[darkpuppet]

Paparoach,Jun 9 2004, 07:06 PM Wrote:Online article:

Now let us differentiate BOV's, diverter and bypass valves. First, a blow off valve (seen top right) is common to high performance applications in that it provides the least bit of compromise. A BOV essentially releases this pressure straight out into the atmosphere. Quite often you will find that these units take on particular shapes, making them resemble musical instruments. I guess some people out there really like to flaunt their gadgets. Just wait ti'll you see how much they impress the ol' 5-0. Aside from this legal dilemma, the second problem you encounter with BOV's is that the mass air flow sensor will cause the engine management system to "think" that the air will go into the engine and in turn will release an appropriate amount of fuel for it. However, a BOV system will vent this air out before it gets to the injectors causing your mixture to run lean. In turn, this will result in unburned fuel to escape into the exhaust system. This is why you often see flames and hear those "pop's" in rally cars. It is unburned fuel exploding in the exhaust system. Doesn't take a genius to figure out that this is not the smartest application for the day to day car. For this reason, reasonable tuners will usually employ a bypass or a diverter valve (see left). These units essentially redirect this pressure back behind the compressor causing the net flow of air to remain constant. This in turn slows the turbine down gradually and allows the air flow sensor to work appropriately.


Is this wrong?

a good portion of that write-up is wrong...

the author needs to be flogged.

if you put more fuel in than air, you run rich.... and a rich running engine is not the cause of the flames in WRC/race cars. That's caused by timing being pulled so that the air/fuel mixture has a chance to go out the exhaust port, into the exhaust, and then is ignited to keep the turbo spooled between shifts.

that, and as the flow of air is concerned, the air is pumped back in-front (to the inlet) of the compressor, and subsequently after the MAF (between MAF and compressor), to let the compressor suck in the extra air, without drawing it through the MAF.

BOVs are suggested because they are slightly quicker, and sound a lot cooler, but if you're running a draw-thru MAF, you can save running rich between shifts, wich can be hard on the engine in the long run.