mbc in series with apc solenoid?

[saabkid37]

how do i install the mbc so that i dont completly bypass my apc system? i did a search and found out about this method but couldnt come up with specific instructions...can anyone help me out?

[boxman]

no, remove the apc sol' and connect the MBC inbetween the compressor and the waist gate,connecting the MBC in with the sol' is the way to do it on 9-3 and 9-5 with trionic 7 which doesn't allow higher boost.

boxman

[ylee coyote]

I would disagree
I ran the mbc in series with the APC for many miles

It does give you a little more protection as long as the boost is not cranked up too much

you simply cut the w hose (hose to the wastegate) and put the MBC in here ...

start off low and work up

good luck

[boxman]

sorry to disagree ylee but as soon as the apc sees the exrta boost it will just cut it down again untill you get to the piont when the apc can't reduce it any farther so you might just as well remove it from the start

boxman

[johncc]

Does it depend on which type of engine management you have? Surely the APC on the LH/DI/APC engines can't "see" boost... it has no pressure sensor. As long as the extra pressure doesn't cause any knock, why should it reduce the boost?

Disclaimer: I could, as always, be talking cobblers

I'm interested because I'm trying to work out all these feedback loops - particularly in the Trionic system - to try and work out why I don't have enough boost.

[marcind]

For more protection u can use map sensor IMHO.

[saabkid37]

well based on my saab knowledge (may not be very good :-? ) the apc solenoid has a thing in it that flaps back and forth and the ecu measures the speed of that...when it reaches a certain speed it cuts boost with the knock all being detected by a sensor in the di. sooo....i believe that if you slowed the pressure to the solenoid it would allow higher boost?

thats why i asked....

[boxman]

Originally Posted by johncc

Does it depend on which type of engine management you have? Surely the APC on the LH/DI/APC engines can't "see" boost... it has no pressure sensor. As long as the extra pressure doesn't cause any knock, why should it reduce the boost?

Disclaimer: I could, as always, be talking cobblers

I'm interested because I'm trying to work out all these feedback loops - particularly in the Trionic system - to try and work out why I don't have enough boost.

the lh apc up to 1990 has a pressure sensor under the dash and from 1991 on has a temp sensor to determine pressure

boxman

[boxman]

Originally Posted by saabkid37

well based on my saab knowledge (may not be very good :-? ) the apc solenoid has a thing in it that flaps back and forth and the ecu measures the speed of that...when it reaches a certain speed it cuts boost with the knock all being detected by a sensor in the di. sooo....i believe that if you slowed the pressure to the solenoid it would allow higher boost?

thats why i asked....

the thing inside the apc sol' that flaps is controlled by the apc ecu and not boost level and its job is to limit the amount of boost that the waist gate sees and bleeds off the unwanted boost, if the boost level is higher than the limit programmed into the ecu, the ecu will flap the apc sol' less so less boost is bleed off therfore plying the waist gate with more boost so it opens so reducing to boost back to the preset limit

boxman

[johncc]

Originally Posted by boxman

the lh apc up to 1990 has a pressure sensor under the dash and from 1991 on has a temp sensor to determine pressure
boxman

That's what I love about this site - always more to learn! Thanks boxman. Does the trionic use the MAP sensor for the same purpose, or does it have another sensor elsewhere?

[boxman]

trionic uses the same sensor as di apc to deturmine boost its the one in the i/c to throttle pipe, the trionic map (manifold absolute pressure)sensor replaces the lh air mass meter to deturmine the amount of air entering the engine

boxman

[ylee coyote]

Wiring it in series does have advantages
by altering the pressure on the wastegate by bleeding the pressure off (bleed mbc) or stopping the pressure getting to it (gated mbc )effectively takes the control from the apc untill the pressure /bleed threshold is reached than apc control is re-established

what this does is radically alter the spool up as normally the apc starts to open the wastegate at very low boost
It does this to stop overboost but it is very conservative
the mbc simply moves it up the boost map hence you do get more spiking but removing the apc entirely you will not have control over the mbc boost threshold...

imho of course

[saabkid37]

ok well i got my turboxs mbc yesterday and installed it tonight in series as i wanted..

verdict - its amazing! I have it turned up to about 20psi. it holds for 3-5 seconds and then slowly knocks me down to 15-16 ish...im guessing beacuse of knock and not due to the apc. So...if i eventually fit a larger intercooler and run some higher octane fuel i should be able to hold the boost and hopefully not toast my motor

[boxman]

well guys you will just have to trust me one this one

if you run your car around for a few days and then remove your MBC you will find that you have no boost 'cus the apc is trying to reduce it and can't so it will have remembered that and will be running on base boost

[saabkid37]

i believe you...but ill just worry about that if i ever remove the mbc...just wanted to let everyone know that it can work while keeping a litle more safety in my opinion.

[boxman]

the apc sol' is doing nothing to protect you engine, what is happening is the di side of it can reduce boost if the apc can't by retarding the spark, this is what is causing your boost to tail off.

to protect against boost spiking take a look here


boxman

[G96nt]

think of it This way..
the Solenoid is told When to open And close by The ECU.
When There is knock, the solenoid opens, and allows the wastegate to "see" The Actual Boost, and open the flapper valve.

if you put the MBC between the solenoid and the wastegate, pressure will NOT get past the MBC until it meets whatever you've Set the preload for.

so, if you've set the MBC for 15Psi, pressure will NOT get past it to open the wastegate To open untilis sees 15Psi. Which means your car will be running equal-to, or greater than "x" boost ALWAYS. no matter what...
if the car is not knocking, the APC will close the "W" line, and the MBC will See NO boost. meaning you running full boost..which is okay.

now, if you DO knock, and the APC opens the solenoid, it won't Affect the MBC/wastegate until AFTER you've Reached whatever Psi you've set the MBC at.

we'll call this.."bad" or..."wrong"
you pick

if you place the MBC between the intake manifold and APC solenoid, you are more or less just lying to the APC.
It may "see" 10Psi, but prior to its knowledge, you have bled off 4 Psi. resulting in the net boost of 14Psi

this Still allows the APC to pull bost according To knock, but It will ALWAYS think it's lower than it is...
This way still allows the solenoid to control the wastegate flapper through it's intended range, and help prevent Detonation. you're just convincing it that there's less boost than there really is.

we'll call this "safer" or "correct"

[boxman]

Originally Posted by G96nt

this Still allows the APC to pull bost according To knock, :

if the apc can pull boost if it sees knock then it can also pull boost if the boost level exceeds the preset limit

if you are getting a reduction in boost when knock accures then it is the ignition that is being retarded which reduces the boost

this debate is going to run and run we may have to agree to disagree :wink:

boxman

[G96nt]

on the pre DI Cars how is timing Adjusted?
MY undestanding, is That there's a diaphram insode the distributor what is "activated" soley on boost.

if that's the case.. then it won't matter...
if the APC is lowering boost, it's retarding timing As a result.

on DI+ Cars, it's possibe that ignition is controlled seperatrely than boost soleniod.
say: map Sensor + knock Sensor +some chart = timing Advance/retard.



what I'm getting @ though... is that if you put an MBC AFTER the APC solenoid, it completely negates anything the APC does.
it'll be a COMPLETE a seperation of solenoid and wastegate, and NO pressure will pass beyond the MBC until it's higher than whatever PSI you set it at.

which means you will run, *at a minimum*, what the MBC is set For. and none less.
which is dangerous.

Especially, since his other post mentioned 20psi.

[saabkid37]

wow...im scared at some of the things i just read...crazy amounts of info ...20 psi was just fpr fun in an attempt to find once and for all where fuel cutoff is...but i got scared to turn it up anymore so i never found it :wink: and have since set it at a nice 18 psi or so

sorry i started a debate here tho lol....

but im confused...G69nt - are you saying i installed it a better way or a worse way? cuz from your explanation it is working just the way i wanted but im kinda confused....