Well, my car is getting tuned tomorrow. I was told by the tuner a few things which I do not know if they are correct or not, as I was under the impression it is other way around, but anyway, here's what I was told:
The SAFC will reduce the psi where boost cut creeps in apparently. His reason is that if you up the boost on the boost controller, the SAFC will make more fuel pumped into the engine, which will make ECU think it is overboosting a lot earlier than if it was on stock tune, and as a result cut the fuel earlier... <--- well that would suck!
Damn, I was under the impression it won't change, or at least minimally go up. Oh well, will see the result tomorrow. I was going to buy a fuel cut defender today but not one shop in Perth has it in stock ready for tomorrow Looks like I'll be getting it tuned twice then, first 15 or thereabouts and then 18 psi.
Tuesday, February 06, 2007 - 06:28 pm, by: Callum Finch(Sigeneat)
Someone will stop me if im wrong, but because the SAFC will pump untruthful (its full of lies) data to the ECU you can acheive a slightly higher pressure before hitting the cut.
For example, the stock boost cut is 1bar as we all know, with a tuned SAFC (conservative tune, not rich and not lean) and other random mods i can acheive 1.2bar before hitting the cut at ~1.25bar.
Whats the FCD for? I was under the impression that you only need a fuel cut defender if you are running bigger injectors or hi-flowed stock ones, and thus able to pump teh j00ce?
Certainly i dont have a FCD with a SAFC (and other bits) at ~210rwkw.
Hmmm, yeah that's sort of what I thought, unless I misunderstood something there. Yeah I wanted the fuel cut defender coz I wanted to boost it to 18 psi, to compensate for the higher lag with steel wheels and all that, which I can't without the FCD. My stupid brain left it all too late and only now realised can't get it in time for tomorrow so will have to put up with this 'milder' tune for the time being. Got stock injectors, curious also if they will handle fuel flow at 18 psi of boost hehe.
So I guess if mine will have the same boost cut as yours Callum, it will still come close to the 300rwhp then, good to know
Tuesday, February 06, 2007 - 07:01 pm, by: Daniel Clarke(Dieseltrain)
Daniel, Braden was running stock injectors at 18psi in his cressida mate. SO shouldnt be an issue. I have seen my boost go to over the 17psi mark and didnt run out of fuel.
Tuesday, February 06, 2007 - 09:41 pm, by: Cihan Aday(Cihan)
Standard boost cut is at about 14psi. Our standard map sensor runs out of resolution at about 4.8 something volts = 1BAR. Boost cut is well before then, at 4.32V. If stop the ECU from seeing over 4.32V you effectively remove fuel cut. To lean the mixture out with a sender bender like the s-afc you effectively reduce the voltage output of the MAP sensor in percentage decrements. Each percent leaner is one percent more boost over fuel cut.
For example; A basic tune with stock turbos running low 11's afrs (read: Rich) pulls about 10% fuel at 4,000rpm. Boost cut is effectively raised from 4.32v to 4.32 x 1.10 = 4.75v. Because the MAP sensor has a resolution limit, the engine runs leaner and leaner as you go over 1BAR (4.32 x 1.12 = 4.85V) if you pull greater than %12 fuel. Until 1 bar, AFR's remain exactly the same. After that they lean out.
You run out of fuel with standard injectors when your S-AFC screen looks like this; 0,0,0,0,0,0,0,0 That is essentially the factory tune which runs the injectors into the high 90's injectors duty cycle. Too many people upgrade to 440cc injectors without needing them.
I rekon 440's can do 290rwkw everyday and standard injectors can do 250rwkw at standard rail pressure. This is based on the factory tune which pushes the standard injectors to their limits (90+ %) out of the box. If you want to keep it in the 80's, 275rwkw is about the limit for 440s and ~245rwkw for the 380's. Every car will vary slightly because of other losses changing the power output at the wheels relative to the engine. (eg, diff oil, trans health, rims, tyre pressures, TQ slip, wheel bearings, lazy caliper piston/s, ancillary bearings etc etc.)
We'll be pushing Maurices car past the 270rwkw mark and see if the standard fuel pump can take it, there is still 'plenty' of fuel left there injector wise.
Thursday, February 08, 2007 - 12:32 am, by: Dennis Weglehner(2jzr31)
It is pointless and detrimental to fit an FCD if you are using a SAFC.
You can tune the car to as lean as safely possible with the SAFC by subtracting a percentage of the MAP sensor voltage, therefore RAISING the boost cut to as high as is safe. If boost spikes to higher than this level you WANT the fuel cut there to prevent lean outs.
Thursday, February 08, 2007 - 10:48 am, by: Cihan Aday(Cihan)
Denis thats not true, if you're using most of your fuelling capacity, boost cut still comes in early (15psi) and there is no way of 'removing it' with an safc indefinitely. You wont be able to go above the percentage you remove or it will lean out more and more. But i already explained this in plain detail.
Daniel, the emanage ultimate is still a piggyback. Its just a much better piggyback than an extremely simple SAFC which is an electronic, adjustable resistor box with a graphical user interface.
Thursday, February 08, 2007 - 11:31 am, by: Callum Finch(Sigeneat)
Daniel, have you got after market dumps?
Talking with a couple of people the theory goes that higher flowing dump pipes will help the turbos spool up enough to be considerably better for the steel wheel converted.
I dont know for sure and i havent had it yet, however im in the process of working out dumps to go in now =P
Thursday, February 08, 2007 - 11:38 am, by: Dennis Weglehner(2jzr31)
Cihan Aday wrote on Thursday, February 08, 2007 - 10:48 am:
Denis thats not true, if you're using most of your fuelling capacity, boost cut still comes in early (15psi) and there is no way of 'removing it' with an safc indefinitely.
My point is that it will be DETRIMENTAL to run both if you are running out of fuel and POINTLESS if you are not.
Fitting an FCD when you have "used up your fuel supply" is a BAD idea.
Once the SAFC has been tuned to as lean as considered safe (regardless of boost levels), its GOOD to have the fuel cut kick in if it leans out further with increased boost. So unless you think its good to lean the engine out further than what you originally considered was a safe limit with the SAFC, don't fit an FCD.
If you really have used up all the fuel supply at any given level of boost, the only sensible option is to upgrade you fuel system, then retune the SAFC. With more fuel being injected the SAFC will be set to minus values and the fuel cut will be raised. This will give safe AFR's and only hit the fuel cut when they become unsafe. Thats the important bit. .
This seems pretty straight forward to me. I originally had a home made FCD which I recently removed when I fitted my GT35, as I now run a SAFC. I will be getting it tuned to as lean as safely possible. If that means fuel cut comes in at 17psi, so be it. Or it might even run lean with no correction so SAFC adjustments might lower the fuel cut. Shock horror! But I would rather a low fuel cut then 14:1 AFRs. If I can't run enough boost to reach my target boost level I will get larger injectors.
FCD's have their place on stockish engines with stockish turbos which are known to run super rich in standard trim. When its time to get an SAFC its time to bin the FCD in you care about your engine.
Thursday, February 08, 2007 - 03:50 pm, by: Cihan Aday(Cihan)
Dennis Weglehner wrote on Thursday, February 08, 2007 - 11:38 am:
My point is that it will be DETRIMENTAL to run both if you are running out of fuel and POINTLESS if you are not.
Okay, but you never *actually* made that point did you.
You're completely overlooking the fact that turbos dont run X psi from idle to redline which means you're SAFC screen isn't going to have -10,-10,-10,-10,-10,-10,-10 across the board now is it? We have a boost curve..
What happens if you hit 15psi at <3500rpm where theres little to no fuel removed? It will boost cut wont it? If you fit a FCD you wont hit boost cut, and it will lean out a few points then continue. That might not be a problem for you because of the turbo's size, but not everyones got a GT35.
Thats the limitation of an SAFC to begin with, you can't get the perfect tune without stretching out your resources and making sacrifices. Get an emanage or powerMOD that'll get rid of fuel cut and allow you to add as much fuel as you want via the injectors directly.
I should also add; What happens when you hit 15psi at part throttle? The SAFC uses the TPS and map imput, it doesnt care what the actual boost is at all..
Thursday, February 08, 2007 - 08:44 pm, by: Daniel Clarke(Dieseltrain)
Using an SAFC to remove Boost cut is MOre dangerous than using an FCD to clamp the voltage to remove it all together.
When i fitted my FCD the voltage was clamped at 4.30V. Running 15psi on the Dyno still produced Afr's of 10:2 from 3500rpm ( full boost, or there abouts) all the way until redline. I even hit 17psi and no boost cut. But my AFR's would still not be within the 11:5 to 12:0's.
Technically, the best way then would be using an SAFC to then adjust the fuel tune and achieve desirable AFR'S. We clamped the voltage even further to get the 11:2's i have now, but anymore and it is will be too lean in the mid range.
So i guess I can run 18psi as long as i can trim the fuel or add more. This would be where and FCD + SFC would be handy for me. Unless i went for an Emanage or something similar.
Dont forget, the more MAP voltage you remove, the More changes you are making to the timing maps. Clamping the voltage at say 3.6V which is around 12psi, means the car ius going to run the timing maps for 12psi. Clamping them lower would mean Timing maps for less boost, which would mean more advance and not enough retard. So Over clamping the Map voltage can do bad things timing wise on a car.
At least the FCD removes the boost cut, and the SAFC is ONLY used to trim and adjust fuel. Thats what it is designed for.
Speaking from experience and the advice from my dyno tuner. Who advised me that i could still pull another 10-15rwhp by richening my midrange and trimming the top end rpm, resulting in an even better power curve than what i have now.
Dan McColl Goo Roo Victoria Active V8 and a Factory Manual XF.
Friday, February 09, 2007 - 12:07 am, by: Cihan Aday(Cihan)
Yes thats clear, but the SAFC doesn't care what boost that input actually corresponds to. All it does is trim or amplify an input signal by specified percentage. That means when TPS is at 100%, it doesn't matter if MAP output is 1.4v (idle) or 3.5v(10psi) - it will subtract X% from it.
Using an emanage for example, you can add fuel at a specific boost i.e. map output. Greater flexibility and more accurate tuning without guesswork.