Hey guys.
Ive looked on here for the answer but everyone has a different answer. I'm looking for the best place to mount my bov. I've heard in between the maf and the throttle body, after the ic but before the maf and in between tje turbo amd the ic. Can anyone tell me where you mounted yours and how does it work for you?

 

I like it near the throttle body so the air can keep traveling the same direction thru the pipes when the throttle closes.

With it near the turbo, the air switches direction to go out the BOV, then switches again when the throttle re-opens. Could be a little lag after shifts. It is mostly a psychological thing, probably doesn't make a big difference!

Some people say it's easier on the turbo to have it near it, but that's debatable.

With the size of a BOV, fitment is what usually decides the placement.

Al

 

Im not sure on the size. I bought the whole kit off a friend but he had it set up for a carb so im moving the bov. I just talked to Precision Turbo and Turbonetics and they said the put it after the intercooler but before the maf. They said if you put it after tbe maf tben the maf is going to read the airflow and add fuel but you wont have the air because you blew it out so it will get rich in between shifts. Kinda makes sense

 

Yeah, definitely before the maf, and probably not right before the maf as they can get finicky when it comes to turbulence.

 

Couldnt say it better myself.

 

Some MAF controlled cars have the vented air from the BOV recirculated into the turbo's intake. No loss of air but the pressure bleeds off since the turbo isn't spooling up during the shift. At least that's how I understand it.
I know DSM guys usually run them that way so they don't get the rich spot and a CEL.

 

Pre-MAF.

 

I have heard this a lot over the years and understand the thought process but haven't seen it to be the case in testing. Maybe if you slowly take your foot off the throttle over a period of time. But turns out the air is always going towards the compressor already when coming completely off throttle in boost. The instant the throttle shuts the intake side of the engine transitions to vacuum the injectors go into vapor lock, thus exhaust load goes away causing a rapid deceleration of the turbine and compressor and the air is also almost instantly going towards the compressor, now your trying to vent that pressure/volume coming back at a fast enough rate so that it doesn't overcome the inertia of the compressor and small amount of turbine load/thrust and send it into stall/surge.


I have tested it in many places, there are more factors involved to say what placement is best for each setup. Ie piping size, intercooler size, boost level and cfm/power at that pressure ratio, ported compressor cover or not etc. These tips will cover the largest array of setups. Get a large valve if you aren't running at least a 50mm, do so. Larger valve relieves pressure faster plain and simple. Next make sure the spring is not too stiff for your setup(max vac at warm idle). Optimally you want the spring just barely strong enough to keep the valve just barely or almost shut at warm idle. This makes for the most responsive valve and allows the valve to fully open at a higher velocity. At idle you should be able to easy push the valve open with one finger. If your stuck between having a slightly too strong spring but the next lighter spring keeps the valve open at idle to far for your liking, default to the softer spring. You can shim it with a flat washer until the valve is more closed at idle without having too much pressure at full compression. To summarize there is no harm in having too soft of a spring the valve with still function properly and close in boost etc. But there is harm in having too firm a spring as it wont allow the valve to open all the way or slower not at all for that matter and can lead to compressor surge and more wear and tear of your turbocharger.

Of all the places I have found on a blow through maf setup the most optimal spot is of course pre maf and also pre intercooler. We got the best results keeping it about halfway to 75% of the way closer to the intercooler between compressor outlet and intercooler inlet. The intercooler acts a volume chamber/surge tank if you will when coming off the throttle, this slows down the air coming back from the tb, giving that small amount of time for the valve to fully open and vent. Its about volume under pressure. So it keeps your largest volume of air at pressure away from the turbo and gives you the best chance of venting before excessively stalling the turbo compressor.

This is not to say another spot wont work when setup correctly, this is just the best spot I have found and where I place it on all my kit designs and why.

 

Wow thanks man. That's really helpful. I was going to put it pre maf but after the ic. It makes sense though. Better off releasing air before it goes through the ic. Thanks again