BOV & wastegate springs
04-06-2012, 12:03 PM
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BOV & wastegate springs
So I'm planning to run about 7-8psi through my new turbo set up.
Do the wastegate and the BOV springs have to be the same PSI?
Wastegate is a Tial 50mm and BOV is a Tial 38mm
Do the wastegate and the BOV springs have to be the same PSI?
Wastegate is a Tial 50mm and BOV is a Tial 38mm
04-06-2012, 12:20 PM
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No, your BOV really only needs to be a few psi, the same boost attempting to open it is the same boost (or very similar) to what is keepint it shut, the spring is only there to give it a little bit of assistance. This is really because the signal line is very small, so you need a spring to conpensate. If you had a massive 1" dia hose hooked up, you wouldn't even need a spring really (maybe 1psi), as the same amount of boost the the charge pipes, is the same amount of boost in the IM (maybee 1 psi less) and the pressure equalizing is what would keep it shut. But since you have this tiny hose (generally 1/4" or so) you can get the IM's full boost in enough time, compared to the charge pipe which has it instantly so it would open on you. Don't be one of those people who cna't understand this philosophy and say they are running 30psi and get a 30psi spring and have terrible compressor surge or BOV flutter. Your spring isn't what holds it shut, the pressure does, the spring is a small assistant.
Another reason for the BOV spring is to hold it shut while your IM is under vacuum, most cars have around -10psi vacuum. So less than 10psi spring and your BOV will be open while idleing.... I think this is not a good idea as unfiltered air could enter and cause damage, but some believe the charge pipes have enough pressure that it wouldn't allow any particles to enter. Synapse is one of the BOV's that is open while idle. Other than that reason, I think synapse is a great BOV. Of course if you have a recirc CBV, then there is no worries if it is open at idle. But I would say for any car under 30psi, 11-15psi is more than enough to hold the boost.
Your WG spring can be as high as you want the minimal boost to be. Boost controller prevents the WG from opening. So if you have 5psi spring and no boost controller, the wg will open at 5psi, but if you put a boost controller on it you can hold up to 30psi... This caries quite a bit and genreally EWG's can hold much more boost with the controller as it has dual ports. But if you want to run 5psi sometimes, and you have a 15psi spring, you can only run 15psi at the lowest. Even with a boost controller, you will be at 15psi min. Boost controller controls the max boost, and the WG spring controlls the min boost. A good rule of thumb is get a WG spring that is a bit more than half the psi you plan to max. ie. 30psi max, get a 16psi WG spring.
If you want to run 18psi and you get a 18psi spring, that is not advisable. As you will most liley overboost quite a bit and you boost controller is worthless.
Though running 7psi.... I would recommend a 5lbs spring maybe on the WG, and as far as the BOV goes... I wouldn't even recommend a BOV at those levels. Lift off surge isn't THAT big of a deal at those tiny psi levels. Your engine will suck 7psi down pretty quick even on closed throttle. I have heard of a few cars running 6-8 psi with no BOV and no issues. But if you got one, a 12psi spring should be enough. 12psi so it holds it shut when idle, and with -10psi vacuum at liftoff plus the charge pipes 7psi, you should be able to open it to vent. You might get a bit of BOV flutter, which isn't a big deal nor does it really ahve any negative effects (other thatn undisirable sound for some). But once your charge pipes drop to 3-4psi, your BOV might try to shut and pressure will have to rebuild to open it and so on. Though I you might get a gobble or two, none of those 3-5 flutters that those higher psi guys get with really stifff springs.
Another reason for the BOV spring is to hold it shut while your IM is under vacuum, most cars have around -10psi vacuum. So less than 10psi spring and your BOV will be open while idleing.... I think this is not a good idea as unfiltered air could enter and cause damage, but some believe the charge pipes have enough pressure that it wouldn't allow any particles to enter. Synapse is one of the BOV's that is open while idle. Other than that reason, I think synapse is a great BOV. Of course if you have a recirc CBV, then there is no worries if it is open at idle. But I would say for any car under 30psi, 11-15psi is more than enough to hold the boost.
Your WG spring can be as high as you want the minimal boost to be. Boost controller prevents the WG from opening. So if you have 5psi spring and no boost controller, the wg will open at 5psi, but if you put a boost controller on it you can hold up to 30psi... This caries quite a bit and genreally EWG's can hold much more boost with the controller as it has dual ports. But if you want to run 5psi sometimes, and you have a 15psi spring, you can only run 15psi at the lowest. Even with a boost controller, you will be at 15psi min. Boost controller controls the max boost, and the WG spring controlls the min boost. A good rule of thumb is get a WG spring that is a bit more than half the psi you plan to max. ie. 30psi max, get a 16psi WG spring.
If you want to run 18psi and you get a 18psi spring, that is not advisable. As you will most liley overboost quite a bit and you boost controller is worthless.
Though running 7psi.... I would recommend a 5lbs spring maybe on the WG, and as far as the BOV goes... I wouldn't even recommend a BOV at those levels. Lift off surge isn't THAT big of a deal at those tiny psi levels. Your engine will suck 7psi down pretty quick even on closed throttle. I have heard of a few cars running 6-8 psi with no BOV and no issues. But if you got one, a 12psi spring should be enough. 12psi so it holds it shut when idle, and with -10psi vacuum at liftoff plus the charge pipes 7psi, you should be able to open it to vent. You might get a bit of BOV flutter, which isn't a big deal nor does it really ahve any negative effects (other thatn undisirable sound for some). But once your charge pipes drop to 3-4psi, your BOV might try to shut and pressure will have to rebuild to open it and so on. Though I you might get a gobble or two, none of those 3-5 flutters that those higher psi guys get with really stifff springs.