Yes, absolutely the stock valve leaks at higher than stock boost levels, as you found out. It does not do this to control boost, it's not supposed to leak at all. The problem comes when you get the car tuned with the stock BOV. Since the BOV is leaking, the amount of boost pressure and the volume of air getting to the engine is less than what the turbo is flowing. So the car is tuned to run nicely with the crappy stock BOV leaking without anyone knowing about it.

Then you switch to a BOV that holds higher boost and doesn't leak, but the car is still tuned to run perfectly with a boost leak. With the new BOV and no boost leak, the engine is getting a larger volume of air and more boost pressure than it's providing fuel and ignition timing for. This causes the car to overboost and run excessively lean and is probably causing lots of knock, depending on how aggresive the tune is.

Moral of the story...

If you like your leaky stock BOV and are tuned with it, that's fine. If you ever swap to a good valve that will hold all the boost you can throw at it, don't run it on the same tune. Get tuned for the new valve right away.

 

100% understand. but i do believe when u have a boost leak, if its minimal the turbo should compensate,thus working harder so you should still receive volume air (boost).

my tune at 24-26psi had NO counts of knock maybe 1 here and there which i witnessed with my own eyes factory tune i would get almost 6 counts of knock so im sure my tune is conservative. im getttng a boost controller. im gonna set my car at 22 psi and watch air fuel. then ill log car this weekened thanks for the help guys

i actually remove the boost pill

 

from what i have learned the leaky bov DOESNT control boost but HELPS the SYSTEM WORK CORRECTLY VIA BOOST PILL. one i removed the boost pill i got 12-13psi. obviously this leaky bov worjks well/ the factory set up and boost pill

 

No, a leaky BOV does not help anything. It's not supposed to leak at all. The only time the BOV is supposed to open is when the throttle closes. When it leaks, the turbo tries to compensate by working harder and pushing even more boost. This drives it more out of the turbo's efficiency range and flows hotter air and less boost pressure is actually reaching the engine.

Your tune had no knock with a boost leak. As soon as you get rid of the boost leak, you start overboosting, which means it's running much leaner with more knock. You're right that the boost pill helps control boost, but the BOV has nothing to do with it. A BOV is not meant to be a boost control device. Getting yourself an aftermarket boost controller won't do anything to take care of the boost leak.

Get rid of that crappy stock BOV.

I'll never understand why so many people will spend thousands of dollars on aftermarket engine parts and ECU tunes, yet leave the terrible stock BOV because they think it's "good enough".

 

The stock bypass valve is not crappy. It was designed to protect the turbocharger from compressor surge with the factory tune and does it's job. Mitsubishi didn't intend for it to seal at boost pressures higher than stock.

The problem with a lot of the aftermarket valves is that the firmer diaphragm/spring settings used to keep the valve from leaking at higher than stock boost levels don't protect the turbocharger as well at part throttle conditions. The stock turbocharger will have a longer life with the stock bypass valve so you have to weigh the pros and cons of swapping it out with an aftermarket valve.

 

I find it odd that the perfectly good OEM BOV is suddenly "crappy" and "leaky."

It sure hasn't been for the entire time the car has been out. It sure hasn't been for some of the top tuners in this forum. And it sure wasn't a problem to use it when creating this car: https://www.evolutionm.net/forums/ev...eo-inside.html And, that's just one example out of hundreds of built cars and tuned cars on this forum.

I think that perhaps the OP has a faulty BOV?

Or, could it be that the OP pulled off a boost hose, changed his OEM-recirculation BOV into a VTA BOV and is wondering why it has problems all of the sudden???

The stock metal BOV on the X is perfectly fine unless you're running well over 30psi. Same goes for the stock metal BOV on the IX. The only stock BOV that really needed to be replaced was the plastic one on the VIII.

 

 

nobody is saying the bov is faulty as other people have mentioned the bov leaks on purpose this is the way mitsu designed it(it makes the system WORK as a whole) thus controlling boost and a/f correctly. as i said before it would only leak momentarily

when i upgraded to an aftermarket bov... w STOCK CONFIGURATION AND ALL HOSES IN TACT LIKE FACTORY. i would get 30 psi spike. but when i went to the stock (leaky) bov boost was normal again.

when i installed a mbc and afterm bov i again controlled boost by also removing boost pills. this proves the stock (leaky)bov works together as AWHOLE to make system work correctly

as i said the stock bov momentarily leaks at 4k even at idle.

 

Yes! Exactly! This is what I'm saying. It's a great valve and it works just fine....at stock boost levels. When you start pushing more boost than the stock 21-22psi, then it's going to start to leak, maybe at 23psi, maybe at 26psi.
The problem with the stock valve is the reference port that puts boost pressure on the bottom of the valve. While this does help the response time of the valve at part throttle, it also causes it to push open at higher than stock boost levels. There are several aftermarket valves that are plenty responsive at low boost/part throttle conditions yet can hold all the boost you'll ever want.
Yes, there are plenty of cars making a lot of power on the stock valve, but that doesn't mean it's not still leaking. Since the valve is recirculated, you're never going to hear the rush of air when the valve pushes open at full boost, especially with a loud exhaust, so you'd actually never know that it's leaking. If the car is tuned to run perfectly on a leaky valve, then obviously it's going to run perfectly. The problem arises when you get rid of the boost leak with an aftermarket valve, yet still run the same ECU map that was tuned with a boost leak.
The OP already stated that the car ran perfectly fine with the OEM valve converted to VTA, other than the fact that he could hear the rush of air when the valve leaked at full boost. He only had the overboost problem when he swapped to an aftermarket valve.
No, the BOV is not supposed to leak. It runs just fine because your car was tuned to run with the leaky valve. When you swap to an aftermarket valve that doesn't leak, the car is still expecting the boost leak to be there, so the turbo still makes the same amount of boost, but none of it is leaking now, so more boost gets into the engine than it's expecting.


Basically this whole issue comes back to spending thousands on aftermarket parts and a tune but neglecting a couple hundred dollar BOV because the stock one is "good enough". It's cheap insurance to eliminate the BOV as the source of a boost leak.

 

ok im running higher boost so thats why it leaks. i was under impression it was supposed to leak cause car ran good this way.

everything u said makes sense hit it dead on THANKS

 

so any suggestions on a good BOV?

 

Does anyone have CONCRETE evidence that the stock BOV leaks at higher boost pressures? Because it seems like its all hear say.

There are however countless cars, like Ryan Gates' EVO X that have run a full season with over 35psi of boost without ever leaking.

Hell even my car that sees 26psi every day hasnt had any issues with the stock BOV. I even have an HKS SSQV that I have installed and the boost level didnt jump up at all so your theory of it leaking at higher boost isnt very sound.

Sorry I say stick with stock, it works the best.

 

IF UR CAR WAS TUNED W STOCK BOV you wont notice a thing(even when its leaking)

 

Can you show me a link or some evidence that it leaks? Im still somewhat puzzled where this information of it leaking has come from.

As I said, i switched my car over from stock BOV to HKS SSQV and there was absolutely no difference in boost levels, performance etc. so it being tuned or not makes no sense to me.

 

The first post of this thread ↓↓↓ shows obvious evidence of a leaking stock BOV:

He hears a rush of air right around when the turbo hits full boost, when he swaps to an aftermarket BOV with no other changes, the rush of air is gone and he's overboosting.

Everyone keeps saying "Stick with the stock valve, it'll hold 30psi, blah blah blah". Is there evidence somewhere that it will hold 30psi? Or is it just the fact that people get tuned running higher boost with the stock valve and the car runs great, so the BOV must not be leaking? If you have the BOV recirculated, you're never going to hear it leak, especially over a loud exhaust. The turbo can push plenty of air and boost pressure to overcome a small boost leak at full boost, so the only way you'll ever know if the BOV is leaking is if you hear it, or actually watch the valve push open when the car is on a dyno. If the car is tuned to run perfectly with a leaky BOV, then obviously it's going to run perfectly with a leaky BOV.

This a mass produced BOV that is meant for a stock car at stock boost levels, around 21-22psi. There's no telling if it'll leak right at 22psi, or 23psi, or 26psi. But why not just swap it out for an aftermarket valve that you know is never going to leak? Compared to all the other aftermarket parts we all buy, a good BOV is cheap.