How to Degree a Cam: Optimising Cam Timing on the Dyno
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Optimising Cam Timing on the Dyno
03.27
| 00:00 | - When we're assembling an engine and fitting an aftermarket camshaft, we need to start with the cam at a known position and this will be the recommendations from the cam manufacturer. |
| 00:10 | This should provide good performance from the cam in line with the cam manufacturer's expectations however that's not to say that this location is going to be ideal for every application. |
| 00:22 | After all, cam timing is a game of compromise. |
| 00:25 | We still can influence the shape of the torque curve of the engine by advancing or retarding the cam from this base position and this can be done on a dyno to help optimise the engine's power delivery for our specific application. |
| 00:40 | These sort of cam timing adjustments need to be done on a sensitive engine dyno or chassis dyno, as often the sort of changes we'll be looking for are quite minor. |
| 00:50 | I recommend starting by getting the engine tuned and then performing two back to back ramp runs to record power and torque versus RPM. |
| 00:59 | The reason I recommend two runs is to ensure that you're seeing consistency and ensure that our results aren't being influenced by heat soak or other run to run variations for example. |
| 01:11 | Once we have a solid base run, we can make a cam timing adjustment. |
| 01:15 | If you're dealing with a single cam engine then you've only got one cam to adjust, and this is going to affect the inlet and exhaust timing events simultaneously. |
| 01:25 | I would recommend either advancing or retarding the cam in two degree increments initially so that you can see the effect of this change. |
| 01:33 | Later one when you're fine tuning the cam timing, you can start getting fussier if you like. |
| 01:39 | In general, advancing the cam will favour lower RPM performance, while retarding the cam will favour high RPM performance. |
| 01:47 | After making the change, I'll then make any required tuning adjustments and perform a further two runs. |
| 01:54 | It's important if you have a cam driven distributor or cam angle sensor, to make sure that your ignition timing is correctly adjusted after each cam timing change, otherwise this may influence your results. |
| 02:07 | Once I start to see a trend from of perhaps a power increase at high RPM, I'll continue changing the cam timing in that direction, until the gains stop or drop away. |
| 02:18 | With double overhead cam engines, we can adjust the intake and exhaust timing independently and hence we can also affect the lobe separation angle, or in other words the overlap of the cams. |
| 02:30 | I recommend starting with the intake cam as this will typically show the most significant effect on engine performance. |
| 02:37 | Once I've settled on the ideal intake cam location, I'll repeat the process on the exhaust cam. |
| 02:44 | Finally I'll then try a further two tests with both the inlet and exhaust cams advanced two degrees and then retarded two degrees. |
| 02:52 | There's a couple of other considerations we need to keep in mind here too. |
| 02:57 | Firstly we should expect that the engine performance will be optimal at or very close to the recommended cam timing from the manufacturer so if we find that we need to make changes of perhaps four degrees or more, then this may indicate that our initial cam timing might not have been correct. |
| 03:15 | Secondly, if we intend to adjust the cam timing, we need to know that there is sufficient valve to piston clearance, and this is something that should be explored during the assembly process. |
