Adjusting boost: need to change wastegate + bov?

[jumpfroggy]

I've been reading upgrade guides, faq's, newsgroups, and everything for the past year, but there's still something I've been wondering.

I have a stock 2G Talon TSI. I have some parts I just got: boost gauge, 1g BOV with uic pipe, and soon a boost controller. I'm guessing I'm making about 9psi from the stock wastegate (about right for stock?). But if I only replace the stock BOV with the 2G, I'll still make the same 9 psi, but the BOV wouldn't let off

So say I get a 1G BOV for my 2G talon, since the 1G BOV can hold more boost. But if I only did that swap (with nothing else), then would that mean I'd be making the same boost (~9 psi due to the stock wastegate?), but when I let off the pedal the 1G is letting more boost build (~18 psi on 1G?) until it opens?

Or maybe I'm thinking about this wrong. Maybe when you let off the gas, it creates a vacuum that causes any BOV to open right then, regardless of boost. But if you're just accelerating and building boost, your BOV has an upper limit before it leaks. So replacing a BOV with one that has a higher rating will do nothing if the boost hasn't changed, right?

 

[perley03]

Since both cars run at 10-12psi stock, you should be fine. The stock 2G starts to leak around 15psi so its a good mod to do if you want to up the boost in the future.

 

[95talon_in_ma]

Think of it this way.
The wastegate controls how much pressure the turbo puts into the intake piping, but cannot reverse flow. When you shift or take your foot off the gas abruptly, the turbo slows down, but not fast enough to let out the reversion of air. The BOV accomplishes this.

Anyone correct me if I am wong, but I beleive the Stock 2g bov starts to open early. Maybe 8 or 9 psi. So you never get the full benefit of full boost at higher rpms as it's always "leaking". I think a 1G eliminates that issue.

Sound right?

 

[xveganxcowboyx]

To elaborate on the above post (BTW, I don't think the 2G blow off valves are that bad...)

The blow off valve does not control boost at all. The advantage to upgrading is being ABLE to hold more boost without leaking. Under boost the BOV is stuck closed. When you let off the gas and your intake manifold goes into vacuum the vacuum opens the BOV, allowing the pressure to escape.

The stock wastegate is what controls boost from the factory. When you add a boost controller you're taking that control away from the wastegate and using the controller instead.


And just for reference the 2G's tend to see a bit more boost than the 1G's (or so I've read) 9-11psi is common on 1G's and 10-12 on 2G's (roughly). Mine ran 9 stock. Hook up your boost gauge before anything else and see what yours is at just so you know.

 

[jumpfroggy]

Ahh, I get it now. The wastegate controls boost, and the BOV only affects it when 1) there's vacuum, let off gas, clutch, etc, or 2) you hit the leak point for the BOV and it counteracts the turbo. So I could put a BOV capable of 30psi in there, but it wouldn't change anything until I up the boost.

So now my plan is to install the boost gauge, drive around a while getting used to max boost, lag, spikes, all that on the stock setup. Then I'm going to install the 1G BOV, drive around for a little while. Then I'm going to put in a boost controller and slowly experiment. Thanks for the answers guys, it's something I always wondered about.

 

[xveganxcowboyx]

You got it!

 

[jumpfroggy]

Thanks again, everyone. Onto the next question!

 

[TheRealist]

Think of it this way.
The wastegate controls how much pressure the turbo puts into the intake piping, but cannot reverse flow. When you shift or take your foot off the gas abruptly, the turbo slows down, but not fast enough to let out the reversion of air. The BOV accomplishes this.

Anyone correct me if I am wong, but I beleive the Stock 2g bov starts to open early. Maybe 8 or 9 psi. So you never get the full benefit of full boost at higher rpms as it's always "leaking". I think a 1G eliminates that issue.

Sound right?

So in this department an automatic would have an advantage over a manual becuase of the fact it wont loose boost or how does that work?

 

[kenamond]

Actually, there's one more piece in the puzzle for controlling boost. The BCS (boost control solenoid) is between (sort of) the compressor housing boost signal and the WGA (wastegate actuator). The stock WGA will open at 9psi if you ran a tube from the compressor outlet straight to the WGA. The BCS "hides" the boost signal until around 11psi of compressor boost.

That's a bit of a simplification. There are two common types of mechanical boost controllers: bleeder and ball-spring. The BCS is a bleeder type. What it does is let some of the pressure from the compressor housing leak back into the intake pipe (look at all of the vaccuum lines). Since some of the air is leaking, the pressure that actually makes it to the WGA is lower than what is in the compressor housing. The diameter of the opening of the BCS nipple controls how much air leaks back to the intake pipe. So when you do the BCS mod and remove a restrictor, you enlarge the diameter of the bleeder, so more air leaks to the intake pipe, the pressure drop between the compressor and WGA is greater, so it takes more boost pressure to finally apply 9psi to the WGA.

If you get an MBC, they're typically ball-spring devices. The get mounted inline from the compressor to the WGA (yes there are other ways to route them, but this is probably the most common "correct" way). The ball completely blocks the compressor boost signal from the WGA until the boost pressure is enough to push the ball out of the way (compressing a spring) and letting the boost signal continue on to the WGA.

So even in the stock configuration, the WGA is not controlled strictly by the compressor boost level; there is another piece involved that lets you go past 9psi.

 

[ovurboost95]

I just installed my MBC I'm now at 15-17 PSI over the original 10psi my Boost gauge always read. My question is should I adjust my A/M BOV for the increased Boost pressure?

 

[JusMX141]

So I could put a BOV capable of 30psi in there, but it wouldn't change anything until I up the boost.

Not really. This is where valves with adjustable spring tension (Greddy) and / or interchangeable springs (Tial) step in.

If you have a BOV on your car that has no trouble holding 30psi, the valve will not open at low boost (which is what you'll be running). If your BOV does not open properly at low boost, you'll back up pressure in the charge piping between shifts and the turbo will suffer from Compressor Surge, which will wipe out the journal bearings and possibly break the turbine shaft. A common symptom of this is Blow Off Valve "flutter".....if your valve flutters, the spring tension is too tight.

For any boost level up to 20psi, I'd recommend a 1G BOV. For boost from 20-30psi, I'd recommend a crushed 1G BOV that has had the Dodge Garage Mod done. We have a Crushed, Dodge Garage-Modded 1G BOV on my buddy's 2G TSi running 22-25psi, and it sounds NOTHING like a standard 1G BOV; it has a totally unique sound. However, if he's not making above 20psi, the BOV will occasionally flutter a little with the quick-release feature disconnected.

 

[fatherbubble]

Just go get a Autometer from Autozone for 50 bucks an install it on your dash..Boost guage

 

[knochgoon24]

I just installed my MBC I'm now at 15-17 PSI over the original 10psi my Boost gauge always read. My question is should I adjust my A/M BOV for the increased Boost pressure?

What do you mean? Are you hitting 15-17psi or 25-27psi. There's a big difference.

 

[ovurboost95]

Stock setup I was hitting a boost of 10-12 lbs, on a Aftermarket boost gauge. With the few small changes I've made including a MBC. I now hit 15-17 LBS of Boost. My question is. I already have a Aftermarket BOV on the car. should I adjust it for the increased boost. I do get the low boost flutter if I don't reach max boost and Shift.(I'm not venting either) But at full boost the BOV opens fine. I just don't want it to boost leak now that i've introduced a extra 5-7 lbs. Thanks,
Isaac

 

[JusMX141]

In theory, if you have the proper spring tension to hold the valve shut at your desired boost level, it should never leak....the spring is not the only device which holds the valve shut.

On boost, the line that connects to the top of the valve (fed from the intake manifold) which is used to draw the valve open under vacuum will now be charged with whatever amount of boost pressure you're running....so if your piping has 15psi in it, there is also 15psi on top of the diaphragm which is working with the spring to hold the valve shut.

 

[pimpin81]

sounds good to me

 

[mentalTSiAWD]

Stock setup I was hitting a boost of 10-12 lbs, on a Aftermarket boost gauge. With the few small changes I've made including a MBC. I now hit 15-17 LBS of Boost. My question is. I already have a Aftermarket BOV on the car. should I adjust it for the increased boost. I do get the low boost flutter if I don't reach max boost and Shift.(I'm not venting either) But at full boost the BOV opens fine. I just don't want it to boost leak now that i've introduced a extra 5-7 lbs. Thanks,
Isaac

I myself wouldn't run over 15 lbs of boost on a stock fuel system. You should use your new MBC to control your boost down to around there.

 

[darkhorizon]

If your getting flutter, you can adjust the BOV down a bit so it WONT hold as much boost.

 

[Bristecom]

So if I were to put an Evo CBV/BOV on my 2G running 14.5 psi of boost, it would be too stiff since the Evo typically runs 20+ psi of boost or no? Can it be adjusted?

 

[JusMX141]

Evo's are still daily-driven cars....Mitsubishi wouldn't put a BOV on an Evo that could possibly damage the turbo if the driver suddenly cuts the throttle without building full boost.

I think you'll be fine.