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Old 09-12-2011, 02:28 PM   #8
Member#: 136396
Join Date: Jan 2007
Chapter/Region: MWSOC
Location: Minneapolis, MN
2015 WRX, 2012 WRX,
2013 BRZ, 2006 STI


Originally Posted by liv4psi View Post
How do you tune for a bov, and how does it hurt the car over time? As far as I know none of that is true.
From Unabomber. Hope it helps.

Are there any negative effects with aftermarket BOVs? Yes. The downside of releasing the air to atmosphere is that it has already been metered by the mass air sensor, and when it blows off, the ECU will be injecting the wrong amount of fuel into the cylinders. The engine temporarily runs rich, meaning too much fuel is injected into the cylinders. On most tunes the target A/F under boost is @11.1:1 or so. Say you are at 11.1:1, then you shift and it vents. It will swing rich, typically to around 9.5:1. That is not that rich and this period lasts for under one second...again, nothing to write home about.

This temporary rich condition isnít usually that harmful. Technically, it can eventually foul spark plugs and even clog the catalytic converter as unburned fuel on the catalytic converter burns very hot, and too much of it can melt the cat. The odds of either of these two conditions actually happening is very, very low though, but that's the theory.

As to blanket "you'll run rich" statements, a BOV will only run "rich" during hard acceleration and shifting as 99% of the time it stays closed.

Can my tuner or engine management tune out this rich period? Yes. There are some forms of engine management that can tune this out. Buying your engine managment soley for this purpose is a poor method of choosing an engine managment system though.
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