MysticSnake]

In a blow through setup on a 96 cobra should i run a blow off valve or a bypass valve?

Should the valve be releasing pressure while idling or remain shut?

What are my options as far as the valve goes, i know Tial Q you can get a 3 psi spring for to make it work with a supercharger but are there any other options?

Tried to search it but i couldnt get a straight answer.

 

[03bluemach]

In a blow thru config you run a BOV . The valve is open at idle and closes at WOT
Any time your on the gas 1/2 throttle or more the valve is closed .. The size of the valve depends on how much boost you want to run .. If i were you i would just go with the vortech mondo or procharger big red and be done with it ..

 

[1996MysticSnake]

I know i need a BOV but from what i understand under light throttle and crusing the valve should be open to prevent surge. Most BOV's at idle are not open and are designed to be closed so how do you go about this?

The 3lb spring for the Tial BOV's solves this problem im assuming?

I just want to make sure i dont have any tuning issues or compressor surge

 

[Myzticsnake]

only time my red race closes is 1/2-full throttle. Around town driving it is never closed.

 

[1996MysticSnake]

Exactly thats what im trying to point out. BPV's only close under a decent amount of throttle.

BOV's are always closed and only open when you lift off the throttle under a boost condition.

So in that case you should not be running a blow off valve on a centri car because you are getting compressor surge. It may be very minimal and not damage the blower but it is present and probably is causing a rich condition in some situations.

 

[BADD281]

3lb spring in a Tial Alpha Q and call it a day. Dumps air just like the big red at almost all times but because of its rounded shape it is near silent compared to the other big valves. Mine dumps 17psi without any surge whatsoever. BOV's work but you will get more throttle plate flutter daily driving and higher IAT's due to the constant air pressure pushing against the mostly closed plate. If you get a light enough spring it will act just like the BPV (3lb Tial spring basically makes it act like the big red and mondo)

Another plus is the Tial stuff is like half the price of the Big Red.

 

[CobraMac]

Exactly thats what im trying to point out. BPV's only close under a decent amount of throttle.

BOV's are always closed and only open when you lift off the throttle under a boost condition.

So in that case you should not be running a blow off valve on a centri car because you are getting compressor surge. It may be very minimal and not damage the blower but it is present and probably is causing a rich condition in some situations.

I don't understand what you are saying, because you have things mixed up and confused...the blow off valve and bypass valve do the same thing. When the throttle is closed there is vacuum...when there is vacuum the bypass or blow off valve is open and allowing air to escape. This means when you are not pressing on the gas at idle, the bov and bpv is open, and in between shifts they are open.

The difference in the two is that the the bpv recirculates the air back into the intake track and the bov vents it to the atmosphere. Most cars that have sensitive air meters use bpv's.

So you have it backwards almost...bovs AND bpvs are almost always OPEN unless the throttle is pressed down. You can get compressor surge on both turbo and centrifugal supercharger applications. And compressor surge isn't that big of a problem with causing a rich condition...the problem is the throttle body is completely shut so and that compressed air has nowhere to go but back at the turbine which is spinning at an incredibly fast speed.

 

[AntiHeightPunk]

i have a blow off valve works well

 

[1996MysticSnake]

So does it matter what brand or type of BOV you use for a supercharged situation? CobraMac from what your saying they are the same exact thing except one vent to atmosphere and the other recirculates.

How about under part throttle situations like crusing down the highway at 2500 RPM?

Ive heard guys say that the spring in the turbo BOV's are too stiff and can create surging in this situation.

 

[03bluemach]

The only difference between the two is the MAF location .. In a draw thru/bypass setup the MAF is before the blower and the air has already been metered so you must recirculate the air back into the supercharger . Blow thru the MAF is on the discharge tube after the blower and doesnt need to be recirculated and this is why you can vent it because the air has not yet been metered .. they both work on the same principle ... Just get the procharger big red or vortech mondo and everything will be fine .. the only way i can think of that would cause a surging issue is if the BOV or BPV arent big enough...

If your still confused just do a google search , Thats the best way i know to explain ..

 

[CobraMac]

So does it matter what brand or type of BOV you use for a supercharged situation? CobraMac from what your saying they are the same exact thing except one vent to atmosphere and the other recirculates.

How about under part throttle situations like crusing down the highway at 2500 RPM?

Ive heard guys say that the spring in the turbo BOV's are too stiff and can create surging in this situation.

It doesn't really matter...some are just more efficient than others. If you have a centrifugal supercharger 99 times out of 100 you need a BPV.

At part throttle the valve should be closed or getting close to it as the vacuum is decreasing and therefore the valve will shut.

The things with the spring is that if you have a strong spring and not enough vacuum then you will get compressor surge because you won't have enough vacuum to open that valve when it needs to be. So just know what your engine normal running vacuum is and then make sure you get the right spring for that BPV. It should say what spring to use for what vacuum level.

 

[BADD281]

BOV's and BPV's are pretty much exactly the same in the sense that they release air based on what vacuum you are at and what stiffness of spring. Turbo applications usually use stiffer springs because there is no need to vent air at all times like a belt driven supercharger. Most BPV's have springs that allow for air to be released at almost any level of vacuum up until close to 0 that way all that air has a place to go. The main difference as said before is one is recirculated, so we can say that a turbo type BOV with a recirculation adapter is setup like a BPV. In terms of running turbo type BOV's (stiff spring) on a supercharger setup it can be done BUT you have to be aware that it will cause stress on the shaft of the blower with all that air being forced back to the impellar at idle and at cruising speeds. It may not do that much damage immediately but it will lower the life of the blower components, mainly mess with the input shaft play and seals.

BPV vs. BOV will depend on your maf setup. Blow through cannot be recirculated so basically you can run BPV's like the mondo but it will just vent to atmosphere. Procharger lists their big red as a bypass valve I believe but I think that is just to designate the fact that it is made for supercharger applications (soft spring).

If you still want to save money but also do things right buy a Tial BOV and order the 3psi supercharger spring with it. Quality pieces that have proven to evacuate very high amounts of boost without surging issues like smaller valves.

 

[1996MysticSnake]

Gotcha i understand now.


Thanks guys

 

[CobraMac]

Gotcha i understand now.


Thanks guys

You're welcome...we're here to help :beer:

 

[DSG2003Mach1]

BPV vs. BOV will depend on your maf setup. Blow through cannot be recirculated so basically you can run BPV's like the mondo but it will just vent to atmosphere. Procharger lists their big red as a bypass valve I believe but I think that is just to designate the fact that it is made for supercharger applications (soft spring).

.

and why is it that it cant be recirculated? Procharger setups are blow through and using the provided bypass valves its recirculated to the intake tube after the filter but before the blower. The bypass valve attaches to the first pipe coming off the blower

 

[01yellercobra]

and why is it that it cant be recirculated? Procharger setups are blow through and using the provided bypass valves its recirculated to the intake tube after the filter but before the blower. The bypass valve attaches to the first pipe coming off the blower

I wouldn't say you can't do it. But that you shouldn't do it. Recirculated air is hot air. The more you recirculate it the hotter it's going to get. Personally I prefer to vent to atmosphere to keep the air charge cooler.

 

[CobraMac]

I wouldn't say you can't do it. But that you shouldn't do it. Recirculated air is hot air. The more you recirculate it the hotter it's going to get. Personally I prefer to vent to atmosphere to keep the air charge cooler.

It's not hot air...its the same as the outside temperature basically...the air hasn't reached the engine yet. So the air has passed the turbine wheel and with a centri supercharger there isn't a hot/cold side. So the air isn't much warmer than ambient.

 

[01yellercobra]

While there isn't a hot side/cold side like a turbo, the blower piping does get hot from sitting next to the engine. Plus any moving air is going to heat up. The more it sits in the piping and is moved through the system the more it's going to heat up.

 

[bottlefed97]

only time my red race closes is 1/2-full throttle. Around town driving it is never closed.

Same here, here's my idle (before being tuned)

[nomedia="http://www.youtube.com/watch?v=XOhYOmLHNKc"]YouTube - Matt's idle[/nomedia]