School me on BOVs

[CorvallisBMW]

I'm trying to get a few more details worked out on my m106 turbo system, and that's led me to the topic of BOVs. Earlier m102 systems had a recirculation system IIRC, but later m106 systems did not. As mine sits, it has no BOV. I understand what they do, but are they needed/recommended for low boost setups in the range of 6-8psi? I don't want to damage the turbo, but I've heard they aren't really necessary unless you're pushing more boost. Also, what triggers the BOV?

[cleanasse30]

A "BOV" is a Blow-off Valve. It is simply a valve that relieves pressure in the intake system when the throttle plate closes. A recirc valve just takes the air that a BOV bleeds to the atmosphere and puts it back in the intake system prior to the turbo. A recirc valve is useful when you run a MAF or AFM because the computer has already accounted for that air. So if you use a BOV with a MAF or AFM, the computer doesn't know the air has left the system and you will run rich for a short time after shifting. If you are using MS and running on speed density I would suggest running one even at low PSI. It will be better for the turbo, and you get the cool psh psh sounds

[CorvallisBMW]

I'm currently running the Miller MAF/WAR system/

[cleanasse30]

I'm currently running the Miller MAF/WAR system/

It would be best to run a recirc valve with a MAF setup, but i don't know too much about the Miller MAF/WAR system cuz i'm going the MegaSquirt route. You could run an atmospheric BOV but you will run rich at each shift which wont hurt anything really, just might make the car run worse on tip in off a shift.

[TheTacoMan]

Best thing would be to talk to kamotors, he ran miller with a couple bov setups.

[ak-]

If you're running a draw through setup (MAF in front of the turbo inlet), you need to recirc. the blow off valve back into the pipe between the turbo inlet and Miller MAF for reasons mentioned above.

Yes, even low boost, you should run one.
BOV's are triggered by vacuum and held shut by pressure. For this reason, I prefer a sequential blow off valve - one that isn't regulated being open and shut with a spring in conjunction, but solely vacuum. (HKS SSQV, SYNAPSE)

[CorvallisBMW]

Don't think I can run the HKS SSQV, I have none of that fancy electronic stuff.

I'm thinking something like this might work though: http://www.summitracing.com/parts/tb...1223/overview/

Add a port to the intake tube just before the throttle body, attach this, then run the outlet to the rubber elbow after the MAF. I could port it in to the 3/4" hole where the valve cover normally vents to.

[golde30]

You don't need any kind of electronics to run the HKS SSQV. Its a mechanical BOV and its awesome. Try to find an older one on CL, the older ones are a polished finish with yellow logo, the newer ones look like cast alum and have weird heat sink looking fins all over.

[CorvallisBMW]

It just seems overly complicated to me?? http://www.hks-power.co.jp/en/produc...v4d/index.html

The new ones look straight out of a F&F movie

[Jaxx_]

http://www.hks-power.co.jp/en/product/blow_off/sqv/index.html

This is the one you're actually wanting, not that electronic mumbo-jumbo.

I have run a BOV on cars with factory management that expect air recirculated and it has never been a problem. Realistically you are off the throttle and you might run a bit rich, but you're off the throttle...

Ideally, the school of thought I have always had is that you should vent to atmosphere before your intercooler, otherwise you are recirculating air that has already been compressed and heated, just to be reheated again. In either case, we're talking a very small amount of air in the grand scheme of things.

I personally would not consider running a BOV or bypass valve on boost less than 7psi or so, but above that I would. It is not uncommon to have high boost setups that don't have a blow off valve that opens below 6psi or so, so I wouldn't feel horrible about it. However having one is, technically speaking, the safe thing to do.

[downforce22]

Depeding on the setup of the m106 which has the intake on the opposite side of the m20, it may make sense to put the BOV upstream of the AFM/Maf. This would eliminate the problem of measuring air that gets vented to atmosphere.

There are also opinions that the BOV should be closer to the turbo vs closer to the throttle body. I think it would make sense to have the BOV as close to the throttle body as possible so when it snaps closed the pressure does not build up in the intercooler and make its way back to the compressor.

That would make the ideal setup
turbo->intercooler->bov->afm/maf->throttle body.
This of course assumes no recirculation since on an m20 the bov would be on the driver side of the car. The m106 you could put a recirc valve in easily since the inlet is on the passenger side of the car.

[CorvallisBMW]

I wonder if the Miller MAF can run with pressure? I guess I assumed it needed to be upstream of the turbo, but I've never confirmed it.

[cleanasse30]

Generally you do put the MAF upstream of the turbo. There is really no reason to run it any other way. That turbosmart valve you linked to would be a good option in my opinion. Just route a pipe from the vavle to in front of the turbo but after the MAF. That is the way most OEM manufacturers run turbo setups when using a MAF to measure air flow (see wrx, mazdaspeed3, etc.).

I think it would be a good idea to use a recirc valve for peace of mind and better driving experience.

Incase that wasn't clear the order should be (air filter, MAF, pipe with recirc valve exhaust, turbo, pipe to intercooler, intercooler, pipe to throttle body with recirc valve attached, throttle body)

[CorvallisBMW]

^that I can do pretty easily, I just need to have a flange or bung welded on to the tube pre-throttle so that there's a place for the BOV to attach.