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Cheap alternative to Z32 Airflow upgrade???

Rowdyr32

By Rowdyr32,
in Engines & Forced Induction

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Rowdyr32 Mentor

Rowdyr32

Posted
Posted

Me and a mate were talking and came up with this as a possibility, think about it before you say "no way", informed replies are what we're after!

On to the idea.

Okay the reason you add a Z32 AFM is to reach the full 5V on the sensor slower than the stock AFM, the Z32 does it slower because it has a larger diameter pipe and therefore less air passing over the hotwire cooling it down.

So why not have a pipe bypassing the AFM from the airbox to anywhere before the turbo? The larger the pipe the higher percentage of air not going over the sensor, and fooling it in much the same way a boost controller affects the wastegate.

So anyone out there tried this? Gotta be a damn site cheaper than ~$300 for a Z32 AFM. If we've absolutely missed something come tell us why it wouldn't work!

- Rowdy & Oosh.

rev210 Grand Master

rev210

Posted
Posted

the afm is measuring (acurately) the airflow/change in airflow. The bypass itself will have it's own flow charateristics which the afm will not account for in it's reading, and not end up in fuel and or timing adjustments.

On the cheap side, you can use the new Apexi S-afc II to run a Z32 AFM instead of going the whole hog ecu upgrade.

Rowdyr32 Mentor

Rowdyr32

Posted
  • Author
Posted

Yeah you'd have to remap your chip, i thought that was obvious, sorry.

But you have to remap it for a Z32 just as you would any other alteration to the airflow. But once you're tuned to the characteristics of a stocky with a bypass then they'd stay the same it'd be good from there would it not?

Rowdyr32 Mentor

Rowdyr32

Posted
  • Author
Posted

So basically you don't know, and in T0nyGTSt 's post he says there's a 10mm difference in diameter (70mm vs 80mm), that equates to 30% more area.

And just coz it aint been tried (to your knowledge) doesn't mean it doesn't work, how'd you think people find this stuff out in the first place?

Edit:

Added rant :(

Clint32 Mentor

Clint32

Posted
Posted

The size is not the difference between the different afm, its the voltage they send for a certain air flow. By setting up what you propose they would be no way to accurately controll how much air went through the bypass pipe. While the engine/turbo may always recieve the same amount ofn air the airflow meter may have different amount passing through it and the engine would never be tuned correctly.

edit. I dont know if tony gtst has actually measured them both, i know from memory after fitting both they were the same size.

Rowdyr32 Mentor

Rowdyr32

Posted
  • Author
Posted

The flow rates in each pipe would be percentage based, depending on relative sizes and mouth properties (a bell mouth sucks better).

Pick someones brains with knowledge about flow dynamics (so i'll have a chat to dad soon) and you should be able to work it out. And as i said before once you've mapped your ECU to it, all done!

Edit:

edit. I dont know if tony gtst has actually measured them both, i know from memory after fitting both they were the same size.

That's assuming you didn't get stooged, if they bolt staright up and no size difference, just what IS the difference between a RB20 and Z32 AFM?

Rowdyr32 Mentor

Rowdyr32

Posted
  • Author
Posted

But why, it's not sampling horsepower, it measures air.

They both have a max output of 5V, i understand if a Z32 has a higher resolution, but that still doesn't invalidate our theory.

It'd still work, maybe not as well, and since you've still got the stock ECU (just re-mapped) a higher sensor resolution wouldn't be usable anyway.

rev210 Grand Master

rev210

Posted
Posted

The problem is flow reading accuracy. The AFM is even more sensitive than a MAP based sensor system and has its benifits especially in low end fuel ecconomy.

flow rates will not be percentage based BTW. they vary against more things than you can poke a stick at, most of them are logarithmic and not linea relationships.

SLY33 Mentor

SLY33

Posted
Posted

Its an interesting idea and you guys seem quite excited about coming up with possibly a new solution to z32 replacement.

my question is, how much power are you chasing, or planning to make?

Apparently lots of people want to "upgrade" to z32 AFMs, when most of the time its not even necessary.

SLY33 Mentor

SLY33

Posted
Posted

To quote Mr HPI himself, Martin Donnon:-

"other than on CA18 or SR20's there is little raw airflow value to be had in changing AFM's. There are all sorts of black magic rumours that the 300zx 80mm AFM has some sort of beneficial effect on engine power, but the reality is that it doesnt."

"the only reason you would ever substitute a Z32 AFM is in extreme high-boost applications where its calibrated range is higher than that found on the RB20 or RB25. At 1.5bar on, you have slightly better chance of tuning with the Z32 unit, but thats about it."

"If you have an RB20/RB25 powered car , dont rush out and change the AFM for the sake of it. All you will end up with is a massive tuning problem"

Clint32, it seems you are right about the AFMs from 32's and 300zx's both being 80mm, and not 70mm on the 32. (according to HPI mag)

rowdy, while its not exactly answering if your idea will work or not, i found the article interesting as many people inc myself seem to be a bit confused about the whole jist of changing AFMs, and thought it could be useful to readers of this thread.

cheers SLY33

Roy Grand Master

Roy

Posted
Posted

They both have an output of 0-5V but what mA??? I think this is why the Z32 unit maxes out at a higher hp figure.

As for bypassing the AFM with a pipe, that flat out wont work. Any air the engine is going to be asked to compress needs to be measured by the ECU. This way it knows the amount of fuel, required injector cycle etc . By passing it means it wont know to allow for the additional air.

As for tuning the ECU to run richer to allow for air bypassing the AFM, that would mean you would have to make another adaptor after the airfilter but before the AFM, (or install another air filter for that pipe) .

Also i suspect it wont be able to be tuned nicely as when the turbo isnt spooling, i suspect the low vacuum in the bypass line may help the engine stall as it would effectively be seen as a leak in the inlet tract after the AFM but before the turbo. (Nothing to stop the air from going out the bypass intead of into the turbo/IC/throttle body.

I think a cheaper method may be grabbing an AFM off a larger displacement car like an L98 350 Chev and seeing if the wiring can be woked out. Either way a change to the AFM means you will require a change to the tune of the engine EC.

skyr33 Contributor

skyr33

Posted
Posted

Airflow meter bypass is mentioned briefly in J.Edgars 21st Century Performance and there is also a pic.It goes without saying that you will also need to remap your ECU.But its the same deal with Z32 AFM.Even though both R33 and Z32 AFMs have 0v-5v operating range, Z32 AFM has different calibration,which means that for a given amount of air it flows,it will output less voltage compaired to R33 AFM.Connecting a resistor to R33 AFM will reduce its output voltage,but the moment AFM maxes out, the output voltage,albeit less then 5v(because of the resistor),will probably stay the same no matter how much more air will be drawn into the engine.Not a good idea.

Rowdyr32 Mentor

Rowdyr32

Posted
  • Author
Posted

Okay so we have:

* A few, maybe but hard to tune.

* A flat out NO.

* Been done/discussed already.

skyr33

Airflow meter bypass is mentioned briefly in J.Edgars 21st Century Performance and there is also a pic.

Thank you. Looks like a trip to the library is in order.

SLY33

Clint32, it seems you are right about the AFMs from 32's and 300zx's both being 80mm, and not 70mm on the 32. (according to HPI mag)

Tony said the R32 AFM = 70mm and Z32 = 80mm.

Roy

As for bypassing the AFM with a pipe, that flat out wont work. Any air the engine is going to be asked to compress needs to be measured by the ECU. This way it knows the amount of fuel, required injector cycle etc . By passing it means it wont know to allow for the additional air.

As mentioned we don't expect to get away without a re-map of the chip, and that'd fix it. If the car is gettin x amount of air, but the ECU thinks it's getting less it wont be a problem so long as your map compensates for it.

Roy

As for tuning the ECU to run richer to allow for air bypassing the AFM, that would mean you would have to make another adaptor after the airfilter but before the AFM, (or install another air filter for that pipe).

As mentioned earlier the idea is to run the bypass pipe from the airbox to after the AFM.

Roy

Also i suspect it wont be able to be tuned nicely as when the turbo isnt spooling, i suspect the low vacuum in the bypass line may help the engine stall as it would effectively be seen as a leak in the inlet tract after the AFM but before the turbo. (Nothing to stop the air from going out the bypass intead of into the turbo/IC/throttle body.

This doesn't seem to make sense to me, NA cars still suck air, and how is two pipes going in to one (bypass and AFM) any different from two throttle bodies into one plenum? That works.

Roy

I think a cheaper method may be grabbing an AFM off a larger displacement car like an L98 350 Chev and seeing if the wiring can be woked out. Either way a change to the AFM means you will require a change to the tune of the engine EC.

How is that cheaper, buying an AFM, working out the outputs, making new electronics for some sort of interface. As opposed to a bit of pipe, a T piece, and a re-map? BOTH would still need a re-map as well ofcourse.

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