R34 maxing out R35 GTR AFM @ 190kw?

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Pr0xm1tyy
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R34 maxing out R35 GTR AFM @ 190kw?

Postby Pr0xm1tyy » Wed Jan 10, 2018 9:45 am

Hey guys,

We've been trying to work this one out for a few days, but thought maybe Matt or someone else a bit more experienced could shed some light on the subject!

Running a single R35 GTR MAF in a housing the same size as a Z32 AFM and it's maxing out at around 190kw. Genuine unit as well.

Have only adjusted the AFM and pipe size from the menu. Haven't touched anything else yet - wanted to hear from someone else what they thought might be the cause of this.

Other than that, car tuned up nicely!

Matt
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Re: R34 maxing out R35 GTR AFM @ 190kw?

Postby Matt » Wed Jan 10, 2018 10:41 am

How much boost was it toping out at? Do you have any logs?

Since my initial testing where we got 300rwkw out of this sensor (in 3" tube) I'm now running larger exhaust wheels in my turbo and found at 6000rpm at 12psi on my customers R35 GTR sensor it was hitting 5.12 volts.

They had the same issue with it topping out, but wired it incorrectly so I'm investigating that... I'm going to try another (new) sensor out to compare that. Might have to change your sensor to an HPX?

Pr0xm1tyy
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Re: R34 maxing out R35 GTR AFM @ 190kw?

Postby Pr0xm1tyy » Wed Jan 10, 2018 10:55 am

Running 10(ish) psi through a HKS2835 Pro S (basically a 3071r) MAF is on the intake pipe if that makes any difference too.

I haven't got logs, I'll go get him and go for a drive tonight or tomorrow and get some logs.

HPX sensor will be my last resort, even a Z32 would work fine for this application - but if I can work with this then I will.

EDIT2: I'm a bit of a noob to this stuff and am trying to understand how it works.

Could the Voltage Quantifier map we've set be wrong? Or is it a case of "It's getting 5v from the MAF so thats as much air as it can read, its like that its the way it is"

Sorry for being a noob.

Pr0xm1tyy
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Re: R34 maxing out R35 GTR AFM @ 190kw?

Postby Pr0xm1tyy » Wed Jan 10, 2018 11:53 am

Another option is that i've been had and its non genuine, but it was just pulled off a wrecked car.

Matt
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Re: R34 maxing out R35 GTR AFM @ 190kw?

Postby Matt » Wed Jan 10, 2018 1:48 pm

MAF voltage is before the VQ map (it is used to index) so it is not that. It seems very low for what it should be

The same part number should mean same MAF for all models

mtnickel
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Re: R34 maxing out R35 GTR AFM @ 190kw?

Postby mtnickel » Fri Jan 26, 2018 9:42 am

Instead of starting a new topic, thought I'd add this in here.
Has anyone measured if the R35 MAF will actually keep outputting higher voltage that 5.1v and how high?
I know the Ford guys (05-11) use nearly the same Hitachi based MAF. It can actually read out to 6.2ish Volts.
They then use a voltage reducer to rescale the maf such that 6v now becomes 5v. You can also linearly shift the map down, but you need to extrapolate the flow for the new 5-6v range. So while the stock unit runs out of flow at 5v @ 300whp, they scale the voltage down and can use a greater portion of the MAF to run say 500-600whp.

The device they use is the diablosport Mafia
https://www.americanmuscle.com/diablosp ... -9604.html

This is nothing more than a voltage reducer. I'm contemplating building one for much much less than the $160US they want.

Options are:

1) Simple voltage divider. While this can be accomplished, I've still got to figure out if there will be any compromises or non-linearities. I've mearsured the ECU input impedance @ about 2.2Kohms. Not sure the output impedance of the Hitachi maf since I don't have one yet.
While this may be very cheap, it would only be applicable/repeatable on my specific ECU/MAF combo.

2) Use an IC/Buffer/amplifier. Probably the smarter way to go is to use high resistors as a voltage divider first, then buffer that signal with an amplifier to feed to ECU. This way if someone else uses the design, it won't be affected by their ECU input impedance.

Just thinking out loud and wondering if others may find this useful. I can get the Ford Maf for $20 all day long and new is $60. If it only requires a few wires soldered and $5 in IC/resistor parts, then it could be a nice affordable way to get a good Maf. It apparently works well in both draw through and blow through. Not only that, but you could tune it as well to your required HP level and maintain as much resolution as possible. (ie, some may need just 5.25 scaled down, others 5.5, or full 6.2). The forumula for the stock Curve can be found as well which allows us to scale it easier.

Thoughts?
ps. It'd also be easy to just put this inside the ECU as well. Just cut the AFM pin, build mini circuit on small board, and reconnect.

Matt
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Re: R34 maxing out R35 GTR AFM @ 190kw?

Postby Matt » Mon Jan 29, 2018 9:52 am

I haven't measured it - since I would have to push maximum airflow on the bench to do this. I attempted a test the other week with vacuum cleaner and only reached about 2.6V from the sensor.

On the vehicle itself, the sensor will peg out at 5.1 volts (which is also the maximum the ECU MAF input will report due to the range of the A/D converter in the ECU)

One experiment could be to use a voltage divider between MAF and the ECU and then halve the VQ map values. If it does indeed go over 5.12 volts (2.6 divided) then there might be a solution there.

mtnickel
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Re: R34 maxing out R35 GTR AFM @ 190kw?

Postby mtnickel » Mon Jan 29, 2018 4:05 pm

I'm fairly certain they read over 5v. I know for the sure Ford one does and I think it's nearly the exact same sensor as the Nissan one. I'm going to try to source a few used sensors and do some testing. Tough to get those flow amounts, but may be able to use an air compressor nozzle or something.
The previous Ford Lightning MAF's were even better in that they read really high (over 8-9v?). So they could really be scaled a lot.

While a resistor would probably suffice, I bought a rail-to-rail opamp anyways to buffer the signal. Got that along with a 4-switch dip switch, mini proto board, and an assortment of accurate, temperature tolerant resistors.

On another note, did the Original poster ever determine the reason for pegging the MAF so quickly? The R35 guys say the 2 are usually good to about 700-750whp on the 3" housings (350-375whp = 280kw?).
The Z32 housing is 75mm ID which is about 2.95", so should at least make that.

mtnickel
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Re: R34 maxing out R35 GTR AFM @ 190kw?

Postby mtnickel » Mon Jan 29, 2018 4:36 pm

Some math from the GTR guys directly:

http://www.gtrlife.com/forums/topic/951 ... try1330611

So, the R35 stock MAF's in a 2.75" housing max out about 5v at about 570whp or 285whp/maf or 212kw.

Moving up to a 3" housing should yield about 3^2/2.75^2 more flow/power = 20% more flow = 340whp or 250kw. That seems about in line with what the ford guys max out a stock MAF at (again, same Hitachi sensor likely).

I'll see about some hands on testing.

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Re: R34 maxing out R35 GTR AFM @ 190kw?

Postby Matt » Tue Jan 30, 2018 12:06 am

Okay thats a big read. Look at that later. Yes I've had reports of them maxing out around 220-250rwkw on one vehicle in 3" tube

However my R34 reached 298rwkw with a R35 GTR MAF on 17psi (3071R turbo) in 3" tube
http://forum.nistune.com/viewtopic.php?f=10&t=2428

The other sensor which a customer only hit 220rwkw on I maxed out before reaching full boost, so need to re-test this again when the weather isnt so bad (40 degree one day and raining the next)

Anyway the 298rwkw is why i've listed it as 444rwHP (which also works when resizing the MAF and in turn adjusting K constant) but that may require re-evaluation


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