blk&blu*j

iTrader: (1)

Of course we love all members to join in

StuntKing

iTrader: (5)

Well i meant can anyone verify INTIMAZY's method on a 1jz?

blk&blu*j

iTrader: (1)

Well as I said in numerous posts I ran 680's on an AFC and still hit boost cut in the 12-14psi range pulling alot of fuel out without a FCD so I would really like somebody else to chime in.

INTIMAZY

iTrader: (5)

Meh. Since nobody else jumped in, here's some material from various other forums, some 1JZ specific, some Supra specific, some just MAP tuning specific for other cars.

All courtesy of Google
https://www.clublexus.com/forums/6488425-post6.html <--moderator on here mentions the fuel cut/SAFC relationship
http://soarercentral.com/sc-forum/me...75/132586.html <----3rd post from the bottom, in particular
http://www.supraforums.com/forum/sho...-need-for-BCC&
http://www.supraforums.com/forum/sho...7403-Fuel-cut&
http://www.supraforums.com/forum/sho...=1#post4503312
http://performanceforums.com/forums/...sing-SAFC-(2jz)
http://www.dsmtalk.com/forums/showthread.php?t=97849
http://www.toyotagtturbo.com/forums/...moves-fuel-cut
http://www.galantvr4.org/ubbthreads/...page=4&fpart=1

I'm not speaking some magic theory. It's been reproduced many time since the last 2 decades. If you understand how a SAFC and any of the boost cut devices work, you'll see why they are virtually interchangeable.

blk&blu*j,
I'm not sure why it didn't work for you. If your car is MAP based and you are overfueled, then I see no reason why it wouldn't. Because you appear to be a Supra guy, the only guess I can make is that your car was a USDM spec motor that ran a MAF sensor in addition to the MAP.

cartmill

iTrader: (3)

just to set you straight, the world you live on is Earth, which has an atmosphere. so when we refer to MAP sensors being 2.3 bar, one of those bars is "used up" for atmospheric pressure.
so a 2.3 bar map sensor uses 1 bar for atmosphere, 1 bar for boost, and .3 bar for more boost.
so a 2.3 bar map sensor can read up to a little under 19 psi.

so i'm guessing you have a 3.5 bar map sensor.

"Q. How is boost measured? (Bar, mmHg, PSI) and How do you convert from one to another?
A. Boost is measured as the pressure that the turbo creates above atmospheric pressure. Normal Atmospheric Pressure (1 atm) = 14.7 psi = 760 mm Hg 1 Bar is not actually equal to 14.7 psi, but rather it is equal to 14.5 psi, = 0.9869 atm = 750.062 mm Hg" -- Garrett Turbo FAQ

^^ exactly right. reducing that MAP signal is doing nothing but make the ECU think you're running less boost than you are. this is obviously (maybe not so obviously) not good, and this is why i tell people not to use AFCs or FCDs unless they have minor mods and they're skating right on the fuel cut threshold (like within half a psi):

what a lot of people don't realize about this concept is that your fuel and timing map stops at that max MAP reading, so if you cap that MAP sensor voltage, the ECU thinks you're still running 13.5psi or whatever you capped it at. so your fuel and timing maps are exactly the same no matter how high you turn the boost up past that threshold. the more boost you run, of course, the more fuel you want and the less timing you want.
this is why OEMs map their ECUs to do a fuel cut below the max MAP sensor voltage, so you don't go over that max voltage and run lean and run more timing than you should.

cartmill

iTrader: (3)

also, OP, keep in mind (after reading all that i just posted above) that INTIMAZY's recommendation of getting 550s and an SAFC2 that you're going to have almost 50% additional injector there, and an AFC can only alter your MAP signal.

what i'm alluding to is that your stock ECU has several supplemental maps, mainly for intake air temp, coolant temp, and cranking (and cranking based on coolant temp probably) that can't be changed by your AFC (ie, not based on the MAP signal), so for all of these maps that are "locked," you're going to have 50% too much fuel (same pulsewidth shot from the ECU with 50% bigger flowing injector = 50% more fuel). this is not a huge problem when you're going from 370s to 550s (ie, not huge injectors), but definitely noticeable, and the tuning/AFRs will be sloppy.

air temp correction usually doesn't get to crazy (like within a few % change unless you have big climate swings) but coolant temp correction can be drastic, like for cold starts, cruising before warmed up,etc.


and INTIMAZY, did any of those links include actual testing of the MAP sensor to show at what PSI it stops reading? (can't click them at the moment)
i was thinking it was 22 psi for some reason.

INTIMAZY

iTrader: (5)

I couldn't find one that shows actual psi range for the MAP sensor. 22psi sounds close enough to be right (2.3bar minus about 1bar for ambient air on this planet = about 1.3bar or ~19psi?? Just a math guess) I remember reading somewhere on some Supra forum that 4.3 volts is the critical MAP voltage for fuel cut.

Thanks for the support cartmill, I agree it's not a great way to tune because you simply trick the ECU into seeing less voltage but I do think that of the two options, FCD or SAFC, that SAFC accomplishes the task more safely and predictably. Here's my reasoning:

Two cars. Both MAP controlled and identical in every way.
Car A uses a fuel cut device of some sort that physically clamps voltage below the ~4.3 volt area.
Car B uses a SAFC that linearly (%age-wise) cuts down the MAP signal seen by the ECU, regardless of how high or low voltage it is.
Both cars running at say 60% injector duty cycle with plenty of headroom.
Both accelerate to the maximum PSI that the MAP resolution allows for. Let's say its 22psi for arguments sake.
When car A passed the 13psi boost cut area, the ECU only saw ~4.2 volts to avoid boost cut, despite now actually pushing 22psi. The car is now at 22psi but the ECU is really only fueling for the 13psi it sees. In my opinion, this is a BOOM waiting to happen.
Car B however, linearly reduced the total voltage the ECU sees from the MAP. When the MAP is sending 4.3 volts to the ECU, the SAFC tuned down say, 20%, intercepts it and only sends 3.4volts. The ECU thinks it's WELLL below fuel cut still and can still linearly increase fueling as psi increases even past the resolution of the MAP sensor. If combined with an AFPR, you can relatively safely make sure you don't run out of fuel in the top end.

Granted, this skewing is NOT a great idea on a big boost car but for smaller setups on smaller 550cc injectors like cartmill said, it's not bad.
The issue that comes up with this linear skew is with timing. Although the SAFC can't directly control timing, because it controls the MAP, it DOES affect timing. Why do I think so? Lets start with a stock timing chart courtesy of some forum guy that owns a PowerFC.

The only general trend you really should notice is that the map generally pulls timing as PSI increases. More boost = more conservative timing. With a SAFC you bypass this because you can be running say, 18psi when in reality you're ECU is timing it as if it was for 10psi.. (these are numbers I pulled out of my a$$, I'm NOT saying that that's exactly what's happening) This can be a problem since the timing could be almost DOUBLE the degrees it would normally be without a SAFC.

Why aren't all 1JZ's ticking car bombs above 13psi? Our ECU's are very conservatively tuned so there is sooo much room to 'trick' the ECU before something bad happens.

phew... that took a while

cartmill

iTrader: (3)

I think you just said the exact same thing I said in the previous post. But with some more detail. :-)
Hopefully people appreciate all this info! Even if they don't, I guess it's a good thing to have this info more easily accessible on this forum. We need an EMS/tuning sub forum...

A lot of people on CL seem to not have a good understanding of how engine management typically works. Maybe I just got spoiled by rx7club and my local car forum over the years.

Vrank

iTrader: (4)

As for the map sensor hitting cut at 4.3, that's pretty damn accurate. I did a lot of logging with my emanage in stock trim and holset trim last winter purposely inducing fuel cut. Ended up clamping at 4.20 volts because iirc the lowest I got under certain conditions was about 4.23v. Luckily with the emanage you can safely manipulate the ecu above cut using their 3.5 bar map sensor. I wish I had all those logs still. It's become a pain in the anus as of late.

INTIMAZY

iTrader: (5)

Exactly
Just want to bury this once and for all so maybe people will refer back to some of this in the future instead of posting "oh hey i want to get SAFC is this gud"

Why isn't there a tuning subforum??
You would figure with all the NA-T's and swaps on here running standalones and piggybacks that it would be useful.

blk&blu*j

iTrader: (1)

For the record Cartmill I run a 5 bar map, and I stopped using SAFCs yrs ago.