If I pull fuel from my ve table @ x rpm, does it lean out wot at the same spot? If so then what part of the ve table is used to base wot(95-100kpa) ?

 

WOT uses whatever spot in the VE table corresponds to your RPM x MAP, interpolated between table values.

So if you have a hot enough engine to pull vacuum at WOT, or you are just running in poor high altitude air, then your MAP will be lower to refelct that, and if your VE tables are set right, you will also have that much less fuel.

 

So I can pull fuel from the Ve tables at 95-100kpa (at x rpm)and it'll be similar to pulling it from the pe a/f vs rpm?

 

Kind of, yes. VE isn't the same as PE, but pulling fuel from the top of VE will have the same effect in the end that pulling fuel from PE would.

Ideally the VE tables should be set 'right' to match the true VE curve of the engine. Then you can tailor your exact WOT AFR by manipulating PE. The benefit of doing it that way is that then you can predicatbly alter your WOT AFR just by changing PE. If you're schlepping around fudging both values to 'dial it in', then you find you need to change your AFR , you'll have more trial and error to get it right because you're not letting the simple mathematical reltionship do it's thing

 

Thanks Ed,

I just wanted to be sure of what I'm doing. All my information has been confirmed. I was working on a high output engine and the ve tables was way,way off. The car was so rich that raw fuel was coming out the exhaust under all conditions. I tuned it for part throttle first. At the same time I just took fuel from the entire table. I wanted to only go into the PE after the car was less rich. That way the wot stuff would be cake. I think the VE tables at 100kpa should be within about 10% before going after WOT tuning. If the VE is fairly close it seems that the PE tables can adjust fuel more precise.

 

VE tables at 100 MAP at or below 3200 rpms would you not be in PE? If so you cannot read that cell and tune your fuel tables in high map areas w/o disabling PE? how can any high map be optimized if PE is engaging?

 

It's difficult.
This where data logging and an ecm bench show their colors.
If you can get near 100 K/Pa you can see what the PW is there. Once you get that number, you can to some degree forcast what you'll need. Since VE drops after peak torque, while you might need some excess richness, you can at least get the VE table close, then when you invoke PE the calculations will be more accurate. then followup with the following,

And/or,
Another way is setting your PE to some given AFR, and then trim the VE table to get your actual AFR to match the commanded AFR.

3rd method is just experimenting until you get it. With experience you can shorten the time it takes, but it still takes time to get it.

 

so do you think that there is a gain in pe resolution (in general), considering once the ve table is close it takes less % to see changes made in PE fueling?

 

Hi Tim, welcome back.

I will try and give a perspective on tuning the VE tables that may shed some light for you. Here is a hint in how to think about SD that may help you in tuning.

As you climb in elevation from sea level, for every 100 meters (or yards), that you climb in elevation, you loose 1 kpa on the MAP sensor. At 1,000 meters (or yards) you will run at around 90 kpa @ WOT. At 2,000 meters (or yards) you will run at around 80 kpa @ WOT.

The goal is to make the VE tables run as close to stoic (14.7) when you are NOT in PE. Tuning with a WB really can help you attain this. Also, due to the thinner elevation, you can run (and even need) more spark advance to help regain performance from the thinner air. This is very similar to why you need higher spark advances when you run a lean AF ratio with Highway Mode.

Once you have tuned your VE tables to always give 14.7:1 when NOT in PE. Then you simply tune the PE tables to provide the desired WOT AF Ratio (somewhere between 12.4 -12.8 for most engines yields the max power).

If your VE Tables are tuned for "elevation" to 14.7:1 when NOT in PE, then once you invoke PE, it will provide the nearly the same AF Ratio when you are in PE regardless of elevation (and MAP value).

Remember a post I made about "tuning a maxed out MAF system" at sea level for an optimum WB reading and then taking the MAF car to 3,000 feet (1,000 meters/yards) and checking the WB AF ratio? The answer was, with a maxed out MAF system, your AF ratio will get richer as you climb in elevation and may have to retune if you climb high enough and wish to maintain an optimum AF ratio for WOT. With SD, you can actually tune the engine to run optimum at all elevations with little need to ever tweak it again.

When tuning the VE tables in SD, an easy way to think of the 80-100 kpa MAPrange is to think "WOT at higher elevations", and tuning for "optimum performance in all elevations". Just get the VE tables tuned first, and then when you optimize PE - it should be optimized for ALL the upper VE values (though you may still need to do a little tweaking if you are an all out racer struggling for every .01 secs).

This is one of the advantages of living in a mountainous area...you actually get to see these differences and need to tune around them.

Hope this helps.

 

It does help out. I have done many things since my departure from here. I have tuned cars at the track.I have tuned cars on the dyno. I have nailed driveability issues on many different engines. Not saying that I'm special but I have matured(tuning wise) in the past 8 or so months. So it's nice to be back. I have alot of info to exchange. This thread was just to confirm if I pull out fuel in the ve table at 95-100kpa area(depending on wot map output) at x rpm, the effect will be the same as removing fuel from the wot af vs rpm at the same rpm. Your thoughts?

 

It will only be the same for the specific MAP value at a particular elevation. The PE table will do it for ALL MAP values.

What you need to determine is whether you VE table is off at a particular elevation (then modify the VE Table) Or at ALL elevations (at which point, you need to use the PE Table).

This is why you always need to tune the VE Tables before you tune PE on SD.

 

what about ve master. When I use that it only tunes some of the ve tables. It is mostly where your normal operating range is. It st ok to have a gap from 3000rpms up that vemaser can leave? I usually just modify the ve tables where the engine runs. Unless the entire ve is way off.

 

I use the "graph function" of TunerCat and use it to "fill in the blanks". You can often see the "shape" of the VE Table forming and use it to extrapolate the rest of the curves.

Also, while I think VE Master is fine for the "most travelled" area of the VE table where you are just cruising around, I don't think it does a good job on the "netherlands" of the VE table...those high kpa values and high rpm values.

For that, I still prefer to just capture a LOT of data and then sort the data by RPM/MAP and then review ALL the BLM/INTs (if you don't have a WB O2 sensor or lock the ECM in open loop and use a WB if you got one). Then, for a particuler RPM/MAP range and use various statistical analysis (mode, mean, standard deviation).

I find a "good dyno hill", disabling PE and sometimes holding the brake works while in 2nd or 3rd gear works great in getting those high rpm/high map values.

Best if you are also close to sea level to start with. If you do all your tuning at 3,000 feet, it's impossible to tune above 90 kpa as you have no data.

 

That's really instructive, thanks Glen.

What SD system are you talking about (the '808s I'm familiar with don't work like this), and how does it know it's time to go into PE mode (ie is it invoked over x kPa MAP for instance)?

John

 

I'm not Glenn but i think i can answer. He's likely talking off his specific experience with '730 ECMs, but AFAIK all SD EFI uses basically the same kind of approach as he is describing. You have main VE and a PE adder on top of that.

As for when you hit PE, in the $8D it's invoked via % TPS vs. RPM.

There is also a minimum MAP constant for PE, but that shouldn't ever pose a problem. I wonder if that constant even really help or does anything of value or if it's just some kind of failsafe? Anyone know?

 

please explain why i have never seen 100 map?. is 100 map only in theory? max is 90 map my car. i have a speed density 7747. is that inability to hit 100map a function of the size of venturi/intake? does that suggest my TB's need to be larger in that the motor needs more air at WOT? sorry if a dumb question but i have visited 90 map often for tuning but never see 100. maybe not in that cell long enough to cause it to populate?
so much to learn. 0deg C this am...

 

Did you read the part about altitude that Glenn posted? I'm pretty sure wisconsin ain't sea level...

Wanna know for sure what your maximum MAP value is. Easy as cake. Turn key to on, observe MAP. With the engine off, MAP = atmospheric.

 

My MAP drops to ~96 at WOT. At engine off / key-on it is 100kPa. 58mm TB and No airbox as a test. I have a restriction in my intake manifold or head! I think it's the 1204 ports on the intake manifold. Keep in mind I rev it high and only see the vacuum at higher RPMs.

Tim

 

how are you able to see fractions of map? does the 7747 and winaldl allow me to read exact % ????

 

I'm running a 730 and we see the exact MAP value.

Tim

 

Isn't it very hard on the engine to run it at stoch at high MAP values? Cylinder temps will get very hot!

 

Nope.

No harder than holding the engine in WOT on a dyno or racing in general. Remember, when not in PE, you don't have the extra spark either. Heat is also generated by the amount of power you are making. You are definitely making less power than in PE.

I also look for detonation as my first sign of problems as well as rising coolant temp. I've encountered neither as I am also logging this as I am doing this. I can't say the same for when I've been in PE.

But if you don't feel comfortable using this method to tune your VE tables, feel free to use other methods you feel are better. This is just the way I have been tuning for a number of years now on a very high mileage engine I may add.

 

Glenn, I'll second your method. I have seen MANY engines go lean on the dyno. That is way harder on an engine than short near-wot runs to tune ve. Not to mention that some engines max peak power at 13.1:1 or so. Oh, and those engines that ran 15:1+ on the dyno didn't see any engine damage.