BOV hell...

airtroop01

airtroop01

Active member
I decided to start this thread to talk about all things BOV related instead of hijacking JL's thread.

Talk to me goose!

Atmospheric blow off?
Recirculating blow off?
Tuning tricks?
 
I really doubt that its due to the location of the re-vent. Many of PTS's kits are built very smiliar.

With any mass air you need to recirc the bypass.

Call Mark Lancaster at TurboF150.com and talk to him.
 
spambell said:
I really doubt that its due to the location of the re-vent. Many of PTS's kits are built very smiliar.

With any mass air you need to recirc the bypass.

Call Mark Lancaster at TurboF150.com and talk to him.
Click to expand...

I agree with you. I've been looking at a lot of turbo systems lately and it seems that in theory the recirculating bov is the way to go.

The thing I wonder about is moving the maf further away from the re-vent location like Tim at Chikenears did in this thread:

http://www.nloc.net/vbforum/showthread.php?threadid=110314&highlight=chikenears

I'll try to get a hold of Mark if I'm not too swamped here at work.
 
Thats what I was considering doing, re-fabbing my inlet so that the MAF was alot further away from the BOV recirc point.
 
I've been venting to atmosphere for about 3 years. The only time I had any kind of stalling/surging problems was when I didn't.

You must have enough spring pressure to close the BOV at idle and cruise. You only want it off the seat during a vent. The only reason to plumb back in between the mass air meter and the turbo is because you don't have enough spring in the gate to keep it closed under those conditions and don't have a gate with enough adjustability to compensate for it.

Going back to the JL thread, think about it Phil, even if you're already metered the air, the throttle body is closed. Injecting fuel for that split second, no matter what, would result in a rich condition, even if the truck wasn't turbocharged. But it doesn't. Why not? Because when the TPS snaps closed, the EEC kills the injectors. It has done this since Ford went to multiport injection.

Just give it a try, close up the intake tract plumbing and leave the BOV open to atmosphere, put a 15 lb spring in the BOV, drive it around. See what happens. That's what I did. ;) Or, if you have the correct flange, ATP makes a BOV with a check valve in it so that it won't open under vacuum, only under pressure.

See http://www.atpturbo.com/Merchant2/m...OD&Product_Code=ATP-BOV-005&Category_Code=BOV and check out the "anti-stall" version.
 
I'll try venting to atmosphere as a test. I need to find something to plug the plumbing up.

My current BOV is a Greddy Type RS unit. It just has a soft-hard dial to set the spring pressure.

I'm trying to understand what's 'enough spring pressure' to close the BOV at idle and cruise but yet stay closed under boost and also open under deceleration. I idle at about 12"-15" of vac. and at cruise I'm at 10" - 0." I'm guessing I would want it to activate the BOV when I'm at 18-20" of vac when I close the throttle body while letting off.

But when do you know you have the spring adjusted too high?
How do you know if you're not protecting the turbo anymore?
 
Well, some of that bears some clarification.

First, the spring only holds the valve closed, really, at idle and cruise (including light decel). If you’re recirculating the BOV (more of a bypass arrangement) it really doesn’t matter what spring you have in there, even if vacuum is pulling the valve open, you don’t care. That’s why centrifugal supercharger guys can use those dinky little Bosch heater valves as a bypass.

Under boost, the pressure across the valve diaphragm is equalized by the pressure being the same on both sides of the throttle body. So, the spring is in there acting on its own to keep the valve closed, exactly as it would if your truck was at rest. You don’t have to have any kind of special spring pressure in it to keep it closed under boost. Again, this is why the supercharger guys can get away with a valve that has basically no spring at all.

When you let off the gas, the throttle blade closes and vacuum (higher than usual) tries to lift the valve off the seat. You want just enough spring to keep that valve closed with that vacuum tugging on it. The pressure spike between the throttle blade and the compressor, however, is going to drive the valve open briefly because the spring is being ALMOST neutralized and there is a significant pressure still in the intake tract. So, the valve unseats until the pressure reaches the point where the spring, still being acted on by vacuum, can get the valve closed. That requires very little pressure at all.

I forgot you had the upgraded cams, so an 11 lb spring (or 11 lbs of spring pressure) should work dandy in yours. I don’t know how much adjustability the Greddy has, but you’ll turn it up until you hear it stop hissing (and the truck stops surging) at idle. Then turn it a little more as a starting point to get it to not open under light decel. Work it higher from there until all light decel drivability mellows out and you get good steady a:f ratios on your wideband.

You really have to be running a lot of boost with that relatively big turbo on an automatic transmission vehicle to ever worry about hurting the compressor. BOVs are mostly for small turbos with low moments of inertia on manual transmission cars that see lots of repeat throttle closings at high boost levels. Not to say that you shouldn't run one, just don't get into too much of an excercise worrying about not harming the compressor.
 
Wow...lots of great info in this thread :eek:ldtu:

I will be watching to see how everyone approches this problem so that I will know how to configure my 03L setup when I start fabbing it up.
 
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To adjust the BOV you can start with almost all tension off of the spring. Start the motor and feel the inlet of the bov. It will be sucking air past it. Tighten the spring until it stops, then you are good to go.

The bov is not causing the issue. I have been datalogging my truck for awhile. The issue is the turbo is still coasting when the throttle is closed and drawing a ton of air past the maf. In a nutshell this confuses the EEC.

We have a few band-aid fixes to get around the issue with tuning.

Best way to fix is go to a blow through config, but I am determined to make it work with a draw through.
 
But that only put enough tension on it to close it at idle, not decel. The BOV should only be open for a vent and should then close again. In my opinion, you need to increase your spring rate.

You only want to BOV is discharge the high pressure spike. It doesn't need to act like a bypass on a supercharger.
 
I had only turned the screw 2 full revolutions to stiffen it up when I was at idle. Should I turn it more? If it helped, it did so minimally.

And do you mean feel the bov outlet instead of inlet? I'm thinking the outlet is the part that clamps to the plumbing that goes to the turbo inlet.

Besides the dashpot tweaks, what other band-aid fixes did you do? I am going to try to get an open loop tune working this weekend to see if that helps things out.

My house is on a circle and so I usually 'coast' around the circle since little kids are often running around and also to spare the neighbors from hearing my exhaust... but when I just coast and the if the turbo is warm I can count on it stalling half way around the circle. My wideband reads lean and the truck hesitates and dies. Also at a light, my A/F is 14.8 or so... and then when I take off, it goes way lean to 17 and will stall or if I manage to give enough throttle then will go way rich to 10.7:1. This same tune with my KB was perfect.
 
FMOS Racing said:


You really have to be running a lot of boost with that relatively big turbo on an automatic transmission vehicle to ever worry about hurting the compressor. BOVs are mostly for small turbos with low moments of inertia on manual transmission cars that see lots of repeat throttle closings at high boost levels. Not to say that you shouldn't run one, just don't get into too much of an excercise worrying about not harming the compressor.
Click to expand...

This was very well said.....the message is if the BOV becomes to much of pain......put it on the shelf for a while. The truck wont sound as cool when the throttle is snapped shut but you wont be hurting anything either.

Dale
 
Mark/Skid,
Thanks for the hint on the dashpot.

Thanks Jody for the continuing guidance.

Thanks Jeff for the sanity check.

I at first was gettting a bit frustrated because I was only bumping it up 2%, 5%, 10%, 15% and wasn't seeing much of a difference. Finally bringing it up the dashpot from 1500 and below to about 200% from the stock setting seemed to make the truck better... at least I'm not stalling around the loop.

Datalogs confirm the turbo continuing to draw air past the maf when the throttle blade is shut. I still think there is a lot of value in moving the MAF further away from the BOV tubing. I might try that when I get some free time.

Making the BOV spring stiffer also helped a tiny bit.
I can tell I have a lot more tuning to do.
Baby steps I guess.

Thought I would share what I found out.
 
Phil,

When you say "continuing to draw air past the maf with the throttle closed," what exactly do you mean? If you're seeing significant airflow, you've got a leak somewhere. A pump can't pump if there's nowhere to pump to...
 
FMOS Racing said:
Phil,

When you say "continuing to draw air past the maf with the throttle closed," what exactly do you mean? If you're seeing significant airflow, you've got a leak somewhere. A pump can't pump if there's nowhere to pump to...
Click to expand...

Hmmm... maybe I should recheck the connections on the inlet past the maf.

On the datalog, I can see areas where I'm off the throttle (tp counts falling) and the maf counts drop some but then stabilize and level out even though rpm is dropping. That could be the BOV adding air back into the system as well. That's when it was stalling on me. It would push the rpm down even further and poof... dead.

I do think the dashpot settings are a bandaid in that they are helping the rpm to stay higher when I let off the throttle and not confusing the EEC as much.

I need to find a PCV plug or something so I can try venting to atmosphere. I didn't manage to get that this weekend.
 
FMOS Racing said:
Phil,

When you say "continuing to draw air past the maf with the throttle closed," what exactly do you mean? If you're seeing significant airflow, you've got a leak somewhere. A pump can't pump if there's nowhere to pump to...
Click to expand...

Seems like since the bov is open at idle (unless Phil changed that) then the turbo continues to recirculate air since it's spinning faster at that point, and I'd expect air to be drawn through the maf as well. Now if the bov is closed then it should have a minimal effect.

Jody
 
Yeah, I adjusted the BOV two full turns stiffer so that the air wouldn't move as much during idle. But I do see it on deceleration and that's when the rpm will plummet.

Driving to work was a lot better today. Stop and go was fine. Cruise was good as usual. Coasting to stop went fine. Still, at the very end when the motor is nice and hot and the turbo is kicking in with almost no lag at all is when the problem gets worse. Ive gotta figure something out. Why's that make a difference? It seems that the maf counts hang at the higher number when I let off then.
 
With the BOV recirculating downstream of the MAF, it should just be recirculating in basically a "loop."

Phil, disconnect the vacuum line to the BOV completely and see what she does.
 
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