Lexus AFM measurements -- only 15% larger?

[twinturbozs]

I also posted this on Supraforums.

I did some quick measurements of my Lexus AFM compared to the stock AFM. I measured the mesh side of the AFM's.

Lexus AFM
width = 2.98"
length = 2.58"

Total area = 7.6884


Stock AFM
width = 2.82"
length = 2.38"

Total Area = 6.7116


According to my calculations the Lexus AFM is approximately 14.5% bigger. Now i dont know anything about fluid dynamics so i dont know how a total surface area of 14.5% more equals into air flow % gains.

What i did notice is the lower portion of the Lexus AFM has a much larger area of unmetered air compared to the stock AFM. Another quick calculations of the unmetered area on both led me to these approximate #'s

Lexus AFM unmetered area: 2.98x.49 = 1.46
Stock AFM unmetered area: 1.11x .27 = .2997


So my conclusion is, how much more flow does the Lexus AFM allow, but how much is actually metered? This may explain why some of us are experiencing stalling issues more frequently than the stock AFM.

 

[jetjock]

Bad math...or I should say wrong math.

 

[bentandbroken]

In fluid dynamics, the volumetric flow rate, also volume flow rate and rate of fluid flow, is the volume of fluid which passes through a given volume per unit time.


You should be calculating volumes; not areas. Lenght X Width X Height or the appropriate formula(s).

 

[mkIIIman089]

My car has never stalled running a Lexus AFM...

 

[Spiv]

Actually, he's quite correct. The volumetric flow is determined based on the area of the crossection where the metering system resides.

Given that, you only get a 14% change in how your system is actually metering (which is ok, because the TCCS will compensate), but the rest of the 10% is from the unmetered portion (meaning you could just pull a hose on the accordian pipe to get the same effect).

Really you're using the same electronics, and the same scaling (until the TCCS takes care of that), so your electronics in any sized housing other than stock is the equivilent of "unmetered air." It just happens to be coming through the same air passage as your AFM electronics, instead of having a little sperator in between. BFD.

 

[jetjock]

Neither has mine. Runs same as stock. For the other poster you're getting warmer. The appropriate formula is not the one posted though

 

[Spiv]

it's a function of the velocity through that area (since that's basically how the AFM operates, I could get into more detail, but you can probably look it up too). Since density, area, and velocity are all related, they make some assumptions about he density (and adjust when they're a little bit off, as in the whole sea-level vs mountains issue).

Your equation is dAv=n, if your constant is the same, and d is roughly the same (obviously pressure drops from sucking in air, but that's basically built into the map), then as you lose area, you gain velocity and vice versa. If your area is 25% larger, your velocity is 25% slower.

So yeah, overall the lexus AFM is 30% larger, which is close enough, considering 550's are actually 25% larger than stock.

You also get some change from basically drawing through a venturi, and you could bust out a much larger equasion to get yourself another % or two closer to the exact numbers, or you could not worry about it (which I believe is what the TCCS does) and just built it into your map.

edit: but yeah, if there's more to how the tccs calculates, I'd love to see the equation. I'm in the process of converting to a different sensor, anything of the sort would be really helpful. In the mean time, I've read basically everything I could find from toyota or otherwise on the matter.

 

[Doward]

So is he right, JJ?

The KV meter, to my understanding, is based on velocity. The frequency that the meter puts out is proportional to the vortices measured via the optics inside, right?

Same volume moving through a larger pipe = slower velocity.

 

[jetjock]

Yes, he's right. Especially about area versus velocity which is, as he pointed out, how the thing works. Seems many don't understand that even though it's basic FD. Another thing I see many don't understand is the different purpose the bypass chamber screw serves on the vane type flow meter as used on the 7MGE versus the one on a GTE. One is effective for idle mixture adjustment while the other is not. The reason lies in the vane meter presenting a restriction at idle while there is none in the Karman. It's why the factory setting of the screw is stamped into the body of the vane type but not the Karman.

It also helps to remember the TCCS doesn't know squat about airflow itself. It only knows frequency. After all, the AFM is nothing more than a transducer. When dealing with the TCCS it's best to think in terms of signal and treat the transducers as a separate issue. That works best for me at least. Finally, body dimensions aside, the formula for Karman generation is F = .2 x V/D where V is velocity, D is diameter of the Karman pillar, and .2 is a constant.

 

[Turbo. Targa. Life.]

JJ, you always manage to fry my brain with every post you make...I love it!!

 

[twinturbozs]

So what is the purpose of the REG reimer screw on the lexus AFM? Is it to prevent more unmetered air bypassing the sensor?

 

[Nick M]

JJ, autoshop said the 2JZGE is on the KV, not VAF. The PM comment was incorrect.

edit:

The purpose of the screw is to change the amount of air is being read by the meter. This changes the frequency, delaying fuel cut.