Magnitude of the Effect of Airflow Correction on Timing

[HLxDrummer]

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!

[HLxDrummer]

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?

[bboyalan]

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.

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.

[dpartinvr4]

what are your IDC's? have you tried reducing fuel pressure, so that you can lessen the airflow correction?

[HLxDrummer]

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.

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!

[i3igpete]

if you are using stock injectors, then the change in timing will be negligible.

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?

[KeithMac]

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.

[HLxDrummer]

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

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.

[KeithMac]

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.

[HLxDrummer]

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..