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Old 02-15-2003, 02:06 PM   #1
mkosem
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Default SAFC on TBI SOHC engines

ok, I'm curious about whether or not an APEXi SAFC would work on a SOHC satty. It seems like it just interfaces with the OBD system which would lead me to believe it would be no problem. Has anyone done this? I know that unit has been installed on OBDI sattys before with good results but this situation is a little different.

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Old 02-15-2003, 07:43 PM   #2
Abe95SC2
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The real question is why bother doing it for 3-5HP when for 2x the price you can gain 39HP by swapping in a DOHC.

Abe.

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Old 02-16-2003, 01:40 AM   #3
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how could I swap in a DOHC for $600? I'd need a speedo, engine, pcm, etc.

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Old 02-16-2003, 01:54 AM   #4
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It's call "JUNKYARD"!!!

...
85 GLH 290whp. http://www.saturnfans.com/forums/showthread.php?t=215679
94 855 389xxx miles and climbing.
00 Insight 50mpg++

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Old 02-17-2003, 10:26 AM   #5
eRic 02sc2
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or a coat hanger, late at night...

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Old 02-18-2003, 09:01 AM   #6
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eric eric eric....I'm disappointed in you...a coat hanger???

Anyways, mkosem, you can do a HEAD swap. But that all depends on the year of your SOHC. I don't know what all is possible but on my 95, it's quite simple. Just get a DOHC head, timing chain and cover, cam cover, and the PCM and you'll be set! Of course you'll have a lower compression and you won't gain 39 hp like Abe is saying, but anyways, you could put JE pistons and then a turbo, or just stock DOHC pistons if you wanted higher compression. But I think that it would be much cheaper than trying to get the whole engine and everything. Unless of course you find a sweet deal on e-bay. Oh wait, you'd have to pay shipping, nevermind!

...
-96 SC2 gets 35 mpg mix city/hw.

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Old 02-18-2003, 09:15 AM   #7
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ok use a slimjim instead. not that I have one or anything like that.

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Old 02-24-2003, 02:02 AM   #8
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I'm currently in the process of a head swap. I'd reccomend not doing it and swaping your engine unless you really want to get to know your car/how cars work or you want lower compression pistons on the cheap. I have a '94 and so far I've spent 15 hours and some good knuckle skin + random gaskets. You may be able to get it done in less if you have better luck with your junkyard than I did.

EzDi

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Old 02-26-2003, 09:45 AM   #9
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You wouldn't BELIEVE how much power is locked up in a SOHC with a bad air fuel ratio. Let me cite an example.

I'm running a custom cam in my car. The cam will be marketed very shortly, so if you really are interested don't ask me questions, just keep an eye open. Anywho ... said cam produced
a peak gain of 2 hp over the same car without a cam, and produced like 8 hp at redline. I had like some reasonable low end loss, it was acceptable to me but it was still like 4.5-6 lb/ft of torque.

So we put an S-afc on after seeing the other test car totally crap out presumably due to AF .. the guy actually lost HP vs non cammed - the hp loss happened EXACTLY where the a/f took a nose dive. So I picked up my S-AFC that was rotting in my room, and installed it in the saturn. Then I took it to the dyno and had them tune/test it. After a mere 7 runs we had it completely tuned. 40 minutes - Thanks kauffman motorsports

Anyways..
End result was the same cam, in the same car, with just TUNING eliminated all low end loss, created a gain from 3k to redline, and a maximum gain of 20 hp (with 6 hp peak gain) vs non cammed.

So what I really wonder is how bad REALLY is the stock saturn computer, and how much power does it lose due to improper a/f ratios at WOT? Either way an s-afc is a great investment if you're doing mods. It can really unlock the hidden horses with an hours worth of dyno time with the right people.

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Old 02-26-2003, 11:52 AM   #10
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Mike are those crank figures or RWHP figures?

Also you might note that the engine in question here is a TBI SOHC. If I remember correctly your car has a MPFI SOHC.

Abe.

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Old 02-26-2003, 11:59 AM   #11
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Very true. I was simply citing an example. That 20 hp was at the wheels.

:-D

Anyways.. the TBI model IMHO has more of a reason to be tuned due to it's even cruder fuel control than an MPFI saturn such as mine.

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Old 02-26-2003, 12:51 PM   #12
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Quote:
Originally posted by Garland
Very true. I was simply citing an example. That 20 hp was at the wheels.

:-D
Very nice! 20 RWHP is nothing to sneeze at.

You know, now that I think about it My hopped up DOHC has more power at ~90% throttle than at 100% (closed loop vs. open loop I presume). This is so evident that I have contemplated making a throttle stop.

Maybe when the ins. co. finally settles with me and I get another car I'll hook up an AFC/e-manage so I can trim the injectors a bit at WOT.

Abe.

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Old 02-26-2003, 01:06 PM   #13
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actually in the coming weeks what I'm going to do is make a fuzzy logic air fuel regulator. What it's going to do is tap into the map, TPS and o2 signals .. use them as input. At less than 85% throttle, nothing will happen. As soon as you go WOT, it will keep you at an optimal fuel trim by adjusting the map signal and tricking the ecu much like the S-AFC .. only this one is not user controlled. There *MAY* be a fine tuning knob on it.. but maybe not. At current time it appears that I will be able to retail it at about 100 dollars a unit. It will be specifically for saturns.

That's all the data I can give right now.

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Old 02-26-2003, 01:09 PM   #14
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Quote:
Originally posted by Abe95SC2
Very nice! 20 RWHP is nothing to sneeze at.
Darn right. Check it out:

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Old 02-26-2003, 11:08 PM   #15
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hmm

--Matt

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Old 02-26-2003, 11:19 PM   #16
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I don't think you would see such a difference without the breathing mods. The stock computer can't understand the airflow curve of a modified engine when in open loop, it's programmed for a stock engine. When you add mods, it doesn't know, but the O2 sensor tells it how much fuel it needs in closed loop, making it run nice, but when you go to open loop, it'll run lean because it thinks there isn't as much air as there really is.
The TBI's poor performance is not due just to it's single injector, it has more to do with the throttle being smaller and having an injector in front blocking the airflow.
With the mpfi using batch fire, the only thing you might get is beter atomization, but I think that might not be so much of an issue because the fuel has longer to mix in a TBI setup.

EzDi

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Old 02-27-2003, 07:10 AM   #17
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I'm not even sure it can understand proper a/f delivery even with a bone stock car. I know the SOHC pcm at 3800 rpm switches to a 12.4:1 a/f ratio in it's fuel map. This is programmed in. It's amazing how mild changes in a/f so greatly affect this car. And really 12.4:1 isn't exactly maximum power. Best power will be found from 13:1-12.7:1 or .86-.91v on the o2 sensor feed. So it's already off from the factory in terms of power gain. Sure, the gain won't be as great as with modifications but given my own personal experience with the saturn pcm I am very willing to bet that there are several horses locked up in a poorly managed a/f ratio.

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Old 02-27-2003, 08:04 AM   #18
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Well, I'm planning on getting Fonzo's intake when his family problems correct themselves. He is holding one for me. That intake has a 50mm TB on it. I also have a CAI that I'll put on around the same time. In addition to that, I have a DynoMax SuperTurbo muffler which made a very noticible difference. I hope to be doing prety well after the intake stuff get's here and on.

--Matt

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Old 02-27-2003, 08:40 AM   #19
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Fonzo's got ALOT of smart mods for the TBI guys. Personally being a SOHC'er myself, I've always been disappointed when I see the lack of availability of mods. I mean it's always Intake, Exhaust, Pulleys, upgrade to dohc...

TBI Guys are just flat out told "Don't even mod it" despite the fact the only thing keeping them from that elusive 15 hp is better a/f management. The internals of the engine are the same between TBI and MPFI/SPFI .. the only difference is a/f management. Yet the better a/f control of the MPFI/SPFI engines yields another 15 hp. Really there is no reason a TBI couldn't make 100 crank hp with better a/f management. Fonzo is really helping the TBI guys out by providing the option of better airflow, which is definately at least half of the equation. The other half would be solved by third party black boxing of the ecu for better fuel control (ala S-AFC).

Good luck mkosem... keep an eye out, we're working to really provide the SOHC market a whole breadth of options to really increase power and make it a more viable platform without having to worry about the amount of time and money that needs to be invested in a head swap.

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Old 03-17-2003, 04:59 PM   #20
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So what up with my SL1 94- I dont no which sohc engine I have. tks.

And y'all are abbreviation happy. Can you help me out.

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