I see alot of boosted cars without them...but the serious ones all seem to have one. When o they become nessecary? I'll have twin turbos and about 6-8 pounds of boost.

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"American made baby. 100% American iron. The muscle among the masses. My hero. Yep, you can take your ergonomically designed, space age, computer controlled, 4 door, cup holding map lighted split double wishbone split fold down retractable cargo covered moon roof piece of transportation and keep it. For I have felt the thunder. And I know the difference!"
JSP Motorsports
ICON Motorsports

 

I'd run one just for peace of mind. I mean, when the throttle plates close, you have a lot of fast moving air in the intake that has nowhere to go, and that means it's going to cause resistance to the turbo(s)..

*shrug*

 

Plus, ummmm.. they sound cool

Anyways, Jester.. ICQ me sometime dude, I wanted to talk to you about your custom TT setup.

77060522

 

BLV's help turbos live a happier life. The backpressure wave caused by slamming the throttle closed under high boost really rattles the turbos bearings.

 

What happens is that the turbos are spinning at 80,000 rpms and pumping a huge amount of air. You close your TB blades as you let off and shift, and all this air gets backed up, stalls the compressor, and goes out through the intake. This sudden shock is terrible for the turbo (80,000 to 0 in a flash) and kills performance because you need to spool up again. The BOV permits the air to go right out of the intake, and lets the turbo freewheel. You ever hear a GN or TTA let off the gas and you hear a chuffing sound?

A.

 

Cool...another item to hunt for in a junkyard I guess thanks guys.

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"American made baby. 100% American iron. The muscle among the masses. My hero. Yep, you can take your ergonomically designed, space age, computer controlled, 4 door, cup holding map lighted split double wishbone split fold down retractable cargo covered moon roof piece of transportation and keep it. For I have felt the thunder. And I know the difference!"
JSP Motorsports
ICON Motorsports

 

I have a bypass valve on my paxton. Everytime I shift I hear a "psshhh"

I'm guessing this is normal? Are the bypass valve and BOV the same?

 

The sound you are hearing is normal. That is the air releasing from the valve. "Compressor bypass valve" is the proper term. "Blow-off valve" is a nickname that Japanese turbo car enthusiasts have for the bypass valve. They are the same item.

Oh, and I sell 4 different brands of bypass valves if anyone is interested. (cheap HRC plug)

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Old: 1989 Formula, 383", DFI, built 700R4, TFS heads, Mini-Ram, Vortech S-trim 15 psi, 3.70 gears
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If youy have an automatic the BOV is really not neccessay and does not make a difference. A manual would have to have one for sure though.

 

There is still some compresser surge with auto cars. Although I agree not as much and I wonder how much damage it causes.

Another good point for having one though, is that it aids in keeping the tubes from coming apart when you let off the throttle and that air needs someplace to go. Ask me how I know. LOL

 

I would not own a centrifigal or turbo car without one. For the price it saves the blower/turbo bearings. Plus it's funny. I love the one on my Typhoon, It scares the **** out of people. My blower one is not that loud but is still saving parts.

 

Huh… let off to shift… interesting idea…

probably one of the better reasons to have one.

To be honest, we've got a lot of people here that feel more comfortable having one but no one that has actually done damage without one.

IMHO, there is a really good reason to have a bypass with a positive displacement blower (decent part throttle gas mileage and if there is anything to blow off between the blower and the intake it WILL blow it off), there's a pretty good reason to have a bypass or blowoff on a centrifugal blower (there is no real way for the wheel to slow down till the engine does, so you force it into surge if you let off partially), but I'm not sure that there is one on a turbo setup unless you own a manual tranny and have a habit of throwing really bad shifts when you're going all out, and then it is more to keep the turbo spooled then to save anything.

 

well, for $30.00 I would rather have one than wonder

 

30 dollar BOV? I would never trust it to last very long for that price. I heard the Tial BOV are the best on the market and never fail on ya.

 

I've got one handmade here in Sweden, it only cost me $50.


Stainless spring will make it last a long time, 2" inlet.

/Anders

 

You swedes are great.

 

Thanks man, but I know you've got a lot of mechanical skilled people over there too.. It's just a question about finding them...

/Anders

 

Yeah, I assume I could go to a performance shop here and they could have one made if I really wanted one made. But I will probably just go with the Tial. Don't know any GOOD bov customer builders here.

 

So whats better...having the BOV release into the atmosphere or back into the intake???

 

Maybe my terminology is different or wrong, I've always called the ones that release into the atmosphere blowoff valves, and ones that route back inline as bypass valves. Which one you can use or need depends what type of metering system you are running as in mass airflow or speed density. I remember my old SVO was not able to run a BOV due to the type of air metering system (vain air meter), it needed to be routed back inline. Speed Density cars should have no problem with a BOV.

 

I dont run a BOV on my setup. The wheel in the turbo doesnt come to a stop when it surges. Not even close. And actually, for all you people that think BOV's sound cool, compressor surge sounds bad ***. There has been no damage to my turbo. I was planing on getting a tial eventually, but I dont know if I want to waste that much money on something that wont do much of anything for me.

 

I am not sure how it sounds on a gas V8. It sounds real bad on the diesel trucks when you shift under a heavy load. If you use a CBV instead of a BOV they don't make that much noise.

I think having a BOV/CBV is just a matter of opinion. Some people like them, some don't.

 

A BOV releases to the atmosphere. A CBV releases back into the intake (air filter side). Either one is fine. A CBV stays open until boost is seen at the intake. It closes under boost and is open at vaccuum. CBV is quieter than BOV.

 

DSM or Volkswagen blow valves are like 30 bucks. They work great. Stock ones work past 24 lbs of boost.

 

looking for a surge valve that is about 1 1/2". links please?

 

ok say you were running a single turbo on a mass air flow sensor car won't you want to put the BOV before the MAF sensor?

 

It's a supercharger and I want unmetered air, so that it doesn't keep dumping in so much fuel on idle. It's real rich on idle.

 

WRT to your problem, sounds like you just need to get it tuned right.

WRT to the actual question, any bypass valve should work fine, even the cheepo plastic bosch ones will be open at idle and part throttle/high vacuum.

 

thanks..where would i find a suitable dealer and which one (size, part number etc) do you think is suitable? when you say tuning, what else can I tune, do you mean getting a PROM? thanks -J

 

I mean getting it tuned on the dyno or someone competent on the street and burning a proper chip for it.

Do a search here or just google it for the bosch bypass valve, there's tons of info about it and you can buy it from most import parts places or a bunch of the blower kit manufacturors.

 

cool, thanks,. the reason I ask, is because I'm trying to tune everything myself. I can't get a dyno tune, cause it's a Prom, not DFI. Also, there aren't any tuners on Long Island that will tune it, cause it's not DFI. Anyway, I was planning on getting the base timing set where I like it and then gettting a chip. What else can be tuned, besides the prom, timing and tps, min idle, etc? thanks for the ideas

 

i havent tried to run mine without an bov,but i was warned against not using one on an engine with over 7psi,mines an automatic and the only time i hear the bov open is either if i free rev it or get on it and get off the gas.when the car shifts im not sure if the bov is opening at all.
heres the one i got off of ebay
cost me like 24$'s
have to see if i can find a better pic

 

That's pretty nice,...but can that one be hooked up to the intake to recirculate. I think I am looking for more of a bypass valve/. -Justin

 

no i bought a to atmopshere bov, i am running a maf system.ppl have had varying results with maf systems with to atmosphere bov's.as far as on my car as long as i keep my valve on a soft setting the car dosent run very rich when the bov opens and even on a med to hard setting it dosent get rich enough when the valve opens on free rev or letting of the gas at speed to cause any stalling.

 

really it is more that auto's do not need them as much as manuals do.
auto's the throttle stays open. when shifting a manual, it blows off to prevent surge.

 

i found this on an audi forum, but it provides a good explanation of the difference between a blowoff valve (into atmosphere) and a diverter valve (into airbox) and when it's ok to use them.
AudiWorld Forums: Since no one else wants to be nice to the NOOb, i'll play devils advocate...

 

great write up...where can i get a bypass. can't find them on the net or ebay, BOV's keep coming up.

 

try searching for diverter valve, i found quite a few hits on ebay. as far which one will work for you, i couldn't tell you that. good luck.

 

i don't know if this is the same as a "diverter valve". but my brother has a BMW E30 cabrio with a nissan SR20DET on about 7-14 LBS of boost (depending on his mood ) and to quiet down his BOV for normal daily use (so no one would know it was turbocharged) he routed it back into the intake with hose. could bairly hear it. then when he went to the track or wanted to sound bad *** he would unhook and plug the hose going to the intake and allow it to vent to open air. this was a MAP car i believe, it had no affect on how the car ran IIRC.

just for giggles here is a link to his build up on e30tech.com INSANE

 

thanks for the info guys....i'll check for divertor...
X,...ican't use a regular bov though becasue I need it to open at vacuum. thanks

 

I use a CBV/diverter piped back to the air cleaner pipe. It is on a 7PSI turbo setup with roughly 450 FWHP, automatic trans. The CBV is from a 2002 VW Bettle (Bosch P/N 710N). There are two part numbers listed for that year at the dealers. I liked the 710N over the 103. It cost $40. The vacuum inlet is on the top of the CBV. It seems to dump enough air that the turbos don't surge when doing a quick throttle let-off at 7PSI.

 

all these people always say its bad for even automatic cars- ive seen turbo buicks and TTAs run with the stock turbo 250K miles- no BOV, low 12 second cars. they dont hurt performance in automatic cars because the throttle blade doesnt close.

even on my GN with a pt 70 i dont run a BOV- theres no need. a little compressor surge as long as its not constant like it would be in a manual trans car is fine

 

heh, I've seen 3.8 'ick motors in the 10's without a blowoff, what's your point?

My point has always been that they are not necessary on most cars period. the only real reason to run one is if the car is repeatedly, badly driven and/or in extreme cases to keep the intake ducting together if you're having issues with that.

 

That is why I ran the CBV. It was a simple $40 insurance for keeping the duct work together and my first turbo setup so I was kind of clueless.

I have driven some rigs with hundreds and hundreds of thousands of miles with a stock original turbo pushing 20 to 30PSI of boost. These turbos see massive surge when shifting gears with a heavy load on the truck. No BOVs and the turbos hold up fine. They make an aweful noise sometimes but nothing more than that.

 

so the CBV is a bypass? does this stay open under vacuum and closed under boost? cause that's what i am looking for. I need it to open under vacuum so when I idle....it circulates metered extra air from the discharge tube back into the blower intake,...but AFTEr the MAF..i dont' want it to be metered.

 

yes, CBV = compressor bypass valve. Under vacuum it is open due to a vacuum port pulling on the diaphram. When boost occurs, the vacuum is shut and no longer does a bypass. If boost exceeds approx. 12 -14 PSI it overrides the internal spring and opens......back to bypass mode.

 

junkcltr. that's exactly what i need...Do you happen to have a pick? also..what are the inlet and outlet sizes? i need about 1 1/2" thanks-J

 

Here is the info for it:

s4biturbo.com: Audi S4 Owners' Resource: mike01s4's diverter valve testing: Bosch 110 vs. Bosch 108 vs. Forge Bypass Valve

I use the Bosch 710N part number. The inlet is 1" diameter and the outlet is 1" diameter.

The 2002 VW Beetle used this CBV. I got mine from the dealer for $40 and it was in stock. They dealer also had the 108 (or 103...I forget) P/N listed for the 2002 VW Beetle. I told him I wanted the 710N.

 

great info thanks! -Justin

 

Pluck it straight from a 1st generation DSM (Talon, Laser or Eclipse turbo), they are good to about 15 psi STOCK, and are known as the best production bypass valve ever made. You can "crush" them to hold about 25 psi as well. It's what i run, as well as thousands of other homebrew turbo guys.