[tvsn94]

I am working om a new turbo project and will be needing a slot maf for a blow thru. shopping around i find that Hitachi appears to be a main manufacture for stock units with pricing of $30-60. I have used an HPX , $200+. unit in past setups and am now wondering where the HUGE price diff comes from and how they get the extra range, and since it seems obvious they aren't making there own wondering what is there modification ?

[skunk]

I imagine the price difference comes from the huge production numbers required for stock units.

I wouldn't try to use a stock unit for your intended application. It will peg. The aftermarket ones are modified to allow for more air to be measured within the 0-5 volt constraints usually scaled based on ECU and injector size.

It is possible to send a stock unit in for a re-calibration but it may be the same as buying a new one.

John

[cgrey8]

This is all true. Stock units are calibrated to deliver higher voltages for the same cross-sectional airflow as compared to the HPX.

The convenience of the HPX units are that you can use them to measure higher flowrates in smaller diameter tubes. You probably COULD use a stock unit if you could figure a way to plumb in a 4-5" tube to increase the cross-sectional area the MAF is measuring and thus prevent the sensor from pegging. The HPX would do the same job in a 3" tube without pegging. That's why you are paying more for the HPX.

[tvsn94]

yeah i have used them ( HPX ) just this way and for those reasons, what my curiosity is, how do they rework the stockers?? for $200 i might give it a try

[skunk]

If what your saying is you want to try and recalibrate a stock unit yourself, I hope you have some mad electronic skills to rework the output. I wouldn't even bother trying to modify the signal after the Maf....there have been many MAF type extenders that have come and gone. Since the MAF signal is of great importance $200 is money well spent.

If your looking for some basic information I know I've seen a drawing somewhere online of the internal circuit. ....you just need to search for it.

Good luck
John

[cgrey8]

If I had to guess at what they are doing, it'd be replacing a resistor. However as he said, it's not an off-the-shelf resistor. It's custom resistors they are putting on that have precision chosen to work with a given MAF. In the old days, precision resistors were literally ground to get their resistance correct.

[tvsn94]

OK, guys you have settled my curiosity for now. THXS
that bit about grinding a custom resistor is fascinating. peaks my curiosity again. LOL

[85GT]

The curve is a function of how much air the sensor read vs the actual air. A larger tube makes it 'read' less for a give flow. You could try the opposite. If you reduce the sensor's opening to read less air, you're get the same thing...

[cgrey8]

OK, guys you have settled my curiosity for now. THXS
that bit about grinding a custom resistor is fascinating. peaks my curiosity again. LOL

They do something similar in most any volt meter that also has the ability to measure current. There's this thick wire that's on the circuit board that the current flows through and you'll notice somewhere on the wire, usually right in the middle or some other convenient-to-get-at-area, there's a crimp in it. That's where each meter gets calibrated to get its current reading correct. The crimp is the fast/production way of just slightly altering the resistance of that wire so that the meter is reporting the current accurately. If you want to see for yourself, get one of those cheap give-away volt meters from Harbor Freight and open it up to see what I'm talking about.

[85GT]

Yep. That was one of our high school projects-making different meters. Back then when it was just analog panel meters, they were all basically 0-50uA meters. We'd have to figure out what resistor to put in series to make it a voltmeter for the range we wanted and then similarly figure out the right parallel resistor for the current range we wanted.

[tvsn94]

OK i get the air flow velocity thing in tube size, but thats not always practical, and i get that altering the window opening could effect same. but the resistor change,,,,,could it be added into a pigtail at the connection??

[cgrey8]

Not likely. MAF sensors are complex beasts. They heat a wire to a specific temperature and then measure the amount of current it takes to keep the heated wire at a specific temperature. The more airflow across the wire, the more current it takes to keep the wire heated. I think other MAF designs use something similar to a strain-gauge in combination with an outside air temp sensor. Regardless what the physical sensor mechanism is, the electronics are managing 3 different things.

• Monitoring the sensor temp
• Controlling the electrical current to the sensor based on a desired temperature target.
• Translating all that to produce a 0-5v signal that is sent back to the EEC.

The mods the aftermarket MAF guys are doing to the electronics are not in the area that sends the voltage back. The sensor still needs to be able to produce that 0-5v signal. Putting an in-line resistor in the MAF harness would reduce the max potential voltage producible which is not what you are trying to do. It'd be like putting a resistor in between your audio amp and the speakers.

So lets walk through a scenario...and I'll use made-up numbers here. A stock sensor might max at, say 4.5v which might be 1000kg/hr. On the aftermarket sensor, 1000kg/hr might be 3.5v. The aftermarket sensor might have the same 4.5v max, but at 4.5v, the flow rate is 2500kg/hr thus allowing you to sense higher flowrates without having to increase the diameter of your plumbing. Putting a resistor in-line with any of the wires going to the MAF would simply prevent the MAF from being able to produce a 4.5v signal back to the EEC. Does that make sense why that's not the right thing to do?

But if increasing the diameter of the plumbing is a possibility AND is preferable to you over buying an aftermarket MAF sensor, then you can do that too. Although most people find having 4.0-4.5" pipes to be a bit much to work with and if they can buy their way out of having to do that and thus keep their 3" intake pipes using an aftermarket sensor, that's the easier route.

[tvsn94]

wow, you are good and you cut to the chase..THX, and yeah that explanation makes sense. As you can tell i am NOT electronics smart , but i can follow a good rational discussion.
the large tube setups will work on a draw thru and can normally be used . but blow thru's are a whole nother problem. i have used both ( 351 supercharged & a inter-cooled turbo setups) the big tube idea wont fit most turbos and give noisy signals. my go to has been the HPX maf but i sure would like to save the $$ if I could figure it out Thanks again

[motorhead1991]

wow, you are good and you cut to the chase..THX, and yeah that explanation makes sense. As you can tell i am NOT electronics smart , but i can follow a good rational discussion.
the large tube setups will work on a draw thru and can normally be used . but blow thru's are a whole nother problem. i have used both ( 351 supercharged & a inter-cooled turbo setups) the big tube idea wont fit most turbos and give noisy signals. my go to has been the HPX maf but i sure would like to save the $$ if I could figure it out Thanks again

You just have to get creative ;)

[cgrey8]

Blow-thrus are a whole different ballgame mainly because the "ambient" temp is much higher than realistic temps. So a normal sensor designed for draw-thru or N/A setups is not designed to deal with the air being much about say 120-150. And once the heavy airflow begins, usually the air temp becomes very near what the outside air temp is. So unless you are in Arizona in July, it's just not likely it'll have to deal with much above 120 degrees at WOT. But in a blow-thru scenario, you are probably lucky if 120 is your boosted air temp. Temps on the pressure-side of boosters can get way on up there, so the MAF has to be capable of sensing the air-temp. Also the temp it is maintaining the heated wire at has to be high enough so that the airflow will cool the wire.

There's a reason why HPX charges what they do. I'm all for finding alternatives to save money. But this isn't one of them particularly in blow-thru setups. BTW, HPX isn't the only aftermarket MAF mfg out there that deals with this and does a good job at it. They are just the only one I know of for aftermarket slot-style MAF sensors.

[skunk]

Putting a resistor in-line with any of the wires going to the MAF would simply prevent the MAF from being able to produce a 4.5v signal back to the EEC

I have always wondered about the idea of reducing the input voltage to the sensor to slow but not reduce the output. I imagine there is already a voltage limiter built into the circuit to maintain accuracy over varying battery voltage available at any given time. My thoughts are it may be possible to reduce and hold input voltage low enough to require more airflow to output the same 0-5v signal. I recall a diagram showing a few Op-amps in the circuit so it may be just a matter of keeping above the working threshold...... I have no idea if my logic is correct....I have forgotten much of my basic electronics.

John

I am not suggesting this is an option.....only a curiosity.