fidelity101

iTrader: (11)

okay I hate vane airflow meters and i'm stuck with it because of the S4, but I know people upgrade MAFs alot in many cars. Alot of people upgrade to 5 wire GM sensor, well I have a nissan (jecs N60) maf pulled off of a maxima, it flows up to 300hp so its more than enough but it is a 3 inch diameter and I would imagine alot more accurate.

but I was thinking would it be possible to wire up my 5 wire maf sensor to my ecu and finally getting rid of of the vane airflow. I know my best bet would probably be with getting an S5 MAF but I imagine that the voltages being sent out from maf to maf are similar, I do have my SAFCII and wideband 02 sensor so I would be prepared for inevitable adjustment.

lets discuss! I know this is on the s4 owners minds heh.

Evil Aviator

The S4 AFM is also good for at least 390hp, which was the estimated hp of the world record setting 10AE Bonneville flats car.

Complete waste of time. Both the S4 and S5 AFMs fall under the "vane" AFM category, and there is no significant performance advantage in the S5 AFM.

Even if you spend hundreds of dollars on crappy add-ons, you would still be running your engine with the stock 1980's computer. Your best bet would be to forget all of the ghetto bandaids and install a standalone EMS.

NZConvertible

A hot-wire MAF sensor outputs a completely different signal to a vane-type AFM. Not only is the curve different, but the voltage signal rises with flow instead of dropping with flow as our ECU expects to see. There are convertor boxes available but I've yet to see anyone use one on an FC.

No such thing...

Rx7TyreBurna

iTrader: (1)

http://howto.globalvicinity.com/gv_w...=120&co=1&vi=1

Interesting site.

stevej88na

<--- It uses a microcontroller for ADC and look-up-table, and a DAC for output. Check my project page linked above by Rx7TyreBurna for the proof-of-concept. The project's been on the back burner for a few too many months now; it turns out miata, protege, and corolla guys are waiting on this as well. Part of my lack of updates is I don't want people attempting this without the proper tools or skills and damaging their engines. I've consulted a community expert on the matter, and we came up with this:

zbrown

Im with Evil Aviator, save your money and buy a standalone...... best money youll spend... or atleast the best i did

fidelity101

iTrader: (11)

I dont have 1600 dollars, my car didnt even cost that much lol.

but no im just curious cause I got some mafs laying around and a the aem UEGO, safcII installed.

WingsofWar

+1 for standalone i wana run get rid of my AFM soon and run a 2step MAP...RAWR

Evil Aviator

If you are short on money then there is even more reason not to bother with this project. Even if you have parts laying around, there are still small costs like fasteners, wiring, wear on tools, etc. Also, the time that you would have spent working on a worthless project can be better spent working overtime at your regular job or at a weekend job. I would sell off the extra parts, too.

Yes, it is very interesting, and that project looks like a lot of fun. However, the S4 RX-7 still suffers from a horrible old EMS computer, no matter what kind of fancy MAF you rig to it. The S5 computer is twice the speed, but it's still not so great. I think newer cars like the Miata would benefit much more than the FC RX-7, assuming that they have a better stock computer.

It would be nice to figure out an easy way to rig a hot wire MAF sensor to a budget standalone EMS though. The nice thing about the hot wire MAF sensor is that it somewhat compensates for engine wear and minor performance modifications, unlike a speed-density system. I think the performance-minded people would still prefer speed-density, but those who don't want to re-tune their car every year or two probably wouldn't mind spending a little more on the hot wire MAF sensor.

NZConvertible

I quite like the look of this project. What really needs to be proved is how much more power is made from the reduced restriction. Given that you're only improving one small part of the inlet tract, and the new AFM will still cause some restriction, I wouldn't expect it to be much. It'd be very interesting to see the results.

A couple of comments on points in the article:

"People often want to replace the S4 air flow meter (AFM) because it is large, can cause engine hesitation, and is not easily ported."

Why do you claim it causes engine hesitation?

"It uses a mechanical flapper to measure air flow, so it is susceptible to bumps when oriented vertically -- and hard cornering when oriented horizontally."

Vertically yes, horizontally no way. The short-duration vertical accelerations experienced when going over bumps and road irregularities at speed are far higher in magnitude than the lateral acceleration encountered during cornering.

"This procedure may not work with S5's, because the AFM intake air temperature sensor appears to have more than one function on an S5, and it is not clear if S5s even have atmospheric pressure sensors."

The AFM temp sensor is only used to calculate mass airflow, just like the S4's. Nothing else. The S5's atmospheric pressure sensor is integral with the ECU so you won't be able to fix its value.

And let's keep this thread on the topic of airflow meters rather than EMS snobbery. We're all well aware how great standalones are compared to the stock ECU, and we're all equally aware of the significant cost of them. When a mod that might cost $100 is being discussed, why would anyone suggest a $2000+ mod instead? If it were that easy, we'd all have one.

stevej88na

Thanks!

Sorry to say I suspect the power improvement for me will only be noticeable on a dyno. Even so, I'd like to see this MAF flow benched at 15" like the S4 and S5 were for relative comparison.

I claim the engine hesitation because of the vertical bump/horizontal steering issue.

As you say, vertical accelerations are usually sharper impulses than horizontal accelerations, but I suspect the AFM is susceptible to horizontal accelerations as well. I can cause a hesitation every now and then on this slow speed right hair-pin corner: http://maps.google.com/?ie=UTF8&z=19...04227&t=h&om=1 (Golf Course Drive onto Shasta, the mapped streets don't follow the hair-pin properly, but you can see it in the satellite photo). Since it's a hesitation similar to what I experienced with a vertical AFM, I attribute it to the AFM as well. Still, I haven't proven it's the AFM, but I'm pretty convinced.

Ahh, thanks for the info! I'll update the article with that. Now I wonder if someone with a spare S5 ECU could look at the traces and see splicing in a constant voltage is possible?

twilight slide

good thing about hotwires, you can run blowthrough. I would like that. I don't know why the full throttle speed guys don't get a MAFT for FCs. . .

NZConvertible

I can't say I've ever experienced any hesitation issues in hard cornering, other than a couple of times turning left when low on fuel. My AFM is mounted properly, i.e. horizontal.

Even if you were able to affect the AFM's output with high lateral acceleration, it would only be a very small change and it would occur gradually as cornering loads increase. That's very different to the very sharp vertical acceleration you get when you hit a bump. A gradual change in AFR won't cause a hesitation (unless it goes very lean), but a rapid change in AFR can.

I imagine if this was an issue it would be very well documented by now, as the same AFM's were used on dozens of different models all over the world. It's certainly the first time I've heard it claimed here.

stevej88na

Good point, though I still wouldn't rule it out. Actually, partway through a response to this, I came to another theory that may be of interest: it may not be the corner's lateral acceleration, but the throttle input through the corner, that causes the hesitation.

Check out the bottom graph; there's a point where the flapper bounces by itself on the way to closing, at about 8Hz. Around 1/8 second after letting off the throttle, the flapper overshoots the actual airflow decrease, and it doesn't recover until 1/3 second. I bet that's incoming air bouncing off closed throttle plates and back at the AFM flapper. I also bet we don't usually notice the hesitation it can cause because by that point the throttle is within range of the TPS. Page 4-41 of the training manual says fuel is cut during sudden decelerations to prevent "bucking", and I wonder if the bucking they want to remove would be caused by this AFM bounce. In fact, the MAF - which I believe is a better look at actual engine conditions here, designed to be less susceptible to reverse airflow - continues to smoothly decrease its airflow reading while the AFM does its bouncing around; the engine is being controlled by something else, ignoring the AFM's antics, and probably partially because of this problem with the AFM.

Say I'm approaching a sharp turn, so I let off the throttle quickly. The intake air is still moving as fast as it was before letting off the throttle, so a reflection off the plates, whose amplitude depends on how much throttle I let off, travels back up the intake and smacks into the AFM flapper. If by that time I still have enough throttle applied to keep the AFM in the ECU's loop, I should feel a hesitation.

SureShot

What I've found is that the passage through the AFM is big enough.
The restriction there is still less than the compressor inlet.
My main problem with my cheap-o rig* was that the AFM hit 100% before 5K at WOT.
On the S4 you can shorten the spring to recalibrate the AFM for higher flow values.
Then you can use an S-AFC to tune the result.

As was said the best way around intake restrictions is a stand alone.

* Cheap-o rig: S-AFC, 255LPH pump rewired, 720CC secondaries, MBC, & an open dump right behind the turbine

StarScreaM2k1

Just a few thoughts...

-Like some said before go with a Standalone ECU (if you can, theres a few in the Classifieds)
-The Greddy E-Manage Ultimate (you can get them off ebay for about 300ish) and apparently those have the ability to remove the AFM (like a standalone would) so that would be an option
-Stick with the Stocker unless its causing you some problems or something, just stick with it. It works, its stock and it can handle 300+ HP.

NZConvertible

Nope, the bucking they're referring to is what happens when coasting down on a closed throttle. I'm not exactly sure why it happens, but anyone used to carbs (which continue to add fuel on decel) will know what I'm talking about.

Another cheap way that works for any AFM is to put in an AFM bypass, so not all of the air entering the engine passes through it. You then correct the fuelling with the S-AFC. Less air through the AFM means it can measure greater total airflows, and as a bonus intake restriction is lowered. Obviously careful tuning is required, but the same is true for retensioning the AFM spring.

The only intake restriction a standalone removes is the AFM. It doesn't help the turbo, intercooler, TB, manifold or ports, all of which are intake restrictions. And see my note about $100 mods vs. $2000 mods.

McHack

Wow, ingenuity in progress.... for a 20 year old platform. I've VERY impressed!

I think the entire 2nd Gen community would be keenly interested in seeing a real world test of this conversion.

Much kudos to Steve for taking this on!