No BOV?

[rarson]

When the throttle plate closes the boost/pressure has no where to go, if you don't have a BOV it would go back towards the turbo

It's not as if the air at the throttle body is traveling back towards the turbo. The air simply stops, because it has no where to go (it can't go back to the turbo because there's more air in the way).

What happens is that the turbo is still trying to push air in to the pipe, but it's getting harder and harder since pressure is increasing and and the compressor is slowing down as there is almost no impulse on the turbine blades (you're essentially moving up and to the left on the compressor map, taking the short route directly to the surge line). As pressure builds, less and less air is able to flow out of the compressor, until flow breaks down and eventually reverses through the compressor.

It's not really the air at the throttle body that is the problem, but the air at the outlet of the compressor, the air that the turbo is still pumping out.

 

[crimsondragon]

What? Throttle plate? No, it can't blow open the throttle plate. The throttle plate has equal pressure distribution on both sides, it's not going to rotate.

It can cause compressor surge, which can damage your turbo. The late 80's to early 90's dodge cars with the intercooled 2.2l engine did not come with a BOV, except in rare cases. Rarely do these turbos fail, however they are only pushing 10-13psi in stock trim. The more boost you push the more damage surge can do.

Bottom line, you can do it, it's not recommended. When you start getting the puff puff puff sound when you lift the pedal, know your turbos life is being shortened by an unknown amount.

If the throttle plate rotating assembly is weak enough, it'll blow the plate in regardless. Read up on Accufab. The shaft is weak as hell unless you weld in some reinforcement. On our stock TB's they're stronger than Accufab. Let's do some math. Take a 1g TB which is 60mm. Now in inches, that would be 2.3622in in diameter. To find area we'll take the formula A=(pi)r^2. Area would equal to roughly around 4.4in area. Say you're running 20 psi. Multiply area with 20. That equates to 87.61lbs of force on our throttle body plate if you let off without a BOV. Now granted, the air will rebound off and into the compressor. That's when we hear fluttering. Air is forced back the way it came since the TB is cut off and air will travel the least resistance. Since you let off the throttle, the turbine will be slowing down as it is and not build anymore boost. The backward rush of pressure will force through the turbine and actually try to spin it the opposite way. Think of a spinning fan and then grabbing it suddenly. That'll add amounts of stress on the turbine shaft since the exhaust side of the turbine is still partially spinning due to exhaust gases still being channeled through. Just think of a roll of clay and twisting it in opposite directions. Twist it enough and it'll seperate in the middle due to the opposite compression and shear forces.

 

[whitetsi95]

It just seems silly to be thinking about running without a BOV, but I get the feeling that the OP is just curious as to what would actually happen in a high-boost situation if there wasn't a valve there.

Thank you. I corrected/edited my post that said I didn't want to run one. I was half a sleep when I typed it. I was at work last night. Being bored. I was just curious about it. But everyone gets all bent over the axle(no bun intened) when someone asks a question that is out of the ordinary. But to the people who answered with out being a duche bag thank you.

 

[rarson]

If the throttle plate rotating assembly is weak enough, it'll blow the plate in regardless. Read up on Accufab.

He was talking about air actually rotating the throttle plate. Since there's equal force on both the top and bottom of the plate, it's not going to rotate. It sounds like you're talking about snapping the TB shaft.

That's when we hear fluttering.

The "fluttering" sound on most cars is not compressor surge, it's BOV chatter.

Air is forced back the way it came since the TB is cut off and air will travel the least resistance. Since you let off the throttle, the turbine will be slowing down as it is and not build anymore boost.

The turbine doesn't build boost, the compressor does. But symmantics aside, the compressor continuing to build boost is the *entire reason* that boost continues to build. Read my previous post.