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Old 05-22-2007, 09:20 PM   #1
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Default AFM- major restriction?

I searched and couldn't find an answer to this.

On turbo 944 porsches there are big hp gains had by swapping out the flapper style AFM for a MAF sensor and ecu reprogram for it. Is the flapper style AFM a major restriction on our turbo miata cars too?

If not great! I'm a happy guy. If it is, what solutions are affordable and workable?
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Old 05-22-2007, 09:29 PM   #2
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i didn't think so when i lost 4 hp & tq at 200 rwhp when i removed it for the 30% larger RX7 AFM.
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Old 05-22-2007, 09:31 PM   #3
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that was becouse it threw your fueling of the rich side Brain properly tensioned etc the rx7 afm should be capable of more cfm. cueball if the restriction worrys you get a MS and lose the flaper all together. I made plenty of good power on stock ecu though you should be fine.
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Old 05-22-2007, 09:33 PM   #4
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Magna, "should" is correct.
As far as can be researched, the stock AFM will flow more air than you can run boost with the stock ECU. Yes, it is a restriction, and guys see gains by going Link/MS and removing it... but I can't recall seeing anybody make a perfect tune on the stocker, then swapping in an RX7 for an equally perfect but more power-producing tune. I've got one for sale if you want to give it a shot. $25shipped.
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Old 05-22-2007, 09:36 PM   #5
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OOOh, too bad. Bigger isn't always better.

Could be the miata design flapper is better engineered than what Porsche used in the mid 80's.
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Old 05-22-2007, 09:38 PM   #6
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ok, then let's look at my AFR.....



Red is with the RX7 AFM; Blue is with the OEM AFM

the OEM AFM flows 300 CFM at 28 in. h2o...should be enough for a bit of power....dunno what the formula to determine the amount of airflow needed per HP....
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Old 05-22-2007, 09:40 PM   #7
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For now I'm sticking with stock ecu so I guess it's a moot point. It's good to know that with MS it can be eliminated though. When I get tired of my bandaid system, and want to really start breaking parts, I'll dump the AFM and start squirting!

Thanks for the quick answers!
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Old 05-22-2007, 09:51 PM   #8
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oh, looking back, when i said 4hp, i meant 2

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Old 05-22-2007, 09:54 PM   #9
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swap in some blue 1.6 injectors and that power will pick up trust me. The AF is way to rich.
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Old 05-22-2007, 09:58 PM   #10
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I would have rather not of had a 14:1 AFR between 3k and 5k, thank you.
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Old 05-22-2007, 10:05 PM   #11
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my runs showed 12.5-12.8-1 with oe fuel pump and my 12-1 and a80% h20/20% methanol blend at 190 or so cc/min past 4 psi.
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Old 05-22-2007, 10:31 PM   #12
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bumppercars.
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Old 05-22-2007, 11:04 PM   #13
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Quote:
Originally Posted by magnamx-5 View Post
my runs showed 12.5-12.8-1 with oe fuel pump and my 12-1 and a80% h20/20% methanol blend at 190 or so cc/min past 4 psi.

those runs are at 12psi, ive taken multiple logs, with 203cc and 265cc injectors and couldn't get any good midrange AFR with an acceptable high-end AFR, so the compormise was 12.5:1 from 3-5K and 10.8:1 from 5.5-7K
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Old 05-22-2007, 11:38 PM   #14
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Let me start by saying my information is based off a Supercharged application which means that I am pulling air through the AFM not pushing it, but ...

I found the AFM to be a restriction. Swapping to an RX7 AFM made about half a pound more boost with no other changes. My before and after dyno runs show about 10 HP difference, but I had also added an EMU so my A/F ratio was much better.

Read more about it here



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Old 05-22-2007, 11:52 PM   #15
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You are pulling air through an MAF with a turbocharger too.

And your post backs up my previous post that nobody has made back to back dyno runs with identical tunes and the only change being the MAF swap.

And I'm confused about the second part. You're saying you saw a hp increase after going EMU??? That's crazy talk.
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Old 05-22-2007, 11:52 PM   #16
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My RX7 afm was tuned was from the start, so that's why my AFRs are very close. I did nothing but pull the stock afm and replace it with a 2.5" to 3" coupler and the rx7 afm, plugged it in, and dynoed again. nothing else was touched, the runs were done within 2 minutes of each other.

I don't doubt it your results; however, it also looks like (12) runs were done in between the comparison with the addition of the EMU, and there is a significant change in the AFR.
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Old 05-22-2007, 11:58 PM   #17
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Sam, he meant pulling air through the throttlebody and into the engine vs. pushing it in with a turbocharger (his supercharger is after the throttlebody, after all).

What this means for a fixed-displacement pump like a supercharger is that upstream bottlenecks are far more evident when you can only pump a fixed amount of air per engine revolution.
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Old 05-23-2007, 12:00 AM   #18
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Old 05-23-2007, 12:11 AM   #19
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Quote:
Originally Posted by Brian View Post
Sam, he meant pulling air through the throttlebody and into the engine vs. pushing it in with a turbocharger (his supercharger is after the throttlebody, after all).
What this means for a fixed-displacement pump like a supercharger is that upstream bottlenecks are far more evident when you can only pump a fixed amount of air per engine revolution.
I don't get it. I understand the theory in the second sentence, but it says in his sig he runs a JSRC. They're still a hot-side install in this order, right:
Filter-MAF-intake-compressor-charge pipe-TB-intake manifold-runners-engine.

That would be sucking through the MAF and blowing through the TB. What am I missing?
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Old 05-23-2007, 12:24 AM   #20
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the TB is bolted onto the SCer....
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