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One good thing to note about the Z32 MAF...

Lots of high-hp non D-Jetro Skylines use dual Z32 MAF's.

Of course some also just convert to D-Jetro, and get rid of the MAF all together. A local Skyline just runs open turbo inlets. No filters or anything. He's got money to burn though.

What about just running 2 stock Hitachi MAF's? How difficult would that be to wire up? More effort than converting a Z32 MAF?

Rather than using two Hitachi sensors, it might be easier to just use one sensor but add a very large bypass around it. That would increase the single sensor's range but wouldn't require as much clever electronics or coding.

Well that might be kinda weird. It doesn't seem like two MAF's in tandum would be a good solution to me. Wouldn't the first MAF obstruct the second? And even if it did work they'd both just read full voltage so what would the advantage be?

Got me again Vikash!

You know what I just thought about. Fuel pressure. If these injectors are rated at a much higher fuel pressure than what we use they don't really do us any good. For example the 370CC's if they're rated for 43.5 PSI that's like 308CC's at our 36.3 PSI right? Or am I wrong about htat?

Well, I dont know if they are rated at a higher fuel pressure, but they are running MUCH richer (to the tune of 10-12 mph) than the stock 270 cc injectors. So even if they dont flow as much as their quote cc number, they still flow more than what you have stock, so if you need to upgrade from a 370cc injector, then a 550 cc injector would be an upgrade, even if it wasnt the true 550 cc. And if you used a rrfpr, then at boost they would be flowing true to rating.

The two MAF's would be in parallel, not in series.

Let me look for a picture...

Nick Wong's R32 from the SCC USCC. Twin Z32 MAF's.

Ok,

so in my case, I am running way rich, possibly 30% richer. Could I 30% bypass my MAF. Meaning the MAF would read 70% airflow, put in 70% fuel, but allow 100% air in?

Or is this where the voltage clamp on the MAF comes in? And is this what they mean by voltage clamp?

Phil - Right, of course the MAF sensors would be in parallel. But I'm saying, just omit one of those sensors; have the pipe go straight to another air filter. You should be able to come up with a one-to-one mapping between total airflow and the signal from that one sensor.

Douglas - In principle, if you can make 30% of the air go around your MAF sensor without disrupting the flow through the sensor, then you would get pulse widths that might be kinda sorta appropriate for 30% larger injectors. It's basically a very simple AFC.

Buuuut.... you'd also get more advanced spark timing. You're already running more advance than you probably should be. So you'll have to run very rich to keep the engine together. So you'd only want to bypass a little bit of air... I don't know if it would be effective or not.

There's no MAF voltage clamp thing relevant to our cars. The only time you want to clamp the MAF voltage is if you have a car with a MAF-based fuel cut.

The problem with changing the voltage from the MAF is that it screws up all load readings.

Thats why the SAFC isn't an IDEAL solution to add more fuel. It alters the MAF signal, to alter fuel, and this changes load computations, which effects timing (possibly seriously retarding timing), as well as some other aspects of running the engine.

Throw a knock sensor code in a modded Turbo Legacy and try to go ON-Boost.

Anything resembling boost, and the car kicks timing to FULL retard. You are actually SLOWER when trying to go on-boost than you are off boost. It's a HORRIBLE feeling.

Ok, I see what you're saying about having the MAF's in parrellel and not in series Phil but do you think they'd both still max out? I guess if it was done right and flow was split between the two you'd get partial readings on both. Hmm.

Vikash, I don't think I'm grasping exactly what you're saying. Are you saying to have a setup like the one Phil pictured above but only one would have a MAF? Then use the one MAF to calculate total flow? How could you be sure each intake was getting the same flow?

You don't need both intakes to flow the same. You just need to be able to say, for example, "Well, the MAF sensor is seeing 123 grams per second. And because I know how the whole thing is laid out, I know that the engine's actually consuming 300 grams per second."

Couldn't you also just cut a hole in the Air filter box and add a nipple with some hosing that would then be routed back into the intake after the maf instead of adding awhole nother filter and all that?

But that fuel pressure thing just got my noodle cooking again. What if you raised the fuel pressure with the stock setup. Lets say you went to 43.5 PSI. Your injectors would then by essentially 443CC right? What's the downside to this? Anyone think the rails and lines can handle the extra pressure?

Yes, you could just add a hose going around the MAF sensor.

Yes, you can just raise the fuel pressure to get some more fuel. And you can do it without buying anything . Just crush the cap of the stock FPR in a little bit to increase the preload on the spring inside.

You'll probably want to put in a nice strong fuel pump, but the rails and lines should easily be able to handle 43.5 psi. I don't see a downside to doing this instead of getting slightly bigger injectors, aside from the extra strain on the fuel pump.

Remember that flow is rougly proportional to the square root of pressure. So, an injector that flows 370cc/min at 36.3 psi should flow about (370*(43.5/36.3)^0.5)=405 cc/min at 43.5 psi. A 280 cc/min injector would become a 306 cc/min injector.

Cool cool, I wonder though if the FPR's for nissans are the same, that'd be a more reliable way.

The Nissan FPRs will bolt right up to our passenger side fuel rails. The problem, at least with the stock Altima ones I've played with, is that the outlet barb is pointed off at an angle, while ours come straight out. It'd probably still work if you just used a long piece of fuel injection hose with it.

I don't know whether stock Nissan fuel pressure is the same as ours or higher.

All the stuff I've seen has said it's 43.5 PSI.

I may have to make a run to the PNP now

Subarupair had a used turbo legacy ecu a couple weeks ago, they might still have one.

vrg3 wrote:You don't need both intakes to flow the same. You just need to be able to say, for example, "Well, the MAF sensor is seeing 123 grams per second. And because I know how the whole thing is laid out, I know that the engine's actually consuming 300 grams per second."

But how do you know that the other intake is getting 177 gps? And what happens if one air filter gets fouled up sooner then the other one and restricts flow to that intake?

I'm not trying to beat down the idea or anything, I'm just throwing out my thoughts. I know it's been a while since I've really chimed in on anything so I don't want it misconstrued (spelling?).

Well I don't think it's somehting that's supposed to be completely 100% accurate. If that was the case you'd be doing something better than tricking the MAFS/ECU. More like an estimation. Like if you're running 25% rich or whatever you'd want to pull in 25% more air, so you size a filter that will flow about 25% of the main filter, right?

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

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.

vrg3 wrote:You'll probably want to put in a nice strong fuel pump, but the rails and lines should easily be able to handle 43.5 psi. I don't see a downside to doing this instead of getting slightly bigger injectors, aside from the extra strain on the fuel pump.

How do you size a fuel pump though?

You don't need to "size" it exactly, right? It just needs to be capable enough. I'd just toss in a Walbro 255lph pump and call it a day.

right, but how do you know how capable it is? If it's just a straight conversion from lph to cc/min multiplied by the number of injectors even the wrx pump should be enough for 405cc/min. Is there a percentage of flow you dont want the pump to exceed?

I think the general rule of thumb is that you don't want to use more than about 75 or 80 percent of the pump's flow as an absolute maximum; above that it's hard to regulate pressure.

But you can't just look at the pump's capacity as a single number (like 255 liters per hour). Flow is actually a function of pressure. I don't know if Walbro or any other pump manufacturers actually publish their flow vs. pressure curves. But generally most OEM pumps give out at pressures that the Walbro pumps can handle easily.