Road Tuning: Optimising Full Power Tuning
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Optimising Full Power Tuning
08.00
| 00:00 | - Since we've already spent a lot of time doing the steady state tuning, we'll already have a lot of our full throttle map pretty well-tuned. |
| 00:08 | If you've followed the ten-step process so far, we should have an engine that is tuned in steady state, up to about 5,000 rpm. |
| 00:16 | This means we only really need to complete the full power tuning above this point. |
| 00:21 | As with steady state tuning, we want to start with a rich mixture, and retarded timing, and slowly creep up on the tune, to ensure a safety margin while we get started. |
| 00:32 | This might sound like a difficult task, when we have no real idea of what the engine may want to see, but there are a few tricks we can use to make an educated guess about the map. |
| 00:43 | Since we've already tuned the full throttle section of the map up to 5,000 rpm, we'll already have a good idea of the shape of the fuel map so far. |
| 00:52 | I would follow this general shape, and extend it outwards to the higher rpm ranges. |
| 00:58 | When you do this, make sure that aren't just copying the 100 kPa full-load row, as often a restrictive intake, will allow manifold pressure to drop slightly at higher rpm, which can have the ECU interpolating between two rows. |
| 01:13 | I'd also add two to three percent more fuel into the top two rows of the fuel map, for my initial power runs, just to make sure I'm going to be safely rich. |
| 01:24 | Now we can look at the ignition map. |
| 01:26 | As with the fuel table, this should be now safe out to 5,000 rpm. |
| 01:31 | We've also copied the timing from 5,000 rpm, across to fill in the remainder of the table. |
| 01:37 | Before we start doing a full power run though, I'll highlight the entire two rows, at the top of the ignition table, and remove two degrees of timing for safety. |
| 01:48 | We're now ready for our first full power run. |
| 01:52 | For our first power run, we're only going to cover the section of the map we've already tuned. |
| 01:57 | I'm going to use second gear, and accelerate from 2,000 rpm, and back off at approximately 5,000. |
| 02:04 | If we've done our job properly, there should be no danger at all, and we should just be a little bit rich. |
| 02:10 | It's important at each step of this process, to listen carefully for any signs of detonation, although at this early stage, we should know that we're safe here. |
| 02:20 | Once we have our first run completed, and everything's looking good, we can start to increase the run rpm. |
| 02:27 | I like to increase the runs by 500 to 1,000 rpm at a time, which lets you start to creep up on the areas of the map which aren't tuned yet, without too much risk. |
| 02:38 | As long as there's no sign of any detonation, I'm only going to concentrate on adjusting the fuel map. |
| 02:44 | We'll deal with the ignition timing, once we have the fuel map dialed in perfectly. |
| 02:50 | Basically, we want to perform a run, check the Air/Fuel Ratio, and then perform any necessary correction to the fuel map, using the have-over-want equation we learned in the EFI fundamentals course. |
| 03:02 | When making these changes, we want to adjust the top two rows of the fuel map, to account for any interpolation, as well as extrapolating these changes out to the next rpm zone, so that the tune is going to be close, when we increase the rpm. |
| 03:17 | Once we've made any necessary changes, we want to do another run, to confirm the Air/Fuel Ratio now matches our desired target. |
| 03:26 | Once our AFR is on target, we can again increase the engine rpm by 500, and move further into the untuned area of the map. |
| 03:34 | We just repeat this process, until we've reached the engine red line. |
| 03:39 | When you are performing these runs, you want to be watching the Air/Fuel Ratio meter very carefully. |
| 03:45 | If the mixture starts to move lean, abort the run, so you can fix the problem and try again. |
| 03:51 | You're always safer to stop and fix any tuning problem, rather than hoping it'll come right by itself. |
| 03:58 | A well-tuned fuel map, should be reasonably smooth, and show the same general shape as the engine's torque curve. |
| 04:05 | If your fuel map looks something like this, then you're probably on the right track. |
| 04:12 | Just a note here about map resolution: While the 500 rpm increments we used, when we initially configured the fuel table are usually fine, if your engine has large changes in VE, across a narrow rpm range, you may find it's difficult to get good control of the AFR. |
| 04:30 | In this instance, it could be worth adding an extra rpm range, to help provide better resolution at this point. |
| 04:37 | Once we have the fuel map tuned perfectly, it's time to adjust the ignition map. |
| 04:43 | This needs to be approached carefully, as detonation can quickly damage an engine. |
| 04:48 | If at any time you hear detonation, abort the run immediately, and remove two to three degrees of timing before trying again. |
| 04:56 | As I've already mentioned, optimizing the ignition table on the road is difficult, with no feedback to let us know what the torque's doing. |
| 05:04 | What we want to do, is start slowly adding timing to the full load rows of the ignition map, a couple of degrees at a time, and then performing another run. |
| 05:13 | In my experience, most engines are knock limited to some degree at full throttle on pump fuel. |
| 05:19 | This means we want to slowly advance the timing, until we just start to hear the onset of light detonation. |
| 05:26 | This needs to be approached very carefully, as extended detonation will damage your engine. |
| 05:32 | If you hear detonation, stop, remove timing from that area of the map, and then begin again. |
| 05:39 | While you won't be able to feel the difference of one to two degrees of ignition timing by the seat of your pants, with experience, you will be able to feel the engine become more crisp, and responsive, as the timing gets closer to MBT. |
| 05:54 | By taking your time, and making small changes, you should be able to quickly build up an ignition map that is safe, and delivers very similar torque and power to an engine that has been Dyno tuned properly. |
| 06:08 | It is worth mentioning, that not all engines are knock limited, and this makes our job harder. |
| 06:14 | In this instance, it's possible to end up with the ignition timing massively over-advanced, since it won't end up causing detonation. |
| 06:22 | In this case, the only option we have is to rely on experience, which obviously you won't have, when you're just starting to learn how to tune. |
| 06:30 | From tuning thousands of engines, I've built some guidelines that I use, to help tune engines which aren't knock limited. |
| 06:39 | For a naturally aspirated engine, I would limit maximum ignition advance to around 32 to 34 degrees at full throttle, and maximum rpm. |
| 06:50 | At full throttle, and around 2,000 rpm, I would set the ignition advance to around 18 to 20 degrees, and then smoothly interpolate between these numbers. |
| 07:01 | For a turbo-charged engine, this gets a little harder, as the timing will depend on the boost pressure. |
| 07:07 | As a guide, I would limit maximum advance at one bar, or 14.5 PSI, to around 26 to 28 degrees at max rpm. |
| 07:17 | As boost increases beyond one bar, I would remove around two degrees of timing, for each 20 KPA step. |
| 07:24 | I find very few turbo-charged engines, that aren't knock limited though, so this is unlikely to be an issue. |
| 07:32 | With a well-tuned ignition map, you should see smooth changes in the ignition timing numbers. |
| 07:38 | Large, or erratic jumps in ignition timing, will result in poor driveability, flat spots, and hunting. |
| 07:44 | As a rule, I don't expect changes of more than five or six degrees, between adjacent cells in an ignition map. |
| 07:51 | Your finished ignition map should look something like this. |
