questions on AFR and VE tables

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Yves
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questions on AFR and VE tables

Post by Yves »

subject : SBC with itb's. Camshaft : 247/248 at.050", .600 lift, 106 lsa

I have a question around AFR tables (i'm a newbie, so please bear with me on this one). I could only do a short drive, since I'm waiting on a suitable filtration system for the stacks.

The engine idles around 69-70 kPa. When I rev the engine standing still, I see the indicator going horizontal over the VE table. During the short run and steady throttle I was seeing it move over the upper parts of the VE table. It only went to the lower parts on decel.

First question I have is : do I need to rescale my VE tables and AFR tables such that it has more resolution in the upper kPa zones and less in the lower kPa zones ?

Do I need to keep the AFR ratios that are currently in the AFR table the same but just change the resolution in the higher AFR ranges.

I know that this is too short to draw conclusions but I kinda want to avoid having to retune everything if I find this out later.

Thanks
elutionsdesign
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Re: questions on AFR and VE tables

Post by elutionsdesign »

I would. Why waste a whole lot of table with areas that you'll never drive in?

Not knowing what you have in your AFR table we can't say if you should change the values but the same logic applies to scaling. For example, its common to delay EGO correction until 1200-1400 rpm so it doesn't influence idle so why have a 800 rpm bin in your AFR table?
Graduate of EFI University.

I build, repair, install and tune Megasquirt systems in North Dakota and beyond!
Yves
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Re: questions on AFR and VE tables

Post by Yves »

Current msq
kaeman
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Re: questions on AFR and VE tables

Post by kaeman »

I have a small block chevy with itbs and I rescaled the table bins to reflect where the engine ran. I have the most resolution in the 60's to 70's and then in the 80's to 90's. My engine also idles at about 67kpa and cruises in the low 70's. but acceleration is mostly in the high 80's to high 90's. I will load my msq so you can look at what I did. with the afr tables and the ve tables bins.
2014-06-21 noise filter2nd analyzed.msq
64 el camino, 383 SBC, 11.7 to1 CR, accufab tb/rhs intake, 44lb injectors, trick flow heads, xr292r solid roller cam, belt drive camshaft, dry sump oil system, 2400 stall, turbo 350, spooled 9 inch, strange axles, 3.89 gears, dual wideband, full sequential fuel/cop, MS3x using 1.4.1 code.
wrenchdad
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Re: questions on AFR and VE tables

Post by wrenchdad »

You would probably get better range over your tables, VE, AIR, and TIMING going with ITB mode for load, it blends in one table SD for the low end and TPS for the upper loads. Work well for my 20v 4AGE with ITB. your idle MAP will probably come down with tuning, mine did.

Just my 2 cents worth, later wd

Edit didn't look at your msq, on my tablet, just guessed you are using MAP for load........ wd
Yves
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Re: questions on AFR and VE tables

Post by Yves »

kaeman wrote:I have a small block chevy with itbs and I rescaled the table bins to reflect where the engine ran. I have the most resolution in the 60's to 70's and then in the 80's to 90's. My engine also idles at about 67kpa and cruises in the low 70's. but acceleration is mostly in the high 80's to high 90's. I will load my msq so you can look at what I did. with the afr tables and the ve tables bins.
2014-06-21 noise filter2nd analyzed.msq
I could be mistaken but it looks like you've uploaded my msq...
Yves
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Re: questions on AFR and VE tables

Post by Yves »

wrenchdad wrote:You would probably get better range over your tables, VE, AIR, and TIMING going with ITB mode for load, it blends in one table SD for the low end and TPS for the upper loads. Work well for my 20v 4AGE with ITB. your idle MAP will probably come down with tuning, mine did.

Just my 2 cents worth, later wd

Edit didn't look at your msq, on my tablet, just guessed you are using MAP for load........ wd
Not sure how your itb's are setup, but mine has a vacuum chamber underneath the runners to which the runners are connected with a hole. It gives a pretty good reading on map.

If I got the info on ITB load correctly you need to first now 3 points with 90 kPa to set the tps switchpoints correctly.

Is there any other advantage to ITB load ? I hear alpha-n is a b*tch to tune.
wrenchdad
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Re: questions on AFR and VE tables

Post by wrenchdad »

Is this a track only car?

The thing with AlphaN for load is at low off idle throttle openings it's tuff to get the fuel where it's correct, especially with ITBs as you get so much air with very small changes in positions. Yes my intake has a vacuum log BUT I still had to add a restrictor and a volume can (inline fuel filter) in the signal line to the ms unit. As far as the switch point goes you can go with the default setting, that will get you up and running to do some logs so you can find what switch point your setup needs.

I ran SD on my ITB engine for a couple of years, then went to ITB mode and now I am running a MAF sensor for load, sticking with MAF gives the total range to tune with and just makes the car much more drivable, IMHO, I understand it's not for everyone but it works for my daily driver.

SO, if you don't have a restriction and volume chamber between the engine and the MS unit I would suggest adding it, you will get better readings. I found a factory made restrictor at Advance Auto, in their vacuum hose help section.

Hope this helps, later wd
Yves
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Re: questions on AFR and VE tables

Post by Yves »

Well the chamber is quite large.

A question on the MAF : the thought has crossed my mine about that as well as it's much more precise. However on a crossram ITB V8 you have basically 2 banks needing a large airflow. Can one use 2 maf sensors (1 for each bank) ?

Maybe another question : I have the sensor inputs (like O2 and map) jumping around quite a bit. The smooth factors are set to 90 which I was told is too high. I was recommended a setting of 50. Is that a more normal setting on ITB's ?
kaeman
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Re: questions on AFR and VE tables

Post by kaeman »

On the subject of lag factors..... I have found that the closer to 100(pure signal) the better. I have found that my engine runs better and better by reducing the lag( going closer to 100) Your engine response is very rapid because of the itb manifold, you don't want something slowing down the information of what is going on with the engine unless you start having noise on your signals, then you let it average the signal by moving down from the 100 towards the 90's or below to get rid of noise on your input provided its not a wire routing or bad ground kind of noise. But if you want the engine to make quick responses to quick changes you don't want to slow down the info to the ecu. I am currently trying to tune a hard throttle stab from idle on my engine ve table its listed under rich misfire lean afr reading...or something like that. but I found that the quicker my ecu found out that the throttle blades opened and that the engine and map reading jumped the better the ecu has been at responding to the problem. the msq I am posting tonight on the other topic had the lag factors set to 100 for rpm, map, tps, and afr. and 95 for bat/clt/mat/ as I recall. the only time I have a stumble is from idle with a real hard stab of the accelerator pedal, during normal driving it drives great and has very good accel(even from idle) and smooth cruising. I am contemplating going to itb mode but haven't bitten the bullet yet.
GOOD LUCK
PS I have been running SD on this engine for about 8 years. I am going through all the new tuning because of changes to the efi system.. upgraded to ms3 from ms1 and 44 lb injectors from 29's. Plus going to add spark control in the near future. I haven't had a problem with the map signal. but I have a small vacuum chamber.. 1/2 id by 2 1/2 long tied to all eight runners my map signal is pretty stable and has good response time.
64 el camino, 383 SBC, 11.7 to1 CR, accufab tb/rhs intake, 44lb injectors, trick flow heads, xr292r solid roller cam, belt drive camshaft, dry sump oil system, 2400 stall, turbo 350, spooled 9 inch, strange axles, 3.89 gears, dual wideband, full sequential fuel/cop, MS3x using 1.4.1 code.
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