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Discussion Starter · #1 ·
With the mbc, we are not suposed to exced 17psi. So we spend money to get an extra 2 psi, what I am missing? Does the extra 2 really do that much more? I just do not understand, please educate me.
 

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okay

the rex has a max boost of 14.5 psi of boost in 3rd, 4th and 5th gear. the max boost in 1st and second is significantly lower, i think at 9psi. the mbc will give you much better high end boost in the lower gears, obviously increasing your starts and 1/4 mile times.

the 2 psi of boost more in the top gears will also be a significant improvement, (14% increase!) not to mention you will hold that boost for a longer time rather than the wastegate opening and releasing pressure prematurely.

dR
 

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Just playing devil's advocate:

You should also realize that the MBC boost may come at a cost to reliability and longevity. Granted this remains to be seen, but given that the WRX hasn't even been in this country for a year, one can't say yet.

Obviously, Subaru engineers designed the system so that there would be much less max boost in the first 2 gears and less boost in the upper RPMs for a reason, namely reliability and longevity of the transmission and turbo. Of course, this may not be a concern of yours, especially if you plan on replacing the turbo anyway, as many others have done.

The other drawback is that there's no partial boost response as there is stock. In other words, while stock, partial throttle input with produce partial boost reponse, making easier and more convenient for daily driving or even autocrossing; with the MBC, as soon as the turbo starts spooling, it just builds to where the MBC is set at the max.

If you don't have a problem with this, then the MBC is definitely the right mod for you. Best bang for the buck. But personally, I put a premium on a balance of performance, reliability, and drivability, and I'm not interested in taking my car to a dragstrip (just got my NASA membership card for 2002!). So I have a Unichip (TurboXS). It's expensive, $700, but I think in the ong run, it'll be worth it. Again, this remains to be seen.
 

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Discussion Starter · #6 ·
Thanks for the last response. I too want everything on my car to last as long as possible; your point are taken to heart, the engineers obvioulsy know what their doing, I was concerned that tweaking their results of their labor might be detrimental. I want the car to drive fast through turns, I'm not into drag strips or racing, only going fast solo on curves, sounds like I'm gonna steer away from boost stuff, stick to suspension.

Thanks again everyone, your quick and infomred decsions are great.
 

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I can tell you from experience a WRX with a MBC is much faster than a stock WRX. I ran a good .5 sec faster with my MBC. It alows the turbo to reach full boost much faster. It also holds full boost longer.
When my WRX was stock it only made 13.5 psi max boost. Thats it. Even in 4th and 5th gear I only made 13.5 psi.
 

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Just what is max boost? 13.5 or 14.2 psi? Well, I have this theory.

I've seen different figures published. For example, the official WRX brochure I received in the mail just prior to the WRX going on sale said the max boost is 13.5 psi. Other sources, especially magazines such as Sport Compact Car, say the max boost is 14.2 psi.

Personally, on my OEM boost guage, boost peaked at just under .1 mPa (or 1 bar or 14.5 psi), so I tend to think that the 14.2 psi limit is correct. However, I've only had the guage on since the weather's been cooler in the late summer.

So I have this theory that the ECU limits the boost when ambient temperatures require lower boost for safety, reliability, etc, to a 13.5 psi limit. For example, I noticed that SGOSWRX is in Florida.
 

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bedabi said:
Yes, the engineers knew what they were doing, but they also knew they had to intentionally put in some restrictions to make the WRX a low emissions vehicle. I mean, what other car do you know has three cats!
I believe old school rustang 5.0's had 4 cats but that was running a true dual exhaust so 2 on each side. 3 cats is overkill I'm sure you'd pass emmisions with just 1.
 

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I just installed a JoeP a week ago, and what I have found is that the main difference is the increase in power in the mid rpm range, because the turbo spools up faster and with no program limits. Yes, the maximum boost if higher as well, but you really notice the removal of the previous limits that others have referenced in this thread. It is a beautiful thing.

The biggest problem you have is keeping your foot out of it. My gas mileage dropped to about 15.5 mpg (back and forth to work) as a result of this upgrade.

I have set the max boost to read approx .105 MPa on my guage, which is about 16.02 Psi. Previously, it would max at .095, which is closer to 13.5 Psi. Now, how accurate my stock guage is, I don't know. It seems to be consistent, and I haven't generated a cel, so I think it must me close.

By the way, if you want a great converter, so you can convert units like MegaPascal to Psi or bar, download this.

ftp://ftp.wsdot.wa.gov/public/Metrics/convert.exe

Bill
 

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I installed an HKS MBC (relief valve type) and tuned it to about 16 psi. I got all of the claimed benefits, much earlier max boost and more power (and I have an auto trans). Then I started reading all of the theoretical reasons why the MBC may hurt reliability and I got paranoid so I turned the boost down to about 12-13 psi. Since most of my driving is 30 miles to and from work I don't need max power for daily driving. The car is somewhat less thrilling now but probably still faster than most of the cars on the street. And I am getting much better than stock gas milage. I am constantly tempted to turn it back up though!

Dale
 

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nuthinspecial said:
The biggest problem you have is keeping your foot out of it. My gas mileage dropped to about 15.5 mpg (back and forth to work) as a result of this upgrade.

Bill
Holy cow! I am running 16.5 PSI on a PE1818F and big injectors and don't get that bad a mileage. You must really push the car hard on an everyday basis.
 

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Guys,

Could someone please tell me if the new 02 Spec WRX also has this reduced boost in 1st and 2nd gear behaviour ?

I live in Australia and my 02 Spec is due to arrive any day now and the above discussion has left me kinda disappointed.

Was the lower boost in 1st and 2nd gears always done on WRXs going back to 94 models etc?

Cheers
Antony
 

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AntMan, they are referring to the '02WRX, as that's the only version we have in the States. However, your '02 Spec WRX could very well be different from ours. Any of you Aussie folks can chime in at any time...;)

Rod
 

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God said:


Holy cow! I am running 16.5 PSI on a PE1818F and big injectors and don't get that bad a mileage. You must really push the car hard on an everyday basis.

I have everything stock and the last refill i got 18 mpg :eek: but i'm good this week i am getting about 20-21mpg
 

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I have everything stock and the last refill i got 18 mpg :eek: but i'm good this week i am getting about 20-21mpg
hmmm....im getting 18mpg all the time, but i also have a fairly heavy right foot. i know unichip can help with mpg sometimes, but does an mbc do anything?
 
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