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Oh, here we go; here's some info from Walbro:

http://www.autoperformanceengineering.c ... specs.html

Found someting interesting
http://www.deatschwerks.com/products.html
If they fit the price isn't as much as I thought but they are rebuilt.
I think I would rather play with a S-AFC and Adj FPR than a MAF bypass. Still an interesting idea, not knocking it.
If I turn down the MAF signal I get more timing? That's great news to me, non intercooled timing map has got to be retarded. And too rich for power.
S-AFC here I come... I'm going to get a WB02 sensor when I get home, got a Adj FPR, use the scan tool to get the timing difference, good butt dyno to tune....

The SAFC modifies the MAF signal.

What's based on the MAF's signal? All computations for load. You'd have to run super rich to compensate for the advance in timing to cover your ass.

In short, the SAFC DOES give fuel control, but it forces you to tune conservatively because of the timing advance. The best non-standalone setup I've seen is to run an Apexi Timing Control unit, and an SAFC. Apexi doesn't make this unit anymore though, and they only made a handfull of them. And they were never digitial.

That way, you can retard timing a bit, and lean the mixture a little more towards stoich. But no digital readout on the timing control makes things kinda hard...

-K- - Bypassing air around the MAF sensor increases the range of the sensor, though, which you can't do with an AFC. And the stock turbo sensor's range is very limited.

hmm, if I'm calculating that right, then the walbro 255 is way overkill for the application even when using 740CC/min injectors, why not go for the 155 or 190 to save some money, or do they even have them for our cars?

I wouldn't say it's way overkill.

Let's say we have an engine well-tuned for 740cc/min injectors, so at peak it runs the injectors at 85% duty cycle. And say we're following the 75% rule, requiring one third extra fuel flow.

((85%) * 4 * (740 (cc / minute))) / (75%) = 53.1725505 US gallons / hour

And let's say this hypothetical monster engine is running stock fuel pressure but 20 psig of boost. That means fuel pressure needs to be 56.3 psig.

So we need a pump that at a minimum flows about 55 gallons per hour at about 60 psi.

According to the data on that page I linked to, we would pretty much have to get the high-pressure 255lph pump. I guess the regular 255lph pump might work, if you upgraded the wiring.

I'm pretty sure they sell at least the 190lph pump for our cars.

I guess I wasn't calculating it right, I was coming up with like 11 gph at 43.5 psi.

And even though I had the 255 lph pump, and it did affect my milage because it was forcing more fuel all the time (ie bad milage), it was not enough to compensate by itself, the too small injectors. However I never used a larger rrfpr, so I dont know if it would have worked in conjuction with my 270 cc injectors and a 4-1 or better rrfpr.

I dont believe that's a problem of the fuel pump. The FPR decides how much fuel pressure the system needs, not the pump. The pump only flows what it can. Unless of course you were overwhelming the FPR. If you didn't reset the ECU it could've been your stock pump was not up to snuff and caused the ECU to learn leaner fuel trims then when you changed the pump, it was supplying enough fuel to bring it back to nominal levels but that was too much fuel for the adjusted map. If that makes any sense

vrg3 wrote:You would know the other intake's flow only by making a lot of empirical measurements.

And then assume they (measurements) don't change?

You're absolutely right that one air filter clogging faster than the other would screw this up. And even if you just used one air filter, you might have one part of it clog faster than the other. I don't know what you'd do about that... or if it even matters that much. I mean, the clogging of the factory air filter's gotta affect the stock MAF's transfer function at least a little. Or maybe it doesn't; maybe that's where some of the airbox engineering goes.

I'm not worried about the reduced flow over just a single MAF (like stock), I'm worried about one of the intakes having reduced flow and the other not having a reduction in flow in this two intake/one MAF setup. It doesn't really matter which one has the reduction either, it would have ill effects either way. Especially if it was on the MAF side. For Instance

* Disclaimer*These numbers are hypothetical and don't reflect actual numbers in any way so please don't try and correct them. They're just for the sake of argument.

Lets say you have 150 CFM on the intake with the MAF at WOT and it's reading 125 grams per second. The second intake without the MAF has 250 CFM and is the equivalant of another 230 gps. Ok, so now you're fueling for a total of 355 gps. So if the MAF side drops to 100 CFM and 90 gps but the other intake for some reason is still getting the full 250 CFM/230 gps, you would get a lean condition right? On the other side, if the non MAF side flow dropped to 200 CFM/190 gps but the MAF side was still at the full 150 CFM/125 gps, you would get a rich condition, true?

Am I onto something here or am I just way off basis? It seems the extra effort to have two MAF's would be worth it for the extra safety.

I understand and completely agree with your concern, Matt. I don't know for sure whether or not it would be an issue in practice, but you're absolutely right that it's something to consider.

It's also something you have to consider when doing any kind of airbox modification even if you're only using one sensor. Remember that the sensing element in the MAF sensor is a small hot wire or hot film. Most of the air goes straight through the sensor without ever touching the sensing element. In a sense, most of the body of the sensor is a bypass around the sensing element. And if you change the flow pattern through that sensor body, you might end up screwing with the factory-calibrated relationship between MAF voltage and airflow. I wonder if that might be part of the reason a lot of people have weird issues when they put cone filters on.

But, yeah, it's probably safer to either use two MAF sensors, or to just have a small bypass around the sensor rather than having a whole separate filter.

OK what I'm talking about is a small increase of fuel pressure and tune AFR with the S-AFC. Also watching whatever changes in timing. I'm not talking about running 740cc injectors with it. What I want to do is tune the timing because I think to run safe with no IC it's retarded. If I run out of injector I would consider the MAF bypass and bigger injectors.

I would make a new MAF sensor tube and stick the hotwire in it.
If not then a bypass from the airbox around the MAF and back in. I don't like the seperate filter idea.

The problem with the larger tube with the stock wire is that you will need to remap the entire ECU.

That means set a value for every single throttle position, at every single RPM and at every single load. You could probably have a resistor or something to drop the values back to stock, but then you have the problem of the ECU thinking it's getting the same air as stock, and you run lean as a mother.

The problem with the SAF-C is that it skew's load measurements.

If you want to adjust timing, you should look into the Apexi ITC timing control unit. That, coupled with the SAFC, and you can get a car to run OK, but not great. Your still going to have to tune rich for saftey.

I do think the best idea, if still on the stock ECU, is to just go with what it does. It throws a bunch of fuel and keeps it as rich as the injectors allow. I wouldn't want to start messing with timing and such when our injectors go static so early because of the maf.

What I was going for was a bigger MAF tube to "match" bigger injectors instead of a bypass pipe.
I know it isn't the best idea but it might work fine, I'm not going to say it's great but if someone wants to try I'm all for it. I would not try this without a wbO2 and some data logging.

How much of a difference would that make though? If the rest of the intake was still the same size wouldn't it still flow the same? Or am I totally off base?

He's not talking about increasing airflow. He's talking about making the portion of airflow that goes past the sensing element a smaller percentage. That increases the range of the sensor.

oh, right.

I noticed something today. The second style air boxes, the ones that have the MAFS coming out at an angle to the rectangular part of the box are the same MAFS as what we use, all the numbers are the same, cept the bottom middle numbers (is that the serial number or something?). So it may not be that detrimental to use a VG30DETT MAFS. This may be the upgrade we're looking for.

I think you are looking at the serial number, yeah. The JECS MAF sensor was the same from 1990 up through 1998, I think.