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how much is too much?

dwhe009

By dwhe009,
in Engines & Forced Induction

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dwhe009 Contributor

dwhe009

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gidday, i have a rb20det with a few mods and i want to know how much further i can turn the boost up before either the air flow cut, or injectors max out.

My mods,

silver top rb20det

t3/to4e turbo, 49mm turbine, 51mm compressor (73mm outside)

3" mandrel all the way through

400 by 600 by 70mm custom intercooler

pod filter

0.8mm gapped plugs

stock ecu

The ecu has vs data rom on it. i assume this is some japanese tuner, I have had to turn the timing down to around 12 degrees before top dead at idle to make it not ping on boost. ( this maybe cos the chip was for good fuel?, i run 96)

any ideas to get a bit more out of the car?

It currently runs about 11psi.

cheers

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RB30-POWER Mentor

RB30-POWER

Posted
Posted

Asking is probally like asking how long a piece of string is.

Best way is to measure the AFM output voltage and measure the injectory duty cycle, under full boost and look for the peak readings for both measurements.

With a turbo like that, my estimate is it won't be able to run much more boost than what you are already.

Take it out on a cold winters night and see if you can get it to cut. The air is more dense and it will more likely cut during these conditions than a hot day.

Cheers.

dwhe009 Contributor

dwhe009

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Posted

what is max voltage out of the standard air flow meter? is it 5.12v?

what about injector duty cycle? how many milliseconds?

I have made up the interface and i use conzult (the free version, for 300zx) to monitor these values. Anyone know of any other good free software that will data log so i can look through a run instead of nearly crashing as i try to look at data real time. ha ha

RB30-POWER Mentor

RB30-POWER

Posted
Posted

They are rated between 0-5V (But in reality they cut around the 5.12 mark)

The injector duty cycle should be measured with a multimeter that has "Duty Cycle" function, or other tool. (Measured 0-99% "on time")

Yes a fuel cut defender will just hold the maximum value in order not to cut it altogether, but of course, if it takes more air than the amount the AFM measures it will lean out real quickk.

Fuel Cut Defenders are so dodgy i don't know why they make them. DODGE!

dwhe009 Contributor

dwhe009

Posted
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Posted

cheers rb-30 power.

I have always wanted to know, is the air flow meter value a value of the volume of air coming in per time (eg second) or the amount of air coming in per cycle of the motor?

Because if you have load (afm) versus rpm maps, then doesn't that mean you have load per cycle of the engine. eg the afm signal may say 2volts at 3000rpm at -2psi pressure and then 4volts at 3000rpm at +7psi boost and still say 4volts at 7psi at 6000rpm? am i correct?

RB30-POWER Mentor

RB30-POWER

Posted
Posted

Its output corresponds to the volume of air going through the meter at that particular time.

Maximum air flow (maximum afm voltage) usually occurs at maximum boost pressure and at the point where the VE (volumetric efficiency-where the motor consumes most air.) of the motor is the greatest. This is usually where peak torque is delivered. Bigger cams change the point where maximum VE can occur, bigger cams will move this point up the rev range, naturally.

Back to what you were saying its output is the volume of air going through the meter at that particular second.

Im not to sure how quick the AFM can actually sample and change its output, it would be almost instantly, lag would be in ms, i would be guessing. It would have to have some lag, for the change in the hot wire temp to change.

But yeah, AFM are the most accurate way of measuring actual air going into the motor. Maps sensors just don't compare.

dwhe009 Contributor

dwhe009

Posted
  • Author
Posted

ok, so it is counting volume per cycle of the motor then. i would be interested in how exactly it does this, how the thing counts air?

I am correct in saying most guys with rb20dets with stock ecu and injectors hit the fuel cut ( afm max) before the injectors run out? does this a safe way to find the limit of my set up would be to slowly turn the boost up until i hit the fuel cut, then turn it back slightly?

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