They both raise fuel preusser right. neither will be able to make you pump or injectors work harder then the max. so what would be the point of useing both at the same time. also why would you use a fmu if and safc does the same thing and more for the same cost.


"Kick azz is my boost hero!!! "

FMU is the only one that raises fuel pressure per PSI of boost...

The SAFC adds more fuel by longer pulse lenghts from the injectors when they open up... it changes the map signal output and tricks the ECU by making it think its getting more air then it actually is getting.

If i said this wrong, i know that the safc adds more fuel eletroncily through your ECU where the FMU adds it mechanicly or in other words by fuel pressure.

All true, yes.

Fuel Management Units (FMU's) are essentially specialized fuel pressure regulators which can provide higher than stock fuel pressures when boost pressure is applied to them. Different rate-of-gain ratios allow FMU's to provide the correct air-fuel ratio under boost pressure, while maintaining stock fuel pressures when the engine is not in boost mode.

An AFC (Air-Fuel Controller), the most common of which is the APexi S-AFC, are used to manipulate the engine's stock MAP sensor signal. This allows the tuner to use different sized injectors, for example, yet still run the engine with the stock calibration tables in the stock computer. For instance, if your engine runs at 16" vacuum with its stock 26 lb. injectors, you can install an AFC and 36 lb. injectors. The AFC will 'trick' the computer into thinking it is running at, say 22" vacuum, when it actually still idles at 16". The computer will then supply the accordingly leaner pulse widths to the injectors, which will prevent them from creating an otherwise over-rich condition. The AFC will have several other adjustment points that allow the tuner to then tailor the remainder of the MAP sensor range.

One thing to keep in mind about any MAP-MAF sensor manipulation system (AFC, E-manage, etc) is that while you can always achieve leaner (higher-vacuum) settings, you cannot add more fuel at wide open throttle with them...as this is where the stock MAP sensor is already maxed out (near or at 5.0v output), these devices cannot add more fuel. But if you did it right, the larger injector the AFC allowed you to install will perform that purpose for you.

This is just a general overview, as there is much more to understand to effectively combine an AFC with an FMU, but to answer your question: Yes, you can combine them, but only for the right reasons. Typically, an FMU is sufficient...and an AFC will not add even more fuel delivery capacity to an FMU. However, if you are also trying to run larger than stock injectors, an FMU alone may not be optimal...but this varies from application to application. Now, if you also add larger cams and a ported head, which will also seriously affect even the non-boosted operating condition, an AFC becomes a must.



Bill Hahn Jr.
Hahn RaceCraft

World's Quickest and Fastest Street J-Bodies
Turbocharging GM FWD's since 1988
www.turbosystem.com

let me get this straight so it would be optimal If I am putting in something that can increase the max output of the fuel it will help when it comes to utilizing the system. but not if I already have an fmu to help with that. but would useing the safc to help fine tune my curve be any good it just seems that people get the best results when there dialed in right.


"Kick azz is my boost hero!!! "

Quote:

FMU is the only one that raises fuel pressure per PSI of boost...

i thought FMU's cant read boost??

FMU's must read boost to function correctly. Their sole purpose is to raise fuel pressure x amount of psi for every one psi of boost it sees. Common fixed rate FMU's such as Vortech or OBX use ratios like 4:1, 8:1, 12:1...and so on.
ECU's can't read boost(Speaking in terms of non-reflashed, non-turboed j-body engines)....maybe thats what you got mixed up.

I forgot to add in my last post that I was under the impression that the FMU raises the fuel to get you into the ballpark and then the SAFC can add/subtract based on RPM-based needs to get a solid A/F. Its kind of like using a paint roller to paint a wall and then using a fine tipped brush to do the detail work.........kinda.....

Quote:

FMU's must read boost to function correctly. Their sole purpose is to raise fuel pressure x amount of psi for every one psi of boost it sees.

i thought it just rasies fuel pressure? like based on throttle? if it could read boost, then you would be set. it would just raise fuel pressure perfectly as boost increases. you still have to adjust the base and WOT fuel pressure.

it can read boost but it is a very simple machine. it rasies it 1-12 or whatever deepening on what you want. but its not smart enough to fine tune the curve thats where a wideband and and safc come into play. as a wise man once said "Its kind of like using a paint roller to paint a wall and then using a fine tipped brush to do the detail work"


"Kick azz is my boost hero!!! "

haha...a wise man....you must not have seen my post where I couldn't figure out how to adjust my AFPR........

I read that haha no worries


"Kick azz is my boost hero!!! "

the fmu raises fuel pressure when the intake manifold pressure changes from vaccuum to boost........... so NO MATTER WHAT the fmu will slow the return line and keep pressure up in the rail............. SAFC2 has other benefits........ knock sensor.......... custom curve......... shows boost pressure, intake manifold pressure..................... GREAT TOOL I want it...... I have a cartech adjustable right now WITH a S/C reflash on a turbo set up .............. that is the ultimate tool !!




JDM Civic Hatch
Status: Parting Out Turbo Kit....
14.224 @ 102.01MPH @ 5.5psi.... 2.3 60'
Next: Civic JDM B16a2 w/GSR LSD Turbo - Goal 300whp 1400lbs...

it was prolly already said im just lazy to read it all..the Safc-2 will fine tune after the FMU


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