Lpt mbc

[Dangerous Dave]

And it doesn't control boost spikes effectively if you leave the bcs connected, according to the fitting guide on VS

Also another update, I've just managed 26mpg driving to and from work 4 times today (all urban driving), I've never got that before.

[1996 850 T5]

I have done it differently on my T5

I have done as alan m said, and plumbed the MBC inline between the BCS and the actuator.

The actuator opening is what stops boost being produced, the BCS just controls the signal to it. With the MBC controlling what the BCS sends to the actuator, its ultimately in control of what the boost setting is.

Thats how I figured it anyhow?

Maybe its just luck, but I dont get any spikes, just constant 10/11 psi

[Jod T5]

You can just fit the MBC in the red line from the BCV to the turbo with the BCV still connected. You won't have to disconnect anything then, just fit the MBC in the vac pipework.

Surely this defeats the object of a MBC as the BCS will have already bled away boost...

"The 'LPT' cars can be run at HPT pressures, however due to the different internals (I believe the cylinder heads are more or less the same, it is the pistons that are different between cars of different compression ratios) you really MUST run a higher compression car on higher octane fuel to alleviate the onset of knock, which is much more likely if you increase the inlet temp by upping the boost pressure on the turbo. If you fitted a bigger turbo on an LPT car but left the ECU program alone, at the basic level you would have a car that has a slightly cooler inlet charge for the same boost pressure, but the boost would move up the rev range accordingly.
LPT cars are designed to mimic bigger capacity cars and give low to mid range grunt, hence the sizing and pressure settings of the turbos.
HPT cars are designed for mid to high end grunt and as such demand a different driving style (i.e. use of revs over 4000rpm) to get the best out of them."
Basically running a MBC on a LPT is going to cause more rod issues than it would on a T5...
Cheers
Jod

[1996 850 T5]

Jod, my understanding is that the BCS is just an electronically controlled bleed valve, i.e. the BCS doesnt bleed away enough to effect the actual pressure in say, the plenum etc, it simply controls the signal to the actautor by bleeding off a minute amount of pressure to the wastegate.

so its the actuator that controls the boost level, so if the mbc is in control of the Actuator, the MBC is therefore in control.

If Im talking cobblers (could be, its just my take on the matter)? please let me know.

[p fandango]

Jod, my understanding is that the BCS is just an electronically controlled bleed valve, i.e. the BCS doesnt bleed away enough to effect the actual pressure in say, the plenum etc, it simply controls the signal to the actautor by bleeding off a minute amount of pressure to the wastegate.

so its the actuator that controls the boost level, so if the mbc is in control of the Actuator, the MBC is therefore in control.

If Im talking cobblers (could be, its just my take on the matter)? please let me know.

the actuators on T-5's are only set to 3psi, its the BCS that raises it to 9.6psi, you've got the principle right but the BCS bleeds off alot more than you think

& Jod you are correct having both the BCS & MBC inline is pointless as the MBC will have overall control of the boost as its totally stopping the air to the actuator so the ECU still won't have any control over the boost (ie no limp home mode)

[1996 850 T5]

Yeah I know what you mean Pedro, but still dont understand your point?

So how would you plumb an MBC so that you still have limp home mode?

[p fandango]

Yeah I know what you mean Pedro, but still dont understand your point?

its the ecu & BCS that controls the boost, the actuator is set low

So how would you plumb an MBC so that you still have limp home mode?

it can't i'm afraid, don't get me wrong i love MBC's but you've got to know what your doing with them

[Dangerous Dave]

I think what he's trying to say is that the ecu doesn't know how much boost the turbo is producing, the bcs operates at set times according to the information available from the inputs that the ecu does have i.e. throttle position, rpm, etc. We are manipulating the boost to almost double what the ecu thinks is there. So if you back off the throttle at a time when the bcs is bleeding off all the air, the the wastegate won't operate, thus causing a boost spike (i guess). Thats why remaps are better as they are programmed with approximate boost levels to match the inputs.

The wastegate actuator operates on a pressure of 1.8psi (for t5 engines). The lpt actuator uses 2.6psi (I think, its on another thread anyways).

[p fandango]

I think what he's trying to say is that the ecu doesn't know how much boost the turbo is producing, the bcs operates at set times according to the information available from the inputs that the ecu does have i.e. throttle position, rpm, etc. We are manipulating the boost to almost double what the ecu thinks is there. So if you back off the throttle at a time when the bcs is bleeding off all the air, the the wastegate won't operate, thus causing a boost spike (i guess). Thats why remaps are better as they are programmed with approximate boost levels to match the inputs.

the wastegate will only open when the boost reaches the maximum level, not when you back off the throttle. As some of the older members will know i'm "anti-remap", what i'm saying is if your going to use a MBC ditch the BCS & just leave it plugged in to keep the ECU happy, don't let it actually control the boost in any way

The wastegate actuator operates on a pressure of 1.8psi (for t5 engines). The lpt actuator uses 2.6psi (I think, its on another thread anyways).

i did see that thread & tbh no idea where they got that information, but i can tell you they are set higher than that (T-5's are anyway)

[Dangerous Dave]

Ah, fair enough mate, thanks for the info.

Anyways, I've left my BCS out of the loop, and I've still got a huge grin.

[1996 850 T5]

Ah, I see what you mean.

Does the BCS have a sensor or is it simply a valve?

[Dangerous Dave]

Its just a valve, so its triggered by the ecu guessing what the boost is.

[Dangerous Dave]

Adjusted it today a little. Now pushin about 11-12psi, been on the motorway, and the ignition cut came in at around 5500rpm at about 11psi, gonna turn it down now.

[1996 850 T5]

Do you mean fuel cut? if so my t5 does the same at 12psi, like hitting dog?

turned it down to 10 and no probs, can go full throttle till gear change

[Dangerous Dave]

yeah, thats it. I turned it down, but a little too much, will try again in the morning

[Alan M]

i did see that thread & tbh no idea where they got that information, but i can tell you they are set higher than that (T-5's are anyway)

From Vadis. The listthat Bomb posted is the one on the Vadis page I have but I don't know how to link it properly.

[p fandango]

From Vadis. The listthat Bomb posted is the one on the Vadis page I have but I don't know how to link it properly.

i've removed the BCS & use an Apexi AVC-R to raise & monitor the boost (accurate to 0.01bar) & with the old 15g fitted & often used to run direct actuator pressure, which ran at 0.3bar

with the brand-new Volvo 19t fitted & running direct actuator pressure it runs at 0.7bar, & i'm certain there wasn't a figure that high on the list posted

[tomtyres]

I had a 3-port bleed valve on my T5, set it to 14psi, and it was spot on!

[p fandango]

I had a 3-port bleed valve on my T5, set it to 14psi, and it was spot on!

i ran mine at 20.8psi

[Alan M]

Duane have you an AFR meter gauge system fitted? What sort of extra cooling did you use to keep the Turbo from getting to hot?