[lsturbointeg]

Found this and find it interesting...what is your take?

http://www.bimmerfest.com/forums/sho...d.php?t=872874

[lsturbointeg]

Any engine gurus want to chime in positive or negative effects

[FenixMike]

Originally Posted by lsturbointeg

Any engine gurus want to chime in positive or negative effects

You know id chime in

You have 3 basic types of blow off valves, and depending on the location, different outcomes of modifying them.

First off, the full recirculating BOV. The operation of a full recirc is basically you let off the gas, the throttle blade closes, excess boost is vented from the pressure side of the turbo back into the intake system pre turbo. This is done for multiple reasons, but more so on newer vehicles (MAF dependent vehicles)... first and foremost for factory cars, it severely keeps the noise down as the "swoosh" is released back into the intake system, and unless you're running an open element system such as Bad Blacks or similar, you likely wont hear much unless you're running a lot of boost. Second, and most importantly for most newer cars (but less of a reason than noise as this can be tuned around for the most part if the manufacturer so desired the noise to be present) is because it recirculates already metered air from the MAF back into the intake system post MAF to keep air fuel ratios proper. A 50/50 or atmospheric BOV would release the metered air into the atmosphere, causing the car to run rich as it has already compensated fuel for that metered air into its calculations, but this is typically only an issue if you are on and off the throttle as opposed to just letting off, at which point the extra fuel really isn't hurting anything. Lastly, in the case you are on and off the throttle, such as with road racing etc, the excess pressure being routed back into the intake system will provide quicker response when building pressure and increasing throttle the next time around (only in this scenario, doesnt make a difference if you are off the throttle for multiple seconds).

Fully Atmospheric BOV - These vent 100% of excess pressure beyond the spring pressure rating of the BOV into the atmosphere. Basically instead of forcing air back into the pre turbo intake system, it vents the metered air into the atmosphere and gives you that "swoosh" sound. There is absolutely nothing positive about these other than the noise, and it degrades performance in every possible way. The only exception is on a vehicle where it was not turbo from the factory and/or doesnt use a MAF system (speed density only), runs insane amounts of pressure to where it would cause malfunctions or issues by recirculating it into the intake system, or you're an idiot ricer. Finally, without any sort of recirculation, If you did need to get back on the throttle after letting off, it takes much longer to obtain positive pressure again when you have vented all the excess pressure into the atmosphere instead of back into the intake system IN ADDITION to the fuel problem you are also now dealing with... again not a huge issue if you're just letting off, but in a scenario where you are on and off the throttle, such as road racing, drifting, or just being an idiot, this will make a difference. Thankfully the small and quick spooling (relatively speaking) turbo on the new 535 thats not a huge issue.

50/50 recirc BOV - in my opinion if you ABSOLUTELY HAVE TO HAVE the neat blow off sound, this is the only way to do it as you're still maintaining some of the function, while also getting some of the noise. As stated by the name, its 50% recirc and 50% atmospheric, so while not the best of both worlds, at least its not also the worst.

Or just get one of those sweet eBay speakers so it makes a Woosh every time you let off.

[lsturbointeg]

Found it interesting browsing thru the bimmerfest forums as know one has done this. I'm not looking to do mine but thought other people might?