Originally Posted by CeeLowe
I am not understanding why the manual controller is needed? Is it solely for boost spike atmospheric changes? I now have a profec b spec2 and cant tell you how it works yet. Im braking in a new clutch and cant boost the car. I have been told over and over not to use the utec to controll boost on my 18G because the factory solenoid wont respond fast enough to regulate boost spike. So my first thought was to change to a gm solenoid. Like I said before is the manual unit necessary or just for spike situations?
frankly i don't think many people would argue with the fact that nothing beats the stability and response of a mechanical boost controller. electronics are nice, but by virtue of their flexibility they give up a bit of that rock solid response. so to that end, i think the utec's EBC algorhythm isn't that bad, plus, it's "free" with the purchase of a utec, so that goes a long way.
to answer your question, yes, the MBC is there for two reasons:
a) provide adjustability of max boost without a laptop and without stopping the car and getting out and popping the hood.
b) provide a boost level which simply will not be exceeded.
a) is really about convenience and laziness! b) is important to me because it seems that with any EBC (not just the utec's) you are always
trading off response/spool time against freedom from spikes. either you've got a quick boost control, or a stable one. maybe it's because i've used an MBC since my first month of owning the car, but having to make that choice is just not acceptable to me!
generally those boost spikes come on during highly transient conditions, when boost pressure shoots up fast. for example, you're past the boost threshold of the turbo, driving at part throttle, then you mash the gas. the boost responds so quickly that the EBC cannot react in time to prevent a nasty spike. (honestly i think this is where a lot of problems arise when only dyno-tuning is used... on the street, things are a lot less smooth and predictable and i'll bet quite a bit of money that boost spikes are what's causing knock when there was none on the dyno. it's just a theory of mine though.)
i also noticed a stability problem when using launch control for flat-foot shifting... when the clutch goes down and the rev-limiter kicks on, my manifold pressure drops to around 14-15psi. the TPS is still at 100%, which means the utec is still using that column for the EBC algorhythm. i complete the shift, pop the clutch and the sudden increase in load gives me a surge of exhaust energy, which causes a nasty boost spike. with the utec solely in control of boost i got a spike of around 3 psi above my "normal" 17psi. that put me up around 20psi, which was WAY too much, and i'd generally get a shift knock when using LC for FFS. if i shifted normally, the boost was better controlled, but c'mon--FFS is VERY COOL...
now, using the MBC "clamp," i get a spike of <1 psi. this is acceptable to me (and my engine) so we are both happy.
(i know i could get it lower, but i'd have to do some relocating of parts in order to shorten hoses, and they would be placed closer to the very hot turbocharger, reducing their lifespan.)
as TMS pointed out in another thread, essentially i am using an MBC with the UTEC to control part throttle boost levels via the GM solenoid. i think this is a great way to look at it. you can't use the oem solenoid to do this since it is a bleeder based system, and you need an interrupter.
i'm going on my second week with this rig and it's the best boost control system i've used yet (first was totally stock, then 3/16" mod, then joe p MBC, then throttle switched wastegate/MBC using the grainger solenoid and an electronic TPS switch, then i added a cockpit bleeder to the MBC, then i went back to the FBC system with the UTEC in control, then i went back to a straight MBC [this time with the much higher quality hallman unit] with UTEC's open loop fueling to mitigate PTFB, then finally the system you see here, [which not only prevents damage from PTFB, it completely prevents it from occuring]). it has been a journey of mine to find a much better boost control system for my car, and i am zeroing in on it.
[OT] eventually i would like to impliment my own outboard PWM controller that takes its signal from TPS and outputs a PWM signal whose duty cycle is proportionally adjustable. low TPS = low DC, high TPS = high DC. because i would still have the MBC clamping the boost limit, it would not have to be very accurate or repeatable--it would strictly be in order to prevent the PTFB as well as provide a smoother throttle response. as a result, the circuit would be pretty simple.
the reason i'd like to do this is so that i can free up the UTEC's boost controller driver to drive a high speed solenoid for water injection. i've heard that some customization of the UTEC's software can be done (with assistance from txs, of course) to change the TPS-based column reference of the boost map into a MAP-based column reference. this would make it MUCH easier to develop your h2o injection map, and having a mappable injection setup is obviously much better than a static one. i'll get there eventually![/OT]