Manual Boost Controller - MBC Comparison

Post by **Legacy777** » Sun Dec 17, 2006 10:45 pm

I got the JoeP Pro-Z installed, and adjusted. It works pretty good. I had adjusted it around town. When I went on the freeway I was getting higher boost levels, so I had to turn it down a tad. I've got it set around 10 psi. Any more then that and I'm playing with the fuel cut.

I posted pics here
http://bbs.legacycentral.org/viewtopic.php?t=29648

Imprezive · Post by **Imprezive** » Mon Dec 18, 2006 1:00 am

Does it spike much? Does it feel like boost comes on quicker?

Post by **Legacy777** » Mon Dec 18, 2006 3:59 am

From the short amount of time I've driven it, it doesn't appear to be spiking. Like I said, I did have to turn it down slightly because I was getting higher boost levels in higher gears.

As for boost coming on sooner, I don't really notice too much of a difference....but I haven't driven it too much.

azn2nr · Post by **azn2nr** » Mon Dec 18, 2006 6:27 am

sorry i didnt put my input in sooner. i had the turbosmart 2 stage on my legacy (will have it on my impreza as well) it worked perfectly for years, no spikes or creeps except for when i had leaky headers (*or headers period for that matter) just click and go. 15psi in all gears. ya get what you pay for with these things imo

Adam West · Post by **Adam West** » Mon Dec 18, 2006 8:09 pm

I just like the clean look if this Joe-P one - nice mounting location/bracket too. Well thought out...Cheers,

Post by **Legacy777** » Tue Dec 19, 2006 7:14 pm

Thanks for the comments Adam

turboleg · Post by **turboleg** » Tue Dec 19, 2006 8:38 pm

Hey that custom job looks like the one I made!

I'll be getting rid of it soon however. The adjustment is crazy on the spring I chose (stupid me). A quarter turn is about 2-3 psi and its hard to adjust to under 11 psi. Ahh, memories...good thing the FCD works well..Yikes!

Hopefully be building my EBC soon...now where did I put those parts.....

Post by **Legacy777** » Wed Dec 27, 2006 12:56 am

Well I've had some time to drive the car with the MBC. I am getting boost creep in the higher gears when on the interstate in the higher gears. I've got the MBC set for about 10-11 psi....so it's just below fuel cut. On the interstate, boost will creep up a little and hit fuel cut.

This mainly seems to be an issue in 4th & 5th. I'll probably back down the MBC a little more, since my initial setup/tuning was done on a more humid & warmer night then it is now.

turboleg · Post by **turboleg** » Fri Dec 29, 2006 3:15 pm

Is there a big change in altitude on the highway?

Post by **Legacy777** » Fri Dec 29, 2006 4:09 pm

nope....it's flat as a pancake down here in Houston. The reason it's doing it is engine load. The engine loads up more in the higher gears.

It is unfortunate, however what I described is a normal characteristic of a turbo car with a MBC. With the stock boost controller or an EBC, it will continuously adjust the duty cycle of the solenoid to keep boost levels where they should be.

Adam West · Post by **Adam West** » Fri Dec 29, 2006 7:16 pm

What exactly does boost creep feel like?...And you are running a FCD right? Any adjustments to that in this situation?

Post by **Legacy777** » Sun Dec 31, 2006 7:44 pm

Basically.....it's just more boost as rpms rise, especially in the higher gears...at least that's where I'm seeing it.

No I'm not running a FCD, and that's the main issue. If I was, it wouldn't be too big a deal.

GotSubie · Post by **GotSubie** » Tue Jan 02, 2007 3:47 am

hey thats what i have it works great just make sure you drill the small bleed hole if you want to run over 17psi.

turboleg · Post by **turboleg** » Tue Jan 02, 2007 11:43 am

hmm...thats interesting. I don't see that much creep at all with my FWD turbo. Suppose the weight and resistance of the AWD would make that much of a difference?

Post by **Legacy777** » Tue Jan 02, 2007 6:38 pm

I think it has to do with the type of turbo you have as well. In addition, gearing, weight, and engine load will probably be the big factors....

rallysam · Post by **rallysam** » Tue Jan 09, 2007 1:12 pm

Legacy777 wrote:It is unfortunate, however what I described is a normal characteristic of a turbo car with a MBC. With the stock boost controller or an EBC, it will continuously adjust the duty cycle of the solenoid to keep boost levels where they should be.

Hmmm... I'm not sure what you're talking about. What you say is true of any closed loop control system. Even with an MBC, the wastegate continuously monitors boost and adjusts to keep boost levels right where they should be, just as you say for an EBC.

You get HIGHER boost at higher RPMs? Are you sure it's not the opposite? With your setup, I would expect boost measured at the compressor to stay fairly constant over RPM b/c that's where the wastegate is measuring; and boost measured in the manifold (which is probably what you're looking at) to DECREASE at higher RPMs due to intake restriction. That's what my setup did, and it's similar. Also, that would be much more consistent with your symptoms of getting more boost in higher gears (b/c you're probably running lower RPMs if you're in higher gears). If your behavior is actually this way, then actually I think there's a lot of advantages to having the boost roll off like that. It's not the fault of an MBC, it's just that the measurement is off the compressor, not the intake manifold like the stock system, but that's good.

Getting actual boost creep (higher boost at higher RPMs) is normally because your wastegate is too small to dump off the added air, isn't it? That really shouldn't be a problem with your setup. Very strange!

Post by **Legacy777** » Tue Jan 09, 2007 7:11 pm

I'll have to double check the higher rpm comment. I haven't driven the car in a while. The problem will initially occur at 3000-4000 I think, and I'll usually let off because of the fuel cut kicking in, so it's hard for me to say whether boost continues to come on as rpms increase.

When I was using the stock boost control, I would get just shy of 10 psi when I had it floored in 4th or 5th gear. It didn't really climb much above that, but usually in those gear at full throttle, I'm hauling butt!

I'll have to look at things again, and update the thread when I do.

rallysam · Post by **rallysam** » Tue Jan 09, 2007 7:33 pm

I found basically zero room for improvement between stock boost level and hitting fuel cut. My ECUs crap stock pressure sensor would read this noisy spiky signal that jumped all over. If I ran at a nice stable 11, the ECU number spiked around from 9 to 13, stepping over the limit often enough to trip fuel cut.

I dunno if everyone has that or if it's just a crap sensor in my car. But, I just decided to get an FCD even though I was only running about 12-13 psi.

Post by **Legacy777** » Tue Jan 09, 2007 7:36 pm

Yeah I haven't found much difference from the stock boost level to the 10-11 I'm running now.

I need a FCD, but just can't decide on EM.....and I don't want to spend money twice, or spend money I don't need to.

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Manual Boost Controller - MBC Comparison