Airflow Meter Options/opinions

[mawzy]

Hi all, just doing some upgrades to car and wanting to see what ppl think after hearing few diffrent opinions.
I'm topmounting a new turbo which has a 4 inch inlet to my 25det, (along with supporting upgrades). I have an apexi pfc to tune with, and as far as I'm aware you can use any nissan airflow meter with these. Is that correct? I have the factory airflow, from what I understand that will become a restricting factor and want to upgrade this. I have a vh41 airflow meter but I've been told they're not as good as a 300zx meter. What are ppls thoughts and facts around the two?
Another thing I'm looking to do is cut the sensor out of the tube housing, if that makes sense and direct fit it to the alloy intake pipe. In doing this does this give me other options? Is there any reason I can't use the factory 25det sensor in a 4inch pipe? It'll still be reading air speed but there'll be more quantity at any one time. But having a complete tune, will this not be accounted for? Any thoughts , advice, opinions will be greatly appreciated.

[89CAL]

You can account for the extra air mass with the power fc. You just have to know what your doing

Are you sure its a 4" inlet to the Turbo and not a smaller inlet with port shrouding or surge slots etc? (Is the diameter of the wheel for the Turbo 4" because I don't think it will be)

In this case you can use a 4" - 3" reducer on the snout and a z32 afm and shouldn't really have an issue unless you push past what the AFM will meter

[mawzy]

Hi, yes I think you are correct has the anti surge slot etc around it. I might have made the mistake here and ordered 4inch join and pipe to suit then. And are you saying it is ok to use a sensor in a slightly bigger diameter pipe like I'm suggesting? No I won't be tuning this, and no I won't be driving round on it before it's tuned. Just wanting to do as much of the spanner work that I can to save some dollars.

[Hadouken]

Or just run map

[robbo_rb180]

maybe try the r35 sensor http://www.skylinesaustralia.com/forums/topic/409392-r35-gtr-air-flow-meter-the-new-z32-afm/

or have a chat with who is tuning your car

[mawzy]

Don't think there is an option for a map sensor with this model pfc. I thought that was just the d jetro model. It seems like the zx meter is a better option? Is there a reason why the actual sensor can't be retro fitted to the 4 inch pipe? Will this cause other issues?

[GTSBoy]

You have to understand what it is that the AFM sensor does. It does not directly measure mass flow of air. It is a hot wire anemometer, which measures air velocity. When any given AFM is designed, they put the sensor into any given pipe size (so, ~3" for many of the Nissan ones) and then range the sensor so that it gives a known voltage output for a given, separately measured mass flow rate of air. Because the pipe size is fixed, any given velocity of air measured at the sensor location will always equate to a given amount of air flow.

Note that the hot wire anemometer, by its very design, accounts for temperature and density differences in the air flowing through the pipe. So it is self correcting in that regard. In that sense, it is actually "sensitive" to mass flow.

BUT......take that same sensor and put it in a 4" pipe and now the flow area in the pipe is 78% greater than before. The AFM will read a given velocity and tell the ECU that X amount of air is flowing, but the actual amount of air will be 1.78*X. This would be very bad.

Some ECUs make it easy to rescale the voltage output of an AFM to a different airflow rate. It is fairly easy with Nistune. I think it can be done in a PFC, but as has already been said, you have to know what you are doing.

[89CAL]

As above. You can tune around it in the power fc when you put the sensor in a bigger diameter pipe but you have to know what your doing and its a bit beyond me

Measure the compressor wheel. If its only 3" you shouldn't have a problem running a z32 AFM as long as it doesn't push over 350rwkw

[1400r]

maybe try the r35 sensor http://www.skylinesaustralia.com/forums/topic/409392-r35-gtr-air-flow-meter-the-new-z32-afm/

or have a chat with who is tuning your car

[ARTZ]

...

.

[ARTZ]

just run z32 AFM in your intercooler piping.. its only 3 inch yeah..?

or get r35 afm as stated...

[mawzy]

Thanks for all the info and details. I was under the impression putting airflow meter in IC pipework has a whole set of it's own issues?

And just wanting to clarify some points. So the airflo meter will alter it's output depending on airflow, and as you're saying takes into account for density and temp to an extent aswell. At it's lowest output it'll be idle and x amount of air will be going to the motor. At full noise it'll be ready max output, with max amount of air passing it. I would have thought the ecu uses that info and have the corrections for fuel timing etc. So by putting into a larger diameter pipe. Yes definately more airflow, but still the same scale, idle will be lowest airflow, full noise will be the most. So the ecu is getting signal from least to most airflow, is it then not up to the tune and tuner to compensate the extra amount of air when tuning by adding more fuel and ignition?

All this in mind, I'm no expert or tuner, and don't plan to do this myself, I'm just trying to clarify in my mind, There might be things I'm not taking into account or thinking of.

[wolverine]

What turbo are you using?

[mawzy]

It's a masterpower turbo, mpr 545, with a smaller .48 exhaust housing. Being a street car, response has been a big consideration. I'm hoping it'll push get around the 400hp mark, wether i get there or not is yet to be seen. Supporting mods, apexi pfc nismo fuel pump, denso 650cc inj, imitation greddy intake, Sinco exhaust manifold, greddy bov, Gtr intercooler, 3inch pipework all round.

Just had a look aswell its actually a vh45 airflow meter, if this helps my case. It looks like it's a 3.5inch diameter caseing.

[GTSBoy]

OK, let's put some made up but concrete numbers against this. Let's image some numbers for an RB20 AFM and some for a Z32 AFM and then we'll imagine what happens when you put the Z32 sensor into a 4". If the table formatting is all stuffed up, I aplogise, but it's not my fault!

Meter idle air flow idle voltage max air flow max voltage

RB20 5HP 1v 300HP 5v

Z32 7.5HP 1v 500HP 5v

4" Z32 13.35HP 1v 890HP 5v

If you change from an RB20 AFM to a Z32 then you just tell the ECU that that is what you've done. The ECU changes the voltage to airflow map that it has in memory to suit the new AFM and is able to handle the fuelling and timing for any given load because it knows the relationship between air flow and voltage.

If you take the Z32 sensor and put it into a 4" pipe, the ECU only knows that you have a Z32 sensor. If you just left it programmed as Z32, then at 1v it will think you have 7.5HP of idle air flow running when in actual fact, in a 4" pipe it will be flowing 13HP. That is a LOT more air than what the ECU thinks and it will not idle because it will be running an AFR of about 25:1. If the AFM was returning 5v then the ECU would think it had the standard 500HP worth of air going through it and fuel accordingly, but in reality you'd have 900HP worth and the engine would have detonated itself to pieces because the ECU never would have put enough fuel in.

If you were to do the above, you would have to go in and manually edit the AFM voltage-flow map so that the ECU can have a hope of working it out. But this line is not linear, and it is quite possible that it won't have the same shape in the new 4" pipe as it did in the 3" pipe. This is why we said you have to know what you're doing". Get it wrong and you are in for a world of hurt, either in being an absolute bastard of a thing to tune or just melting the engine.

Thanks for all the info and details. I was under the impression putting airflow meter in IC pipework has a whole set of it's own issues?

And just wanting to clarify some points. So the airflo meter will alter it's output depending on airflow, and as you're saying takes into account for density and temp to an extent aswell. At it's lowest output it'll be idle and x amount of air will be going to the motor. At full noise it'll be ready max output, with max amount of air passing it. I would have thought the ecu uses that info and have the corrections for fuel timing etc. So by putting into a larger diameter pipe. Yes definately more airflow, but still the same scale, idle will be lowest airflow, full noise will be the most. So the ecu is getting signal from least to most airflow, is it then not up to the tune and tuner to compensate the extra amount of air when tuning by adding more fuel and ignition?

All this in mind, I'm no expert or tuner, and don't plan to do this myself, I'm just trying to clarify in my mind, There might be things I'm not taking into account or thinking of.

[ARTZ]

Thanks for all the info and details. I was under the impression putting airflow meter in IC pipework has a whole set of it's own issues?

.in some ways its preferable...

[GTSBoy]

But in many other ways it sucks balls.

[mawzy]

GTSboy, thanks for the info. At the end the day I'm shovelling shit uphill really. I went had a chat with a local tuner today, he also didn't recoment changing airflow meter size. Didn't go so far to bag the pfc but recomended using a link ecu, which is an option I like and would do, but I already have the pfc, and link will stretch my bidget a bit farer than I'd like. There's no real rush here, so will take my time a bit, see if I can on sell pfc, or will make the intake 3inch and stick with zx airflow. thanks for all your inputs.

[89CAL]

I dont understand why there is still conversation going on. If your only planning on running 400hp, and this is the turbo you have/are getting:

http://www.hevosvoima.com/shop/index.php?main_page=product_info&cPath=1061_139&products_id=7216&zenid=ee393e36663da3d33860180f52610388

Then it has a 4" compressor inlet and only a 3" compressor wheel. Therefore a 3" AFM is not going to be a restriction. A 3" to 4" reducer will be fine

I've already said this before, Just get a Z32 AFM, set it in the Power FC and be done with it. Theres no need to go putting the sensor in a 4" pipe. While I understand it might look a bit neater, its not worth the trouble of setting new air flow voltages etc

[ARTZ]

But in many other ways it sucks balls.

same can be said for standard location

GTSboy, thanks for the info. At the end the day I'm shovelling shit uphill really. I went had a chat with a local tuner today, he also didn't recoment changing airflow meter size. Didn't go so far to bag the pfc but recomended using a link ecu, which is an option I like and would do, but I already have the pfc, and link will stretch my bidget a bit farer than I'd like. There's no real rush here, so will take my time a bit, see if I can on sell pfc, or will make the intake 3inch and stick with zx airflow. thanks for all your inputs.

keep your intake 4 inch if you want...and your PFC

man for one example, hypergear ...he has been running his AFM in his intake pipe forever.....it works a treat...plenty of people do it

also if you for some unforseen reason smash your intercooler or split a pipe, but you still need to drive home your car is more likely to run with the afm closer to the TB because its reading the air your engine is actually getting...this is also a major benefit of running MAP...