Newbie VE question
Newbie VE question I have tried to do a search and can't find my answer. I am seeing all of these forumlas to calculate and tune for VE, but what do you change and why? Lets say you come up with the value for your VE, now what? What do you compare it with and where/what would be benefical to change? Also, my MAF table is stock, but I am running a descreened MAF, will that have an effect on anything?
Thanks
Thanks
I am a newbie to tuning too so experts please correct me if i'm wrong. When you change your camshaft (or heads, etc) the increased overlap kills your volumetric efficiency at low rpms. When you start your car it runs in open loop off the ve tables using rpm, map etc. If you don't change your ve tables after your cam swap your pcm will think the car is taking in more air than it really is and make you run rich causing the engine to surge or stall. So what do you change your ve values to? A lot of people change them to 50% at 400 rpm, 75% at 900, etc, and adjust using a trial and error process. Calculating ve from your maf readings would eliminate the trial and error, allowing to figure out the engine's true volumetric efficiency. I guess ve is used in a lot more places than open loop idle, but i think this is the most common reason for changing your ve tables.
Thanks for the reply. I tried to figure this out today and this is what I came up with. I did the formula for one of my data points and it was something like this. The calculated VE was 1364 and my VE table showed at that MAP and RPM, 1280. So do I change this table to 1364 and do more loging? What effects will this have on my car?
Here is another problem that I am having. My ltrims are way negative. At idle they are around -8 to -12 and at cruise -6 to -10. Should I adjust this with my IFR table first and then mess with the VE table or what? Sorry for the questions, just trying to get a better understanding of this.
Here is another problem that I am having. My ltrims are way negative. At idle they are around -8 to -12 and at cruise -6 to -10. Should I adjust this with my IFR table first and then mess with the VE table or what? Sorry for the questions, just trying to get a better understanding of this.
You need to do as much logging as possible and take the avergae of the data for those map/rpm values. If you are handy with access you can run queries that will average the data at those given points. Or you can download CrisB's LFA which will take in the log file and do all the calculations for you. Remember to remove all decel fuel cells and this will warp the data.
I think I covered everything
I think I covered everything
http://automation.slowcar.net/
When you export the log file remeber to export only the pid names and you wont get any errors
When you export the log file remeber to export only the pid names and you wont get any errors
Staging Lane
Joined: Dec 2003
Posts: 95
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From: Hayward, CA
Maf As far as the MAF sensor being descreened it would be ideal if you could find a stock untouched MAF sensor to use while you dial the rest of the tune in. Then when you feel you have that covered put you descreened MAF sensor back on that way you can see what affects it has and then adjust the MAF Freq chart in the pcm to correct for it.
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I appreciate the help. I still have one question. What effects does the VE table have on the performance of the car? Basically what does it effect? Sorry for the questions, just trying to get a better understanding of this.
I have tried to use ChrisB's analyizer, but am not quite understanding WHY the changes are being made.
I have tried to use ChrisB's analyizer, but am not quite understanding WHY the changes are being made.
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Verdad Gallardo The ve tables seem to be the base calculation for fueling. Decreasing the ve leans out the mixture and increases it richens the mixture. This is extremely important when running aftermarket cams esppecially cam that are big and dont want to idle or cams that surge. This tables main job is to tell the pcm how much fuel the car needs for a certain map and rpm. THe other tables are multipliers which add or subtract from that number to help dial the mixture in further