bov theory is this true?

[sofly1990]

alot of people told me that if i want to put the hks blow off valve vta i would have to tune the car so i wont have problems...yay or nay?

[2010 Rallihead Sportback]

NAY just recirculate it

[Blaze]

Maybe we can talk Mike from RRE into posting up a BOV FAQ. He can explain this better then I can, but I'll give you the short version.

Speed/Density cars meter airflow based on air temperature, air pressure and a calculations my accountant can't understand. VTA BOVs work great on these cars because the air fuel ratio is calculated after the throttle body. We do not have Speed/Density systems.

We have MAF (Mass Air Flow Systems). A MAF system (among other things) consists of a sensor (in our case a hot wire) which is located in a the plastic cylinder just behind the air filter box. As air flows through the MAF, it sends a signal back to the ECU which calculates fuel allowances based on the metered air. And this is key to why you want to recirculate a BOV. So for example, if the MAF reads 10 units of air, the ECU will provide 10 units of fuel to match and everything is happy.

Now add a BOV into the equation. The BOV is basically regulated hole in your intake system. If it's closed, there's no hole. If it's open, then you have air leaking out. If the BOV is recirculating, you'll notice that the escaping air sent back into the intake system at a point BEFORE the turbo and AFTER the MAF. So, if you have 10 units of air coming in, 2 units may escape through the BOV, but they are added back to the system. This means you still have 10 units of air to match the 10 units of allocated fuel. In short, things are still happy.

If you are venting the BOV to the atmosphere, you have now lost 2 units of air. So in this scenario, the MAF has told the ECU to provide 10 units of fuel to match it's 10 units of air. BUT, because you only delivered 8 units, you wind up with too much fuel. Your car suddenly runs too rich and hesitates, backfires, stalls or idles poorly.

I could rant for a while about why you never want to VTA, there are too many reasons to count. What I will say is that you do not want to "tune" around the problem and you do not want to run a piggy back computer that claims to stabilize your idle. These are bad news.

The best BOV for the car (IMO) is a factory metal BOV out of an MR. (Mike will tell you the stock plastic one will give you equal performance. I just don't trust plastic in a hot turbo engine for long durations, so I switched. If you just HAVE to let everyone on your street know you're turbo, cause the louder the swish, the bigger your penis, then you will want to run an open filament air filter (which will require a re-tune), purchase metal MAF pipe and move the BOV as close to it as possible.

Hope that helps,

Blaze

[MTZL]

Prepare to waste some gas...
I also have EVO IX BOV & aftermarket BOV from EVO VIII.
Im currently running a stock bov with stock RA turbo Custom tuned to Stock EVO X power. :D (Stock 08 evo = 215-230whp)

Until you upgrade your stock turbo, stock bov is fine.;)