Variable Cam Control Tuning: Multi Bank Engines
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Multi Bank Engines
04.33
| 00:00 | - One more complexity that crops up when we're tuning the cam timing is on V configuration or horizontally opposed engines where there are 2 banks of cylinders. |
| 00:09 | In this style of engine, regardless whether it uses continuously variable cam control or fixed cam timing, it's very important to ensure that the valve timing events are identical on both banks of cylinders. |
| 00:22 | This is something that's easy to overlook and it may not even be immediately apparent but if there are cam timing differences from one back to the other, it'll affect the volumetric efficiency of the engine as we move through the rev range. |
| 00:35 | At best, this will impact on the performance the engine can offer but at worst it could also result in harmonics or vibration that could potentially be destructive. |
| 00:45 | A case in point here is a Honda NSX I tuned many years ago. |
| 00:49 | The 3.2 litre V6 engine was stock however it had been fitted with vernier cam gears which had been adjusted to the same degree markings on each bank. |
| 00:59 | The intention had been to future proof the engine for later on when the client decided to fit aftermarket cams. |
| 01:06 | On the dyno, it was apparent that there was a significant variation between the air/fuel ratio on each bank of cylinders. |
| 01:13 | This isn't necessarily uncommon however the 2 telltale signs were the magnitude of variation which was around 15% at low RPM and the fact that the variation changed throughout the rev range. |
| 01:26 | One bank started with a negative trim at low RPM and by the rev limit had steadily moved to a positive trim. |
| 01:32 | This is a classic sign of a cam timing issue which was confirmed with the compression test. |
| 01:38 | One bank of cylinders showed test results that were consistently 15-20 psi higher on each cylinder due to the effect of the valve timing events. |
| 01:47 | If you're dealing with a fixed cam engine fitted with vernier cam gears then it's important during the cam degreeing process to accurately degree both banks of cylinders. |
| 01:57 | Many engine builders and tuners try to take shortcuts here and apply the vernier timing marks from the cam pulley on one bank of cylinders that they've degreed to the other bank. |
| 02:07 | The reality is that there's no guarantee that this will give you the same results and there's too much potential for error to creep in from variations in the cam gears themselves through to the way the cam has been ground and even variations as a result of machining operations on the engine such as the block being decked or the heads being skimmed. |
| 02:28 | On engines with continuously variable cam timing, we have a different set of considerations because the ECU needs to be able to control each bank of cams separately in order to track the cam target that we've chosen. |
| 02:42 | This might sound complex but the reality is that we're just doubling up on the requirements for a single cam engine. |
| 02:48 | Each bank has a separate cam position sensor and a separate control solenoid. |
| 02:54 | The way this works is that essentially we have both cams tracking the same target table rather than a separate table for each camshaft. |
| 03:02 | This all comes back to the fact that we want the valve timing events to be the same on each bank. |
| 03:08 | Part of the process of configuring a multi cam engine control system is also calibrating or zeroing the cam position on each bank. |
| 03:17 | This is something we'll cover in detail as we move through the course. |
| 03:21 | A subtle aspect that many novice tuners incorrectly assume is that we can control 2 cams off a single output from the ECU. |
| 03:30 | The assumption here is that if we simply provide the same pulse width modulated signal to both cam control solenoids then we'll achieve the same result. |
| 03:38 | The reality is that this isn't the case and there isn't a direct correlation between the duty cycle being applied to the solenoid and the cam angle that we'll achieve. |
| 03:48 | To illustrate this, let's look at some data from our Toyota 86. |
| 03:52 | Here, we can see the cam timing for the inlet cams on each bank of the FA20 during a ramp run on our dyno. |
| 04:00 | Overlaid on this data is the cam target in red. |
| 04:03 | We can immediately see that the cam timing on each bank of cylinders follows the target very closely with only minor variations through the run. |
| 04:11 | In the next group of data we can see the duty cycle being sent out to the 2 cam control actuators. |
| 04:17 | While for the most part we can see the duty is similar, you can clearly see that they aren't identical and there's also the occasional spike in duty cycle on one bank or another to correct a deviation from the target. |
