Blow Off Valves

[bboyt3nsk]

ok...dont make too much fun of me but why should you not use Blow off valves for daily driving???Im not eactly sure why.but in my head you would think it would be better because it lets out all excess pressure fast....and sometimes in a cool sounding way........Now hit me with your knowledge!

[clay payton]

you should always use a BOV on turbo cars.

some blow offs vent to the atmosphere, some vent back into the intake. the ones that vent back into the intake will prevent you from momentarily running rich when you back off the throttle (at least on some cars)

if you momentarily run rich, you may glog the catalytic converter over time.

but really, i don't think anyone would say to not use a pressure release valve (BOV of Bypass valve) when using forced injection.

[Infini IV]

For daily driving, it would be better to use a bov. Only in the more extreme cases where racers want to minimize their lag will they run without a bov... Think about it, a bov lets out all the pressure in the system (from turbo - intercooler piping - intercooler - intercoolerpiping - intake manifold). Once you let out the pressure that's in there, you have to re-fill it again.

At the same time, running without a bov for daily driving can result in quicker turbo damage. The air in the system bounces back when the throttle plates are closed and can literally slam against the compressor wheel of the turbo. Depending on how much you boost, that continued slamming action will eventually destroy the bearings in the center cartridge of the turbo.

[pio_masaki]

I've seen one after it died from compressor bouncing, it wasn't pretty. It came off a Supra MKIII with a bad BOV, it wasn't opening so all that air was bouncing back against the impellar, meanwhile the exhaust wheel is still attempting to turn it, either way the shaft was beginning to twist and the cartridge was so shot the impellar dug a groove in the housing. I won't even get into the damage to everything getting those shaving into the oil system UGH.

A method that alot of turbo from the factory cars use is to vent the BOV back into the intake, pre turbo inlet, post AFM if equipped, it helps to take that air pressure/force and keep the compressor spinning so it helps to reduce respool time after shifts. I did it on my supra (GReddy Type S) and from a 6 psi shift I came back on at 3 psi, so it does help, if only a little, I never tested it at 10 psi since I rarely ever need that much in daily driving. It also helps to keep the BOV system quieter, like with my GReddy venting, its REALLY loud, and everyone from a block away can tell its turbocharged, now wether or not they believe my little 80's car made that noise, thats up to them. Daily driving I keep the BOV open, only when I plan to run do I put it back into the intake. But the point about clogging up the cat is true, mine is already starting to dirty itself up, all that extra fuel getting dumped can give interesting sound effects and light shows at night.

[blargonator]

actually B.O.V.s are not good for daily drivers. they may sound cool but i gave another thread this link. www.streetracersonline.com for a daily driver you should get a forge diverter or dump valve. at the website it should have a list and hover over features and it will say turbo or something and then once you are at that look near the bottom and it will say blow off valves or something.

[pio_masaki]

I may be wrong, but I covered everything that was there, and I gave reasons for it. On a side note, that page was wrong (at least, in my head) on one point. It said that..well here "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." Most likely simply a typo, or maybe it is correct and I'm wrong, but this is how I see it.

I covered this, however, that does not cause the system to run lean, rather it runs rich, its adding fuel for air thats not there, which is why that fuel gets sent to the exhaust for that muffler detonation, which is something I also mentioned.

As for the air divertor or dump valve or whatever else it mentioned, thats exactly what I did with my GReddy Type S, ducted it back into the intake, my reasons were different, however it does the same. While I did it for respool times to be lower, it also fixes the in between gears rich condition, which also helps to eliminate the fuel in the exhaust and the backfires that go with it.

My reasons for choosing it to run open for daily driving may be wrong, and even hurtful to the car over time, but other then the clogging of the cat it doesn't offer much else in terms of damage. Running rich can cause problems, sure, but it doesn't run THAT rich, and not for that long (unless you're really slow at shifting). At highest the A/F gauge has moved one bar towards rich, which for my Supra, is simply average, it does that under boost anyways, it doesn't go so far into rich that the ECU thinks its dangerous. Of the AZ Supras here, almost ALL of the turbo'd ones run open BOVs, and none have had any problems resulting from it, wether it be luck or just a well designed car, I don't know, I can't say a 240 can do the same and live through it.

My Supra pops and blows out flames all day and night (well, not really, but she does pop a few times per drive, depending on air temps and driving style at the time), and she doesn't seem to care, and the police don't seem to mind since the flame is so minimal it rarely ever makes an exit, simply a glow, now the once in a great while it actually exits the exhaust I have to really be getting on and off (well, drifting) of the throttle.

Feel free to flame me for anything I have said anyone, but this is just what I've learned since moving to a turbocharged vehicle. As always if I am wrong I'm more then happy to take it as a learning exp.

[blargonator]

actually i think you are right because most people have been talking about their cars running a little rich. i thought supras are notorious for being able to run high boost <: -) actually how is your supra because i have got information about them from just one person. could you email me any info about yours at blargonator@hotmail.com

[pio_masaki]

I thought that was right, but there may have been something I missed, hehe.

Anyways, back to the topic that this started on, I can't see any reason not to run a BOV in a daily driver, unless you are concerned with that minor rich condition, in that case go with whatever system you feel most comfortable with. I chose my GReddy Type S for its design, allowing me to duct it back into the intake whenever I wanted, which makes it act more like the dump valve they were talking about. It also quiets it down so the popo don't get attracted to it, but around here they don't seem to care one way or the other about it (I also try to keep it down around them).

As with all mods, its really up to you, its your car and your money, if you want to go safer for the engine overall, go with a dump valve, if you don't mind a little rich now and then (very minor) go with an open BOV. Just make sure its tuned well enough that the engine doesn't bog or stall coming off boost or revs, that means its venting out so much air that its basically flooding itself, which IS bad for the engine.

[Boro86driver]

if you don't run a BOV your going to smoke check your turbo really quick. the only question is venting into the air or back to the intake tract. i wouldn't worry about running rich while you shift... it won't hurt anything. its running lean (TO MUCH AIR NOT ENOUGH FUEL) that will screw up your motor bad.

[pio_masaki]

Boro, I agree 100% on the turbo death without a BOV, or venting of some sort, but running rich can also cause some damage to the engine, just not in the amount that can be caused by a properly tuned engine and BOV. Then again, I would think an engine thats not proply tuned by the point where the fuel system is high flow enough to fry the engine due to richness from the BOV would have a properly tuned atmo BOV anyways. Only way I could really see it happening would be the BOV set so soft that its leaking air constantly and the fuel system isn't compensating for it, but even then its not really due to the shifting richness, just running rich in general..blah I think I wandered off topic..sorry.

[marshun]

well lets assume that your turbo motor is running right. that little bit of richness wont effect the motor. it takes ALOT of fuel and heat to get predetonation..

[pio_masaki]

Yes, it does take tons of heat and fuel to actually damage the motor, my point was just in extreme cases it can be possible, however VERY unlikely that it will happen, even with an atmo. bov, short of a clogged cat, nothing much will happen anyways.

My 7M-GTE has run an atmo. bov (Greddy Type S) for almost two years, cat is still fine (a little black, but that happens anyways I would think). Just recently did I duct it back in, and even then I only do it when I need to decrease my spool times after shifting. Day to day driving, like to work and back, it runs open.