Challenger Posted May 26, 2009 Share Posted May 26, 2009 Im aware that the stock turbo intake has the "pop off valve" to protect the engine from any over boosting. Im looking at raising the boost in the next couple weeks assuming I get everything back together and running good. My question is... is it best to just put a plug in the hole and attach the bov to the j pipe just in front of the TB. Ill be rerouting the BOV vent into the afm to turbo tubing as is needed. Thanks Quote Link to comment Share on other sites More sharing options...
240zBoy Posted May 26, 2009 Share Posted May 26, 2009 Lol I don't believe the question is, is it best but should be is it possible. I think somewhat is on the hunt for a little vrroooommm psst.lol. Anyways, I believe the BOV that everyone uses has a larger opening than the stock "Pop off valve". Not 100% sure though. Quote Link to comment Share on other sites More sharing options...
Challenger Posted May 26, 2009 Author Share Posted May 26, 2009 Well although that sound is very nice, I wont be getting it since Id be venting to right in front of the turbo, you might hear a little "ffff." What are you getting at about the BOV opening size? Quote Link to comment Share on other sites More sharing options...
jeffer949 Posted May 26, 2009 Share Posted May 26, 2009 Yes just go get a plug and plug the pop off valve. Ive heard of some people crushing it to increase the spring pressure but i never messed with it. I just took it off. And on the bov yes it should go as close to the tb as possible theoretically but i think mine is a good 8-10 inches before and it works fine. Quote Link to comment Share on other sites More sharing options...
Tony D Posted May 26, 2009 Share Posted May 26, 2009 Why when the stock BOV in #4 intake runer is very efficient as long as you aren't running some ungodly boost number, or have added a lot of volume to the delivery system (like an I/C and all the piping)? Plug the Emergency Relief Valve at the rear of the manifold with a pipe plug. As long as you are in the 10-12 psi range, you should be fine with the stock turbo and J-Pipe using the Nissan BOV in the intake runner. No complex piping to run to the rubber hose between the AFM and throttle body, and you keep the added benefit of vacuum control for less oil suckdown on drop-throttle situations. This 'has all been covered before'... Quote Link to comment Share on other sites More sharing options...
Challenger Posted May 26, 2009 Author Share Posted May 26, 2009 Alright, thanks. Yes Tony I understand this has all been covered but being that many of the posts were quite old, and in some cases I wanted to confirm what I found... Ive had some problems reading stuff and believing it... Quote Link to comment Share on other sites More sharing options...
Tony D Posted May 28, 2009 Share Posted May 28, 2009 Age has very little to do with engineering principles or the construction of a 30 year old vehicle. If it was true in '05, it's likely still true today, especially physical placement of compoentry! LOL Quote Link to comment Share on other sites More sharing options...
slown280z Posted May 29, 2009 Share Posted May 29, 2009 I'm currently at 10psi with stock everything except Megasquirt. I shimmed the pop-off valve at 12psi. I finally got the car running nice, with a 45gph fuel pump and stock injectors at 12:1 AFR, the stock injectors are very close to 80% duty cycle, which many consider the safe limit for injectors. I'd say be safe and keep it at 10psi until you get bigger injectors and a I/C. I've had no problems with the stock bypass, though on another car I would get surge when we added a big I/C (and that's when I added an aftermarket BOV). Quote Link to comment Share on other sites More sharing options...
tyler031734 Posted October 30, 2009 Share Posted October 30, 2009 Why when the stock BOV in #4 intake runer is very efficient as long as you aren't running some ungodly boost number, or have added a lot of volume to the delivery system (like an I/C and all the piping)? Plug the Emergency Relief Valve at the rear of the manifold with a pipe plug. This 'has all been covered before'... Wait... A BOV relives a build up of pressure BEFORE the throttle plate to help the turbo stay spinning, the safety valve makes sure there is no chance of over pressurization due to a bad waste gate AFTER the throttle plate. you close the tb, crate large vacuum and open the BOV. how would the safty valve be very efficient and reliving boost if its in vacuum? Quote Link to comment Share on other sites More sharing options...
Challenger Posted October 30, 2009 Author Share Posted October 30, 2009 The J pipe is pressurized and the intake manifold has a vacume. Air flows through the safety valve. Quote Link to comment Share on other sites More sharing options...
tyler031734 Posted October 30, 2009 Share Posted October 30, 2009 The J pipe is pressurized and the intake manifold has a vacume. Air flows through the safety valve. what are you trying to say? when the mani is in vacuum the safty valve sucks? lol Quote Link to comment Share on other sites More sharing options...
skib Posted October 30, 2009 Share Posted October 30, 2009 Wait... A BOV relives a build up of pressure BEFORE the throttle plate to help the turbo stay spinning, the safety valve makes sure there is no chance of over pressurization due to a bad waste gate AFTER the throttle plate. you close the tb, crate large vacuum and open the BOV. how would the safty valve be very efficient and reliving boost if its in vacuum? the stock pop off valve and a BOV do not serve the same function Quote Link to comment Share on other sites More sharing options...
Tony D Posted October 30, 2009 Share Posted October 30, 2009 Yeah, Tyler... The BOV is not the emergency relief valve. The BOV in stock form is in the #4 intake runner, and uses the vacuum on the manifold present on drop-throttle to accomplish evacuation of the J-Pipe through a FAR smaller orifice than you would need dumping the same pressure and volume to atmospheric pressure. BOV's operate (all valves in fact...) on the principle of differential pressure across the valve. Venting to the manifold has 10psig air in the J pipe venting to near 25" HG "Vacuum" in the manifold. That is 2.2 psia. So you are venting 24.7psia (10psig) in the J pipe through a 1/2" orifice to a 2.2 psia area meaning that 1/2" orifice has a 22.5 psi delta pressure. Using standard engineering calculations you can determine flow through that orifice. If you use a 'standard' BOV dumping to Atmosphere you are dumping that same 24.7psia to a 14.7psia area---a delta pressure of only 10psi! You can see just from that example that a BOV, to function as well as a STOCK BOV positioned in #4 Runner will have to have at least 2X orifice size to give comparable results. That means maybe a 25mm BOV, but it all depends on the flow coefficient across the valve. With a lot of the crap out there, you will need a significantly larger valve size. It is possible that a .5 orifice with almost a 23psi delta will be flowing far more than a 1 or even 1.25 orifice with only 10psi across it. "This has all been discussed before" Quote Link to comment Share on other sites More sharing options...
Challenger Posted October 30, 2009 Author Share Posted October 30, 2009 what are you trying to say? when the mani is in vacuum the safty valve sucks? lol Yes it does "suck." TB is closed so there isnt any air being added, engine is still sucking in air, turbo is still spinning. Quote Link to comment Share on other sites More sharing options...
tyler031734 Posted October 31, 2009 Share Posted October 31, 2009 the stock pop off valve and a BOV do not serve the same function THATS WHAT I SAID:icon45: Quote Link to comment Share on other sites More sharing options...
tyler031734 Posted October 31, 2009 Share Posted October 31, 2009 Yeah, Tyler... The BOV is not the emergency relief valve. The BOV in stock form is in the #4 intake runner, and uses the vacuum on the manifold present on drop-throttle to accomplish evacuation of the J-Pipe through a FAR smaller orifice than you would need dumping the same pressure and volume to atmospheric pressure. BOV's operate (all valves in fact...) on the principle of differential pressure across the valve. Venting to the manifold has 10psig air in the J pipe venting to near 25" HG "Vacuum" in the manifold. That is 2.2 psia. So you are venting 24.7psia (10psig) in the J pipe through a 1/2" orifice to a 2.2 psia area meaning that 1/2" orifice has a 22.5 psi delta pressure. Using standard engineering calculations you can determine flow through that orifice. If you use a 'standard' BOV dumping to Atmosphere you are dumping that same 24.7psia to a 14.7psia area---a delta pressure of only 10psi! You can see just from that example that a BOV, to function as well as a STOCK BOV positioned in #4 Runner will have to have at least 2X orifice size to give comparable results. That means maybe a 25mm BOV, but it all depends on the flow coefficient across the valve. With a lot of the crap out there, you will need a significantly larger valve size. It is possible that a .5 orifice with almost a 23psi delta will be flowing far more than a 1 or even 1.25 orifice with only 10psi across it. "This has all been discussed before" "This has all been discussed before" than why do you still call it a BOV when you should know it serves a whole different purpose. how do you supose the STOCK PRESSURE RELIVE VALVE to work in such a manor? if the intake has more than roughly 8psi it RELIVES it your understanding of air flow is impressive, but PRV AND BOV are diffrent Quote Link to comment Share on other sites More sharing options...
tyler031734 Posted October 31, 2009 Share Posted October 31, 2009 Yes it does "suck." TB is closed so there isnt any air being added, engine is still sucking in air, turbo is still spinning. i disagree with this statment as well, BOV opens to release the build up of a turbo pushing air so it will not try to ''go backwards'' into the turbo slowing it down. if the PRV sucked air it would be unmeasured and unfiltered plus the motor wouldnt drop in revs so fast. try reving your car and give it a 1/2" vacuum leak. maybe I am missunderstanding your statment:redface: Quote Link to comment Share on other sites More sharing options...
Tony D Posted November 1, 2009 Share Posted November 1, 2009 "This has all been discussed before" than why do you still call it a BOV when you should know it serves a whole different purpose. how do you supose the STOCK PRESSURE RELIVE VALVE to work in such a manor? if the intake has more than roughly 8psi it RELIVES it your understanding of air flow is impressive, but PRV AND BOV are diffrent Obviously you have not read a single word I said. You have two devices on the manifold: A BOV An emergency relief valve... The BOV (as I have consistently stated) is in the #4 intake runner. The Emergency Relief Valve is in the manifold plenum, and serves absolutely no function on a modified engine and should be plugged/removed. Either you have missed this entirely (and I can't see how) or you are simply ignoring it. My terminology is consistent and I have taken great pains to refer to the emergency relief valve in that manner specifically to prevent it's confusion with the other device being discussed. OTHERS may be incorrectly referring to the emergency relief valve as a 'blow off valve' but I have not. Mainly because I call it an emergency relief valve and it's a TOTALLY separate function from what a BOV does. Is this that difficult to follow? Quote Link to comment Share on other sites More sharing options...
tyler031734 Posted November 1, 2009 Share Posted November 1, 2009 my bad.... I could swear that a stocker never came with a bov, I took my old mani to the scraper so i cant just go look at my old one, ill try to find it in a hanes or my other books, but i feel I will have no luck... got a pic of one? Like i said i realy dont thing such a best exists. Quote Link to comment Share on other sites More sharing options...
Tony D Posted November 1, 2009 Share Posted November 1, 2009 "This has all been discussed before" Your ignorance of the function of the devices present in your ZXT manifold is not my problem to resolve. The part numbers have been posted here in the past. It exists, your ignornace of it's existence or not. Left Photo, thing capped and with the hose clamp in the intake manifold #4 intake runner? There it is. I get sick of arguing about wether something that is present in the manfold and can clearly be seen in photos of the turbo intake manifold with people who don't take the time to notice it's there. Or understand it's function. "Search" The photo above was found in like 20 seconds using the search feature here to find an L28ET Intake manifold... Quote Link to comment Share on other sites More sharing options...
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