| Message |
Nothing wrong with a blow off valve in the correct application. A BOV released dis-charged air into the atmosphere and requires the turbo to suck in new air. A recirculation valve releases the turbo dis-charged air in a loop that feeds into the inlet of the turbo. It is more work to plumb a system for a recirculation valve, but a recirculation valve is always better because it is feeding the turbo on release, rather than needing to suck more air when the discharged air is released outside the plumbing. Having neither a BOV or recirculation valve is bad because when you close the throttle plate, the moving air has no where to go and causes the turbo to stall. A MAP based fuel system reads the vacuum/pressure in the intake manifold and provides fuel based on just what occurs in the engine, it does not look at or care what happens in the plumbing. Running a BOV on a MAP based fuel system causes no issues at all with tuning and is perfectly fine, but still less efficient than a re-circulation valve. In a Z32 that retains the stock MAF or MAFS, the ECU is reading the air that moves through the plumbing,(What the turbo is sucking) the ECU is supplying fuel for any new air the turbo sucks in because it is simply measured by the MAF.
With the stock system having a recirculation valve, any air released from the re-circulation valve gets pushed right back into the inlet of the turbo. This helps keep the turbo spinning, but also keeps the system sealed, any air released goes right back into the front side of the turbo and feeds the turbo with pressurized air. No new air enters the maf that the engine is not digesting.
Changing the plumbing to a BOV, allows air to vent outside the plumbing, this causes the maf to pull in new air for any air released by the BOV, the turbo moves a lot of air even when not making pressure, any air blowing out is being metered by the MAF(S) and is causing the ECU to provide fuel for the metered air.
The system is NOT designed to work with a BOV because it reads the air moving in the plumbing, changing the plumbing to vent some of the air screws with the mixture. You can make changes to the fuel tables to compensate for the problems blow off valves cause to the tune, but your making a mess of the tables that will not be correct at all loads.
The stock recirc valve has light springs to allow the valve to open easy to keep the turbos spinning, and to keep the turbo from stalling. If you run light springs with BOV's, the car will not even idle, it will simply cause the mixture to surge, the idle to bounce up and down as it changes the mixture from one extreme to another. The reason why this occurs is because the BOV continues to open and close changing the mixture that changes the vacuum of the engine. If you run a stiff spring in a BOV, you can make it work, but it is anything but ideal and your causing the turbo to slow and stall from the valve not opening.
Running a BOV in MAF based fuel system is simply foolish and requires the tune to be less than ideal for it to work.
The larger the pipes, turbos, BOV's, the more issues having BOV's will cause in a MAF system because your simply moving more air that is metered by the plumbing.
 |
 |
