Blow Off Valve?

[turbohcar]

Why spend $500 on a BOV if the turbo is going to last many thousands of miles?

I agree on the reasons why you wouldn't if it's been proven you don't need one but I want to know WHY you don't need one. BTW, top of the line units from HKS and Tial don't even cost $500 It's more in the $200-$350 range. I believe it took me about an hour to bolt my Greddy Type S up and I had to make a new flange. There are only two vaccum lines to hook it up so installation is not hard at all. This one has an extra vaccum line for low boost surge protection. The low boost port feeds off the compressor housing of the turbo and the regular port feeds off of vaccum from the intake manifold.

Do a search on "compressor surge". It is NOT the noise when you let off the gas. I bought a BOV to combat comperssor surge when I went with a big turbo. Some combos get it, some don't. It's about drivability. Stick shift cars drive smoother with a bov. Car bucked and surged at shifts and at part throttle. Now it drives smooth again.

Buicks ignore the MAF when you let off the gas for the most part, no need to recirculate.

I'm not totally sure we're on the same page here. Yes, a BOV may make a car more pleasant to drive (since it's not bucking and snorting on decelleration), but it's more about keeping your turbos in one piece. For a more visual analogy, just think of the turbo shaft as your crankshaft. Would you want your crank shaft stalling on decelleration? Spin for a couple seconds, stop instantly, spin for a couple seconds, stop? Not only is this hard on the bearings but hard on the shaft. It puts a lot of stress on the shaft itelf when the remaining exhaust gas is trying to bypass the turbine wheel and can't do it fast enough because it's not able to spin the wheel. I did a search and found much the same thing. People having trouble when upgrading turbos because of surge. I still cannot find a good argument why Buicks are able to defy Physics.

It is NOT the noise when you let off the gas.

Then what IS that noise? Because I can't think of one other thing that could make your car run like crap on decelleration and make sounds like that.

 

[CTX-SLPR]

I read the post rather fast so this might have been covered in here but the reason stick shift cars need BOV's is too keep the turbo spooled between shifts. Most stick cars can't shift while at WOT or even part throttle so you slam the blades shut when you clutch then open them backup again as you let the clutch out. The booste pressure has notwhere to go but back across the turbo compressor causing it to decellerate rapidly and the noise you hear is the pressure waves colliding between manifold air and compressor air as the blades sweep past the exducer opening in the scroll. So you don't have to re spool the turbo after every shift you vent the compressed air out of the uppipe to atmosphere or on the suction side of the turbo so the inertia of the turbo keeps it relatively spooled during the shift by eliminating the pressure gradient across the compressor. Auto cars go straight from one gear to the next at WOT so there is no need to vent the compressed air durring a shift. This probably also contributes to the durability of the turbo on an auto car since only under panic braking or at the top end of a run does the turbo see compressor surge.
As for why the car doesn't snort and such under decell... from what I know about Buick computer code, and its not much, there is special programming for decelleration conditions based on the TPS and such that tells the car to ignore the MAF readings and go into closed loop off of the O2's like at idle. Again I don't know much about the code but that seems to be the case.

Just some info,

 

[I eat Z06]

i have a 2001 subaru wrx bov and redirects it back through the intake before the maf, as subaru does from the factory. it also stopps the falling on its face and stumbling when you have to slam on the brakes.

Actually the BOV on Subaru's recircs after the MAF, just before the turbo, in the turbo inlet pipe. The inake on t3h scoob is airbox, maf, slinky rubber, turbo inlet pipe, turbo, i/c w/BOV, TB.

I plugged the recirc hole on my turbo inlet pipe and ran atmospheric with a Greddy type RS bov. The only downside is afterfire every once in a while.

Nick

 

[GNVYUS 1]

I have both a GN and a 91 turbo talon, both have tons of work and both are auto's.

I have run both cars without blow offs and with and I must say, blow offs are a total waste on both cars with auto's.

I spent $300 on my GN's blow off and about $200 on my Talons and both cars still get compressor surge down low. My Talon had a slight benefit by not bucking as much with the addition of the blow off but still, not a big deal as it was not stalling or anything just a bit annoying on the highway.

Most import turbo owners use a blow off because the car came with it and they are manuals. But because GN's are auto's we have 1/4th the need for blow offs ( shifts ), and so do the auto Talons and Eclipses.

When I did not have one on my Talon for about 15K miles it had a lot more bucking when you would get off it, but it still gets some surge through the turbo with the Forgemotorsport blow off. I bet if I did not chicken out and install one on my auto Talon, the turbo would last a long ass time just like my GN turbo's have. Its lasted 15K without one and most DSM people would of said I was stupid etc,

But like Blacksixpack said, his stock turbo lasted 175,000 miles!!!

Enough said right there on this topic with blow offs and automatics. :tongue: