Variable Cam Control Tuning: Optimising Vernier Adjustable Cam Control
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Optimising Vernier Adjustable Cam Control
23.06
| 00:00 | - In this module we're going to be demonstrating the process involved in optimising the cam timing if you've got a conventional fixed cam style of engine that has been fitted with vernier adjustable cam gears. |
| 00:11 | In our example we're using our Nissan SR20VE engine which is a conventional SR20DET and we've swapped a Nissan VVL cylinder head onto this engine from a P11 Primera. |
| 00:25 | This is a relatively common combination and the superior flowing head provides massive improvements in performance compared to a conventional SR20DE or DET cylinder head. |
| 00:38 | We've fitted the P12 cams that are in the cylinder head with a pair of Kelford vernier adjustable cam gears and this runs off the conventional SR20 cam chain arrangement. |
| 00:48 | This does add a little bit more complexity to the task because in order to make a cam timing change, we do need to actually remove the rocker cover. |
| 00:57 | In a lot of engines using a cam belt particularly this is much easier. |
| 01:00 | There's usually or at least often a removable part of the cam cover that we can take off for the purposes of our tuning, giving us nice and easy access to the vernier adjustable cam gear or cam gears. |
| 01:14 | In our case it is a little bit more time consuming but you will come across this on some types of engines, particularly those that do use a cam chain. |
| 01:22 | One key aspect that you do need to be mindful of when you are making adjustments to your cam gears in this way is looking at how the base timing or base ignition timing of the engine is derived. |
| 01:36 | In a lot of instances, this will be derived from a cam angle sensor or sometimes even a distributor that is run directly off one of the cams. |
| 01:44 | If this is the case then there's going to be an extra step required here because when you adjust the cam timing on the cam that drives the cam angle sensor or the distributor, this in turn is going to impact your base ignition timing and if we don't address this then it's going to at best affect our results because what we're going to essentially do is end up advancing or regarding our cam timing and at the same time advancing or retarding our ignition timing. |
| 02:13 | Obviously if we want to see the true impact of our cam timing change, we want to hold all of our other parameters as close to static as possible so I mean here our fuel delivery and our ignition timing as well as our temperatures and pressures as you'd expect. |
| 02:29 | If we're advancing or retarding the ignition timing with our cam timing, this will impact on our results and worse case if we end up with our ignition timing over advanced and we run into problems with detonation, then this could also be potentially damaging to our engine so that is probably the key tip that we do need to keep in mind with engines that run that cam angle sensor or distributor straight off the camshaft. |
| 02:53 | In our case while the P11 cylinder head does in stock form use a distributor, we've actually converted here to direct spark coil on plug and we are using a crank trigger system so in our instance, we don't actually need to worry about this, we will be solely focusing on changing our cam timing, the ignition timing will not be impacted. |
| 03:15 | And we need to talk a little bit about the process we're going to go through here. |
| 03:19 | We're going to start by getting our engine up and running, getting everything up to operating temperature and we're going to perform 2 base runs. |
| 03:27 | And when I am doing this type of optimisation, understandably there is a bit of down time where we have to shut the engine off and make the cam timing adjustment. |
| 03:36 | And this down time does affect the temperatures and allows a little bit of time for heat soak and aspects like this. |
| 03:42 | So when I am making cam timing adjustments in this way, generally once I've made my adjustment I'll do 2 pulls on the dyno back to back and this just makes sure that we are getting consistency and gets rid of some of those run to run variations. |
| 03:55 | Typically I'll do 2 runs and I'll actually focus on the second of those 2 runs for my comparison to see whether I've gained or lost. |
| 04:03 | The reason that this is important, other than the fact we need to get rid of that heat soak that I've just mentioned is that often we will be looking for relatively small improvements and if we're looking for small improvements these can often be hidden in run to run variation due to that heat soak so it's just about trying to be as consistent as we can. |
| 04:23 | At the same time I'm always going to be trying to start my ramp runs from the same engine coolant temperature, oil temperature and air temperature or at least holding those parameters as close to being the same as I possibly can. |
| 04:34 | Now we also need to just discuss the starting point for our cam timing. |
| 04:39 | I know a lot of tuners and engine builders will fit a set of aftermarket cams with vernier adjustable cam gears and simply fit them on the 0 marking on the cam gears and then degree them on the dyno. |
| 04:50 | And while yes we can get results in this way, what it means is that we've got no idea where the camshaft centrelines are. |
| 04:57 | We've also got no idea how much we can advance or retard the cam timing before we run into potential problems. |
| 05:04 | Remembering from the body of the course as well what we want to be mindful of on our intake cam is that as we advance the cam timing, this is the area of danger because we're getting the valve opening closer to the point where the piston is at top dead centre moving into the intake stroke. |
| 05:21 | Conversely on the exhaust cam, retarding the camshaft brings us closer to the potential of having piston to valve contact. |
| 05:28 | So it's always advisable to have a really good understanding of exactly how much you can swing the cams without any risk of mechanical damage so this is why it's always advisable to degree the cams to the manufacturer's recommendations to start with. |
| 05:45 | That should at least get you in the performance ballpark and then you should only be needing to make minor adjustments of perhaps 2-4° from that starting point. |
| 05:53 | Alright now that we understand what we're doing, we're going to get our engine up and running here on our dyno and we'll get it warmed up and we'll perform our first 2 base runs. |
| 06:03 | Alright we've got our engine up and running, up to temperature, we're ready for our first run so let's see what our results are. |
| 06:29 | Alright our first run complete there, we're showing about 430 wheel horsepower and what we're going to do is we'll save that run and we'll straight away just repeat exactly the same run. |
| 06:40 | So we'll give this a reference name and we're going to call this baseline 1 and that's just going to allow us to easily reference that once we've done our second run. |
| 06:51 | We'll be able to see the second run overlay on top of that first run, just to see what sort of run to run variation actually does exist so let's get our second run underway now. |
| 07:18 | So we can see in this case, our second run there has netted us basically exactly the same so we've really seen almost no run to run variation which is ideal but it's not always going to be the case. |
| 07:29 | Always best though to do those 2 runs just to see what sort of variation if any exists. |
| 07:34 | We'll call that, we'll save that run and call that baseline 2 so we're going to be able to use that for our reference as we move forward and we're now ready to perform our first cam timing change. |
| 07:43 | Now what we're going to change here really depends on what we're trying to achieve. |
| 07:49 | In our case if we look at our power curve here we can see that our green line for our power is still climbing right at our, the end of our run at 7500 RPM. |
| 07:58 | Now some of that is impacted by the fact if we look at our boost curve above, we can see that our boost curve actually is still continuing to climb as well so that artificially increases our power curve at higher RPM. |
| 08:11 | So it's not 100% a true indication of what the power curve of the engine looks like but in our instance what I want to do is try and improve the low end performance of the engine and I don't mind sacrificing some high RPM performance. |
| 08:24 | Now depending on where our cams are currently degreed is going to to depend on exactly what we may want to do but in general if we want to improve our low RPM performance, advancing the cams is generally going to achieve that aim. |
| 08:38 | We want to make one change at a time here. |
| 08:41 | Given that we know that our engine performance is going to be more sensitive to intake cam timing, it makes sense that we're going to start there. |
| 08:50 | So what we're going to do is advance our intake cam by 2°. |
| 08:54 | This starts with requiring us to remove the coil system from the rocker cover. |
| 08:59 | Once we've got the coils out of the way we can then remove the rocker cover. |
| 09:04 | Now a trick that I do use on some engines, while I am doing this just to speed up the process is to only use maybe 4 or 6 of the rocker cover bolts to secure it while it's on the dyno during the tuning process. |
| 09:16 | Of course once we've actually got the cams degreed to our liking, we can then fit the remaining bolts. |
| 09:23 | Once we've got access to the cam wheels on the front of the engine, this is a case of using a strong arm on the crankshaft pulley so that we can rotate this. |
| 09:32 | We're going to simply loosen the cap screws that lock down the vernier cam gear and we're going to need to rotate the crankshaft so that we can access all of those, some of those will be blocked by the front of the cylinder head so we can't get access to all of those without rotating the crankshaft. |
| 09:51 | The key here is what we want to do is make sure that the cam wheel is aligned so we can see the degree markings on the cam wheel. |
| 09:59 | We want to leave one of our locking bolts at least tightened down slightly and that way we can make sure that the cam isn't going to move due to the valve spring pressure when we loosen them all off. |
| 10:11 | We can then get a ring spanner onto the cam pulley bolt and we can gently rotate the cam pulley until we've advanced the cam, in this case 2°. |
| 10:22 | Generally when I am starting I'll make 2° movements, once we're really starting to get down to splitting hairs on the final results we can make smaller movements but 2° is generally enough that well actually be able to see the effect of our cam timing change and get a bit of an idea as to whether we're going in the right direction. |
| 10:41 | Of course once we've moved the cam to our new positon we're going to tighten up those vernier locking bolts again and again rotating the crankshaft so we've got access to those, it's then a case of refitting our rocker cover and we can get our engine back up and running. |
| 10:58 | Alright we've got our engine back up and running after making our cam timing adjustment. |
| 11:02 | It's now a case of getting the engine running on the dyno, getting rid of all our heat soak, getting our temperatures under control and peforming our 2 ramp runs to get an idea of the difference between our baseline. |
| 11:14 | Now we're going to leave our baseline up as a reference on the dyno while we do this, we'll jump ahead and we'll just show you the second of our ramp runs. |
| 11:40 | Alright we can see with our run there, we've made 425 horsepower at the wheels. |
| 11:44 | It's very difficult to tell during that ramp run whether we've really made much of an improvement, looks like there was a slight improvement down low but we can definitely see compared to our reference run we have reduced our power up top which is exactly what we'd expect from this change and I'm absolutely OK with that if we can claw back some low RPM peformance. |
| 12:03 | Let's save this run now and we'll overlay it directly so we can get a better idea of exactly what the result of that change has been. |
| 12:11 | All I'm going to do here for simplicity is call this run intake plus 2. |
| 12:16 | When you're only making 1 or 2 changes this might not seem too relevant but when you are making a lot of back to back ramp runs, it's a good idea to use a naming strategy like this just so you can reference back to your earlier runs and know exactly what that run entailed. |
| 12:31 | Let's save that and we'll overlay. |
| 12:33 | Alright so with our 2 runs overlaid on top of each other we can see that the cam timing change, while the difference has been minor it has done exactly what we'd expect. |
| 12:42 | The last run we just did with our intake cam at plus 2° is in yellow, our baseline is in red so we can see that right through this mid range here we have seen a small but real improvement in performance. |
| 12:54 | Particularly around this area here we're seeing around about a 4 horsepower increase. |
| 12:59 | It's not until we get up to about 6500 RPM, maybe even 7000 RPM we start to see that our previous run with our cam timing at 0, our red line does take off at the top end but again I'm trying to sacrifice a little bit of top end performance here for an improvement in our bottom end so while the change that we've just seen hasn't been significant it indicates we're going in the right direction. |
| 13:23 | Now what we're going to do here is use a little bit of common sense. |
| 13:26 | If we advance the cam timing like we've just done and we see an improvement in the area that we're interested in optimising, simply put we're going to go further provided that we know that we've got the room to swing that cam further without the risk of piston to valve contact. |
| 13:42 | So in our case, we'd simply go another 2°. |
| 13:44 | On the other hand if we've made that change and we saw no improvement or worse still we've gone backwards well, we'd simply reverse that change and actually try going 2° the other way so we'd try regarding our camshaft from this position a total of 4° or in other words 2° retarded from our baseline run. |
| 14:01 | So for our next change we are going to go another 2° in our intake cam and see the results of this. |
| 14:09 | We're not going to show you the process in the engine bay because it's a rinse and repeat of what you've already seen so let's make that cam timing change and we'll get our engine back up and running. |
| 14:18 | Alright we've got our engine back up and running, the intake am now plus 4° from our baseline and while we do our next runs we're going to end up with our last run which was plus 2° as well as our baseline reference, both on the screen at the same time so we'll be able to see in real time what gains or losses we've got. |
| 14:35 | Again we're going to want to get rid of any heat soak and again we're going to be performing 2 runs so let's jump ahead and we'll just have a look at the 2nd of those runs now. |
| 15:02 | OK so with that run complete there we can see that we've actually gained quite noticeably through the mid range, even compared to our last run at plus 2°. |
| 15:11 | Looks like with that particular run as well we're almost back up to where we started in terms of our peak power. |
| 15:16 | That could still be down to some minor run to run variation but what we'll do is we'll save that run and we'll overlay it on top of our last runs so that we've got a better idea. |
| 15:25 | Of course we're going to call this plus 4° so let's have a look at what we've got. |
| 15:30 | Alright so straight away we can clearly see that our green run which is our plus 4°, it's a winner basically everywhere. |
| 15:36 | Compared to our baseline in red we can see that our baseline does still show slightly better performance up above 7000 but we really are splitting hairs, the difference here between our green run and our red run is only around about 2 horsepower. |
| 15:52 | On the other hand though if we look at let's say 5000, 5200 RPM, we can see that we've gone from our original baseline, 233 horsepower, we've gone all the way up to 250 so really powerful gain in our mid range with no real loss in our bottom end. |
| 16:10 | So we're again heading in the right direction. |
| 16:13 | With these sort of results we'd simply go further again. |
| 16:17 | Now before we do that I just want to talk about our fuelling because we've ignored that at this point, we've got our lambda being plotted down below so we can see that particularly right down at the start of the run, our red run here, at the start of our run at about 2500 RPM we can see there's quite a substantial difference here between our red run and our green and yellow runs and this is something we need to be mindful of. |
| 16:42 | Particularly if we are making manual adjustments to our fuel tables. |
| 16:45 | Obviously as we adjust our cam timing we can expect the volumetric efficiency will change requiring differences in our fuelling and we just want to make sure that our fuelling isn't dramatically different because this in and of itself will influence our results. |
| 17:01 | In this case we really haven't seen a significant change to our fuelling right the way through. |
| 17:05 | It's only that original ramp run there in red that we'd see a slightly leaner air/fuel ratio right at the start of the run so we can disregard that. |
| 17:13 | What we're going to do, because in this case I know that I comfortably can move the intake cam at least another 4°. |
| 17:20 | We're simply going to go again and we'll advance our cam another 2°. |
| 17:24 | Again we'll jump ahead to the point where we've made that cam timing change and we've got our engine back up and running. |
| 17:30 | We're back up and running with our intake cams 6° advanced, we've got our temperatures under control again and we're ready to complete our second ramp run, let's have a look at our results. |
| 17:57 | Alright so from looking at our run during the ramp run it looked like we really still aren't giving anything away and potentially there was a gain over our previous run with our cam advanced 4°. |
| 18:09 | Let's save that and have a look and see how that actually does stack up. |
| 18:13 | Alright so we've got a few runs going on now and we'll get rid of some of our previous runs so for example we know that our yellow run which was advance 2° really not the one we want there. |
| 18:24 | Doesn't really perform that well so we'll get rid of that so now we're overlaying our red run which was our baseline, we've got our green run at plus 4° and we've got our white run at plus 6°. |
| 18:35 | And we can see we're starting to get to a point of diminishing returns here, we have actually seen a small improvement with the cam advanced 6° here, we haven't really given anything away in the top end, we're very much similar to where we were, in fact if we compare our plus 4, our green run, 431 horsepower there at 7500 RPM, we've actually dropped about half a horsepower there give or take, we're down to 430 but I'd really be splitting hairs over that. |
| 19:03 | What we can see though is we have gained very marginally here through around about 5000 RPM and then we've got another little blip here at about 6700 RPM. |
| 19:13 | Given the relatively small improvement though, although we haven't really given anything away, I'm not going to go any further on our intake cam timing. |
| 19:23 | I know that I can safely go another 2° but in this instance I don't suspect we're really going to see much more improvement, we may start to go backwards so we're going to leave our intake cam there advanced 6°. |
| 19:35 | The next step here, we're going to start looking at our exhaust cam and again we could go either way with this. |
| 19:43 | Going to start here by advancing the exhaust cam 2° and we'll see what effect that gives us. |
| 19:49 | Again we're not going to go through demonstrating the process of making that change to the cam timing, it's exactly the same as what you've already seen so we'll get that done and get ourselves back up and running again. |
| 20:00 | Alright we're back up and running with our exhaust cam advanced 2°, let's get another run on the dyno and we'll see what the result of that change has been. |
| 20:26 | So we can see with our run complete, we actually picked up a little bit of power there right in the top end as well, 432.8 let's call it 433 horsepower. |
| 20:35 | Let's save this run and overlay it because it was difficult during the run to really pick up how much of a difference that exhaust cam timing change made. |
| 20:43 | Alright so we've got 3 runs overlaid here together, our red line which is our base run, we've got our purple line which is the one we've just completed with our exhaust cam timing advanced 2°, our intake plus 6 and we've got our white run which was with our intake at plus 6 so let's just get rid of our baseline run for a second so we can just overlay just the last 2 runs and see solely the effect of our exhaust cam timing. |
| 21:08 | And you can see we are really starting to split hairs. |
| 21:11 | There has been that small improvement in performance right up in the top end where we've picked up about 2 horsepower and realistically if I click through here, we can see that in almost all situations here, the exhaust being advanced 2° has shown a very very small net improvement but generally we're talking around about a horsepower or thereabouts. |
| 21:33 | We have seen right in the very bottom end that we're actually doing a little bit worse off but given that we're only down at around 2700 RPM here I'm really not too worried. |
| 21:42 | Now from this point here we've obviously seen a small but measurable improvement from our exhaust cam advance, I don't suspect there's really much more power or torque on the table here given how small that change had been but given we've gone plus 2° we've seen a gain, from here we would continue and try plus 4° and see if that's given us a gain. |
| 22:03 | From here as well, once we've gone through the process of optimising our intake cam then optimising our exhaust cam timing, we need to understand that when we do move the exhaust cam, this can have a knock on effect to the optimal intake cam timing so it can be an iterative process of going between the intake then to the exhaust and the back to the intake cam again. |
| 22:25 | I'm not going to do any further runs here because the process is simply a repeat of what you've already seen. |
| 22:32 | It is really important though just to mention that once you are comfortable with the final results of your cam timing, it's essential to go back and properly lock up those locking bolts for our vernier cam gears using a product such as loctite or something similar just to make sure that nothing is going to move in use. |
| 22:52 | The other aspect here of course is once we've finalised our cam timing we would also need to go through and apply any required changes to our fuel and ignition tables to tidy those up. |
