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Old 04-27-2006, 09:17 PM   #1
charcoal
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Default NA SOHC w/SAFC-II for increased mpg?

I'm baaaack...
with the price of gas going nuts, I'm wanting to score a higher mpg.
Geez, who doesnt??
There was a long thread about heating the intake air to nail a boost in mileage but it seemed to boil down to actually fooling the IAT and pcm into enriching the fuel mixture. Sorry
Did I miss anything else?

A while back I penned a post about the SAFC-II and got crapped on for it, but I'm persistent in my belief that through the use of a SAFC or similar device, operating just rich of stoch will yield a 10% or greater fuel economy without risking engine damage. I suspect that the OEM programmed PCM mappings contain a safety margin to exploit because the 1.9 saturn motor seems to run lean as evidenced by the presence of excessive carbon residues in the exhaust tract regardless of engine condition or driving style.

When I begin the testing phase I will have more to report on this. I'm considering water injection to offset these risks but in the final analysis, gains usually come at some risk.

I am not interested in whipping the pants off other drivers, just in accomplishing 45mpg (or more as I'm optimistic).

Sorry for the long post, but my questions are:
-and I feel kinda dumb asking this because it seems so obvious:
1. The SAFC can alter the fuel quantity to increase power by causing the pcm to deliver more fuel, but can it be programmed to deliver less?
The SAFC is capable of multiple program storage and retrieval capability, can programs be changed on-the-fly, in other words, given a changing driving condition, can an alternate programmed response map be loaded and executed at any time? RTFM yeah, but any glitches?

2. The WBO2 sensor, must it be a 5 wire sensor? Will any WBO2 4 or 5 wire sensor suffice? Any preferences?
Does anyone know of the life expectancy of the heated (5) wire sensor?

Great Forum!

Thanks in advance.
Charcoal

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Old 04-27-2006, 09:36 PM   #2
98greenSC2
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Default Re: NA SOHC w/SAFC-II for increased mpg?

I have my SAFC2 set to run a little lean during normal driving. I have it set at -6% at idle and it tapers off to 0% at 4500rpm. I know the PCM will adjust for these values and I'm still running at stoich. I'm doing this on the theory that by reducing and perceived amount of air going into the engine(the SAFC only adjusts the MAP sensor signal), the PCM will advance the timing a little and that may help with better throttle response, increased low end power, or maybe slightly better fuel economy. So, in theory, I'm running safely at stoich with slightly advanced timing. Whether or not it works, I dunno. It's not hurting anything.

To do what you want to, you'd have to use the SAFC to adjust the fuel trims beyond the PCM's limit. That'll set off a SES light for sure. The PCM will fight your changes in closed loop within its limits.

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Old 04-27-2006, 10:00 PM   #3
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Default Re: NA SOHC w/SAFC-II for increased mpg?

Quote:
Originally Posted by charcoal
I suspect that the OEM programmed PCM mappings contain a safety margin to exploit because the 1.9 saturn motor seems to run lean as evidenced by the presence of excessive carbon residues in the exhaust tract regardless of engine condition or driving style.
I may be wrong, but I was under the impression that the 1.9 motors ran rich (also, that running rich is safer than running lean-that can lead to pre-detonation, or something, I believe).
I'm just trying to help, and I'm not positive. Someone please correct me if I'm wrong (but please be kind about it-even if I'm totally off my rocker).

...
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Old 04-27-2006, 10:20 PM   #4
charcoal
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Default Re: NA SOHC w/SAFC-II for increased mpg?

Spank me for having a swiss-cheese brain...I can never remember rich from lean.
Shows how much I've diddled with fuel systems, but I'm trying.

Yes, and Thank You 98 for explaining a bit about what the SAFC does to control the fuel system.
I'm not too worried about a winking SES light. I got that already despite my efforts to fix a persistent quad driver fault.

Are you using the stored program feature the SAFC has?

Anyway, if the pcm fights with the SAFC for control then maybe there is a better approach? I'm not ready to remove the pcm and go fully aftermarket engine management.
Charcoal

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Old 04-27-2006, 10:28 PM   #5
scsomike
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Default Re: NA SOHC w/SAFC-II for increased mpg?

what is a SAFC and what all does it allow you to adjust?

i think bob wound up getting like 53 mpg with the IAT mod and heated intake, i think the thread finally died though. might hit him up on a pm.

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Old 04-27-2006, 10:42 PM   #6
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Default Re: NA SOHC w/SAFC-II for increased mpg?

The SAFC is a Super Air Fuel Controller. This is a piggyback device that works with the existing PCM fuel system and sensors.

http://www.turbosaturns.net/articles/SAFC%20install.htm

The turbo saturn group (and others) discusses these and apparently a blinking SES is a symptom of an erroneous installation? I'm not sure...
On page three of the install is a programming and troubleshooting paragraph.
They dont say anything about the pcm fighting with the SAFC, only that it 'confuses' it...?
charcoal

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Old 04-27-2006, 10:55 PM   #7
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Default Re: NA SOHC w/SAFC-II for increased mpg?

The heated air intake system discussed/used in another thread works to increase MPG in TWO ways. It makes the PCM "see" the hotter "thinner" air which causes the PCM to LEAN out the fuel mixture, AND (more importantly) it actually SUPPLIES that heated air. It works WITH the existing system instead of fighting with it, or trying to "fool" it.

(Gasoline also vaporizes more readily in HOT air than in COLD)

LEANER mixtures = HIGHER MPG
RICHER mixtures = LOWER MPG

The only real problem with running consistantly too lean is you risk burning valves due to increased combustion temperatures. The PCM should compensate for this well within reason, provided you are working WITH the OEM system instead of against it. In short, if you can provide the PCM with operating conditions like those seen in the desert (HOT thin air) the car will generally get better MPG numbers than if you provide the PCM with operating conditions like those seen in the arctic.

This is why turbo charged engines require higher octane fuel and most use intercoolers as well (to COOL the very HOT (but also dense) turbo compressed air, AND provide a fuel that RESISTS detonation at high temperatures.) In a HOT air NA (normally aspirated) system, the air is HOT but NOT dense. So a lower octane fuel can be used. (Its about the oxygen content in relation to the temperature of the incoming air charge)

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Old 04-27-2006, 11:17 PM   #8
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Default Re: NA SOHC w/SAFC-II for increased mpg?

Quote:
Originally Posted by charcoal
I am not interested in whipping the pants off other drivers, just in accomplishing 45mpg (or more as I'm optimistic).
If this is your goal, it's probably silly to spend $500 on an S-AFC II and a WB02 setup. It would take you forever (or longer) to recoup that cost.

Give this a look: http://www.turbosaturns.net/forum/viewtopic.php?t=23786

I will be trying this myself in the near future. I need to take care of a few other things first however (O2 sensor, and possibly new plugs and wires).

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Old 04-28-2006, 09:25 AM   #9
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Default Re: NA SOHC w/SAFC-II for increased mpg?

Quote:
Originally Posted by DTDSasquatch
If this is your goal, it's probably silly to spend $500 on an S-AFC II and a WB02 setup. It would take you forever (or longer) to recoup that cost.
I really wish people would stop saying stuff like that. If somebody wants to achieve better gas mileage then I'm all for it! So what if it takes them a year or more to break even. They've been using less gas which is the key. It won't take that long to break even if gas prices keep going up.... which they certainly will.

Better gas mileage = less demand for gas = lower prices.

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Old 04-28-2006, 11:24 AM   #10
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Default Re: NA SOHC w/SAFC-II for increased mpg?

Quote:
Originally Posted by sps SOHC
I really wish people would stop saying stuff like that. If somebody wants to achieve better gas mileage then I'm all for it! So what if it takes them a year or more to break even. They've been using less gas which is the key. It won't take that long to break even if gas prices keep going up.... which they certainly will.

Better gas mileage = less demand for gas = lower prices.
Hey, I'm all for better gas mileage too. I'm just not willing to spend that much money on such a small improvement (if any). If he wants to do it, I couldn't care less.

As far as the environmental aspect of the situation: Activism is a luxury that some of us can't afford. (I stole that quote from a play I recently saw in Philly, but it applies here.)

I want a VW with a TDI engine, but I'm not going to spend $10,000 on a used one for the sole purpose of getting 50mpg (vs. 30mpg in my SW2). If I already owned a TDI and was considering buying a Greasecar kit for $800, that would be a different story. The fuel would be free, and it would not be long before I saved that $800.

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Old 04-28-2006, 12:49 PM   #11
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Default Re: NA SOHC w/SAFC-II for increased mpg?

I have considered the costs involved, and if this undertaking were done intelligently, I only have to make the technology purchases and development ONCE. Part of the overal goal is to make this system somewhat portable -or at least transplant-able.
But then there is always the possibility that someone will want to buy my car WITH its mods that provide 45+mpg.
Would anyone pay 2k$ for a car with this feature in light of 4-5$/gal fuel?
Would anyone pay 27k$ for a hybrid...the approximate amortization works out like this:
Saturn: 0.11$/mile
Prius: 0.41$/mile
Including fuel ($3.19/gal) and maintenance over 100kmiles

The upfront expense; you said it well DTD, 10k$ for a TDI wont save a bunch if you are only after saving spendable income but if I take a 1k$ Saturn, add a .6k$ fuel mileage 'kit' then the amortization works out very cheaply.

-but not as tremendously as cheapybob's clever solution. Wow! we had no idea THAT was possible. DTD's right...scrap the funky electronics and strap on some tubes and insulation!! Whoo hoo!

I am trying to maintain some level of OEM originality and in contrast to bob's solution, an electronic piggyback seems an ideal approach to a cockpit 'switch off' method of restoring OEM functionality. Why would I want this? Because conditions change and contingency dictates rapid flexibility. <sorry for the cerebral explanation>
Another benefit of the SAFC system is it allows the monitoring, display and recording of data useful in adjustment and verification of performance. A terrific way to monitor your ride and prevent damage -for a tech-head like me its a big plus!

Thanks Wolfman; drilling down through the facts...there seems to be some misleading information with respect to application of the SAFC and, if I survive, my ignorance will pass.

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