Lpt mbc

**Dangerous Dave** · Sunday 22nd February 2009, 13:25

So whats this the fuel cut at 12psi?

How do you get around it?

Or is it something more drastic than that?

**p fandango** · Sunday 22nd February 2009, 13:51

Originally Posted by Alan M

Duane have you an AFR meter gauge system fitted?

no not yet, i've got to get bigger injectors (currently running at 99.7% injector duty) so i'll get one fitted as soon as i get some sorted

What sort of extra cooling did you use to keep the Turbo from getting to hot?

tbh i can't remember what spec BT had got at the time, the benefit of the reverse flow would of helped it

**p fandango** · Sunday 22nd February 2009, 13:54

Originally Posted by bomb192uk

So whats this the fuel cut at 12psi?

How do you get around it?

Or is it something more drastic than that?

no totally standard, when i first fitted the MBC it ran well at 15psi but i didn't realise i'd got a split vac pipe. When i replaced it she boosted to 20

i don't recommend anyone try going anywhere near that high, 13psi is considered a safe limit

**Dangerous Dave** · Sunday 22nd February 2009, 19:21

Anyone know how the ecu knows its at 12psi? Or is it the knock sensors that trigger the fuel cut?

**timbo_1975** · Sunday 22nd February 2009, 22:01

ECU calculates boost pressure from throttle position and air temp sensor and MAF reading.

**Dangerous Dave** · Sunday 22nd February 2009, 23:01

So is the fuel cut bad for the engine?

**p fandango** · Monday 23rd February 2009, 07:46

Originally Posted by bomb192uk

So is the fuel cut bad for the engine?

its there to protect your engine so not exactly bad, but once you've hit it you'll know how aggressive it is & won't want to hit it constantly for your own pleasure. Mine was set so close that any excess load would cause it to cut in, if i wanted to floor it i had to throw it down 2 gears

boost cut is normally around 15psi

**Jod T5** · Wednesday 25th February 2009, 00:37

Originally Posted by timbo_1975

ECU calculates boost pressure from throttle position and air temp sensor and MAF reading.

Actually the ECM does not calculate boost pressure but i accept the ignition will cut due to knock and Maf sensor inputs....There is no air temp, other than the input temp (maf) on the 850, the 70's are different....
Cheers
Jod

**Jod T5** · Wednesday 25th February 2009, 00:47

Originally Posted by p fandango

i ran mine at 20.8psi

Hey Duane...

Currently i am getting a compitant 19 psi using the back of a Rica with a MBC (yes all those years you have been on at me)....Not a hint of cut, strong but quick boost....AFR is good..I expect there is a little to play with...Running 15g and stock zorst too...

Best
Jod

**p fandango** · Wednesday 25th February 2009, 01:37

Originally Posted by Jod T5

Hey Duane...

Currently i am getting a compitant 19 psi using the back of a Rica with a MBC (yes all those years you have been on at me)....Not a hint of cut, strong but quick boost....AFR is good..I expect there is a little to play with...Running 15g and stock zorst too...

Hi Mate, hows things?

well what can i say, MBC is the way to go lol. Always looks good seeing the needle go off the clock, i haven't tried it with the speedo yet tho lol. Have managed to find the higher boost cut off the ECU yet, just interested how much higher it is than standard? Are T-5's dar to run or what, i notice neither of us have got any fuel lol

take it easy mate

**Jod T5** · Wednesday 25th February 2009, 13:36

Originally Posted by p fandango

Hi Mate, hows things? well what can i say, MBC is the way to go lol. Always looks good seeing the needle go off the clock, i haven't tried it with the speedo yet tho lol. Have managed to find the higher boost cut off the ECU yet, just interested how much higher it is than standard? Are T-5's dar to run or what, i notice neither of us have got any fuel lol take it easy mate

Hi Duane...
The car was supposed to run a pressure of 9.x psi, which allegedly crept up to around the halfway mark on the instument panel dial....I never owned a new one so i cant collabourate this, however alot of the 850 i have found myself involed
with are only producing around 6psi which is really only about a third of the scale in my experience...The reasons for this are more likely to be down to bolt ons rather than the engine itself....
I like to keep the tank empty as i am working on a less weight/more speed theory..lol
I would expect that a stock car would be able to make 10psi with a peak to 13 without hitting ignition cut....
Best
Jod

**timbo_1975** · Wednesday 25th February 2009, 14:30

Originally Posted by Jod T5

Actually the ECM does not calculate boost pressure but i accept the ignition will cut due to knock and Maf sensor inputs....There is no air temp, other than the input temp (maf) on the 850, the 70's are different....
Cheers
Jod

I was refering to ambient air temp sensor. - i am aware the 70's use the sensor mounted in the front bumper, and the 850's the one within the MAF.

And yes, the ECU does derive boost pressure- thats how it knows how much to modulate the BCS according to its look-up tables.

**Jod T5** · Wednesday 25th February 2009, 23:00

Originally Posted by timbo_1975

And yes, the ECU does derive boost pressure- thats how it knows how much to modulate the BCS according to its look-up tables.

Yes that is correct, it can derive pressure from its sensors, however it can not read direct boost pressure, which i guess you know already....

Cheers
Jod

**timbo_1975** · Wednesday 25th February 2009, 23:45

Indeed, which is why i said "the ecu calculates boost pressure from..." !

**Dangerous Dave** · Wednesday 4th March 2009, 16:00

Just an Update....

Had to move the mbc from its position on the upper engine mount bracket, as the mbc was getting very hot with the heat from the engine, etc (not that it matters, but just in case) and adjusting it was a nightmare as it was burning my fingers. I have a strut brace, so i've relocated it on that above the abs unit (see pic) and its much cooler now.

**mk3phill** · Thursday 5th March 2009, 00:56

sounds like a well worth while investment

,.. dude whats the silver box,.. catch tank??

**Dangerous Dave** · Thursday 5th March 2009, 19:09

yep, its actually a 'catches bloody everything' tank, as there's so much ££££e that comes out when I empty it, mostly its water and oil mix.

I was an reading EPE magazine from November 2008, and they've got a DIY circuit that you can fit into the line between the ECU and the BCS to variably control boost via a variable resistor mounted on the dash. Basically it intercepts the signal from the ecu to the BCS and delays it a bit.

They also had a fuel cut bypass module to build too, but it works off the input from a MAP sensor, and our cars aren't fitted with those.