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?

i didn't think so when i lost 4 hp & tq at 200 rwhp when i removed it for the 30% larger RX7 AFM.

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.

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.

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.

ok, then let's look at my AFR.....

https://www.miataturbo.net/braineack...d/rx7vsoem.jpg

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....

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!

oh, looking back, when i said 4hp, i meant 2 :rofl:

https://www.miataturbo.net/braineack...rx7_vs_oem.jpg

swap in some blue 1.6 injectors and that power will pick up trust me. The AF is way to rich.

I would have rather not of had a 14:1 AFR between 3k and 5k, thank you.

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.

bumppercars.

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

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

https://www.miataturbo.net/braineack/dynos/KIF_0392.jpg

https://www.miataturbo.net/braineack/dynos/KIF_0393.jpg

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.

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.

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?

the TB is bolted onto the SCer....

the supercharger has a throttle body pre blower. the tb before the intake mani is replaced with a dummy tb

that's why you always hear about the "throttled volume" issues with superchargers and not turbos

The fixed displacement pump is the biggest difference with a super. If flows a fixed CFM relative to engine RPM at whatever the inlet pressure is. If you lower the pressure at the super's inlet, you flow less air mass, and get less boost and less power. With the turbo, less inlet pressure will just cause less drag on the compressor wheel, causing it so spin faster, and still suck in nearly the same amount (mass) of air. The boost on a turbo being controled by a wastegate also ensures you still get the same boost pressure even with more intake restrictions. You will need more pressure in your exhaust manifold to generate that boost and you will loose some power, but not nearly as much as a super charger would.

Super chargers are much more sensative to air restrictions before the inlet of the pump, which is why a more free flowing AFM has more effect on them.

I never knew that about the JR setup. It makes some sense now.

https://www.miataturbo.net/forums/at...6&d=1179892018

that's superchargers in general, not just the jrsc.

From reading this forum it's my understanding there are a lot of dummies with superchargers. Now we know that sc's have dummies x 2.

There are only two ways I know of to really tune an AFM. One involves a dyno and a spec Miata shop and they make 'adjustments'.

The other way is described here:
http://forum.miata.net/vb/showthread.php?t=144196

The 'frankenmeter' is sitting on my shelf and is still available. (I don't have enough posts yet to use the classifieds, sorry!)

No at 8 psi not with MS though with the stock ecu and RRfpr. I essentialy just maxed what the stock injectors where good for. This was with the stock AFM BTW.

You are correct. It was not back to back runs showing horsepower changes. We were talking about restriction. The increased boost especially on a supercharged application is evidence of removing the restriction. You can see by the air fuel lines that considerable tuning changes were made between the two runs. Turning up the boost in supercharges only happens with changing how fast you spin the blower OR how well the blower can get the air. The comparison of boost values is a direct comparison of the restriction of the air flow meters and air filters. The dyno runs were not done for the sole purpose of measuring the efficiency of the AFM but do show some empirical data. The link shows further restriction evidence from removing the AFM completely although that data is based on EMU logs not dyno runs.

To summarize what I was trying to represent, the supercharger saw less restriction with the RX-7 AFM as evidenced by the increased boost pressure.

I believe it form the blow-through perspective, and even on turbo setups because talk of increased boost without and AFM or a larger one (i never really paid attention).

but I think on a turbo setup, since only a bit of vacuum even exisits behind the AFM at something like 12psi, it's not a big deal.

I believe the results of DIY auto tune and link showed that afm removal made about a 10% difference in stock trim with out major timming changes, and just some more sorted fueling. So in short the only reason for rx7 afm is to modulate fueling better. I love to hear the noise of my intake sucking in the air from my filter. :D even with the AFM installed