jayc72

iTrader: (14)

I don't know for sure. I guess it depends on how sensitive the MBC is. If the MBC is set to open at 8psi, will it close at 7.5psi? Will it open and close instantaniously?

That's why someone needs to try

Ben

iTrader: (33)

I don't know, but wouldn't think the resultant ocillation in fuel pressure would be very fun. Maybe a simple pop vent to atmosphere isn't correct for the application. It would have to be coupled with a second bleed. So the resultant would be a pressure rise with boost that progressively reduces its rate of rise. So then there would be two additional adjustments: the pressure to begin the venting event, and the rate of bleed at the vent. Now it should work. ?

Braineack

iTrader: (62)

I wonder if a smaller diameter outlet on the MBC would help relieve some pressure...just not all, like the BEGi unit's small port

Ben

iTrader: (33)

I'm thinking something along the lines of a mbc that vents through a needle valve instead of a standard port. Then you could control the pressure dump pretty precisely. Whatchya think?

Braineack

iTrader: (62)

im seeing a trip to ACE Hardware tomorrow.

jayc72

iTrader: (14)

At worst it won't work. At best I'll look like an internet god. Likely somewhere in between.

magnamx-5

iTrader: (7)

yes

adbradley

iTrader: (2)

I was under the impression that most guys were running 8:1 and that 12:1 was to much fuel...

Ben

iTrader: (33)

He uses a safc to cut fuel.

bradley, you got a fuel pump right?

olderguy

iTrader: (19)

If you are running the OEM fuel pump, stay with the 12:1

Ben

iTrader: (33)

I spent a little while thinking about this. Essentially the concept creates a rising rate fuel pressure regulator with 2 stages of rise. 2 stage linear, not progressive like I wrote in an earlier post. The first stage would be absolutely identical to a current FMU where the FMU builds fuel pressure with MAP linearly where the rate of fuel pressure rise is controlled by bleeding pressure to atmosphere at the needle valve. The second stage would start at the point when the pressure relief valve opens. When the prv opens, we can then vent additional pressure to atmosphere at a time determined by the prv's pop open point and a rate determined by the second needle valve.

So let us assume that we set our stage 1 needle valve bleed to rise fuel pressure at the rate of 8 psi to every 1 psi of boost pressure. Let us then assume we set our pressure relief to open after 4 psi of boost pressure, and we set our second needle valve to increase fuel pressure at the rate of 3 psi to every 1 psi of boost with any boost over 4 psi

Result of above assumptions:
1 psi boost pressure --> +8 psi fuel pressure
2 psi boost pressure --> +16 psi fuel pressure
3 psi boost pressure --> +24 psi fuel pressure
4 psi boost pressure --> +32 psi fuel pressure
STAGE 2:
5 psi boost pressure --> +35 psi fuel pressure
6 psi boost pressure --> +38 psi fuel pressure
12 psi boost pressure --> +56 psi fuel pressure



Bear in mind my assumed rates are arbitrary, so observe the data as conceptual/hypothetical, but not necessarily correct for the application.

magnamx-5

iTrader: (7)

i got the safc after trying to run some 460's for all my dyno runs so far i haven't had one. it did help me on top end and driveability though. just not with the 460's. i first stated doing the mbc fmu tweak with my low impedance 305's that i ran for a while and it slowed the fp ramp up becouse my injectors where doing silly things being the wrong impedance and all on boost transition.

adbradley

iTrader: (2)

no i only have the stock pump...

magnamx-5

iTrader: (7)

80 psi is gonna limit you a 190hp migth help with headroom but for the time being you should be allright.

adbradley

iTrader: (2)

whats a safc?

adbradley

iTrader: (2)

im not lookin for that much power to start out with anyway

magnamx-5

iTrader: (7)

Safc is an Air fuel controller it plugs in between the ecu and afm and tweaks the signal +-50% not the best but for 200 bucks it aint bad i am probably gonna get MS if i cant hit 300whp on stock ecu. if not some nos then MS and 350+whp hopefully. Good luck man

adbradley

iTrader: (2)

do you think this will be drivable magna, 12:1 fmu, no bleeder of any kind, 1.8 injectors, and stock fuel pump?

magnamx-5

iTrader: (7)

oh yeah that is what i had for my first setup. minus 1.8 injectors but the 1.8's made driveability better esp on real hot days.

jayc72

iTrader: (14)

I wouldn't assume you'll get 80psi out of the pump until you confirm it with a pressure gauge while driving. The pump out of my 93 would only give me 65-70psi under boost.