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EFI Tuning Fundamentals: Table Resolution

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Table Resolution

08.39

00:00 - Now I want to talk a little bit about how we can configure the tables that we've just learned about.
00:04 Most aftermarket ECUs will allow the number of RPM and load zones to be altered, and a common mistake I see novice tuners make is to use way too many sites, thinking that a higher resolution will make for a better quality tune.
00:19 In reality, this isn't necessary and usually just creates more work for the tuner.
00:23 The reason we don't need to go crazy on the number of zones is because the ECU interpolates the results between two zones.
00:31 This means that if you're exactly midway between two zones the ECU will output a result that's the average of the numbers in the two zones.
00:40 Interpolation assumes that the engines VE will vary in a linear fashion between two sites.
00:46 And normally, this is a reasonably safe assumption.
00:49 Where this breaks down, however, is when we have an engine that exhibits a very rapid change in VE over a short RPM range.
00:57 We may see this with a very aggressive cam profile or an engine fitted with a cam switching system like Honda's VTEC.
01:05 In this instance, interpolation will probably not be enough to cope with the rapid VE change, and adding some additional resolution around these areas is the fix.
01:14 The guideline I use when configuring a table is to use 500 RPM increments on the RPM axis.
01:21 I will normally add another RPM row down around the idle area where we want slightly finer control at perhaps 750 RPM, for example.
01:30 I'll also add an RPM row anywhere that the engine shows a very large change in VE.
01:36 This allows ample control over air fuel ratio without creating a lot of extra work behind the laptop.
01:42 Deciding on increments for the load axis is a little more complex, since it will depend on the type of load sensor being used.
01:49 MAP is by far the most common input on an aftermarket ECU.
01:53 And normally, with a MAP sensor, I'll use increments of 20 to 25 kPa.
01:59 We may, however, want more zones in the ranges where the engine idles and cruises to provide finer control.
02:05 In this case, you can bring those increments down to perhaps 10 kPa in these areas.
02:10 Remember though that we can always add additional zones to the fuel and ignition tables later if we need to without adversely affecting the tune so we don't have to have our tables configured perfectly before we start tuning.
02:23 I'll typically start with a very basic table configuration and then add zones as I deem necessary once I begin tuning and I actually see how the engine responds.
02:32 If I've got a rich or lean area in the middle of two of my existing zones where the air fuel ratio is perfect, I'd simply go ahead and add a zone in between to allow me to correct that specific area.
02:44 In order to produce a tune that offers silky smooth drivability and response, the fuel table is more critical than the ignition table.
02:52 What this means is that when we're driving the car, we're much more likely to notice a lean hole in the fuel map, than we are to notice an ignition timing that's perhaps a few degrees off optimal.
03:03 This means that the resolution on the fuel table is generally more critical than the ignition table.
03:09 To demonstrate the power of interpolation, we're going to have a look at a dyno demonstration now, where we map an entire engine using a fuel table with just four sites and see how the results compare to a more conventional fuel table with multiple sites.
03:24 For this practical demonstration, we're going to have a look at exactly how powerful the interpolation inside the ECU is.
03:32 We're going to do that by performing two wide-open throttle full power ramp runs on our Nissan 350Z, and we're going to perform those two runs with tables, fuel tables, with vastly different resolutions.
03:48 Now before we get going, let's have a look at our ECU setup.
03:52 For this demonstration, we're using a Link G4+ ECU.
03:56 However, what we're going to look at the concept is totally applicable to any ECU and any engine platform for that matter.
04:05 So here we have our main fuel table.
04:07 And the axes here, we've got our RPM on our horizontal axis, and we've got our manifold pressure or load on the vertical axis.
04:17 You can see, for the most part in this table, we're using zones every 500 RPM approximately.
04:25 There are some discrepancies there.
04:27 You can see that in certain instances, I've been using slightly tighter zoning where the engine has moved through a large change in VE over a relatively narrow RPM band.
04:40 What we're going to do is perform a full power run with this complete high resolution table.
04:47 That is the sort of resolution that we might expect in a typical tuning job.
04:52 We're going to perform a full power ramp run now, and we're going to see the results in terms of power at the rear wheels, as well as our measured air fuel ratio on our main line chassis dyno.
05:03 So let's do our first run now.
05:24 So that's our first run complete now, and we measured 149.5 kilowatts, or 200.5 horsepower at the rear wheels at 6100 RPM.
05:36 So on the bottom of our screen here, you can see that we have our power in kilowatts being measured.
05:43 And then at the top of the screen you can see that we have our air fuel ratio this time being measured in units of lambda.
05:53 Okay, so now we're going to save that run, and we will call that Test 1 so we can reference it later.
06:01 Let's jump back into our laptop software now, and we're going to make a change to the resolution of our main fuel table.
06:09 Now to demonstrate this, the power of interpolation, what we're actually going to do, I'm going to import a previous table that I've already setup.
06:19 And in this case, you can see that now we only have four zones to our main fuel table.
06:25 We've got zero RPM and minus 100 kPa, the same load point at 7,000 RPM, and then under wide-open throttle, maximum load at zero kPa.
06:36 We've got zero RPM and 7,000.
06:39 So we've only got four points in that entire fuel table.
06:43 Let's do another full power ramp run now, and we will see how exactly that affects our power and our air fuel ratio control.
07:20 So there's our second run complete now, with only four points in our table.
07:24 And you can see that our maximum power this time is almost identical.
07:28 We're down a couple of kilowatts at 147.9 kilowatts at the wheels, or 198.4 horsepower.
07:37 If we analyse those two runs overlaid, you can see our power on the bottom.
07:43 The two runs essentially overlay right on top of each other.
07:47 There's almost no difference.
07:49 When we look at the air fuel ratio, of course we do have some discrepancies, in particular here at low RPM, around about 3,000 RPM, we have a rich point which we couldn't control with just four points in our fuel table.
08:04 Now I don't recommend that you try tuning every car with only four points in your fuel table.
08:10 This is just simply taking the concept of interpolation to extremes and showing you what the ECU is able to do.
08:18 And this is a good way of showing you that you don't need to have too many sites in your fuel or your ignition tables.
08:25 You definitely don't need to be packing in too many sites because the ECU is able to do the hard work for you in the background.