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Thread: Magnitude of the Effect of Airflow Correction on Timing

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    Forum User verified Feedback Score 0 HLxDrummer's Avatar
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    Magnitude of the Effect of Airflow Correction on Timing

    Well I was out tuning my stock car a little last night at 6 psi on stock turbos. Stock with hotwired fuel pump I was running ~10.4 AFR at 6,000 RPM at 6 psi for reference.

    I was aiming for basically a flat ~11.2 AFR at this boost level. To achieve this I had to add a good bit of fuel from 3,000 RPM to 4,500 RPM and remove a good bit from 7,000 RPM down to around 5,000 RPM.

    I know as you remove "airflow" that the ECU will advance timing but I'm not sure how much is normal. Right now my timing goes from ~16 (according to MMCd) at 4,500 RPM (positive correction) to ~25 at 5,000 RPM (negative correction). Around 6,000 RPM timing is mid-high 20's and it starts knocking with a low 11's AFR.

    I think low 11's AFR should be possible at 6 psi on a stock car and I am thinking the timing is causing my problems. Is it normal for a little bit of negative correction to cause such a jump in timing?

    At ~10.7 AFR to redline I wasn't getting any knock and maximum timing advance was ~27. This seems really high to me. I'm assuming it would be better to have it rich like this with more timing but I was hoping to get a bit leaner and maybe even add in some timing to offset the boost drop off at high RPM (15 psi dropping to around 8 with advanced timing there) but obviously this isn't possible.

    Any input? Thanks!

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    Forum User verified Feedback Score 0 HLxDrummer's Avatar
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    I have an eManage Blue with timing control. You think it's better to have a normal AFR with dialed back timing? Do you think my airflow correction is causing the advanced timing? Is this timing way too high?

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    SDSU Alumnus verified Feedback Score 4 (100%) bboyalan's Avatar
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    Quote Originally Posted by HLxDrummer View Post
    Around 6,000 RPM timing is mid-high 20's and it starts knocking with a low 11's AFR.

    I think low 11's AFR should be possible at 6 psi on a stock car and I am thinking the timing is causing my problems. Is it normal for a little bit of negative correction to cause such a jump in timing?

    At ~10.7 AFR to redline I wasn't getting any knock and maximum timing advance was ~27. This seems really high to me. I'm assuming it would be better to have it rich like this with more timing but I was hoping to get a bit leaner and maybe even add in some timing to offset the boost drop off at high RPM (15 psi dropping to around 8 with advanced timing there) but obviously this isn't possible.

    Any input? Thanks!
    Mid-high 20's and even low 30's are quite normal especially if you were running WG pressure. In regards to AFR, every car is different in what "works" for it. Timing-induced knock can be masked with a richer tune [as you have been experiencing] or tuned out with your EMB's ignition map. I once tuned Eric's 16T car at WG 6psi, 550's, and 12.0:1 AFR on sky-rocketed factory timing maps without any detonation. Another stock fuel and lightly modified local VR-4 was showing 31* at 10psi. Both of these mentioned observations were on 91-octane.

    Quote Originally Posted by HLxDrummer View Post
    I have an eManage Blue with timing control. You think it's better to have a normal AFR with dialed back timing? Do you think my airflow correction is causing the advanced timing? Is this timing way too high?
    Yeah, I would personally keep it in check as the ECU likes to be a little drastic in its decisions, such as heavily pulling timing when exposed to "high" counts of knock.
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    Member Not Verified Feedback Score 4 (100%) dpartinvr4's Avatar
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    what are your IDC's? have you tried reducing fuel pressure, so that you can lessen the airflow correction?

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    Quote Originally Posted by bboyalan View Post
    Mid-high 20's and even low 30's are quite normal especially if you were running WG pressure. In regards to AFR, every car is different in what "works" for it. Timing-induced knock can be masked with a richer tune [as you have been experiencing] or tuned out with your EMB's ignition map. I once tuned Eric's 16T car at WG 6psi, 550's, and 12.0:1 AFR on sky-rocketed factory timing maps without any detonation. Another stock fuel and lightly modified local VR-4 was showing 31* at 10psi. Both of these mentioned observations were on 91-octane.


    Yeah, I would personally keep it in check as the ECU likes to be a little drastic in its decisions, such as heavily pulling timing when exposed to "high" counts of knock.

    Hm.. I wonder what my issue is. One of my intercoolers is banged up on the end tank from the previous owner, that probably isn't helping. I also did about 10 pulls in second gear with little breaks in between, but it was a cool night.. Running 93 octane, too. (I also just remembered that I did have the timing advanced 1-2 on the EMB at 6 psi so I guess I'll start by putting that to 0).

    I previously ran 16 psi at pretty lean AFR (don't remember exactly, just tried it out when I first got my wideband to see if I had enough fuel) with no knock, if that means anything.



    Quote Originally Posted by dpartinvr4 View Post
    what are your IDC's? have you tried reducing fuel pressure, so that you can lessen the airflow correction?
    I'm running a stock fuel system right now with a hotwire. Do you think ~10 on the eManage airflow map would be enough to cause a drastic change in timing? I know people with aftermarket injectors sometimes do a lot more than that on the airflow map and it is hit or miss whether they have timing induced knock, so why would my "small" correction cause a problem?

    Makes me think it has something to do with the actual AFR.



    Thanks for all the advice guys!

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    Advanced Tech? verified Feedback Score 0 i3igpete's Avatar
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    if you are using stock injectors, then the change in timing will be negligible.


    Quote Originally Posted by Pete
    using gatecrasher's new decode of the spyder timing maps, a huge assumption that load % is nearly linear with airflow reading. This is the result if airflow readings are HALVED, as if you had 720cc injectors installed.



    resultant timing error with these adjustments:
    1000 = -6
    2000 = -9
    3000 = -12
    4000 = -10
    5000 = -7
    6000 = -5
    7000 = -4


    and what's the status on this puppy, can i make my new timing adjustment guidelines shareable on 3si or no?
    Last edited by i3igpete; 12-01-2010 at 11:05 AM.
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    At the end of the day you have to decide which setup feels faster to you, I personally hate pulling timing out as it makes the car feel flat. I`d rather run slightly richer or a better octane fuel one way or another..

    Have you verified your base timing is correct, should be 5-7 degrees btdc.
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    Quote Originally Posted by i3igpete View Post
    if you are using stock injectors, then the change in timing will be negligible.
    That's what I thought.. I wonder what is causing the low 15* to jump all of a sudden to mid 20's then? Thanks for all the info I'll have to give it a day or so to sink in

    Quote Originally Posted by KeithMac View Post
    At the end of the day you have to decide which setup feels faster to you, I personally hate pulling timing out as it makes the car feel flat. I`d rather run slightly richer or a better octane fuel one way or another..

    Have you verified your base timing is correct, should be 5-7 degrees btdc.
    Ya I see your point, just want to make sure nothing mechanical is wrong and that what is happening makes sense you know?

    I have a 1993 so timing isn't adjustable at the CAS but good idea.

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    If you have a look at the timing maps, a small change in percieved load (2 row change) can have a massive effect with timing.

    Where does your knock start? worste point for me is 4250 rpm where I thinng maximum torque sits.

    Silly as it sounds if you bump your boost up to 10 psi (to alter the load row) and trim fuel to gt 11.2:1 you may not encounter any knock, that`s how people size their injectors for use with an AFC.

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    Quote Originally Posted by KeithMac View Post
    If you have a look at the timing maps, a small change in percieved load (2 row change) can have a massive effect with timing.

    Where does your knock start? worste point for me is 4250 rpm where I thinng maximum torque sits.

    Silly as it sounds if you bump your boost up to 10 psi (to alter the load row) and trim fuel to gt 11.2:1 you may not encounter any knock, that`s how people size their injectors for use with an AFC.
    I was thinking that timing didn't change much after looking at the maps. Am I looking at them wrong? If you look at ~6,000 RPM when it goes from 400 load to 160 there is actually no change (at least on this maximum timing map). Doesn't really coincide with what I am observing on the logs though (how timing jumps 10* when I go from positive correction to negative).

    My knock starts around 5,500 RPM (right where I go from positive correction to negative - therefore right where timing jumps from ~15* to ~24*). Maybe it's the sudden change in timing and I should just leave the airflow correction at near zero for lower RPM? The ECU wants like 13.5 AFR at 3,000 RPM and 6 psi which I thought was a little lean so I added correction down low.

    That does sound wierd that turning up the boost would help but I see what your saying - higher load will make the ECU lower timing, correct? So at 6 PSI I would be best to just pull back a bit of timing and move on to higher boost levels?

    I was shocked the ECU wanted such a rich AFR at only 6 PSI at redline (10.4:1!). This does make it seem that the correction made the big timing jump, but doesn't go alone with what Pete posted..
    Last edited by HLxDrummer; 12-02-2010 at 01:52 PM.

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