Brad-ManQ45 Posted June 29, 2006 Share Posted June 29, 2006 I am going to MS and intercool my '83ZXT and even tho MS is MAP based, I intend to recirulate because of faster spooling/recovery after drop throttle. I want one that will "leak" at idle for quickder acceleration on the street. I know that the DSM BOV does this, but are there any aftermarket units available that do the same thing and capable of holding 20+ lbs of boost? I have looked and can't find any that specifically state this...., TIA, Brad Quote Link to comment Share on other sites More sharing options...
Clifton Posted June 29, 2006 Share Posted June 29, 2006 The only reason to recirculate is to keep an efi with an afm happy. It won't keep it spooled any better. Dumping the excess hot air back to the inlet would be of less of a benefit than venting to atmsophere. Having one that leaks would just reduce the volume, reducing the boost. Quote Link to comment Share on other sites More sharing options...
Brad-ManQ45 Posted June 30, 2006 Author Share Posted June 30, 2006 Old discussion - introducing pressurized air (after the intercooler) back before the turbo will keep it spinning faster than venting to atmosphere. A bypass that leaks a little at idle will allow more air into the engine at "tip-in", and closes up when boost hits. The added air makes for more exhaust flow and quicker spool. Quote Link to comment Share on other sites More sharing options...
Clifton Posted June 30, 2006 Share Posted June 30, 2006 Sounds like theroy. I don't see the benifit of introducing 200*+ air into the turbo inlet that will no longer be pressurized as the volume isn't that much once released. The impreller is designed to pull air in, not be driven by incoming air attempting to overcome the velocity of the air already entering. It would be horribly inefficient. I run a pretty big, laggy azz turbo and have no problem on shifts. What turbo are you running that is hard to keep spooled? How does a leaky bypass let more air in? Once your WOT, How can get anymore air in the engine than the TB will let into the manifold? Quote Link to comment Share on other sites More sharing options...
Brad-ManQ45 Posted June 30, 2006 Author Share Posted June 30, 2006 The air coming out of the intercooler is much cooler than 200 degrees, the pressurized air is being KEPT in the intake system and isn't getting any hotter because the turbo isn't compressing it any more, and I've already stated that once boost hits, the bypass valve would not leak, so you effectively bypass the turbo and get more air at tip-in. This is why Mistubishi and other manufacturers used this type of bypass valve, for off idle throttle response. If you wish to contest either of these points, please do so after doing a search here in this forum for BOV and bypass, reading the threads that pertain specifically to these subjects - there were only 5 or 6 informative ones, so it shouldn't be too much of a burden. Quote Link to comment Share on other sites More sharing options...
Nigel Posted July 1, 2006 Share Posted July 1, 2006 My Subaru Legacy Turbo BOV opened at -5inHg. And my 1G Mitsubishi Eclipse BOV opens at -15inHg. So the factory engineers obviously see some benifit to this... Nigel '73 240ZT Quote Link to comment Share on other sites More sharing options...
240hoke Posted July 1, 2006 Share Posted July 1, 2006 Vortec Bov's remain opened until boost hits. Quote Link to comment Share on other sites More sharing options...
Brad-ManQ45 Posted July 1, 2006 Author Share Posted July 1, 2006 Thanks 240hoke! Quote Link to comment Share on other sites More sharing options...
Clifton Posted July 2, 2006 Share Posted July 2, 2006 The air coming out of the intercooler is much cooler than 200 degrees, the pressurized air is being KEPT in the intake system and isn't getting any hotter because the turbo isn't compressing it any more, and I've already stated that once boost hits, the bypass valve would not leak, so you effectively bypass the turbo and get more air at tip-in. This is why Mistubishi and other manufacturers used this type of bypass valve, for off idle throttle response. I guess it could be under 200* if your boost was low enough and ambient temps were low, go over 20 psi and forget it if temps are high. Either way good luck with your quest for better tip-in/ idle throttle response/ quicker spool. Quote Link to comment Share on other sites More sharing options...
Brad-ManQ45 Posted July 2, 2006 Author Share Posted July 2, 2006 Thanks Clifton. This will be a daily driven car, so response is a biggie for me. I haven't done the math, so I don't know what the temperature will be after the intercooler, but the main point was that no more heat would be added while the turbo freewheels, so heat ain't the issue. Quote Link to comment Share on other sites More sharing options...
yo2001 Posted July 2, 2006 Share Posted July 2, 2006 Z32 BOV opens at idle/low throttle to improve throttle response. Quote Link to comment Share on other sites More sharing options...
zguy36 Posted July 3, 2006 Share Posted July 3, 2006 I'm with clifton thinking that you aren't going to get jack difference with tip in throttle response by going with the recirc valve instead of the plain old blow off valve. The valve isn't going to flow enough air to be able to increase the pressure on the inlet side of the turbo. Keep in mind that you have a giant air inlet on the intake side of the turbo, AKA air filter. Any attempt to increase inlet pressure of the compressor will just be lost out through the air filter. A good filter can flow over 800cfm of air with negligible pressure drop. Try dumping enough air through your bypass valve to build pressure against an air filter to increase the inlet pressure of your turbo? Not going to happen. Thats like trying to use one of those computer duster air cans to pressurize your living room. Now, since the recirculated air has already been under your hood and gained heat (200degrees is an overexageration), you are at a loss because you inlet air to the turbo is warmer than ambient. Quote Link to comment Share on other sites More sharing options...
yo2001 Posted July 3, 2006 Share Posted July 3, 2006 point of the leak at idle is to allow the air to be taken in from the charge pipe before the turbo. It's allowing better throttle response via shorter path to the intake. Which is going to get the water out the cup faster? coffee straw or McD's extra large long straw? Quote Link to comment Share on other sites More sharing options...
Clifton Posted July 4, 2006 Share Posted July 4, 2006 It is a small leak, atleast on Z32's. The bov is not fully open. Maybe the Vortec ones but they are designed for a supercharger application were volume will still be produced under no load. If they are not set up soft enough they won't open, or open enough at the low psi stock systems run at. Mine will open under full vac with no boost but not at idle, don't need it to. Throttle response isn't going to be improved with a small leak from 29"-5" of vacuum, well maybe if you are running 1.5" tubing. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted April 26, 2008 Share Posted April 26, 2008 This is an old thread but since I used the search function to find "BOV open idle" which is what I just realized my BOV is doing, I thought I would post. Yes, my BOV sits about 1/2 way open at idle. Even with about 1" spacer behind the spring for extra pressure it's open at idle. It holds boost fine but I feel like it releases to open too early when I am backing off the throttle. Sometimes it opens when I am still in partial throttle and partial boost. I tried putting some grease on the valve slider to dampen the valve but it made no difference. It seems like it gets too much vacuum too soon. It's a TurboXS race valve vented to atmosphere. Any tips? The vacuum source is pretty much the middle of the intake manifold. Can I try picking up the vacuum signal somwhere where it's less strong? Maybe I need to put in a parallel hose with check valve and restrictor. The check valve will close during vacuum and force the vacuum to go through the other line which would be restricted with an orifice? Quote Link to comment Share on other sites More sharing options...
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