Ok i have the my turbo kit sitting on my garage floor. the maifolds,turbo, intercooler all that jive. getting that stuff on the car is not a problem, making it run is however. i have brough tup the idea of using a SAFC2 a few time on here and everyone tells me to just go with a $2000+ stand alone like the Accel DFI or the FAST. but i don't have that kind of money right now and i really want to get this turbo on the car soon. my plan is to use a Acceleronics box to run 72#injectors, a FMU with the proper disks to increase fuel presssure , and an APEXi SAFC2 to tune the air fuel properly. this is all for a STOCK 97 LT1 automatic. i will eventually be building a 396 that can handle more boost but that is on down the road a ways.
for now i figure the 72# injectors will allow me to run less fuel pressure with the FMU and still get the proper amount of fuel while not having to worry about my stock injectors crapping out or the lines being under too much pressure. the SAFC2 will allow me to fine tune fuel thoughout the power band. i can get all the above mentioned parts for just under $1,200 including the injectors.
can anyone can tell me why this would not work, not that its a cheap way(the point) or the least popular way? i understand that many people will not agree with this setup but will it work? thank you for your help, i have been stuck on all this for a month and i really want to get this car put together before the new year.

 

I don't think the SAFC will work that well. It sounds like it works similiarly to the MAF translator. Why not tune your AFR with LT1_edit instead? How much boost are you planning on running?

 

LT1 edit would cost $500 plus at least $100 for a laptop. a SAFC2 is $285
since i'm prolly not going to see above 500hp on this stock motor i am thinking i can get away with bigger high inpedence injectors for awhile, like 30-55#. that way i can get injectors cheaper and i won't have to buy that box.
I plan on running the highest boost i can without blowing things up, we'll see how that goes.

 

You don't need a laptop. You can use a regular PC. You just have to be willing to lug it in and out of your house when you want to make changes. However $500 vs $285 is a big difference. I would only caution you that trying to go the cheaper route usually ends up costing you more. Although you probably heard that before. If the SAFC works out let us know.

 

Ditto, if you can't afford it now. Save up and do it right. 72# injectors with a properly set up FMU will handle what you need to throw at it... Unless you are crazy like Jordon and Brady

 

The SAFC will do wonders for your setup. I had one in my 300zx twinturbo. Ran it with bigger injectors, dual MAF, at 20psi. Never did it buck or backfire. The great thing about it is that it has live time tuning. The LT1edit takes awhile to change programs and must be loeaded to the PCM which takes awhile longer. You can convert air flow from idle all the way to redline at 0-100% throttle all in about 1 minute. Trust me this will work for you. I would however not use an FMU. You already have huge injectors, why not use it? If you set high throttle at say 85% and low at 15% the controller will actually sense the boost and add fuel. At 85% throttle you will just about always be boosting and 15% you won't. SO on the low throttle table just leave it alone and on high throttle bump the fuel up. The controller will have a linear curve and correct by itself. You can also see the correction the controller doing so if it does buck on you you can see when and how much it is correcting and then adjust it. At WOT though I don't think you will have much problems just at part throttle and deceleration

BTW, this is my experience with another car and maybe very different for an LT1.

 

I think that alot of people will tell you it won't work because no one has ever tried it. I'm not even sure if it's compatible with the LT1 PCM, or how it even works. I can tell you that the route I went was ditching the OBD2 PCM (I have a 97 as well) picked up a 95 OBD1 PCM, bought tunercat ($100) and a cable ($80 at the time) and free Datamaster software, and I had everything I needed to tune my car. I ran 42# injectors with stock lines,FPR, and a dual intank fuel pump setup, and made 542 rwhp, and 622 tq with the injectors basically maxed out at 96% duty cycle. Keep the boost low and tune the stock PCM for it until you can purchase the FAST. you can get up to 55# injectors that are high impedance style injectors.

Care to elaborate more on how the APEXi SAFC unit actually works? Is it a piggy back system that takes the inputs/outputs from the stock PCM, and modify's it? Running 2 MAF's thru this system would sound like a great idea if you could import 1 signal back to the PCM.

Bill

 

The AFC works by taking the signal coming from the MAF to the PCM and converting it to whatever table you set for it. It is a highly advance piggyback system. It can do wonders but when you get to running high boost you need something like F.A.S.T. If someone were to run 10psi or less this unit would be perfect.

Running two MAFs for an LT1 wouldn't be a great idea unless you somehow built a twin entry intake manifold. The 300ZX I had had twin everything which includd turbos, IC, TB so it would seem like adding twin MAF would give much more power but it only gave like 5hp if that

 

the SAFC would not allow you to control timing, and the PCM can only sample as high as ~11kHz, which any decent FI setup will exceed - so there is no real way to add fuel through the pcm without actually tweaking the pcm itself. So no, it would not work as advertised with our pcm (it may interface, but it wouldn't do what youw anted)

For injectors you could get buy on high-z injectors depending on your power goals - look at the racetronix 57lb/hr injectors - they actually run okay for such big injectors.

The other option you haven't mentioned is just taking it to someone to tune. you are talking about spending 300 for the SAFC - plus to get it dialed in figure a minimuim of 150+ for wideband dyno time. For that 450 you could easily pay a professional to tune the setup.

 

He is installing bigger injectors which will let him cut the signal quite a bit already. 72# injectors compared to the stock 24# is a big change. Once he cuts the signal down with the SAFC he can then turn up the boost and be safe, to what point I don't know. The best way to find out is to install the SAFC with the injectors and see

 

save the money and get a FAST unit. I paid $1800 new w/o2, but that was like 3 years ago. As for injectors im selling mine, there 72# siemans. They have low miles on them maybe 8K.

 

Great input guys keep it coming!
Chris B: what do you mean by the PCM can only sample to 11~kHz? i am not into the super technical lingo yet and i have no clue what you are refering too please elaborate.
LT1RX7: i think you understand what i am saying. with the bigger injectors and the SAFC i can leave the fuel pressure at lower levels and open the injectors for a shorter time than the stockers. and the SAFC will allow me to tune the Hi and Lo for WOT under boost and driveability out of boost. but wouldn't you think an FMU with a small ratio would help? the bigger injectors could be tuned on the Hi, at WOT, under full boost, with the FMU doing its work. and the tune the Lo with out boost and the FMU not affecting fuel pressure. i am just thinking that there would still be problems without a FMU. you are prolly right when you say that at 85% throttle there is pretty much no chance of not being under boost, and if you set up the injectors that way then you would be all good at the top. but would that mean i would have to floor the pedal to safely spool with out going lean at say 50% throttle and high boost? i mean could i not half throttle and play with someone instead of go ***** to the wall everytime?

now that i think about things more would i really need 72# injectors with the stock motor and low boost? i mean SmokenZ made awsome numbers with just 42#ers. if i stuck with high-z then i could save not buying the box.

this is all still just ideas for me i have not bought anything but the turbo kit itself. i talked to a buddy of mine today who builds turbo drag cars locally and he is going to try to get me into a buy for a FAST bank to bank system. so if i can get that for a good deal then that is prolly the route i will go. if not then i will be buying the SAFC really soon.

 

So you are going to try and swap out injectors and not properly program the pcm? That's a really bad idea. The transfer function for frequency (which is the domain the afc will work on) to flow is an exponential relation to flow rate (the domain the air/fuel setup works up).

Is the SAFC capable of mapping out this function at that rate (vs. linear, polynomial, etc.?)

Also 72/24 = 3 - stock maf is good up to 450rwhp, so this would be adjusting the maf so it's good for roughly 1350rwhp.

Now if you are making say 550rwhp, you are giving up over 50% of your range - you have just increased your granularity greatly (meaining car will not run as well). If you don't take it all the way up to compensate then at all part throttle positions your fueling will be off.


And again, this will not give you any boost referenced timing capability - which you can do with a stock pcm + tuning or with fast. So add on another 300-400 bucks for an ignition that can retard timing vs. spark - so we are already at 700 bucks here. Add in 350 for the impedance converter and you are at 1050. Add in 350 for a wideband and you are at 1400. How much was a FAST setup again?

Get the specs on the SAFC (what kind of signal it takes - frequency, PWM, voltage, etc., what it can output, and it's tuning capabilities) - but I seriously doubt it will work properly or well.

And again, you could go to Ed Wright, whomever, and get the car dynotuned for less than you are talking about doing it here.



our maf outputs a frequency signal - the pcm will not read a value higher than 11.26kHz, and with a stock tune that will be about 430g/sec. No matter how much higher the SAFC outputs a signal (higher signal = more fuel) the pcm would not read it.

Now it seems you are trying to increase the injector and not tell the pcm about it, but alter the MAF signal. The problem is injector flow is going to be proportional to airflow, but the SAFC sees frequency, and frequency is not linearly related to airflow - it's a very steep exponential curve - so a 20% cut in frequency could be a 5% or 50% cut in fuel depending on where you are. The SAFC would have to know the MAF transfer function for this to work properly.

Again, I don't think this is going to work - a FMU would be a better choice. (but I still wouldn't do that).

If you want to keep it simple keep your hp under 550rwhp or so, get the racetronix 57lb/hr high-z injectors, a 255lph intank pump, an ignition box or LTCC, and take it to someone to tune it.

Chris

Chris

 

yeah i mean if i install 72# injectors then i will have to get the stock PCM changed, but wouldn' t that be cheaper than getting a complete custom program? and i never thought about the timing deal. i new it might be a problem at high boost but around 10psi tops would pulling timing matter? would FAST allow me to tune the timing? i have no clue what all the specs are on the SAFCwww.Apexi.com
i am about to put the turbo on with just a FMU and hit the dyno to see where the problems occur and buy whatever i need to fix them. if it comes to a FAST system then i guess thats what it will be. i mean the only real way to find out what will ultimatly work for me is to try right?

 

Yes, pulling timing is an issue with just about any amount of boost. The stock LT1 computer has no way to sense boost, the MAP sensor only reads from -14.7 to 0. It has no way to know to adjust timing/fuel curves when the supercharger/turbocharger begins making boost. I'm running 7 PSI with a retard box (not the best solution, but it works) and I typically see 10-16 degrees of timing retard under boost (1.5-2 degrees per pound of boost depending on how it's adjusted) plus what the computer pulls out. As far as fuel goes, I ditched my FMU for a bigger set of injectors and a custom tune. Still working on the tuning part, but at least I'm not overworking my injectors by any means.

Oh yeah, your STOCK 97 LT1 isn't going to last long under 10 PSI of boost (less if you don't figure out some way to retard the spark and get enough fuel to it), so you'd better start building that forged 396.