After Some Mafless Ecu Options

[Sydneykid]

I have thought of doing this before and in concept it will work and maybe some guys have used it as well...BUT

In reality I think it is very risky due to the following...

There is no way that you can be assured that you will maintain a 50/50 airflow split...I appreciate that from a tuning point of view it does not really matter if it is not exactly 50/50 airflow between afm and bypass because you just tune to to suit anyway...BUT what happens if or when the ratio between the measured flow and the non measured flow changes...This would definately happen if you were using two seperate filters...one for the afm and one for the bypass...Even is they are mounted side by side one will get dirtier quicker then the other..Also when you are tuning on a dyno you dont have road speed air entering the engine bay so your tune may instantly change as soon as you get out on the road...

If you try and use the one filter connected to both the afm and bypass to get away the above issue, unless your design is very well thought out, the afm vs bypass ratio will also change with differing atmospheric conditions such as the ambient air temp, humidity etc This is due to small changes in the flow characteristics of air due to changing temp, humidity etc etc etc..A good design would achieve laminar flow within the filter in all locations which in practise would be very difficult to do especcially when you are seperating the aiflow into two individual flows...

My suggestion would be dont do the afm bypass thing...

All relevant, but what sort of % difference (dyno versus real world) are we talking about here? I would be very surprised if it was 1%, even 2% is stretching my comprehension. So tune it 5% safe (rich) and you have pretty much covered any potential A/F ratio issues. The standard ECU knock retard will handle any ignition timing effects. Sure it's not ideal, but as a short term cheap fix I don't see it as being terrible.

Cheers

Gary

[**RB2530**]

All relevant, but what sort of % difference (dyno versus real world) are we talking about here? I would be very surprised if it was 1%, even 2% is stretching my comprehension. So tune it 5% safe (rich) and you have pretty much covered any potential A/F ratio issues. The standard ECU knock retard will handle any ignition timing effects. Sure it's not ideal, but as a short term cheap fix I don't see it as being terrible.

Cheers

Gary

Thats the thing...The difference may be small and insignificant OR large and significant. Even if you are using the stock ECU you are not protected if you bypass the afm...I know...I have one rb25 stock piston in 50-100 pieces sitting in my desk draw because the BOV plumback hose came off the intake pipework...

I think it is fair to say that the 'potential' for varying ratios is very great especially if you use two individual filters, one for the afm and one for the bypass...you are dealing with airflows at very low pressure and it wouldn't take much to change the balance significantly...My gut feel would be up to 20-50% difference over time...

From a risk point of view even if the likelihood is low, the consequence is high so the risk is still unacceptable...I would only run such a setup if I had EGT or AFR monitoring running all the time. Even then I would be concerned about the tune changing suddenly...

Thats just my opinion though but as always I have put up the reasons behind it...

[Adriano]

you know that when you max out the AFM it runs like a map sensor anyway? ie: no more load increase, so no more 2d tuning from that point on

Paul you have said this many times, and i dont see your point, if the boost increases with a map sensor, so does the load, with a maf, the load wont increase if its already maxed, i see this as worlds apart in tearms of tunability, and tuning past the limits of the AFM also isnt a satisfactory solution, as any slight variance in load from the tuning load, whilst still holding 5v will give completely uncontrolled or unpredictable AFR's.

The only similarity i could see is if you maxed out the MAP sensor, which is never really a concern, as 5 bar map sensors are easily obtained.

Edited March 27, 2008 by Adriano

[Adriano]

I would either go Autronic P&P (about $2700), or rb25 or rb26 PFC with appropriate AFM(s), have a look in the fabrication section for my custom AFM. Other option is RB26 PFC Djetro. I certainly wouldnt consider any other option, especially the two you have mentioned.

[paulr33]

if you run say a map sensor setup and my boost controller is set to say 18psi

from the time my motor reaches 18psi until redline and i change gears, the pressure is always 18psi

so the map sensor signal doesnt change, lets say its 2.2v which means 18psi

so from 3500rpm to 7500rpm map1 is 2.2v and we run on 1dimension (rpm) tuning as load never changes

if you run say a AFM sensor setup and my boost controller is set to say 18psi

from the time my motor reaches 18psi until redline and i change gears, the pressure is always 18psi

so the afm sensor signal changes all the way to redline (or until it maxes) as more and more air comes in

depsite pressure being fixed at 18psi, pressure does not equal volume.

so from 3500rpm to 7500rpm afm1 is 2.2v and increases slowly either until it peaks or maxes out

so load will always increase - albeit very slowly, but it will until you max airflow for the engine or the afm sensor

in the situation lets say you run a Z32 and peak it at 5v at say 4900rpm

boost is still 18psi and hasnt changed and remains constant but more air is coming in

and will keep doing so until redline

AFM1 runs to 5.1v at 4900 and doesnt increase and remains at 5.1v until 7500rpm

so from 4900 to 7500 we run 1dimensional tuning - just like the maps sensor

there no unpredictable AFR's or "melt piston" style situations as the load axis doesnt increase but the RPM one does (same as the map sensor style)

[2rismo]

Did you have change the trigger in the CAS and/or the ignitor? They used to cause problems with Autronics. We had a Nissan at Bathurst with an Autronic no talk problem last weekend.

Cheers

Gary

No and no. They caused a problem on previous revisions but they're now designed to work with the standard gear.

[Adriano]

Paul, i think this is probably about the only thing i disagree with you on. Say your MAF car is tuned for your 18psi on a 30 deg day, with the AFM maxing at 5000 rpm, if on a cold night(say 10 deg), you have a little overboost say to 20psi, there is no way the ecu can know there is additional airflow, hence leaning out, and no reduction in timing.

You would be surprised how much difference intake charge temp makes to A/F ratio's if there is no compensation, which the maxed MAF situation is, I recently tuned a subaru EA82t, without intercooler, then with intercooler, it was a map sensor ecu without the air temp sensor. It wasnt running lots of boost, so the difference in intake temps would not be enormous, but definately there. Originally tuned for 12:1 A/F ratios, when it came back the Intercooler had increased the density of the air to the point where the full load A/F ratios headed towards 14.5:1

My other concern with running a tuned maxed AFM setup is if it is tuned fro 18 psi, what happens at 16 psi. Assuming the AFM is still maxing, it will still be running the same load point as 18 psi, but with less airflow, so it will run rich as buggery.

All this is good and well for most people, as if the AFM maxes at 5000 rpm, there really isnt too much of a problem, as 99% driving will not show the problem, but something which maxes it at 3500rpm(which is entirely possible with an rb30) could easily spell disaster and poor driving characteristics IMO

[Risking]

Load points vary drasticly in different conditions like Adriano has mentioned.

If a MAF is maxed its maxed and Id certainly never recomend someone to tune behond its scope. Esspecially if its maxing out early in the rev range.

Only other option id consider than those mentioned would be the E11v2.

Seems alot of people have differnent oppinions but ive been using one in my race car for the last 6 months and it does everything perfectly.