So I decided to make my own intercooler piping today.

Bought some alum piping off Ebay and went at it welding my *** off.

I wanted to try to vent the stock BOV to atmosphere to see what happens.

I ran into some issues when VTA the stock IX BOV.

Symptoms: Part throttle boosting the car would stumble on itself going retardedly rich into the low 10's and 9's. At full throttle the car ran fine.

What I think is happening is the IX BOV is leaking at low boost...and perhaps also at higher boost, but the turbo is compensating for it so the tune remains fine at higher boost.

I've read a bunch of threads stating the IX BOV is "good" for a certain amount of boost, but I really hate assuming stuff is true (especially on this forum)

Does anyone have thoughts or a different explanation of what is happening?

I recirc'd the BOV and the car ran perfectly fine afterwards.

I have tuned another EVO with a blitz DD BOV and it is VTA with no issues tuned with EcuFlash. So what I"m thinking is that the aftermarket BOV doesn't leak and therefor the car ran fine.

 

DV's generally have softer springs than dedicated VTA BOVs. In a properly working setup, a DV will not full close until WOT. This applies to some VTA BOVs as well, but they don't generally vent as much as a DV at idle and partial throttle.

I did the same thing you've done here with my VW. At part throttle you could actually hear the DV venting ... it closed up around -10 in/hg.

You're experiencing the basic problem with a VTA setup. A soft spring will vent metered air and cause a rich condition at idle and part throttle. By stiffening the spring enough you can keep it closed at idle, but you are likely to get compressor surge when the valve opens to release boost.

 

The stock DVs are not at full clamp under part throttle acceleration, neither are most aftermarket VTA DVs. It all has to do with the design and setup of the Valve.

It is all about the pressure differential across the valve as well as the spring preload. The car will go rich under part throttle with a VTA because the air that was already metered by the MAF is escaping to the atmosphere and not going into the engine via the recirc. Under higher boost (whatever the DV is full clamped at) the car will run normal, but have fun shifting Flames!

 

Slightly off topic.

I want to create my own uip. Did you go with 2.5" OD?

Did you use the stock pipe that joins the ic and modify it so it goes under the intake?

 

Thanks guys.

That's exactly what I needed to know.

Either get a working BOV, or keep it recirc'd.
I don't mind flames after letting off the gas. No big deal.

 

So why would people want to keep using the stock diverter valve if it's made to leak under part throttle?

 

Leaking at part throttle does not really effect anything as long as the DV is still plumbed back into the intake.

The stock Valve supposedly holds boost well and there is no reason to replace something that works fine.

Also I think the stock BOV provides the best drivability of any valve out there.

 

It leaks enough so that it'll drastically affect the metering during part throttle boosting if VTA.

Why would any boost leak be "ok"?
Even if plumbed back through the intake you're losing pressure.

 

You aren't losing "pressure" if your engine is pulling vacuum. Once the pressure equalizes or goes positive (boost), the valve stays closed.

Under partial throttle the valve does vent a little in some instances ... it has to do with the UICP pressure being different from manifold pressure due to the throttle plate position. Think of that part throttle vent as another form of boost control.

 

I measure boost from the manifold.
At 8psi manifold pressure my IX diverter valve is **** leaking back into the intake.

If it were simply vacuum leak, it would be fine but this was clearly in positive pressure.

 

At partial throttle UICP pressure is greater than manifold pressure. This pressure difference overcomes the DV spring tension. That is why it leaks. It's working as intended, I promise.

 

Ah. Understood.

I still don't like the idea though.

Maybe it's BOV time for me.

 

More than likely it's speed density time for you as well ... but that means you'll be leaving us here in the ECUFlash forum ... /cry.

What you'll run in to with a VTA is more of the same. the difference will be the spring tension. Most of the time it's too weak and vents like you are seeing now, or it's too tight and doesn't vent enough. You've really got to meter air after the valve to get the car to run anywhere near decent.

On my VW, I simply ran w/o the MAF and the ECU ran off of the MAP just before the IC. This isn't an option on the Evo.

 

That was one of the things I was looking into when I first got the EVO and started tuning it.

I love tuning speed density. I won't touch a boosted IS300 unless it's speed density now. No more messing with MAF.

But on my EVO I'm starting to like it more and more.

I'm tuning a kid's evo right now that's running ecuflash and VTA. Running fine no problems and no boost **** leakage from the BOV.

 

And the compressor isn't shuttering when the BOV vents?