Most of the turbo setups i have seen have the blowoff valve on the hot side but i have seen a few on the cold side.Any reason for this?

Im shooting in the wind here as my google results come back. I work on subarus all day long and the bov is right next to the throttle plate. I worked on a couple rb20's and its also near the throttle plate. I would imagine is has to do with response time or somthing. Isnt there essentially a wave pulsed backwards off the plate as soon as you shut it? Maybe location has to do with the lag time between throttle closing, diaphragm response, and "catching the wave". Honestly it probly doesnt matter and from what ive read you dont even really need one unless your pushing some serious cfm or want it to perform and last like OEM. (if you strap on a turbo run it 4-10 psi on something i dont even think you need it with a life of 1-3yrs?)

Honeslty im probly wrong but theres what ive read and assumed heres google: **this is good** LMAFO


http://www.dragsource.com/index.php?nav ... letoview=7

The vast majority of people will tell you that you are supposed to place your blow off valve within a couple feet of your throttle body. I am here to tell you that this is not the best location for your blow off valve.

The best location for your blow off valve is going to be in between your turbo and intercooler, on the hot side.

Think about it. If you put the blow off valve on the cold side (after the intercooler), you are pushing hot air through your intercooler for nothing. This increases the speed at which your intercooler and motor become heat soaked.

By putting the blow off valve before, or even on the intercooler itself - you allow all of the hot compressed air to escape to atmosphere prior to passing through the intercooler. A blow off valve does the same thing no matter where you place it on the charge piping. Knowing this - it's only logical to put it in a place where it relieves hot air rather than cold air.

Here's a good article to back when SCC magazine was still itself.

http://www.modified.com/tech/0701_sccp_ ... ewall.html

I read it when this issue first came out and still think its much more practical than the whole nearly negligible increase of heatsoak of the intercooler. I'd much rather waste cooled air once while keeping intake flow in one direction than cool it twice in an attempt to slow heatsoak while pushing more volume back and forth throught the induction system. The pro doesn't seem worth the cons in the latter theory.

Having said that, my bov is still on the hot pipe. Why? Because that's where the flange came on my piping kit, the recirc plumbing is a little easier this way, and my car is not a full out track car to where it bothers me enough to move it. Kits prob come this way just for the simple fact that there's more room to mount a valve on that side.

I have heard that both sides work as long as the BOV is setup properly.

I placed mine just before the throttle body and recirculated it into the intake charge.
I ran with no BOV to test the car at 7psi on a t3/t4 turbo and I got some nasty surge and it made my car stall everytime I came out of boost.

Once I ran the BOV the car runs and idles LIKE STOCK. I use a greddy RS and i love it! Not one issue.

here's how I setup mine:



Hope it helps!

I am going to go with a setup like you have,sounds like it works pretty good.

sx moneypit wrote:I am going to go with a setup like you have,sounds like it works pretty good.

I haven't had any problems with the Greddy valves.

Just so that you know (and i read this on another forum regarding Greddy recirculated BOVs), when you buy a Greddy BOV open it up and there will be 2 springs inside the valve (one small one inside a bigger one).

Remove the small one from inside and put the BOV back together and leave it on the softest setting (which it already should come in from factory). This makes it work on recirculation mode correctly as Im guessing otherwise it would be too tight to recirculate properly.

I removed it and it works perfect.

Thank you for the good information!

While the pros and cons of either set up have been discussed, either location should be fin from the standpoint of a BOV's primary purpose: preventing surge. For recirculated BOV's in particular, the logistical aspect is probably the most dominant consideration.

^ +1
Put it wherever you have room... run blow-through MAF and don't give a crap about recirculating.

I read something other day that said blow through is not a good idea. That the maf not designed to do that or some mumbojumbo..... I guess our mafs arent really made for boost so its doesnt matter anyways eh...

Never ran blow through but i might try it on my next one.

Issue there is if the MAF is plastic housing it can blow. Or pop off the sensor part of the MAF housing. But those issues usually don't arise until over 15psi.

People use metal housing or epoxy the sensor part. Or Cobra MAFs are metal.

Well to kill some more birds since you shot that to death! I also browesed some information reguarding aftermarket intakes. I believe it was on the cobb tuning website. Anyways it was a tech article by them talking about maf housing size which im well aware of. Then it went into saying how important piping is before the maf. It brought up examples of bends right before the sensor or if the air is not smooth (they used big word?). They made some very notable points that an uneven flow across the maf could cause intermitten lean/rich conditions blahh blahh blahh......

What you think about all that mumbo.

In the end they said your modified maf piping should resemble the factory in distances from throttle body and filter. I guess thats why they call it tuning LMFAO.

another read for you guys below! i read a bunch stuff cant get enough i guess tryin to reinvent the wheel here........

http://www.ehow.com/how_12143597_diy-maf-resistors.html

^eh!!!!

I did have an idea or routing a hose around the maf sensor with some kind of adjustable part so i could lean out fueling. I know for shur it would work but not shur about effects on idle or partial throttle. I also considered the air not being even at all throttle positions but maybe make a custom housing or someting. Im aware its not a very good idea in general but id assume armed with a wideband and maybe some kind of aftermarket knock sensor you'd be pretty safe.

Im having trouble figuring out what timing would do at the moment. I believe it would advance as you made the bypass larger so you would probly want to retard base timing quite a bit. I figured it could compensate for larger fuel injectors combined with fmu and maybe........ eh time to read more

What you're talking about is a "hacked MAF" system. It is OLD engine technology, but it works really, really well. I actually have the exact setup you are talking about on my Miata. I ran hacked maf on the factory ECU and E85 with 550cc injectors prior to going to my full stand-alone system.

The key, which you've hit on in a previous post is that you make the bypass far enough ahead and after the MAF so that you don't disturb laminar flow patterns (I think that's the big word you were talking about).
Major components of flow turbulence are flow/velocity, and bends/baffles. So if you have higher HP, you actually have to have smoother transitions/longer lead-ins around your MAF. Lower power isn't as important.

biggie wrote:Issue there is if the MAF is plastic housing it can blow. Or pop off the sensor part of the MAF housing. But those issues usually don't arise until over 15psi.

I was thinking about doing this for my new setup, but I've heard of some people still popping them open at 8 psi.
I'm hoping those are just due to the MAFs being in bad condition.
Fingers crossed!

I've only ran Cobra MAF, so no experience relevant for me.

PapaSmurf2k3 wrote:
What you're talking about is a "hacked MAF" system. It is OLD engine technology, but it works really, really well. I actually have the exact setup you are talking about on my Miata. I ran hacked maf on the factory ECU and E85 with 550cc injectors prior to going to my full stand-alone system.

The key, which you've hit on in a previous post is that you make the bypass far enough ahead and after the MAF so that you don't disturb laminar flow patterns (I think that's the big word you were talking about).
Major components of flow turbulence are flow/velocity, and bends/baffles. So if you have higher HP, you actually have to have smoother transitions/longer lead-ins around your MAF. Lower power isn't as important.

NICE!

old technology more like cheap tricks that are pushed under the rug by aftermarket
That might be a bit brash i believe it comes down to just dumb people not taking everything into account strappin up and runnin it. Hence why for example fmu's get a horrible reputation everywhere. There are obvious limitations there!

anyways cheers on that response Papasmurf

That's some great information guys!

Also, I've been running blow through Z32 N62 MAF for years with no issues (along with NISTUNE, so I don't have a bypass hose around the MAF or anything).

I'll try and get some pics of my Miata setup. The top is easy to see, but the bottom, where the hose starts, not so much. She's pretty buried.

Another question, if you have a properly working BOV vented to atmosphere why do some people have stalling issues? Shouldn't the valve be completely shut when the engine idles down?

With blow thru you shouldn't have issues.

Issues occur with Atm Vented BOV with the MAF on intake. MAF reads the air, then BOV releases metered air, causing bad A/F mix at that time.

biggie wrote:With blow thru you shouldn't have issues.

Issues occur with Atm Vented BOV with the MAF on intake. MAF reads the air, then BOV releases metered air, causing bad A/F mix at that time.

Correct. By the time the engine reaches idle RPM, the mixture is still messed up and the damage is done. It sort of "free-falls" to stall.

Just some food for thought, supposedly you can tune for an atmospheric bov with the mafs on the intake. I mentioned it to EFI before I ordered my new tune and was told it could be done, haven't really tested it yet though. I've been running my bov to atmosphere for going on 4 years with my old tune and have only stalled once, and that was with pushing the clutch in after a 4th gear pull.

I've read it can also be done with an safc. Something about decel ...

Its the same concept i believe when they induce backfires on purpose in rally cars to spool the turbo when throttle is shut. This provides "full spool when exiting a turn. I dont know how they prevent the engine from stalling tho....maybe really high idle speed or something?

Chris28 wrote:Just some food for thought, supposedly you can tune for an atmospheric bov with the mafs on the intake. I mentioned it to EFI before I ordered my new tune and was told it could be done, haven't really tested it yet though. I've been running my bov to atmosphere for going on 4 years with my old tune and have only stalled once, and that was with pushing the clutch in after a 4th gear pull.

What brand BOV and how much boost have you been running?

Turbonetics Raptor, 8 psi on a t28. Probably not enough boost to matter. Now I'm running 15 psi on a Precision 5431, I'll give an update when I put some actual miles on it.

Chris28 wrote:Turbonetics Raptor, 8 psi on a t28. Probably not enough boost to matter. Now I'm running 15 psi on a Precision 5431, I'll give an update when I put some actual miles on it.

Thanks Chris, i was just looking at one of those on Turbonectics web site!
I am going to be running a JGS turbo setup with a Turbonectics 10784.
Starting on the install this weekend!

It sounds pretty cool and doesn't leak under vacuum so I'm happy with it. I traded a broken Greddy BOV for it, I just looked at the price of them new and I'm glad I didn't pay that much!

lexcrob wrote:I've read it can also be done with an safc. Something about decel ...

Its the same concept i believe when they induce backfires on purpose in rally cars to spool the turbo when throttle is shut. This provides "full spool when exiting a turn. I dont know how they prevent the engine from stalling tho....maybe really high idle speed or something?

The engine wouldn't need to idle because the drivetrain would be spinning the engine.
Normally when you're engine braking, the ECU shuts off the injectors. I'd guess with anti-lag, the ECU dumps fuel in instead.

Anti-lag usually times the spark so you get maximum exhaust velocities.