184 | Tuning Ghost Cam HP Tuners
It’s a controversial topic for the purists among us, however the fact remains that there’s a large number of people out there who want the lumpy idle associated with a large cam profile, without the associated downsides of fuel consumption and driveability. In this webinar we’ll look at the ‘ghost cam’ technique that offers a similar lumpy idle without the expense of a physical cam upgrade. In this webinar we’ll be using the HP Tuners software coupled with a LS2 6.0 litre V8.
- Hey guys it's Andre from High Performance Academy, welcome along to another webinar. And in this webinar we're going to be discussing a relatively controversial topic which is tuning in what we refer to as ghost cam. Now for today's example we are going to be using our SS Commodore fitted with an L98 engine. So we're going to show one technique of setting up ghost cam. In this particular example, the L98 engine is a single cam push rod engine.
What this means is that the cam timing or relationship between the intake valve and the exhaust valve is obviously fixed. So we can't actually adjust our cam timing so we're gonna be showing a technique where we're going to be altering our ignition timing. On a lot of the more sophisticated engines particularly the Coyote Boss engines, fitted to late model Mustangs where they have quad variable cam control, this can also be affected by adjusting the cam phasing or overlap as well. So I say it's controversial because essentially it is a trick. What we're trying to do is electronically create the lope of a large aggressive cam profile that provides a lot of overlap.
I think particularly for a lot of enthusiasts with the V8s in particular, that large lopey idle of an aggressive cam is something that a lot of enthusiasts sort of aspire to. But of course this comes with a few downsides. First of all is the cost of the cam swap. It's a reasonably involved job to perform a cam swap. While yes of course fitting the right cam into your engine is going to provide you with a significant improvement in performance, this performance improvement is usually realised higher in the rev range, and it also comes with a reasonably big sacrifice in that a really large aggressive cam profile is going to destroy your around town fuel economy.
So that's something that a lot of enthusiasts maybe aren't prepared to go down that path. So regardless of your own personal thoughts on ghost cam, we're going to talk about what it is, how it works and we'll see how we can set this up using HP Tuners on our SS Commodore. As usual, we will have a section for questions and answers at the end of the webinar. So if there's anything I talk about today or anything related to the topic, please ask those in the comments and the guys will get those through to me. OK so as I've already mentioned here, we are running a single cam engine.
Our cam phasing between inlet and exhaust is fixed. So we can't get the loping idle by increasing the overlap duration. So we've got no option there. What instead we're going to do is use another technique where we are adjusting the ignition timing aggressively at idle. Advancing and retarding the ignition timing significantly and very quickly, and this tends to give a similar effect to that loping idle, or similar sound to that loping idle.
So I'll go over the theory of this for a start. So what we're looking for here is affecting the idle speed by advancing or retarding the ignition timing. And this is a technique that most OEs are using to aid idle speed control anyway. So primarily with the idle speed control system there will be an air bypass. In our engine here the air bypass is controlled with the throttle body.
So physically the butterfly on the drive by wire throttle body opens and closes to bypass more or less air and control our idle speed. And I like to think of this as a coarse adjustment. The problem with doing so is that adjusting the throttle body can make quite a large different to our idle speed and it also tends to be a little bit slow to react. So what we find is a lot of OEs supplement the drive by wire throttle body opening with an idle ignition control system. So what this does is it advances or retards the ignition timing in respect to the idle error.
So what we do here is when the idle speed is above our target, by retarding the ignition timing, what we end up doing is reducing engine torque and as we reduce the engine torque, the engine speed naturally falls away. If on the other hand our idle speed is below our target, by advancing the ignition timing, we increase our engine torque, and this has the effect of increasing our idle speed. Now a caveat with this is that generally in order to get a good result from idle ignition timing, we wanna be setting our base idle air bypass, so that we're achieving our idle target with an ignition timing value that is retarded from MBT. So if for example we find that, or it's very hard to find MBT accurately at idle anyway. But ;et's say for example our MBT timing at idle was 30 degrees.
If we had our idle ignition timing set at 30 degrees, we're not going to have any potential to advance the timing and increase our idle speed. Either way we go from MBT, if we advance our timing or we retard it, our torque curve is dropping away. So on either side we're going to end up with our torque reducing and our idle speed will drop. So instead of setting our timing on MBT, we might choose to set our base timing around about 15 or 16 degrees. This gives us the ability to advance the timing up 15 or 16 degrees give or take, towards MBT, get that increase in engine torque, but we can also retard the timing on the other side.
Alright so what we'll do, let's jump into our VCM editor software, so we'll head across to my laptop screen and what we're going to do is head across to our spark tab here. And the aspects we're going to be looking at here are our idle adaptive spark control. So there are a number of tables here and this is actually one of the advantages if we're gonna be setting up ghost cam on a street driven car. What we can actually do if it's an automatic is we can adjust the aggressiveness of the idle adaptive spark control based on whether the car is currently in park or neutral, or whether we're in gear. So what we'll find is if we have genuinely fitted a really large aggressive cam profile, yes it's gonna give you that nice lumpy idle that everyone wants.
But this does come with some serious drivability downsides as well. And when we're in gear the car's going to generally want to lurch a little bit, it's gonna push against the brake pedal and generally be a little bit less pleasant to drive. So what we can do here is we can separate the tables out and we can tune the ghost cam to only be active when we are in park and neutral. Let's have a quick look at these two tables. So what I've just clicked on there is the over speed table.
And what we've got on the x axis here is RPM. But it's not really RPM, it's our RPM error from our target idle. So you see all of these numbers as we go across to the right in this table, the error essentially is increasing and we're moving further and further above our target idle speed. So what we can see is that we've got our spark adder below this and for example if we were 48 RPM above our target, we can see that this spark adder table will remove seven degrees. So again just reiterating, removing the timing, reduces our engine torque, and the idea is that it drops our idle speed down.
Let's have a quick look at our under speed table. So this is exactly the opposite. This is where we are below our target idle speed and we can see we've got the opposite situation occurring. We've got the ECU adding timing there. So let's just head across to our scanner.
And we'll just get the logger running and we'll have a quick look here at what's actually happening to our spark. So we can actually see this in action. So at the moment we've got the engine sitting there idling at 550 RPM. And we can see the third group down in white we've got our ignition advance. So we can see that our ignition timing is scrolling backwards and forwards, it's not moving too much.
We're seeing a minimum of maybe about 11 degrees and a maximum of about 15 degrees. So this is just in response to that idle speed moving around. That is the idle adaptive spark tables in use. And what we'll do hopefully we can just switch across to some audio of the car idling for a moment. We'll just give you maybe 10 seconds of that so you can get an idea of what it sounds like with the stock adaptive idle spark tables in place.
Let's do that now. OK so that's basically what a stock system is gonna sound like, albeit we have a set of inch and 7/8th stainless headers and a three inch cap back exhaust system fitted to this car. Alright so the theory that we're going to go through here is that in order to make the idle a little bit more lopey, we're going to be a lot more aggressive on the amount of ignition trim that is applied. And this is relatively straightforward to achieve. So we are gonna go through a quick example of how to do this now.
And then probably following that, we're going to end up going into some questions and answers. So this is gonna be a relatively short webinar. If you do have any questions that you'd like answered, then this is gonna be the optimal time to start asking those. Alright so what we've got here, I've just started here with our park and neutral under speed tabs. So this is where we are adding timing.
And basically you're going to need to play around with this table and generally we're gonna be playing around in this area here, up to an error of maybe about 80 to 100 RPM. And we're going to want to make the numbers much more aggressive. So there's no magic bullet I can give you here as to what numbers need to go in this table. A really good place to start is by simply highlighting the entire table and multiplying the numbers by two. What I'm gonna do, just so we can get a really good idea of how aggressive this can be, I'm just going to make these a little bit larger.
So at 16 RPM error I've just increased the value there to six degrees. We'll leave the rest as they are. So we'll close that table down now, and we're going to come across to our over speed error. And again we can start by doubling the values in this table. And this time though we're going to again be a little bit more aggressive in the areas where we're only just slightly above our target idle speed.
So let me just go through there and we'll make a few changes here. Just got some numbers that I've gone through here that I know are gonna give a reasonably good idea of how this effect works. Alright so we've got some numbers in there now. What we're going to do is just connect our scanner, I've already done that, and we can flash those changes into our ECU. In this case we've got the option to write to the TCM as well as the engine control module just to speed the process up here.
We're not making any changes to the automatic transmission control module. So we're only going to be writing here to the engine control module. And this is one of the downsides of course with reflashing. When we make any of these changes, it does require us to flash the change into the ECU. These changes aren't made live like we can with an aftermarket standalone ECU.
So it does get a little bit time consuming. In this case the write on this particular controller, our E38 ECM, only takes around about 45 seconds. But there are certain ECUs that I have reflashed that take 20 minutes or more. So when your flash time takes that long, it's certainly going to make you really second guess whether you wanna make that last change and how accurate you really need to get your calibration. Alright so we've got that calibration flashed in now.
What we'll do is we'll get our engine back up and running. And first of all what we'll do is we'll just head back across to our scanner. We'll just get our scanner logging, and that'll take a little while for everything to settle down but straight away you can see that the magnitude of the spark is much greater than what we had before. We're seeing numbers from negative values all the way up to around about 30 degrees. Now as I said I've purposefully made this quite aggressive.
So we can really see the effect of this. Chances are you're probably not gonna wanna go quite as far as I have here. But again what we'll do is we'll switch to our audio, we'll give you 10 seconds or so, so that you can actually hear the effect of that simple change we've made. OK so pretty effective. Now I'll be the first to admit, you're probably not going to fool everyone into thinking that you've just fitted the most aggressive cam in the world into your engine.
But as you just saw, it took about 30 seconds for me to make that change. So for a lot of people this is gonna be about as much as they want and they're probably not actually going to want to go to the expense and trouble of fitting a genuine aftermarket cam. So of course in enthusiast groups this may also end up with you becoming a bit of a laughing stock. That's a decision that only you can go down and it's a decision only you can make. As I said at the start, this is definitely a controversial topic.
So you do need to treat it with a little bit of care and understand what you're getting yourself in for. The last thing I wanna show you here is let's just head back across to my laptop screen for a moment and we'll have a look at our scanner. So we can see we've still got our spark values here jumping up and down dramatically as we already saw. Probably also I should mention is a lot of that lope is coming from the fact that, well it's a little hard to see, our idle speed is now changing much more dramatically than what we saw with our stock adaptive spark tables. So what I'm gonna do now is just pull the automatic transmission into drive, and we'll see straight away everything smoothes out.
We see that our RPM smoothes out, we also see that our spark advance is now back to stock, we're only seeing the timing move around a few degrees. We can see how smooth the RPM trace is and that means that once we pull the car into drive, our drivability is going to be unaffected. The car is still gonna pull away from the set of lights, drive through a service station carpark as smoothly as it did when it was stock. Alright we'll move through and we'll have a look at some questions now. So if you do have any more questions, please ask those and I'll do my best to answer them.
OK our first question comes from Daniel who has asked, does this impact the spark plugs much, i.e. will it cause fouling? Well no it won't because we're actually not changing the fuel delivery at all. All we're doing is changing the spark advance and that doesn't affect our air fuel ratio. The air fuel ratio as its name suggests is the ratio between the amount of air and the amount of fuel trapped inside the cylinder at the point where the intake valves close. So our spark advance doesn't actually affect our air fuel ratio.
Assuming that we're still achieving complete combustion. So no we're not gonna get any fouling, and that can be a problem with a large cam although not when we actually have got the tune dialled in properly. Bazarro has asked, what contributes to the pop d cell? Is it cam overlap or timing or from the fuel film being consumed with no spark? So generally it's not actually a cam overlap aspect as much. What we need in order to get a popping on over run, is we need unburned fuel and air passing through the combustion chamber. So generally what we find is that with most OE calibrations, the fuel injection is disabled on over run.
In GM lingo it's called deceleration fuel cut off and this helps both emissions and fuel economy as well as preventing that. So by eliminating the deceleration fuel cut off, we're going to be having fuel and air pass through the combustion chamber and some of that is likely to end up popping in the exhaust. Dwayne has asked, does this affect oil pressure? Yeah it can in so much as the idle speed is going to be affected. So our oil pressure really is tied in intricately with our engine RPM. Given that the oil pump is crankshaft driven ultimately.
So yes if you drop your idle speed, you are going to see a drop in your oil pressure. Generally, that particular example there as I've said is probably quite dramatic just to really show you the effect of the idle spark table. So probably if I was setting this up, I wouldn't quite go that dramatic, hence the amount of variation in our idle speed is probably also going to be less dramatic. I haven't personally seen any downsides from this. We've generally in most GM vehicles, got plenty of oil pressure at a sensible idle speed so it's not a huge issue.
Vince has asked, is this simply for sound and plus one on the spark plugs fouling? Yeah absolutely there is no performance advantage from this at all. So I'll be really clear about this, it is simply for the sound. Again this isn't gonna be for everyone, but I know there's a lot of people out there who do want this sort of feature and wanna know how to set it up. And yeah again the spark plug fouling is not gonna be an issue for you. Five Speed Formula has asked, what's the best way to tune the lope out of a mild cam at idle.
So you wanna go the opposite way. This is a little bit tricky because if you've got a mild cam, and you've got some overlap that's occurring there that's causing the lope at idle, this is a little bit trickier to get around. There are a couple of aspects you can use to help with this. One of them is to increase your idle speed. Generally you'll find that the lope of a mild cam becomes more significant or more obvious at a lower idle speed.
And this is actually a trap that a lot of tuners fall into when they've fitted a mild or aggressive cam to an engine, they try to keep the idle speed where it was stock and that's often not gonna work. So here we're looking at an idle speed of about 550 RPM, with some of the bigger cams that we fit to the LS engines, we're going to actually raise that idle speed up to around about 750 to 850 RPM. So that's the first thing. The other thing I've found, and this is not generally so much about the lope at idle, that's really an aspect that we're not gonna get rid of completely. But that lope also tends to cause some drivability problems, particularly at low speed where you're just moving through a carpark for example and you're barely touching the throttle.
And what I've found does help reduce that is to purposefully retard the spark timing in that area where you're at very light throttle, very low speed cruise. Now what that does is it reduces our engine torque. So there is a downside to our engine performance there. It's going to be detrimental to our fuel economy. But what it does is it tends to smooth out or reduce the effect of the surging or that loping at idle.
So it can be helpful there to you. Vince has asked, does this affect the off idle acceleration? So with this particular set up, absolutely not. Again, we're only cheating here, it's only active, in this case, the way I've set it up, when we're in park or neutral. And it's only active when our foot's completely off the throttle. So as soon as any of those aspects change, the ghost cam effect goes completely away.
So of course again that's not gonna fool too many genuine enthusiasts, if you're sitting there with your car idling with a nice lopey idle, you jump in it, pull it into drive, and all of a sudden it idles perfectly stock like a factory car, that's probably gonna be a pretty big giveaway that you're maybe fudging things a little bit. Andrew has asked, I have had issues with the idle wander using a Bosch throttle body and pulse width modulation. How effective is timing correction, and how much timing adjustment do you normally use? OK so first of all, what I would say is given the very brief amount of information you've given me there, I would say that something else is probably an issue here and I wouldn't be suggesting that you use idle ignition control for fixing a problem with your air bypass to your throttle body. So it's really important that the base idle air bypass tables are properly calibrated. Probably getting a little bit beyond the scope of today's webinar as well.
You may wanna check our archive on idle ignition control, as we've got a number of webinars that specifically detail that. So particularly there as well, you're going to need more air bypass. So a larger throttle opening when the engine is stone cold, versus as it comes up to operating temperature. So getting that base table correct is essential. And then we're really using the idle ignition control on top of that as a fine tuning exercise.
So normally when I'm tuning this, I would like to make sure that my spark advance doesn't retard back past about five degrees. Particularly if you are consistently running with very retarded timing, this is gonna put a lot of heat into your exhaust system and into your engine bay so you definitely wanna watch that. I definitely wouldn't be advocating running with the spark advance sitting consistently in the negatives, that's not gonna be a good look. And likewise you don't wanna advance the timing past true MBT. As I've already discussed, pretty hard to actually find that at idle.
But generally that's gonna be maybe somewhere between 25 and maybe 30 degrees as well. Cameron has asked, can you cause knock by doing this? Obviously you aren't under load so it may not hurt the engine but is it a concern? No absolutely not. You're not going to have any problems with knock. And even if the engine was to knock under these conditions, because as you've correctly said, there is no load there, you're definitely not gonna cause any damage. But of course you have complete control over how far the timing is advanced using the idle ignition control so there's really no issue here.
CW Long has asked, are there any risks with doing this on a direct injection engine? Not specifically. With a direct injection engine, you've got a lot more flexibility on where exactly the injection event is occurring. So I mean really the only thing we need to watch there is to ensure that the injection event isn't occurring anywhere near where our spark is occurring. But that's general DI Tuning 101 anyway. Our next question is how would this be done with quad cams such as a Subaru AVCS? So what we can do here is instead of using the idle adaptive ignition tables, is we can actually change our cam phasing so we're genuinely creating overlap at idle in exactly the same way as we're going to end up with overlap if we are fitting a larger cam that has much more duration.
That's generally going to give us more overlap. So this is done in the cam target tables as opposed to our idle adaptive tables. Jeff has asked, I doubt we'd see much difference here with a push rod single cam Donk but in the case of quad variable cam timing, how much gain do you generally see with the OEM cams if you tune for max effort, as opposed to the OEM style efficiency drivability emissions, assuming these motors have four cam phases from stock of course? Good question there Jeff and the answer really comes down to the particular engine you're tuning. One of the engines that I've had a lot of experience with is the Subaru FA20 engine. Spent a lot of time optimising the cam timing maps with the factory ECU using EcuTek on our development car before it was turbocharged, and in all honesty the gains there were quite minimal.
There were a few kilowatts here and there, it was certainly worth doing, but after probably spending upwards of 20 hours on the dyno, I came away with more frustration that I did gains in outright power. There are other vehicles though where I have seen genuinely impressive gains from the cam timing. So it really is just a case of testing to see how your particular vehicle responds. Alright guys that's brought us to the end of the questions. Some good ones in there on what is relatively simple in terms of the topics we've dealt with.
Probably isn't gonna be for everyone, but there you go, there is ghost cam, there is how you can use your idle adaptive spark tables to create a ghost cam effect. As usual, if you do have any further questions after this webinar has aired, please ask those in the webinar section of the forum and I'll be happy to answer them there. Thanks everyone for coming and I'll see you next time.