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$85.00 Dawes Boost Control Valve ("race" version) http://www.dawesdevices.com

Before: Best 0-60 time = 10.5 seconds at 60F
After: Sloppy 0-60 time = 9.1 seconds at 70F

And if you're really short on bucks, you can do it for $35.

Easily the best and most cost-effective mod I've done to my car. The Dawes Mechanical Boost Controller (MBC). Thank You, Chris (pass-variant) for turning me on to this wonderful device! This bypasses the N75 valve, which is notorious for imprecise boost control. You leave the N75 plugged in, so the ECU doesn't know it's not operating (i.e. no CEL's). Disconnect the N75 from the Wastegate and connect the Dawes between the wastegate and manifold vacuum. Shazaam! Your boost is now totally and completely controlled by your right foot. This mod is worth it even if you keep the stock boost level of 7 psi. The turbo will start spooling at 1600 rpm. It's absolutely amazing at 11 psi. This car is such a rocketship now, my wife is scared of it and has given it back to me! Yippee! This car has been transformed! It now has power proportional to (stock) handling and brakes. Time to start upgrading the suspension... (But first a new timing belt [59K miles] and while I've got the front end off, an ECS crank pulley!)

I tried this mod because I'm not ready to chip yet, and posters on this forum said that the stock fuel map is good for .8 bar (12 psi). My car is running great at 11 psi, and extensive road testing has confirmed to me that I'm not running too lean (Thanks, Scott [scotty_passat] for your analyses of my VAG-COM logs). This road testing and data-logging has also confirmed to me the effects of altitude on my car, i.e. it really sucks. Lack of air at 6000 ft. causes the boost to drop down to 7 psi at about 5200 rpm (that's my theory, anyway). The car just won't flow more air than 125-130 gm/s. I'll be driving to Tennessee (low altitude) in about two weeks, so I'll do some more runs there to verify my theory. And increase the boost higher, O2 sensor and A/F ratios permitting. If I can get away with 12 or 13 at sea level, then I know it will be OK here in Albuquerque.

It is so cool to have wrested control away from the ECU and back to me. It has some drawbacks, though. Having boost controlled by ECU is safer, especially when engine is cold. The MBC is indescriminate and will give you full boost at low engine speed when cold, whereas the ECU knows the engine is cold and will limit boost accordingly.

Dawes' standard controller is only $35. I opted for the "race" version, which was $70. It activates .3 seconds quicker. I figured that an extra $35 was worth the quicker response. I also ordered the "deluxe tubing kit" for $15 - I didn't really need it, but I thought "what the heck." I also ordered Dawes' really cool A/F meter, but I think I will be returning it as the narrow-band O2 sensors in our cars don't seem to work with his meter, which requires wide-band sensors. Jury is still out on this one.

Installation:

(1a) Don't try this mod unless you like to tinker with your car and are willing to accept the consequences of a blown engine if you screw up.
(1b) Don't do this mod unless you have a boost gauge and a way to check A/F ratios e.g. VAG-COM or an accurate A/F gauge.
(2) Standard install is to take the vacuum line (from N75) off the wastegate (WG) and plug it with a screw. Install the angled end of the Dawes to the WG, and the straight end to manifold vacuum.
(3) An alternate method is to install the other end to the turbo nipple (TN), which gives greater protection against boost spikes.
(4) I could not get my big hands in there, so I simply took the entire airbox out. Then I took the PCV valve off the intake tube. This gave me (barely) enough room to maneuver. I started taking off the water line to the turbo (to get more room), but quickly decided against it when the coolant started pouring out.

(5) Since I had the airbox out and could get to everything, I decided to start by connecting the Dawes to the TN. So I removed both N75 hoses (the clamps were a b**ch), and capped off the two fittings on the N75 with some leftover large vacuum caps out of the misc. parts bin. Connected the Dawes directly between the TN and the WG.
(6) Initial road tests showed the valve came from the factory set at a paltry 3 psi. But even at 3 psi, you could feel the turbo spool up quicker. You adjust the boost by lengthening (decrease boost) or shortening (increase boost) the valve via a threaded rod and locknut. One turn corresponds pretty reliably to 2 psi.
(7) I ran it up to 9 psi. Ran pretty good for a day, then the next day the problems started showing up. It was my fault - see "Don't remove MAF screen" for details. http://clubb5.zeroforum.com/zerothread?id=24815
(8) After the MAF screen snafu got fixed, I set it to 11 psi. Awesome results. The turbo would start spooling at 2500 rpm or so, with 5-7 psi immediately available. The N75 would never give me that! Then I decided to try running it off manifold vacuum. I was getting some wierd pulsing under certain circumstances, and thought that maybe manifold vacuum would be a more accurate signal (i.e. same signal that the DV is using) for the Dawes to operate from. So I plugged the TN hose with a screw, and connected the Dawes (via a "tee") to the same vacuum circuit as the DV and my boost gauge.
(9) WOW! Manifold Vacuum is the one to use - it starts spooling at 1600. Wow. This car screams. I'll restate the 0-60's here:

Before: Best 0-60 time = 10.5 seconds at 60F
After: Sloppy 0-60 time = 9.1 seconds at 70F

And the "sloppy" time was at only 10 psi max boost, because I had just heat-soaked the I/C. I noticed that I got my 11 psi back after a couple minutes cruising on the freeway. And remember that I'm at 6000 ft, and the boost falls off to 7 psi at about 5200-5500 rpm. Can't wait to see my numbers at lower altitude...

Repeated caution: this bypasses ECU control of boost. Putting full boost on a cold engine, especially at low rpm, is a good way to seriously shorten the life of your engine. Don't do this mod unless you are willing to take care of your engine. If you want to be able to just hop in and go, then get a chip instead. Chips have other advantages, too. You don't have to worry about your A/F ratio. And you can get MORE boost with a chip, because the chip can increase fuel flow and do other things. Also - the Dawes maxes out at 15 psi. There's a trick where you can get an extra psi or two, but you really don't want to do that unless you are already chipped and have the fuel map to do it. If you are already chipped, the Dawes will probably eliminate any surging or boost spikes that you may have.

OBTW - I did my I/C mod on the same weekend - I installed the Audi S4 fender vent, the MY2000 larger I/C duct, cut my grill openings, and cleaned out the I/C with gasoline. I know this helps sustain the increased boost. Get some air flowing through your I/C, if you're not already. Plenty of posts here on CB5, including FMIC, if you need to know how.

One final note: My favorite part of this mod is the controllability of the boost. With the N75, it seemed like you never got the same boost curve twice. The Dawes is totally consistent. The engine and the power and the boost gauge and my right foot are always in lock-step with each other. Wow...

A final final note - still get some wierdness when backing off the throttle under certain circumstances. It's either a DV issue, or the TC is unlocking and going "clunk", or all the extra torque is revealing the limitations of the stock rubber snub mount. I have a Greedspeed mount on order...

<<![CDATA
 

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Re: Dawes MBC Review and Install - My FAVORITE Mod! (Rusty)

Glad you like it Rusty. Definitely the best bang for the buck if you are willing to, as you said "take care of your engine"... but not best for everyone.

Side note- I have only used this on DBW car's... specifically MKIV K04 applications, with open exhaust, to solve overboost problems due to the slow reacting N75 setup.

I'm guessing rusty, that the application on the DBW car's would be a little smoother, simply because the ECU has the input of a separate manifold pressure sensor to adjust the fuel mapping, so it's not depending (retrospectively in a sense) in the fuel trim, and O2 soley to keep the fuel correct.
 

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Re: Dawes MBC Review and Install - My FAVORITE Mod! (Rusty)

Have you tried it configured with the N75 valve connected (to OE vacuum lines)?

I think if you configured it this way, you'd still get higher than stock (7psi) boost since N75 retains control of the pressure signal (from compressor housing to WG actuator). An "air bleed" via the MBC (between compressor and N75) would mean the WG would take longer to open since the magnitude of the pressure signal acting on the actuator would be slightly reduced (i.e. some pressure through the MBC instead of acting to open the WG actuator). ECU signals opening of N75 on non-DBW cars based on engine load (i.e. input from MAF sensor and engine speed sensor). DBW cars use the MAP sensor (as Chris mentioned).

One other thing, make sure you buy the highest octane possible when using this. If you ever have predetonation (from bad fuel), the ECU will do the following in an attempt to control/eliminate it:
1.Retard ignition timing
2.Richen fuel mixture
3.Reduce boost

By taking boost control away from the ECU (by use of DD), you've taken a "protective mechanism" (i.e. designed in "safety") for your engine away from the ECU...and allocated that "mechanism" to your right foot instead.

Good Luck


edit: first paragraph for clarity

<![CDATA[Have you tried it configured with the N75 valve connected (to OE vacuum lines)?

I think if you configured it this way, you'd still get higher than stock (7psi) boost since N75 retains control of the pressure signal (from compressor housing to WG actuator). An "air bleed" via the MBC (between compressor and N75) would mean the WG would take longer to open since the magnitude of the pressure signal acting on the actuator would be slightly reduced (i.e. some pressure through the MBC instead of acting to open the WG actuator). ECU signals opening of N75 on non-DBW cars based on engine load (i.e. input from MAF sensor and engine speed sensor). DBW cars use the MAP sensor (as Chris mentioned).

One other thing, make sure you buy the highest octane possible when using this. If you ever have predetonation (from bad fuel), the ECU will do the following in an attempt to control/eliminate it:
1.Retard ignition timing
2.Richen fuel mixture
3.Reduce boost

By taking boost control away from the ECU (by use of DD), you've taken a "protective mechanism" (i.e. designed in "safety") for your engine away from the ECU...and allocated that "mechanism" to your right foot instead.

Good Luck


edit: first paragraph for clarity

[Modified by Electron Man, 7:19 AM 10/9/2002]
 

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Discussion Starter · #4 ·
Re: Dawes MBC Review and Install - My FAVORITE Mod! (Electron Man)

I only put Chevron Supreme in this car, or Mobil or Exxon if I'm in a different part of the country. If I'm ever in a pinch, I'll use another brand, but always the highest octane available.

That's a good idea and I had thought of something like that but had no idea what effect it would have and it's a beeyotch getting down in those tight areas and messing with those hoses BUT... I'm willing to do anything for my sweet little engine. I need more details, however.
TN = Turbo Nipple, WG = Wastegate

Stock = TN --- N75 --- WG

Please rediagram to show where to put MBC? Thanks - Rusty


[Modified by Rusty, 12:09 PM 10/9/2002]

<![CDATA[I only put Chevron Supreme in this car, or Mobil or Exxon if I'm in a different part of the country. If I'm ever in a pinch, I'll use another brand, but always the highest octane available.

That's a good idea and I had thought of something like that but had no idea what effect it would have and it's a beeyotch getting down in those tight areas and messing with those hoses BUT... I'm willing to do anything for my sweet little engine. I need more details, however.
TN = Turbo Nipple, WG = Wastegate

Stock = TN --- N75 --- WG

Please rediagram to show where to put MBC? Thanks - Rusty


[Modified by Rusty, 12:09 PM 10/9/2002]

[Modified by Rusty, 12:09 PM 10/9/2002]
 

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Re: Dawes MBC Review and Install - My FAVORITE Mod! (Rusty)

<BLOCKQUOTE>quote:<HR>where to put MBC?<HR></BLOCKQUOTE>

I'd try it like this...

With Dawes => TN --- MBC --- N75 --- WG

It probably won't be as "snappy" (boost @ 1600rpm) as it is now though. MBC will still keep the WG closed until you see 11psi, but you'll have some protection from N75. OTOH, boost may end up being "rougher" (not as smooth) than without N75 "in the loop".
 

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Re: Dawes MBC Review and Install - My FAVORITE Mod! (Electron Man)

I do not fully understand how the N75 works. It seems as though boost would still be limited to 7 psi... Can you provide or point me to a good explanation? Thanks - Rusty
I don't understand fully how the MBC works, either!


<![CDATA[I do not fully understand how the N75 works. It seems as though boost would still be limited to 7 psi... Can you provide or point me to a good explanation? Thanks - Rusty
I don't understand fully how the MBC works, either!


[Modified by Rusty, 4:10 PM 10/9/2002]
 

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Re: Dawes MBC Review and Install - My FAVORITE Mod! (Rusty)

did some more crunching, here's your rough "butt dyno" results:



something is up with the 7 psi data at upper rpms, the hp continued to climb. assume that it rolls off like the 11 psi plot at upper rpms.

if you fit an average line through the plots, looks like you've gained ~15-20 whp and 20+ ft-lbs wtq.


also note how the curves match your maf reading: (ie boost hits at 2600-3000 rpm)



i'll rerun these as we discussed when you send me some more data (trying to figure out the best way to "dyno" withthe tip)

now time for
 

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Re: Dawes MBC Review and Install - My FAVORITE Mod! (Rusty)

<BLOCKQUOTE>quote:<HR>...how the N75 works<HR></BLOCKQUOTE>

All the N75 does is control timing of the pressure signal that opens the WG actuator. The AEB code WG actuator opens the WG with ~7-8psi of pressure. The actuator is a fail closed (spring loaded) device.

By installing the Dawes MBC, you bleed off some of the pressure that would go to the WG actuator; so at ~11psi boost, ~4psi ends up "leaking" (bleeding through MBC) and the WG actuator sees the remaining 7psi (then opens to limit boost to 11psi).

Try one (and only one) short run to ~4K rpm in second gear with the signal line disconnected from the WG actuator to see what happens (watch your boost gauge
).
 

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Discussion Starter · #9 ·
Re: Dawes MBC Review and Install - My FAVORITE Mod! (Electron Man)

Ahhh, knowledge...
Thanks Scott - I'll have you some fresh data today, complete with Fuel Trim runs. Yeah, that's really wierd how the 7 psi HP keeps climbing... It's so frustrating to not be able to disable kickdown on my early '98. My only tranny coding options are 00000 and 00010. Neither of them affect the Tip. The 00010 setting gives much better (sportier) shifting in Auto mode. But nothing for the Tip - yuck. I HATE the kickdown. Why inna hell - oh, I'm getting off topic. I think a Tip Chip is in order here...
Thanks, Electron - Your explanation makes sense. I will meditate upon it until I finally "get" it.
 

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Re: Dawes MBC Review and Install - My FAVORITE Mod! (Rusty)

Oh, dang, I just got it! I had always assumed that the WG would be a fail open device, for safety. This whole thing makes far more sense now, but is a little more scary...

One question - what about idle (and other "vacuum") conditions - is the WG closed or open, (I always thought it was open at idle), and if it is open, how is it kept open? If the WG is closed at idle, then I assume it's completely up to the DV to prevent boost?

Dang, we need a lightbulb symbol...
 

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Re: Dawes MBC Review and Install - My FAVORITE Mod! (Rusty)

Correct me if I am wrong. This is how it was explained to me, At an Idle your car pulls a vaccum on the diaphram of the DV to open and recirculate any small amounts of boost made. Without this you would stall the turbo from lack of exhaust being produced to force the turbo along. Then when you get on the throttle enough to spool the turbo up to make a positive pressure in your manifold the DV valve slams closed and all boost is directed into your engine up to wastgate limitations.
 

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Re: Dawes MBC Review and Install - My FAVORITE Mod! (JEM)

the wastegate is actuated by boost, so it's closed at idle. The DV does not "prevent boost," not sure what you were getting at there. During boost the DV is closed. There is nothing on the intake-side of a modern turbocharged engine that limits boost.

JEM: It wasn't clear by your post, but you understand that the wastegate limits how much exhaust gas goes through the turbine, not boost pressure directly, right?
 

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Re: Dawes MBC Review and Install - My FAVORITE Mod! (Macabre)

<BLOCKQUOTE>quote:<HR>the wastegate is actuated by boost, so it's closed at idle. The DV does not "prevent boost," not sure what you were getting at there. During boost the DV is closed. There is nothing on the intake-side of a modern turbocharged engine that limits boost.

JEM: It wasn't clear by your post, but you understand that the wastegate limits how much exhaust gas goes through the turbine, not boost pressure directly, right?<HR></BLOCKQUOTE>

No, I thought the wastegate was on the intake side of the turbo so when you build too much boost then it just dumps the excess. If this is not the case and the wastegate limits how much exhaust goes through the turbine then where does the excess go. That doesn't make sense to me how I explained it. Just for example say to took 100 CFM of exhaust flow to spool your turbo to full boost and you engine under full throttle made 120 CFM, you would make more boost then allowed by the wastegate. So you are saying that the wastegate limits how much of this exhaust gas goes through the turbo to make the maximum allowed boost. So what happens to the rest of the exhaust if it is not allowed to go through the turbo, there isn't any other way for it to get out except through the exhaust side of the turbo. There is no other route.
 

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Re: Dawes MBC Review and Install - My FAVORITE Mod! (JEM)

No, the DV diverts the boost left over in the plumbing to the throttlebody when the throttlebody closes. Vaccum actuates the DV and it pulls the valve up diverting boost back into the intake after the maf. The wastegate is closed at idle, but the DV is open, so what little pressure the turbo might offer is diverted.
 

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Re: Dawes MBC Review and Install - My FAVORITE Mod! (JEM)

<BLOCKQUOTE>quote:<HR>So you are saying that the wastegate limits how much of this exhaust gas goes through the turbo to make the maximum allowed boost. So what happens to the rest of the exhaust if it is not allowed to go through the turbo, there isn't any other way for it to get out except through the exhaust side of the turbo. There is no other route.<HR></BLOCKQUOTE>

The wastegate could be called an exhaust bypass valve. When the wastegate opens, exhaust gas is routed around the turbine. It still exits through the vehicle's exhaust system in most cases (though some cars have the wastegate vent right to the atmosphere, not emissions friendly). It's more clear how this works in vehicles with an external wastegate. It's a little harder to visualize the system with the K03's internal wastegate.
 

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Re: Dawes MBC Review and Install - My FAVORITE Mod! (Macabre)

I knew about the DV with the exception of how the DV is opened and closed, but I had no idea about how the wastegate actually worked thanks for clearing that up for me. Makes much more sense now.
 

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Re: Dawes MBC Review and Install - My FAVORITE Mod! (JEM)

Aren't turbos fun??? I still can't keep all this straight in my head yet, but it's getting there...

BTW - still enjoying the MBC... even more now that I have suspension to match!
 
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