Tuning: Timing effecting AFR
Thread Starter
Instructor
Joined: Nov 2012
Posts: 240
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From: Carrollton Illinois
Tuning: Timing effecting AFR
You can see my mods in my signature, essentially I'm working further into my tune to improve it. I just have a few basic questions. Originally I kept the timing tables completely factory after the cam and headers. I have slowly added timing across the table (3 degrees across the table, but never exceeding 46 degrees, while WOT conditions max out at 33 degrees (95-100kpa). So, I had my BLMs ±1%, now that I adjusted timing I am +5% rich across the board. Does this mean that I was not burning all of the fuel it injected since my timing was too retarded and now that I advanced it (giving more burn time) it is showing that too much fuel has been given? In other words I was pumping our raw gas through the exhaust? I have a firm grasp of the concepts of tuning and the structure but this is a relatively new venture for me. The car really seems to like the additional timing, throttle response and drivability both clearly increased. Lastly, where do you find the limit with max part throttle timing and closed tps timing? I currently have my closed tps timing at 27 degrees @ 800 rpm (idles at 750) and this smoothed out my idle quite a bit compared to the factory 23 degrees. Also, with my current timing setting I am not getting any spark retard.
Thank you!
-Colton
Thank you!
-Colton
Last edited by CMiller95; Oct 19, 2017 at 11:20 PM.
Melting Slicks
Joined: Dec 2008
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From: Mystic CT
retarded timing requires more fuel and has a higher egt due to fuel burning in the header rather than in the cylinder. What are you using for a target AF ratio and what fuel not brand as that is of much less importance
Race Director
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From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
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Knock counts is part of what you look at to determine if too much timing has been added. When you get close (within a degree or two), a roller dyno can dial in precise tuning. Assuming later years are similar, it's almost a necessity since the car goes into open loop during WOT.
If it helps, I like this page for an overall summary of EFI tuning considerations.
Thread Starter
Instructor
Joined: Nov 2012
Posts: 240
Likes: 18
From: Carrollton Illinois
My wot timing was set at 33 from the dyno tuning so that’s why I haven’t changed it. For some reason I didn’t want to go over 46 so when adding to the timing table I didn’t add to the value if it was already 46. My wot AFRs are still good around 13.1 (wide band in car). Thanks for the replies everyone, it seems like I’m on the right track as to why it pushed it rich. I’m running 93 octane fuel but sometimes have to run 91 if I travel.
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Race Director
Joined: Nov 2003
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From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
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If the mixture is "lit" late (and as ddahlgren mentioned exhaust temps (egt) goes up), you HAVE to assume too much fuel is present to be burned in time. Too much fuel in the exhaust would register as rich by the O2.
The intuitive conclusion is what's stated by 383vett above.
Race Director
Joined: Nov 2003
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From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
C4 of Year Winner (appearance mods) 2019
My wot timing was set at 33 from the dyno tuning so that’s why I haven’t changed it. For some reason I didn’t want to go over 46 so when adding to the timing table I didn’t add to the value if it was already 46. My wot AFRs are still good around 13.1 (wide band in car). Thanks for the replies everyone, it seems like I’m on the right track as to why it pushed it rich. I’m running 93 octane fuel but sometimes have to run 91 if I travel.
I wouldn't think you'd NEED more timing than stock...even in the lower ranges with performance changes. When making an engine more efficient, less timing is often the case....unless you LOWERED compression with your build?
My instinct is you should returning timing back to what you had before this recent attempt/iteration.
Thread Starter
Instructor
Joined: Nov 2012
Posts: 240
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From: Carrollton Illinois
FE1 is a reference to my factory suspension package, although I should probably take it off. I raised my compression a hair with a slightly thinner head gasket but nothing major. I have completely factory heads. Essentially the only true changes to my engine in reference to air in and air out is headers and a cam that is similar to a hot cam. I have had no retard due to the knock sensors yet. I adjusted my VE tables and got it back to + or - 1% on the BLMs.
Race Director
Joined: Nov 2003
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From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
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Just to clarify....Did your BLMs get higher or lower with the advanced timing? If they went higher, that means it got leaner and needed more fuel...which is what should happen.
Lower BLMs mean it's running rich. I decided it might be worth while to make sure you weren't thinking backwards.
Lower BLMs mean it's running rich. I decided it might be worth while to make sure you weren't thinking backwards.
Thread Starter
Instructor
Joined: Nov 2012
Posts: 240
Likes: 18
From: Carrollton Illinois
It was definitely running richer, I could see it on my wideband and I had to lower the VE values to correct it. Its been running great with no knock codes at all. The only thing I can think of and its far out is that due to the retarded timing I was continuing to burn into the headers. By time it gets to the O2 (long tube headers) sensors it might read it as a good mixture. When I advanced the timing it changed how that burn occured (ie no longer burning while in the headers after it was pushed out). This is super far fetched in my opinion but its the only reason I can come up with
Race Director
Joined: Nov 2003
Posts: 12,221
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From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
C4 of Year Winner (appearance mods) 2019
It was definitely running richer, I could see it on my wideband and I had to lower the VE values to correct it. Its been running great with no knock codes at all. The only thing I can think of and its far out is that due to the retarded timing I was continuing to burn into the headers. By time it gets to the O2 (long tube headers) sensors it might read it as a good mixture. When I advanced the timing it changed how that burn occured (ie no longer burning while in the headers after it was pushed out). This is super far fetched in my opinion but its the only reason I can come up with
Are you certain, the additional advance you programmed in isn't triggering your knock sensor?