BOV (Blow off valves) generally have a horrible reputation, rice is a word people like to mention but do BOVs make more power?
A blow off valve vents boost pressure from the turbo, directly to the atmosphere between gear changes. Factory cars have a BPV or recirculating pressure release valve.
If a BOV is so great why aren’t they fitted to cars from the factory?
1-Noise. A BOV makes the tttttssshhhh noise with every/most gear changes
2-MAF (Mass Airflow Sensors). For cars with a MAF, releasing air to the atmosphere can cause rich fuel mixtures because we are dumping air that has been measured by the MAF to the atmosphere rather than putting it in the engine.
This can be fixed but we need to put to place the valve after the BOV which can effect accuracy and reliability of the MAF. Generally MAFs are designed to be placed after the air filter where there is no boost pressure and temperatures are lower.
Noise on the other hand is almost unfixable
Okay, enough background, do BOVs make more power and/or make the engine happier?
By venting the pressurised air from the turbo directly to the atmosphere there is less restriction for the vented air (vs channeling into a tube, piping back to the intake and feeding into the intake) so response times should be faster.
Because we do not have to channel the pressurised air into a tube, the volume of air we can vent is potentially much larger especially with BOVs like TIAL
And thirdly we are not recirculating hot/warm air back in front of the turbo during gear changes, so for a short period of time after the gear change, the engine is getting cooler air with a BOV.
If I can get past the noise and if I can fix the MAF issue should I fit a BOV to my daily driver?
Probably not, the benefits of a BOV will probably not be felt on a road car because they are not driven hard enough for long enough and because we dont care about tenths of a second when driving on the road.
In short, you probably wont find any benefit to running a BOV on a road car
On a race car?
Sure, noise is irrelevant and we need anything that might help us go a tenth of a second faster.
BOVs in Summary
On a road car, it is hard to argue having a BOV, a race car is a different story
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