12 replies to this topic

[Justin Baltrucki]

I have seen lots of posts about opening and adjusting the 1.6 AFM. I have been tuning mine by increasing the clock spring pre-tension.

Stock AFM the AFR was in the 9's above 6 grand and I have it into the high 11's now, and will likely go even higher.
The issue I am having now is that it won't idle very well with this setting.

I know there is a bypass adjusting screw under a metal cap on the top of the AFM.
Is it legal to drill out the cap and adjust this bypass screw?

I believe it would be legal, however I have not heard this mentioned before and i don't want to irreparably modify my AFM.

Thanks

[davew]

This may be considered a biased opinion, because I sell the adjustable regulators, but here is my 2 cents

Any adjustment in the air flow meter is only to fool the ecu into thinking less air is being used. By the time you get the AFM tuned enough to get the number you want at full throttle, the idle numbers are too far off.

My method is to run an unmodified Air flow meter and make all your adjustments with an adjustable fuel pressure regulator. Your idle quality will be normal as will cold start drivability.

Dave

[James York]

Its been a while since I have had my 1.6, but first thing is I would let the experts adjust your AFM.

But if you are set on doing it, I will offer these observations. Your AFR sounds way too rich (9:1), even for a factory AFM. Are you sure of it, or is there something else an issue with your car? I would get 11s with a factory unit.

Second, just tightening up the clock spring to keep the flapper from opening as far, is the WRONG path. You are creating a choke point and essentially limiting your air to the engine. Yes it will improve your AFR, but you are cutting down air/power. In AFMs I had adjusted the door had much less tension than factory and but had the contact position reading the door position adjusted to permit the correct AFR. It's been too long since I have looked at the inside of one, so I forget the exact details of adjustments

I would say driiling your AFM, ie modifiying, is illegal as that is not an adjustment to the unit. But that is just my opinion.

Third, you can get a kit like Dave mentions and leave the AFM alone.

[Todd Green]

I know there is a bypass adjusting screw under a metal cap on the top of the AFM.

There is an idle screw under a rubber cap on the intake side that you can use to adjust your idle after messing with the AFM. You shouldn't have to drill your AFM unless I'm not understanding your issue (or you are saying you cannot adjust it enough with the IAS):

http://www.miata.net/garage/isc.html

[davew]

As Todd says, there is a screw on the throttle body that acts like a needle/seat valve. Opening the screw (counterclockwise) will increase the idle speed as it creates a larger bypass area when the throttle plate is closed.

Make sure to adjust this when setting timing to +/- 900 rpm

Dave

[Bench Racer]

Justin, IIRC previous to 2011 an adjustable fuel pressure regulator was not legal in Spec Miata. Pre 2011 people used bluprinted AFM and now that the adjustable fuel pressure regulator is legal people use a normal AFM and an adjustable fuel pressure regulator. The AFR numbers and Dyno numbers tell the difference of the two process.

[Justin Baltrucki]

As Todd says, there is a screw on the throttle body that acts like a needle/seat valve. Opening the screw (counterclockwise) will increase the idle speed as it creates a larger bypass area when the throttle plate is closed.

Make sure to adjust this when setting timing to +/- 900 rpm

Dave

The bypass I am speaking of is an air bypass around the AFM flapper door. This is inside the AFM itself under a round metal anti tamper cap. This allows air to bypass around the flapper door in the AFM. More bypass around flapper = leaner idle. It is used purely for idle AFR adjustment at the factory. I want to close this down so the idle airflow pushes the flapper door more at idle and provides a better mixture at idle.

I am running SSM and I beleive that the adjustable fuel pressure regulators are still illegal for 2012. In a perfect world a combination of the 2 would shape the ideal AFR curve. I imagine that the AFM modification provides more ignition timing up top as the ECu will show a lower air flow value and increase the timing. For classes with limited idle timing values a more agressive timing curve from the AFM adjsutment may make more top end power than a fuel pressure only adjustment.

I was also surprised to find my bone stock baseline that rich at high rev's. The AFM was sealed when I got it, and everything else appears unmodified. I had a fresh wideband sensor that calibrated correctly and read ambient air on decel. I beleive I am at 8 teeth tighter on the AFM spring to get into 11's for AFR. Remember SSM = stock airbox,16 degrees max timing at idle, I just have an old mazda crate engine, but it seems to pull even with some of the other SSM's.

I agree that more clock spring is more resistance to airflow, however bending the wiper arm and softening the spring to compensates violates the "open and adjust, but not modify".
I feel that the idle afr mixture should be allowed as its an adjsutment, I just wanted to know if anyone else had done this and if they had issues.

thanks

[Sphinx]

Justin, IIRC previous to 2011 an adjustable fuel pressure regulator was not legal in Spec Miata. Pre 2011 people used bluprinted AFM and now that the adjustable fuel pressure regulator is legal people use a normal AFM and an adjustable fuel pressure regulator. The AFR numbers and Dyno numbers tell the difference of the two process.

Can someone tell me what this "blue printing" involves? Reliable sources told me that it is actually a change on the circuit board that's inside. No?

[High Chair]

Can someone tell me what this "blue printing" involves? Reliable sources told me that it is actually a change on the circuit board that's inside. No?

There are those that run modified AFMs in 1.6L cars and yes it involves a bit of solider and no it's not legal. That does not keep people from doing it or one engine builder who shall remain unnamed from doing it and providing them to his customers. It does work and will keep the AF ratio flat all the way across. I can tell you this; it is easy to tell which ones are modified from the sound of the car and it is easily protested. Dave has the right approach in my opinion; fuel pressure seems the way to go with the 1.6 with maybe a little tweaking of the AFM itself. That is what I have seen as of late and the numbers are better than just playing with the AFM, as is the drive ability.

[Jim Drago]

We sell blueprinted AFM's that are not soldered that are definitely better than stock or spring adjustment, they are listed on the store. If it were my car.. I would put a good AFM on it or a FP regulator and see what you got first. I think the best results will require a little bit of both. That being said, Buras's 1.6 was good out of the box, zero adjustment to blueprinted AFM other than rotating to about 45 degress with the the spin bracket and no FP regulator. I also have a hard time believing you are in the 9's? I would certainly double check ratio as you could melt the car down easily if that number is incorrect.

[SaulSpeedwell]

We sell blueprinted AFM's that are not soldered that are definitely better than stock or spring adjustment, they are listed on the store. If it were my car.. I would put a good AFM on it or a FP regulator and see what you got first. I think the best results will require a little bit of both. That being said, Buras's 1.6 was good out of the box, zero adjustment to blueprinted AFM other than rotating to about 45 degress with the the spin bracket and no FP regulator. I also have a hard time believing you are in the 9's? I would certainly double check ratio as you could melt the car down easily if that number is incorrect.

90% misinformation in this thread, but Drago is pretty close to 100% right

Adjustable FPR only is perfectly fine up to a point, but this neglects the fact (and I do mean fact) that the AFM is a "restrictor plate" above a certain flow - on my local Dynojet (the same one you see at most of the Runoffs and NASA Champs), that happens around 116-117 HP. To make power above that level you NEED a *properly and legally* adjusted AFM.

The AFPR is absolutely useful, will be better than a stock AFM, and is easier for shifting the curve up and down - but reshaping the curve and eliminating the restrictor plate effect can ONLY be done by *properly and legally* adjusting the AFM.

Tightening the spring tension will only make the RP effect worse - because you are robbing Flow Paul to pay Lean Peter. You will make more T/HP than "stock", but you will simultaneously limit your potential to 116-ish DynoJet HP (OH weather and pump gas). You need to detension the door and then jockey the board and wiper to net out at a leaner tune than stock. This requires quite a bit of iteration, a relatively deft touch, and cost you more in dyno time and motor blowup opportunity cost than if you simply buy a *properly and legally* tuned AFM.

Best T and HP won't be anywhere near correlated to "flat" or theoretically ideal A/F ratio, but until TIming and Scoring starts giving awards for Best Theoretical AFR, you shouldn't worry about it.

I've seen the results of the "perfectly flat A/F Ratio" version of AFM that, presumably, is being referred to above - the A/F Ratio was indeed perfectly flat, but the driveability AND the Torque and Horsepower were atrocious. That car picked up 3-4 T and HP when the AFM was replaced with a *properly and legally* adjusted AFM. If you ever see the 1.6 fuel and timing maps (or check for full advance on a car running the "perfectly flat" AFM) you will see why.

[Jim Boemler]

Can you give a description of the "properly and legally" tuned AFM, since you see it as so crucial? Given that until recently AFMs were adjusted with the idea of running at stock fuel pressure, are those earlier adjusted AFMs no longer "proper" for adjustable fuel pressure? What difference would you expect?

[SaulSpeedwell]

Yes, but you seem to be mistaking my attempts to be clear and accurate as being an indication of 'crucial'-ness. I was simply trying to distinguish my comments from those related to illegally modified and/or improperly adjusted units.

No.

Minimal, depending on how far the car is off of the usual spec (39 psi).

New trend: 1 of 5 cores I see are damaged from hamfisted adjustment. Also, many have suffered corrosion inside - if you are not going to do any final dyno tuning, and you live somewhere moist/tow the car open/race in rain, you should be making some attempts at resealing the cover.