i know that on a manual tranny, the BOV is mainly used when shifting, releasing pressure when taking your foot off the gas to shift. what about on auto trannies? when will the bov be used then, since you hold the throttle open through the entire period of acceleration. will it still 'sneeze' when the tranny shifts because the engine is not taking in as much air even if the throttle is wide open?

 

Throttle principles are basically the same whether automatic or manual. Eventually you're going to stop accelerating.

 

i know, but when referring to an auto tranny, when are you going to hear the sneeze of the BOV?

 

Whenever the turbo needs to spin down. If the car's going at full boost at 5.5k and then it shifts to 3k and where it'd normally be spinning much slower...it's gonna release backpressure. Someone feel free to correct me if I'm wrong, but I don't see why the principle would change at all.

EDIT: Unless you can trick your ECU into undertsanding where all that excess air is going, you're probably not going to hear much of the BoV because you won't be venting to atmosphere.

 

oh ok, so it doesnt depend on how open the throttle is, but how much air is being sucked in... so when you are redlining in first, and then the tranny shifts to second and you go back down to say 2,500 rpms, even though the throttle is wide open the whole time, the engine is not sucking in as much air, so the BOV release pressure?

what a question, eh?

what i mean is if you have a manual or auto tranny, the BOV will sneeze at each shift then?

 

I don't know for certain, but that was my take on it.

 

well the thing is...the most vaccume inside the motor is just after you let off the throttle. this is what pulls the BOV open. then after the engine revs down or you open the throttle again the vaccume goes down and closes the BOV..

i believe even when the auto changes gears it won't open the BOV because the throttle plate is still open so vaccume doesn't get a chance to build up to open the BOV.

SO, if you floor it in an auto you won't hear the BOV until you let go of the gas. the throttle plate closes, engine makes maximum vaccume which pulls BOV open, air goes out BOV instead of deflecting off the closed throttle plate which would go backwards through the turbo (BAD).

 

oh, okay. so would the turbo mostly stay spooled up then throughout the whole time you have your foot to the floor and the tranny shifts?

 

Don't quote me on this but the auto's i've seen turbo'd actually had no BOV. 2 reasons-1)the tranny ie:torque converter couldnt handle the boost above 6psi. To much stress on stock systems. 2-the people i've seen where only running like 6lbs and didn't need it according to them! The BOV principles i know of act on pressure differentials not just vacuum or positive pressure. Thus in an auto when your car shifts you create a pressure shift from the lower rpm levels. This causes the BOV to open. Now it is quick as you are boosting again keeping gas to floor. Thus you really don't want to lose the boost to much. BOV actually uses boost pressure to keep close as well as vacuum to open. As i've said don't quote me on this but this is my understanding of the BOV operation. ROCK can you verify this?? You could call RRM to find out if you are concerned on this matter. They will set things right.

 

BOV is still last line of defense as far as building too much pressure. Whenever pressure is excessive it will relieve itself. Could be just a small throttle adjsutment, 100% t.p to 70% tp for example.

ROAD/RACE
http://www.roadracemotorsports.com/

 

what about the strength of the torque converter he was talking about. is 6lbs really too much boost for stock systems?

 

NTran should drop by this thread, seeing as how he's got an automatic.

<edit> I already PM'd him.

 

If you have an auto tranny you will hear a little of the bov when it shifts, but if you really want to hear it; hit like around 3000 rpms and let go of the gas pedal you will hear it. I don't think 6psi is not too much for the auto actually i think it is the perfect amount of boost for an auto tranny. Rite now i am running 5 psi

 

i forget, about how many psi is 1 bar? is it about 7 psi?

 

If you really like the BOV sound, there's a virtual BOV for sale in Japan. About $250, form what I can remember. Two different sounds!