Getting the most out of your Apexi S-AFC= Stock MAF honeycomb removal

[DJAuggie]

Originally posted by Innovator


That's really bad. 22 is about the most you'd want to see at WOT and pump gas, and still be safe.

More timing means more power to a point. Then you start detonating, or start needing to run too rich.

22is bad? I get 25-27 at 8PSi! Can anyone else confirm that 22 is bad. I always heard that a steady increase with no dips is good.

-Shawn

[2root4u]

Looking through my previous datalogs while idling and gasing, the lowest my timing ever goes is 25. Is something jacked up or could the datalogger be reading it incorrectly? Peak is 50.

[Gabe92RTTT]

Timing will show a lot higher when you are not at WOT, so you are fine 2root4u.

I have been around a lot of DSM guys, and if they are at 32* at WOT, then they are tuned really well. I have no detonation and my timing is a steady curve upwards and hits 33* of timing at redline. I am actually threatening to run lean as my IDC is 95%. My correction factors are actually only at 10-15% on the hi side as I only have 450cc injectors.

[Multiades]

...but this mod WILL NOT net you less advanced timing.

You are essentially making up some of the correction at the MAS, and some of it with the AFC, but the TOTAL correction is still the same. You are only able to change the airflow signal (in this case by using two combined methods instead of just one), but you are not changing ANYTHING relating to the ECU's internal mapping.

In other words, if you were to measure the frequency of the airflow signal going into the ECU, you would find that at a particular airflow (say x boost at y rpm) and a particular a/f ratio, you have the exact same signal at the ECU with either method (SAFC correction only vs. SAFC correction + honeycombs removed).

I'm not saying this doesn't have potential benefits (it does, if you can make it work reliably -- better flow and a higher peak flow accuracy with the stock MAS), but the concept that it is changing the total "corrected" airflow is a fiction.

-Chris Wood

[Innovator]

Sir, you are incorrect. My timing retarded 6 degrees with this mod.

In theory you are correct, but the AFC does in fact advance the timing with high correction factors, and removing the HC's has more of a retarding effect than electronically altering the signal.

Three prominent tuners use the same method. Sometimes logic doesn't apply Chris.

My max HZ reading is 2400 now. It used to go to 2800 and then the A/f would get wacked. Somehow the lower HZ reading is tied into the lower timing. I'm not really sure why.



Besides, the timing light and the dyno don't lie. I have all the proof I need

[Innovator]

Originally posted by DJAuggie


22is bad? I get 25-27 at 8PSi! Can anyone else confirm that 22 is bad. I always heard that a steady increase with no dips is good.

-Shawn

That's fine with stock boost.
22 is good with 15+ psi.

[Multiades]

Originally posted by Innovator
Sir, you are incorrect. My timing retarded 6 degrees with this mod.

In theory you are correct, but the AFC does in fact advance the timing with high correction factors, and removing the HC's has more of a retarding effect than electronically altering the signal.

Three prominent tuners use the same method. Sometimes logic doesn't apply Chris.

My max HZ reading is 2400 now. It used to go to 2800 and then the A/f would get wacked. Somehow the lower HZ reading is tied into the lower timing. I'm not really sure why.



Besides, the timing light and the dyno don't lie. I have all the proof I need

There are other explainations for it, but the theory IS correct because it MUST be. The only way to change A/F ratio without adjusting the ECU itself (directly) is to adjust the airflow value.

No matter what, for a certain actual amount of air massflow, a certain size injector, and a particular A/F ratio, the ECU MUST see a particular number. Any variation in those factors requires a variation in the airflow signal, and conversely, any change in airflow signal REQUIRES a change in one of those variables.

The only possible explaination for the changes you have observed, is that you are flowing more air (mass) at the same boost. Because you are flowing more airmass at the same boost, a higher frequency signal is required to inject the appropriate amount of fuel to mainain a particular airflow. The ECU runs less timing with a higher airflow signal (based on its internal maps).


The change from a peak of 2800Hz with honeycombs, to a peak of 2400Hz without is to be expected and NORMAL. You are only reading that signal as it comes from the MAS -- before it is "massaged" by the AFC.

Note that this change essentially proves my point because a lower frequency MAS signal for the same airflow essentially tells us that some of the correction is made at the MAS (and the remainder at the AFC).

If it doesn't make sense, there is always a reason. There isn't any magic in this business. Not that you could be blamed for thinking that this would result in less correction and less timing for those reasons -- I thought the same thing until what I just explained occurred to me.

Hope this helps,
-Chris

[BlackStealth]

I think Innovator is on to something. The Talon community already can increase their injectors 22% bigger (450cc->550cc) without adding unwanted timing advance. How? They swap out their 1G MAF to a 2G MAF which incidently flows 22% more. The ECU is unaware that the injectors are making the car rich by that 22% factor. And again, the ECU is unaware that the 2G MAF is making the car run 22% leaner. Overall, it's a nice coincidence that doesn't require a "fuel computer".

Now, here's something that would make a great project. Take a spare 3S MAF and hollow it out 100% and retrofit a 3" GM MAF combined with a MAFT. The ECU would only see the air measured in the 3" chamber. The remaining air passages would be "unseen" by the ECU and could be used to offset the over richness caused by the larger injectors. The overall correction factor used on the MAFT or SAFC will be much less and won't lie as much to the ECU. The net result is the ECU won't advance the timing as agressively as before.

[Innovator]

Originally posted by antero
I think Innovator is on to something. The Talon community already can increase their injectors 22% bigger (450cc->550cc) without adding unwanted timing advance. How? They swap out their 1G MAF to a 2G MAF which incidently flows 22% more. The ECU is unaware that the injectors are making the car rich by that 22% factor. And again, the ECU is unaware that the 2G MAF is making the car run 22% leaner. Overall, it's a nice coincidence that doesn't require a "fuel computer".

Now, here's something that would make a great project. Take a spare 3S MAF and hollow it out 100% and retrofit a 3" GM MAF combined with a MAFT. The ECU would only see the air measured in the 3" chamber. The remaining air passages would be "unseen" by the ECU and could be used to offset the over richness caused by the larger injectors. The overall correction factor used on the MAFT or SAFC will be much less and won't lie as much to the ECU. The net result is the ECU won't advance the timing as agressively as before.

Your AFC setting seem very rich. I have a similar setup, and with the FJO, I'm closer to -30 LO across the board, and -30 from 1K to 4K, and -39-39 above on Hi. You may be leaving a bunch of HP on the table... I was still on the rich side there. Now all has changed with the gutted MAF.

[Innovator]

Originally posted by Multiades
There are other explainations for it, but the theory IS correct because it MUST be. The only way to change A/F ratio without adjusting the ECU itself (directly) is to adjust the airflow value.

No matter what, for a certain actual amount of air massflow, a certain size injector, and a particular A/F ratio, the ECU MUST see a particular number. Any variation in those factors requires a variation in the airflow signal, and conversely, any change in airflow signal REQUIRES a change in one of those variables.

The only possible explaination for the changes you have observed, is that you are flowing more air (mass) at the same boost. Because you are flowing more airmass at the same boost, a higher frequency signal is required to inject the appropriate amount of fuel to mainain a particular airflow. The ECU runs less timing with a higher airflow signal (based on its internal maps).


The change from a peak of 2800Hz with honeycombs, to a peak of 2400Hz without is to be expected and NORMAL. You are only reading that signal as it comes from the MAS -- before it is "massaged" by the AFC.

Note that this change essentially proves my point because a lower frequency MAS signal for the same airflow essentially tells us that some of the correction is made at the MAS (and the remainder at the AFC).

If it doesn't make sense, there is always a reason. There isn't any magic in this business. Not that you could be blamed for thinking that this would result in less correction and less timing for those reasons -- I thought the same thing until what I just explained occurred to me.

Hope this helps,
-Chris

There is no doubt that the timing is lower now than before. The car is blisteringly faster as well. Combo of more air and less timing works!

Somehow your theory doesn't apply to this situation, logical or not. Even if it HAS to be true as logic would dictate , the car is running less timing 6-8 degrees retarded) and is MUCH faster.