safc tuning...

[Kreator]

Alright someone clarify me on this one...

The ecu controls the injectors using the airflow amount.
When car is boosting, the sensor registers higher airflow at lower rpm (say the amount of air going through at 5000rpm na is now going through at 3000rpm at boost).
So, as long as the ecu has a map for that amount of flow, it will adjust injectors correctly.
At some point, amount of airflow will jump off the ecu map, and the computer will open it for the amount of time registered for the last max flow causing a leaning condition.

Correct?

Right now i'm running 460cc and SAFC tuned for -45% across the board on an n/a car. When the turbo goes on, the ecu will be still getting a registered flow amount untill about a little less then twice the amount of stock airflow. Will there be a need for additional tuning to make car run safely, or just for precision?

[swalltr207jg]

the easyest way to tune the safc is to have a wideband 02 sensor so you can see what your a/f ratio is and adjust thrue the safc as necassary

[limpgtx]

Or dyno-tune

[swalltr207jg]

Or dyno-tune

yup a dyno would be nice.....however if you unlucky like myself there isnt one close by

[Kreator]

well there is one by me, but i was trying to avoid dyno tune with an a/f and a pyro. Now i have both, and i can tune to some degree, but i very much desire to understand how hte process works. My guess is the safc is there to compensate for when the airflow runs off the ecu map. Taking this into account, considering that the BPT can run on a BP ecu up to 10 psi, anything under that (well relative to turbo size) should be ok (obviously not perfect, but fairly safe) with no safc tuning? I know people said that a/f maps for the BPT on BP ecu arent that great, but i'd guess its more related to the compression difference.

[swalltr207jg]

well there is one by me, but i was trying to avoid dyno tune with an a/f and a pyro. Now i have both, and i can tune to some degree, but i very much desire to understand how hte process works. My guess is the safc is there to compensate for when the airflow runs off the ecu map. Taking this into account, considering that the BPT can run on a BP ecu up to 10 psi, anything under that (well relative to turbo size) should be ok (obviously not perfect, but fairly safe) with no safc tuning? I know people said that a/f maps for the BPT on BP ecu arent that great, but i'd guess its more related to the compression difference.

The safc2 takes the redings from the vaf and converts them to what you want them to be, then relays that to the gtx ecu.......basically all your doing is moving the gtx fuel curve a/f ratio up or down using the safc2.....if you add bigger injectors you can flow more fuel, your still using the stock gtx's fuel maps though....unlike a standalone where you can make your own

[Lex]

basically, you're tricking the car's ECU into thinking there is more or less air coming into the motor relative to how much there actually is. The VAF meter in our cars uses a voltage range to tell the computer how much air is coming in. The computer references this voltage with the voltage value seen by the O2 sensor (which tells the motor if it is running too lean/rich) and the engine RPM and from there it decided how long to keep the injectors open for - therefore how much fuel to deliver to the engine. The ECU knows this through what is known as a fuel map. Think of it as a graph: for X voltage value seen at the VAF (air) and, I should have an injector cycle Y long (fuel). All this is calibrated in the ECU by knowing a set fuel rail pressure and set injector size.

You can trick the ECU into delivering more or less fuel by changing the following:

1. Injector size. Getting bigger injectors and keeping them open for the same amount of time (same cycle length) results in more fuel delivered. The reverse happens with smaller injectors

2. Fuel rail pressure. Increasing the fuel rail pressure squeezes more fuel through the injectors for the same cycle length. This is fairly intuitive and people use rising rate fuel pressure regulators ir FMU's to increase the fuel pressure and get a richer mixture.

3. Changing the voltage seen by the computer from the air flow meter (VAF). If the computer sees more air, it will give you more gas. This is what an AFC does. You can change the voltage seen by the computer from the VAF as a percentage of what the VAF is actually reading. This can make your mixture more rich or more lean for a certain RPM value.

You must remember, that just as swalltr207jg has mentioned, using the 3 methods stated above to deliver more (or less) fuel is still based on the fuel map (graph) programmed into the ECU you are running. Therefore the solutions above are not ideal for best tuning results since you do not have a way to actually change the fuel map itself and therefore are limited to that particular map. On a non-modified car, the map programmed into the ECU gives you a good balance of performance and economy. With mild modifications, you can run an AFC and mildly tune the car to take advantage of the mods.

However, on a heavily modified car, the maps programmed into the stock ECU are no longer adequate for running the engine properly. This is when you have to turn to stand-along computer solutions that are fully programmable and tunable - aka make your own fuel maps.

These units are expensive and require a lot of time at the dyno in order to be tuned for your particular setup - but they are ultimately the best solution.

Hope this info helps.

[Kreator]

i know all those things and how the safc works, and what it does you guys misunderstood me

here is what i'm getting at:

so the stock injectors are about 230cc. I put the 460cc rx7 ones when the car was still na. Obviously, tuning safc for -50% would make up for the doubled amount of flow. agreed? I tuned my for -45% just to be on the safe side, but thats beyond hte point.

The fuel maps on the stock ecu are safe for na and although for a boosted application might be on the lean side, still fairly applicable as long as the amount of flow is still registered.

So does this mean that the safc ONLY comes into play after the turbo is off charts? In other words, while the amount of flow is still registered by the ecu the straight line condition of -45% is fine, and then after it goes off there is safc tuning required? From past experiences, na ecus usually support higher flow than stock (bpt on na ecus up to 10psi, ka24de ecus on 240sxs supporting up to about 7 psi) so does this mean for low boost application stock flow maps will manage it?

Ok i think i confused everyone including myself..... so i'll cut the crap.
does this make sense:

safc maps assuming beginning of spool up at 3K rpm, full boost at 5, 460cc injectors and 7 psi boost

1000 - 45%
2000 - 45%
3000 - 45%
4000 - 35%
5000 - 20%
6000 - 20%
7000 - 20%

[swalltr207jg]

still a little confused as to what you are asking but I'll give it a shot. I think your trying to ask if the safc2 is necesarry throught the whole rpm range, or if its just necassary when the stock gtx fuel map isnt supporting enough fuel for the added boost? correct? If those are the rpm points that you are tuning too, and the percent that you are changeing the stock maps, then you shouldnt have a problem with going too lean, dependant on the amount of boost your running, turbo etc........however you could make additional adjustments to lean it out even more at lower rpm....since the gtx ecu runs a little rich at lower rpms anyways....and then even richer at higher rpms, but you have basically the right idea. Haveing more fuel at higher rpms where your going to be running more boost is the safe way to go.....Your deffenately going to be rich though using those adjustments up until about 3000 rpm when the boost kicks in on the vj-20......Like I said earlyer though the best solution to know how your engine is doing is to get a wideband 02 sensor and monitor your a/f ratios and adjust the safc-2 accordingly.....as it sits now your probably running pretty rich even under boost.....the stock gtx injectors are almost good for 15 psi using stock fuel maps, youll only lean out at higher rpm's. Since you have 460cc injectors I'd assume your running pretty rich

[Kreator]

still a little confused as to what you are asking but I'll give it a shot. I think your trying to ask if the safc2 is necesarry throught the whole rpm range, or if its just necassary when the stock gtx fuel map isnt supporting enough fuel for the added boost? correct? If those are the rpm points that you are tuning too, and the percent that you are changeing the stock maps, then you shouldnt have a problem with going too lean, dependant on the amount of boost your running, turbo etc........however you could make additional adjustments to lean it out even more at lower rpm....since the gtx ecu runs a little rich at lower rpms anyways....and then even richer at higher rpms, but you have basically the right idea. Haveing more fuel at higher rpms where your going to be running more boost is the safe way to go.....Your deffenately going to be rich though using those adjustments up until about 3000 rpm when the boost kicks in on the vj-20......Like I said earlyer though the best solution to know how your engine is doing is to get a wideband 02 sensor and monitor your a/f ratios and adjust the safc-2 accordingly.....as it sits now your probably running pretty rich even under boost.....the stock gtx injectors are almost good for 15 psi using stock fuel maps, youll only lean out at higher rpm's. Since you have 460cc injectors I'd assume your running pretty rich

well yes, that would be exactly my question. Rich is rather what i'm shooting for, instead of blown engine Actually the maps right now are still -45% across all rpm (a little rich, but thats the way i like it) and as i ran the car up to 4K rpm neither hte pyro, nor the a/f reflected on any abnormal mixture condition. This is 7psi on a T3. Maybe i should just go and get it dyno tuned.

[swalltr207jg]

well yes, that would be exactly my question. Rich is rather what i'm shooting for, instead of blown engine Actually the maps right now are still -45% across all rpm (a little rich, but thats the way i like it) and as i ran the car up to 4K rpm neither hte pyro, nor the a/f reflected on any abnormal mixture condition. This is 7psi on a T3. Maybe i should just go and get it dyno tuned.

rich is good at first till you get everything dialed in, till you notice that that premium gas your puttin in your car is going quite a bit faster.....you could take it to the dyno or get an lm-1 a/f ratio monitor theyre pretty awesome its like haveing a dyno without haveing to go to one theyre pretty pricey though.....guess you have to decide which would cost you more in the long run.
Also theres a lot of tuning that you can do to save gasmileage and what not under the point where your turbo starts to spool, detonation can occur here also, but its not as big of a deal as when your under boost....plus dont know if you care or not, but pretty rich a/f ratios will kill your cat in much shorter time ....so if you have to worry about emissions thats a prob. Youd be surprised at how rich you are actually running I'd guess 9 or 10 to 1 which is pig rich.....not too good for power either.

[RALLYBP_94]

Very interesting guys..
Just what i needed to tune my SAFC.
By the way Kreator.. I'll be running a T3 on a B8 block and DOHC head, but Im planning on boosting a little more than you..

[Kreator]

Very interesting guys..
Just what i needed to tune my SAFC.
By the way Kreator.. I'll be running a T3 on a B8 block and DOHC head, but Im planning on boosting a little more than you..

well gotta start somewhere you know Don't know how far you are on your turbo project, but 7 psi is scary enough. My tires/suspension/brakes are having hard time to keep up with the car. Dunnow the actual numbers but butt dyno probably puts the car at ~180hp and its fast enough

swalltr: well lm costs about $300.... originally, a friend of mine was supposed to buy it and let me use it, but he wussed out.... well actually we decided to save up for mig/tig welder instead.

like i said, right now car runs fair, egt is within *spec* the a/f reads decent, but that pos is inaccurate.... like it ever was, for everyone: NEVER (mark my word) NEVER buy a narrowband a/f gauge for tuning. Only as a bling bling factor. Otherwise its worhtless.

I'll see if i can find a dyno around to get the car ran at to look at a/f ratios...
For now, i think i'll mod the setup about to something like this:

1000 - 50%
2000 - 50%
3000 - 48%
4000 - 45%
5000 - 45%
6000 - 45%
7000 - 40%

yes? no?

PS: oh and the Blitz SS is THE ****

[swalltr207jg]

well gotta start somewhere you know Don't know how far you are on your turbo project, but 7 psi is scary enough. My tires/suspension/brakes are having hard time to keep up with the car. Dunnow the actual numbers but butt dyno probably puts the car at ~180hp and its fast enough

swalltr: well lm costs about $300.... originally, a friend of mine was supposed to buy it and let me use it, but he wussed out.... well actually we decided to save up for mig/tig welder instead.

like i said, right now car runs fair, egt is within *spec* the a/f reads decent, but that pos is inaccurate.... like it ever was, for everyone: NEVER (mark my word) NEVER buy a narrowband a/f gauge for tuning. Only as a bling bling factor. Otherwise its worhtless.

I'll see if i can find a dyno around to get the car ran at to look at a/f ratios...
For now, i think i'll mod the setup about to something like this:

1000 - 50%
2000 - 50%
3000 - 48%
4000 - 45%
5000 - 45%
6000 - 45%
7000 - 40%

yes? no?

PS: oh and the Blitz SS is THE ****

that should be fine

[Maz1.8T]

I think that Kreator has the good approach with using the SAFC.

I always thought it would be smarter to use bigger injectors that are more than sufficient for max boost/hp targeted then use the SAFC to lean the off-boost part of the rpm range so that the engine doesn't run pig rich off boost making horrible gas mileage and hard start-ups.

I think using the SAFC to make smaller injectors run 150% richer from 2500 rpm to redline is scary. Sustained 100% duty cycle on the injectors is baddd and it really can't garantee the injectors are up to the task running 150% on the SAFC.

It's so easy just to calculate the proper injector size then choose wisely:

This is from the megasquirt.info web site... very usufull infos over there even if you don't use their fuel management:

InjectorSize = (HorsePower * BSFC) / (#Injectors * DutyCycle)

Duty cycle is usually around 85% but I like to use more like 75% ... gives a better margin.

*BSFC is the amount of fuel your engine uses to make 1 horsepower for one hour. It is usually between 0.42 and 0.58 at wide open throttle. Normally aspirated engines with efficient combustion processes are at the lower end of the BSFC scale [~0.45], supercharged engines tend to be towards the higher end [~0.55].

Or just use this table as generic guideline:



Have fun turbo freaks!!!