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Practical Standalone Tuning: Transient Tuning

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Transient Tuning


00:00 - Transient fuelling refers to acceleration enrichment which is essential if you want an engine that responds smoothly to sharp changes in throttle position.
00:09 While it's possible to tune acceleration enrichment to a degree on the dyno, you don't feel the response on a dyno as you would on the road.
00:17 I find the best place to tune this is on the road or track.
00:20 It's quite easy and doesn't take a lot of time.
00:23 The parameters available to you will depend on the brand of ECU you're tuning.
00:28 The Motec M150 uses a very special and unique acceleration mode which models the fuel film.
00:35 Since this is quite complex and unusual, we'll use a more conventional Motec 100 series ECU for our example.
00:42 Generally you'll have parameters to describe sensitivity which basically defines how much the throttle must move to request accel enrichment.
00:50 Enrichment volume, or accel clamp, which defines how much extra fuel will be supplied.
00:56 And accel decay which defines how quickly the accel enrichment is removed.
01:01 Each parameter will need to be tuned to suit your particular engine, although I find that most modern ECUs have default parameters which are pretty close usually.
01:10 This means you aren't starting from scratch and it speeds up the process.
01:15 An engine will require more acceleration enrichment at low RPM when air speed is low and this will reduce as RPM and air speed increase.
01:24 To accomodate this, the accel tables are usually two dimensional with RPM on the x axis.
01:31 I tune the accel tables by driving the car in second or third gear at each RPM in the accel table and testing the response when the throttle is stabbed open.
01:41 You want to watch what the air fuel ratio does as well as feel how the car responds.
01:47 While the air fuel ratio may show up problems with accel enrichment, often the response is not fast enough to truely show what's happening.
01:54 I start with the enrichment tables first.
01:58 Basically I'll adjust the enrichment numbers based on what I'm seeing on the air fuel ratio meter and what I'm feeling.
02:05 If we don't have enough accel enrichment, you'll feel a hesitation and see a lean spike on the air fuel ratio meter.
02:13 If you have too much enrichment, the engine may bog and you should see a rich reading.
02:19 Adjust each RPM zone until you have smooth and clean acceleration performance.
02:25 You may notice that above 5000 RPM you have little or no acceleration enrichment.
02:31 This is pretty typical since air speed is so high at these RPMs, that additional enrichment isn't usually needed.
02:38 Next we can look at the decay rate.
02:41 Often this doesn't need to be touched but if you notice the air fuel ratio is initially good as you open the throttle, but then moves either rich or lean, you can alter the decay time to fix this.
02:53 You're looking for a nice smooth transition in the air fuel ratio from your normal cruise mixture to the wide open throttle target mixture.
03:01 Lastly we can change the sensitivity if needed.
03:05 The aim here is to only bring in the acceleration enrichment when it's truely needed.
03:11 If the sensitivity is too high, you may end up with unwanted accel enrichment during small changes in throttle position.
03:18 If it's too low, you may find that moderate changes in throttle position result in a slight bog or doughy response from the engine.
03:26 My advice here is to use data logging to check what level of accel enrichment is being delivered and drive the car over a wide range of situations, varying your throttle position.