Summary

Adjusting the point in the engine cycle when the injection event occurs can have a significant affect on the way fuel is delivered into the combustion chamber. In this webinar we will discuss open valve vs closed valve injection strategies and discuss techniques for adjusting and optimising the injection timing.

Transcript

- Hey, it's Andre from the High Performance Academy, welcome to this webinar, and today we're going to be looking at injection timing in the Haltech Elite ECU. We're going to be using our Nissan 350Z for this demonstration, but the principles we're going to be talking about here with regard to injection timing are really applicable and relevant to absolutely any engine, whether it's naturally aspirated or forced induction. So you'll still be able to get a lot of information from this webinar that's applicable to other platforms. So what we need to start by doing is, really defining what we mean by the term injection timing. It's relatively simple, yet I know this is an area that a lot of tuners simply ignore entirely or overlook, or don't properly understand so first we need to get an understanding of what the term means, and simply put injection timing, we're talking about the timing of the injection pulse, when the injector is actually delivering the fuel with regard to the location in the engine cycle.

And really this is an aspect that's related specifically to any engine that is running full sequential fuel injection, where each individual cylinder can be timed to deliver fuel in a specific location relative to the engine cycle on that cylinder. So let's start by discussing now what we're actually trying to achieve when we're adjusting our injection timing, and really what we're trying to do here is ensure that the fuel being delivered by the injector is being introduced into the cylinder in a form that is easily combustible. An area that's easy to overlook is that liquid fuel itself is not particularly flammable, it won't burn very well, so in order to get a good combustion event and make the best from the fuel and air being introduced into the cylinder, we really need to need to make sure that the fuel is being introduced in a very finely atomized form, or even better still, in a vapour form where it's very very easy to be combusted inside the combustion chamber. So that's the aim, what we're trying to do is move the injection event around, so that we can take advantage of certain aspects of the engine design, and ensure that the fuel being delivered by the injector is going to make its way into the cylinder in an easily combustible form. So, now let's discuss why it may not be delivered in an easily combustible form, because surely if we're delivering fuel out of an injector, and it's relatively nicely atomized, then that's the end of the story.

That's all we need to do. Well, that's not always the case, and there is a little bit more going on there. This sort of really cut that does also tie into a previous webinar, which we talked about with fuel film modelling on the MoTeC M1. So, when our injector delivers fuel, some of it will inevitably wet out the port wall and actually form a fuel film on the port wall. It may also get fuel hitting the back of the intake valve, a lot of this is going to relate to the injector location and the injector angle, as well as the injector spray pattern.

And what this entails is some of the fuel will end up forming a liquid, which then will tend to run into the cylinder instead of being delivered in a nicely atomized form. So there's a lot to consider here, and what we're trying to do is get the injection event happening so we make the best out of that fuel being delivered. So let's have look now at what's happening inside the engine in regard to the engine cycle, and if we can just jump across to my laptop I've got a really crude drawing here of the cam timing, or valve timing events. And I just want to talk about the locations in the engines. So first of all we're going to talk about this point over here, it's labelled as TDC, we can see at the bottom it's also got a label which says 360.

I'm gonna have to be a little creative here because the numbers I'm going to be talking about in terms of our location in the engine cycle and specifically our injection timing events kind of are going to work backwards with here, with this drawing, but this point here labelled as TDC, this is TDC on the compression strokes. So typically our ignition event is going to be happening sometime a little bit before this point, so sometime a little bit before TDC on the compression stroke. So we move back and our next point here is labelled BDC, so this the bottom of the cylinder, the piston is at the bottom of the cylinder after having gone through our intake stroke. Remember it's the intake stroke where that fresh charge of fuel and air is being ingested into the cylinder. So we've got this cam opening here, I'm just going to really crudely highlight so we know what we're talking about.

So this is the opening of the intake valve and this is the point where the fuel and air is going to be drawn into the cylinder. Regardless of what we do with our injection timing, the fuel is obviously not going to make its way into the cylinder in a port injected engine until their intake valve is open. So this is one of the key aspects here. So in general we're going to have our intake valve opening sometime before the piston reaches top dead centre, just before initialising the intake stroke. And it's also going to remain open some number of degrees after the piston has started going back up the bore into the compression stroke.

We've also got our exhaust valve opening here drawn out as well, which is happening in the cycle. Less relevant to our interests here, but just so we've got a full idea of what's going on. So if we come back here we've got this point again that labelled TDC, so this is TDC as the engine is about to move from the exhaust stroke into the intake stroke. So our piston is at the top of the bore here. Now this is what I was saying before, our numbers just need to be worked a little bit backwards here.

When we're talking about our injection timing, the injection timing is always listed as relative to top dead centre on the compression stroke. So this is our point out here on the right-hand side of our graph. So if we had a value of zero for our injection timing, we would be firing the injector at TDC. Now, I'm going to talk very shortly about what I actually mean by firing the injector, so let's not worry about that too much right now. So if we were using an injection timing value of 360 degrees for example, that would mean we were firing the injector 360 crankshaft degrees before it top dead centre on the compression stroke, which would equate to this location I've just highlighted here, TDC as the engine moves from the exhaust stroke into the compression stroke.

And typically we might expect to see numbers in a base map somewhere in the region of perhaps 360, to maybe 450 degrees. So that's going to give us a window that looks something like this. So on the face of it what this looks like is we're now injecting the fuel before the intake valve closes. Which may not sound particularly intuitive or particularly logical, where we're injecting the fuel against a closed valve. And remember, what we're trying to do is introduce that fuel in an easily combustible form.

If we're injecting against the back of a closed valve, it might sound logical that what's going to happen is that that fuel is going to form liquid pooling, we've already discussed that that is not an ideal situation and it's not going to be easy to combust, so what's going on here. Now, there's two generally accepted techniques for our injection timing event. The one we're talking about here, where we're using an injection timing event somewhere between perhaps 360 and maybe 450 degrees before TDC, this is referred to or known as closed valve injection. And as its name implies, we've already found out we're injecting the fuel against a closed valve. Now, the reason we're going to potentially do this, it's used in a lot of OE applications, is because under normal operating conditions once the engine is up to its normal operating temperature, what's going to happen is the intake valve as well as the port walls, are going to be incredibly hot.

Particularly the intake valve. So by injecting the fuel and allowing it to sit in the port and against the back of the very hot intake valve, what it's going to do is actually vaporise. It's going to form a vapour, and we know that it's very easy to combust this vapour as opposed to atomized fuel droplets. So then when the intake valve opens on the next intake stroke, this vapour is then drawn into the engine. Now that's not 100% bulletproof, we may still end up with some liquid fuel also entering the cylinder and this is one of the problems we face.

So that's the instance of closed valve injection. The other way we can deal with our injection timing is with open valve injection, and again if we can drop back into our diagram here. In this case we would be typically selecting an injection timing angle probably somewhere around about perhaps 180 degrees. So we're injecting the fuel, as its name implies, when the intake valve is open. And this would be the way that it would logically make more sense to most tuners, we know that the valve is not in the way of the fuel being drawn into the cylinder, so we've got that atomized fuel leaving the injector and making its way directly into the cylinder.

As we've discussed though, pros and cons with each option, and particularly when the engine is at operating temperature, we can get an advantage using closed valve injection by taking the advantage of that heat in the port wall and the intake valve to help vaporise the fuel. Okay so, now I've talked a little bit here about the injection event. I've been quite generic when I've talked about this. That's because depending on the ECU, and in some cases even on how the ECU is configured, the injection event may refer to different things. The most common way and my own personal preference is to configure the ECU to work in terms of what's known as end of injection, shortened to EOI, and what this means is that the injection angle value in our table will relate to the point when the injection event finishes.

Again, coming back to our little graph here on my laptop screen, for me this makes the most sense because if I'm looking at, let's say, a straight line might be helpful. If we're looking at an open valve injection event, and we want to make sure that the injection event finishes while the intake valve is open, end of injection makes the most sense. In this case I can select an injection event, an injection timing of 180 degrees, that will refer to the end of the injection pulse, and what that will mean is depending on the exact pulse width and RPM, et cetera. The injection event may start somewhere out around about 300, 320 degrees before TDC and it will finish at 180 degrees. Essentially the start point is a continually moving target, based on the injection pulse width being used at the time, and the end point is going to be fixed at our injection angle.

Other options for representing this value, we can have start of injection. As its name implies, the complete opposite, what this means is that we're going to end up with this variable end point for our injection event. So for me personally this doesn't make much sense, it doesn't work how my mind works, I like to know when the injection event is going to finish. That's what I'm going to base my decision off. And the other way, it's relatively rare, but some ECUs will also look at a middle of injection event, so as its name implies it's looking at the midpoint of the injection event and the injection event will extend both before and after that.

Again, you simply need to understand how your particular ECU works, so that you are not working at cross purposes with the way that the injection timing is actually operating. Okay, one thing that needs to be understood as well, if you are going to being using a closed valve injection strategy, understand that in order to get that vaporisation of the fuel off the hot engine parts, we do need heat in the engine. And what this may mean is that you're going to get worse performance during cold start, particularly in cold climates, when the engine components are cold, particularly the valve and the port wall. This is going to result in the fuel pooling out and forming a liquid which is going to tend to be drawn into the cylinder in a liquid form. So this will have an impact on your fueling requirements during cold startup.

It's also probably not a big concern for us in the aftermarket, but it will have a knock on effect for your engine's emissions as well during that startup. Okay, before we move into having a look at the process of tuning this, it's worth just discussing the aspects that can affect the optimal ignition timing. And they really, they are quite dramatic and this is why we can't necessarily hope to apply one set of, one injector timing value to every engine that we tune. So first of all we need to consider the way the fuel is being delivered to the engine, and this will relate to our injector size, also the injector location and the distance of the injector from the intake valve. The injector spray pattern also goes hand-in-hand with these aspects, and how well the injector is able to atomize the fuel being delivered.

This to a degree also comes down to the fuel pressure that we're using. So, as you can see straight away, there's a number of parameters there that can affect what is the optimal injection timing. If you are running staged injection, so you've got two sets of injectors, and they're a dramatic difference in distance from the intake valve, even in this case you may need, or probably will likely need to run different injection timing for both sets of injectors to get the best result. And then obviously engine temperature and air speed will also affect the injection timing. So it's typical when we look at an ECU that has an adjustable injection timing table it's typical to have that set up as a 2-D, or even sometimes a three dimensional table, where RPM and perhaps manifold pressure or throttle position is taken into account as the two axis inputs.

Now it's important here to also understand what we can realistically expect with our our injection timing. And in my opinion this is starting to get to the last few percent of really optimising your tune. And for that very reason, we'll find that probably greater than 90% of tuners out there in the world, either don't know that injection timing is an adjustable parameter in many cases, or simply overlook the injection timing tables and leave them at whatever the default values were set to. This comes from the fact that chances are, your engine's going to run quite well, and perform perfectly with default values in these tables, so in that case, why bother. And the other aspect is a lot of tuners don't understand how these tables work, what injection timing is, and how adjusting the injection timing can influence the engine's performance.

Hopefully my explanation so far will already put you ahead of the game, because you now understand what's going on inside the engine and what we're trying to achieve. So it really is starting to get down to those last few percent. Now a good example here where injection timing was used to to provide just that last maybe, one or two horsepower, was in a number of the controlled race classes. And I'm thinking here about the likes of British Touring Car Championship, also V8 Supercars in Australia, basically anything where there's very tightly restricted rules around the engine development, and the engine builders and engine tuners in this case are really looking for any edge they possibly can. So in this case, timing the injection event and trying to get optimal results from that injection pulse become increasingly important.

So you're not going to be expecting here to make a change to your injection timing and magically see another 20 or 30 horsepower appear on the dyno screen. It's simply not like that, and we're going to have a really brief demonstration shortly, and you're going to see that any change we do note is often almost indiscernible. So it's very, very difficult to see sometimes what we're looking for, or what we're actually gaining. And the other thing to consider as well is what we can realistically achieve. And what I mean by this is, if we want to move the injection event around within the engine cycle, we need to look at how long the injection event is anyway.

So it's not uncommon for a lot of modified engines or even a lot of factory engines to be running at perhaps 80 to maybe even 90% injector duty cycle at high RPM and high load. Now, in that instance when you've got the injector open or for almost all of the engine cycle anyway, it's understandable that moving the injection timing around is probably going to have little to no effect on the engine performance. At low RPM on the other hand, now we may be only operating with perhaps 5 to 20% injector duty cycle, our pulse width is much shorter, so this gives us a much bigger window in the engine cycle to move the injection event around and perhaps see the result or advantage of doing so. Now this brings me back, the reason I've covered that off, is this brings me back to the examples that I gave where they're being used, injection timing is being taken advantage of in a race engine. In those instances, if you really want to be able to take advantage of injection timing, it's important to size the fuel system and injectors so that your maximum injector duty cycle is kept a lot lower, perhaps as low as 60 or 65% maximum.

So this just limits the length of the injection pulse width and allows, again, that headroom to move it around, the bigger window if you'd like, to move it around within the engine cycle and see those potential gains. Again, if we're out at 85 or 90% at high RPM where a race engine's going to spend the majority of its time, understandably, there's little to nothing to be gained there. Okay, I'm going to move into questions and answers after I've completed this little practical demonstration here and given you some guidelines on the approach that I personally use for tuning injection timing. So please speak up if you do have any questions, put those into the chat box and Colin will transfer those through to me. Likewise, if anything that comes up while I'm doing this practical demonstration you'd like me to explain in a little more detail, please also ask that in the chat box.

Okay, so we've already discussed the fact that typical numbers we may expect to see might be in the region of 360 to 450 degrees before top dead centre. What I'm going to do now is, we'll just get our engine running here on our dyno, and get our fan operating. And let's just jump into our laptop software here. Probably not that software. Let's just jump into our laptop software here, and we'll have a look at what we've got going on in front of us.

So let's just allow this to get running, right, we're up and running. So this is our Haltech Elite engine management software, and if we want to change anything to do with our injection timing, we need to move right to the bottom of our ECU navigator bar on the left-hand side, and the injection timing data is listed under the injection systems so, for those of you looking for it under the fuel submenu up here, this is not the place you're going to find it. So let's move back down and see what the data actually looks like. So if we click on this you can see that by default, this is a two dimensional table relative to engine RPM. And while we can have three dimensional tables, what we're trying to do here is achieve the best results possible with the minimum amount of fuss and really, as I've already discussed, injection timing in itself is generally getting towards the pointy end of the optimization we're likely to do in EFI tuning.

So simply spending some time on the two dimensional table is going to get you probably most of the gains that are available. Obviously if we want to tune a three dimensional injection timing table, the time spent, the requirement to tune that table, increases greatly and the results often don't warrant that. Again, in my own personal experience. So on the right-hand side you can see we've got a graphical representation of this table, these numbers. And you can see that at low RPM we've got numbers in the region of about 380 to 390, and if we get up to a high RPM you can see that the injection event happens a little bit earlier, we're in the region of about 450 degrees.

So again, just as I said, sort of relatively typical values and again, most tuners won't even bother touching those they'll just leave them at the default values. We're going to have a look at making some adjustments though, and what we're going to do is make our adjustments at 2000 RPM. So I'll just get our engine running. Just get into fourth gear here and bring the RPM up to 2000, and just get us up to a relatively stable operating speed. Now, the process of optimising or adjusting our injection timing, we really want to start this process before we go and make any adjustments to our injection timing.

We really wanna make sure that our VE table is relatively well tuned for a start. We wanna make sure that we've got that pretty close, but at the same time I'll temper that with the fact that if our injection timing does prove to show a dramatic increase in torque and power, then we're also going to generally see that coupled with a change in our measured lambda, so this may also require us to go back and make iterative changes to our VE table as we fine tune and optimise our injection timing. So it is an iterative process, and not too dissimilar to adjusting our cam timing. And the reason we may see our lambda, or air/fuel ratio change, is because when we move towards an optimal injection timing, what we find is that more of the fuel being delivered by the injector is being combusted, so hence the measured air/fuel ratio tends to move a little bit richer. If our injection timing on the other hand, if we go the wrong way and we're introducing the fuel in a manner that's not easily combustible, we're going to see our air/fuel ratio move leaner.

Now often, as we move towards an optimal injection timing, we will see a small but measurable increase in our torque, being showed by the dyno, however we're using these two metrics to decide on the direction we're gonna go with our injection timing. We're looking at our lambda, and we're also looking at our torque. Of course, if you are interested in emissions and you're using a five gas analyzer, we've got a lot more data there and this is really one of the key aspects that OE manufacturers are considering in their injection timing, they're really much more interested in emissions than power, torque, or just about anything else. Okay so, what we're going to do is we're going to make some changes to our injection timing. I think for simplicity what I'm going to do is do this in two ways.

We'll do this purely based on the laptop screen for a start, and then what we're going to do is come back and have a look and see if we can see any change in our engine torque on the dyno while I make changes. I'm just going to come back and trim my VE table, so I'm right on lambda one at the moment. So I've just done that, now I'll also note that at the moment I'm not running in closed loop mode so the ECU is ignoring any feedback from the oxygen sensor, and we've got in terms of lambda is what we're going to be running with and it's only going to be affected here by any changes I make to the injection timing. Okay, so we've just highlighted the three zones here, I'm doing all three zones just so any effects of interpolation are completely ignored, and what I'll do it I'll start by setting them all to 450 degrees. Now what I'm going to do is I'm going to smoothly decrease these ten degrees at a time just by using the Shift and Page Down keys.

And what I'm going to do at each point is just pause very briefly, and we're just looking at our lambda. Just to see the effect of our lambda. Now, you can see that, while it is a little bit variable, when... Nope, it's gone back, yeah okay. At this point here, so we've gone from 450 down to 370.

We saw our lambda actually just spike a little bit leaner, it does actually seem to have settled down now. So I'm just going to continue. So what we're looking for is a relatively small change. We want to, at each point that we change our injection timing, we want to pause and allow everything to settle down. So you can see here, this is what I was trying to demonstrate, at this particular point we have moved a little bit lean with our injection event of 320 degrees.

So we've gone from 450 down to 320, and when we see the injection, the lambda reading move lean, remember this means that the fuel is delivered in a form that is less easily combustible. So basically some of the fuel being delivered by the injector is not being used by the engine. So again, we're talking really small changes here, down at 200, 210 degrees, and just right now we're in that zone of open valve injection. We can see that our lambda, if anything, is very slightly leaner than what we had when we were up at 450 degrees. So I'm just going to move back up, all the way through to 450.

Now, we'll just come back to an idle and just talk about those results because I understand it can be quite hard to deduce what's going on there. What we need to do is go through the adjustment range there, that I've just gone through, and I wanna look for trends where our lambda is moving either richer or leaner and we want to make sure that those trends are repeatable. Often, and really this has been a pretty bad example and unfortunately this is the case with our 350Z, it doesn't demonstrate the situation as well as some engines I've tuned, it seems to be relatively insensitive to injection angle. But what we're looking for is those areas where the lambda becomes repeatably richer, or repeatably leaner. And remember, what we're looking for there is ideally a richer air/fuel ratio.

Remember our injection pulse width has remained the same, so if we see the air/fuel ratio move richer, this means that more of the fuel being delivered by the injector is being combusted. So where our gains can come from there, if we see our lambda move richer, we can then go back into our VE table, trim the VE table, this is going to reduce the injector pulse width and in turn that can offer us an improvement in fuel economy and potentially lower emissions. The flip side of this is the other metric that we wanna be looking at, and monitoring while we're doing this is also our engine torque. And we're going to go through this example again, and hopefully I haven't thrown Colin too far under the bus here, because ideally what I'd like to be able to show you guys is our torque gauge on the dyno at the same time as we can see our injection timing values, our 2-D injection timing values, on our laptop screen. So hopefully Colin is going to be able to demonstrate that.

What I'm going to do is just get ourselves running in fourth gear again and we'll get everything stable. Now remember, we're starting here again from 450 degrees, now before the demonstration starts I'll again apologise, because in this particular instance we don't tend to see a really dramatic change in the torque with our VQ35. It again is not particularly sensitive to our injection angle. Right, let's get us back to a fairly stable operating point here. And again, I'm just going to jump in.

I've just increased our load and I'm just going to jump back in and I'll just get our fueling back on track so that we're starting with a similar base as our first example. Alright. So let's go back to our injection timing. Now, hopefully at this point you can see our torque being displayed. You can see that it was sitting at around about 89 to 90 newton metres.

Now this also requires a little bit of skill on the part of the tuner to read, because the ignition timing is, sorry the engine torque, is always moving around slightly so we want to be very, very consistent with our throttle while we make these changes, and we want to be looking at the torque shape, it's also useful if we can view this graphically on our torque graph below our gauge, it sometimes gives a better indication of exactly what's going on. So sitting at lambda one earlier, our lambda one target again, and we're sitting now at about 100 newton metres. What I'm going to do is just gradually reduce our injection angle, and we'll see if we can get any noticeable change to our engine torque. Still sitting basically the same so, as I've said, we're not likely to see dramatic changes here, although we have jumped from about 99 to 100 newton metres, up to about a stable 102, 103, dropping from 450 down to 350. Our lambda is still sitting at lambda one, I'll continue reducing our injection angle.

And we can see that we're now at 300 degrees injection timing, we've actually picked up another small increase in torque, we're sitting now at about 107, 108 newton metres. And we'll just keep going down and what we'll potentially see is that our torque will start to drop off a little bit. We'll keep going down, so we're now in that region of our closed valve injection, and we can see that, yeah, our torque has dropped back down to around about 100 newton metres. Alright, we'll just stop there and come back to idle and we'll just talk about that. So again, the magnitude of the changes we're looking for here, in both our torque as well as our lambda or air/fuel ratio, are incredibly small.

And this does makes this frustrating to accurately tune. Again, probably a good reason why a lot of tuners simply ignore it. If it's close enough, they'll just run with it. But if you are prepared to spend the time often we can see those small improvements in both fuel economy and potentially torque. In that case moving from 99 to 100 newton metres up to 109, 110 newton metres.

Obviously a torque change of approximately 10% there so, not a ridiculous change by any stretch of the imagination. So that's the process we're going through there, what we're looking for is either our air/fuel ratio to move richer, or ideally an increase in torque. You may not get both happening at the same time, in which case obviously if we're seeing an improvement in torque, that's what I'm going to favour chasing. Obviously we really want to make as much engine torque as possible, so if we are seeing an increase in our engine torque, that's great, that's what we want. Alternatively, sometimes we're going to see almost no discernible change in our engine torque but we will see our air/fuel ratio move around slightly, in which case we want to focus on the richest mixture that we see, at that particular point, then we can reduce the numbers in our VE table and achieve an improvement in fuel economy.

Now I've only looked there at steady state tuning, and obviously we can steady state tune at this table at various points. I don't normally see a requirement to tune in 500 or 250 RPM increments here. We generally see that the trend, if there is going to be a trend develop, in our injection timing table will be relatively consistent with regard to RPM. If you do wanna go to the trouble of 3-D tables, and set up load as a load axis, manifold pressure or throttle position as a load axis, then the trend that we're likely to see with regard to load is also generally relatively consistent. So what this means is we can be quite coarse with the points that we tune, and then simply interpolate between those points.

Or alternatively set up our break points in our table initially to be much more coarse than the 500 RPM increments I've got here in our base table. Of course we also want to see what happens at higher RPM under ramp run conditions, so we're actually replicating real world acceleration conditions. And in that case my general trend there is once I've got the table relatively tuned in steady state and I've got a trend developing, I'm going to extrapolate that out into any untuned areas, do my ramp runs, get my fueling pretty close, and then I would start making adjustments to the injection timing table and at this point I would make across the board changes right through the entire rev range. When you're doing this, again, understand that we are looking at relatively small changes typically, we need to make a big enough change to our injection timing to actually show the effect of that change so, in that case we probably want to start by making 20 or even 50 degree incremental changes from one run to the next. And once we've actually seen the effect of the that change, we can notice a change on the dyno.

This is going to help guide us with the direction we want to go. So for example, if our starting point was 400 degrees, I might start by doing a run at 400 degrees, then a run at 450 degrees, and a run at 350 degrees. And this will guide me on the direction that the engine wants to go, and then once I've got that direction I can continue moving in that direction until I see no further change. Of course then we can start looking at smaller incremental changes rather than 50 degrees. Alright, so hopefully that's given you some insight into what we're trying to achieve there, and an approach that is applicable in real world conditions on the dyno that's not going to end up eating up a huge amount of your time.

Remember though, be realistic with the sort of expectations you've got. Remember, if your injector duty cycle is getting up above perhaps 80, 85%, the realistic expectations for gains at that point are obviously going to become smaller, we don't really have any window in which to move our injection timing around. And also, even that being said, if we've got a large potential window to move our injection timing, the sort of gains in terms of torque and horsepower are generally in the order of a percent or a few percent, they're very small. Alright, I'll jump into our questions and see what we've got there. If you've got any more questions, please ask them.

TDEChamp asked, have you had experience using rod to stroke ratio to calculate piston velocity and calculate the highest piston velocity to be used for injection timing? No, not something I have considered using myself. The rod to stroke ratio will affect the dwell around TDC for those who aren't aware, it will affect the dwell of the piston around TDC and particularly will also affect the way the piston accelerates away from TDC. And in particular, this can have an effect on the cylinder filling during the first, perhaps, 30 to 60 degrees of crankshaft rotation during the intake stroke. So it's going to have an effect on the cylinder filling, it's also going to have an effect on the way the fuel is being delivered to the engine. I haven't done any testing that I can really give you any detailed replies on there, in terms of how that can positively or negatively affect our tuning.

One of the aspects with rod to stroke ratio is that for the most part it's a fixed aspect of the engine design and not something we as tuners are going to be delving into or adjusting. So in that respect, as with a lot of aspects with the engine design, I concentrate more on an experimental approach where I simply try adjusting a parameter and seeing how the engine responds to it. And in general I find, for a real world approach to tuning, that we as professional engine tuners are going to be applying, this is a time efficient way of deciding what the engine wants as opposed to calculating theoretical values and then applying those, seeing if they're correct, and then experimenting from there. Sorry for the long winded reply, I hope that it answers your question. MitchDetailed has just asked, if it wasn't covered earlier, I wanted to confirm my suspicions if this statement is true: Under idle finding optimal injector timing will also be noticed by increased vacuum.

Not actually sure that I can give you an answer there. It's something I haven't considered myself. It's not something I've really given any thought to, and I probably need to apply my brain power and a little bit more detail, to whether that's a likely aspect. What I'd say there is two things, first of all, the injection timing is going to become, this is probably something I should have touched on in the main body of the webinar, the injection timing is more prevalent, or has more effect, at lower engine speeds and lower injector duty cycles just because we have that aspect of now we have wider window that we can move the injection event around. Obviously our idle and low engine speed, our air velocity into the engine is also much lower.

So what were looking at here again, our injection timing can affect our air/fuel ratio, we're going to be able to measure that. It's also going to potentially have the effect of adjusting our engine torque. Remember the two metrics we're sort of basing our decisions on. Now, when we've got the engine at idle it's obviously not producing any torque that we can measure on the dyno, so that's not particularly helpful, but just like when we're optimising our ignition timing at idle, the same principle goes there, when we see an increase in torque what we are going to notice is the engine RPM will tend to increase so, it's probably what I'd be looking for more specifically than an increase in vacuum. But, as I said, not something I've considered, you may well be right there.

Bellotech asked, is this tuning more necessary on daily driven street cars or race cars as well? Look I've applied it to both, probably in just about equal quantities. Again, this is, I keep reiterating this, but just understand that this is starting to get to the pointy end of really optimising the tune so, whether it's worthwhile making these changes to the injection timing is really a decision only you can make. And I do urge you to, at minimum, have a very brief look at the injection timing table. Move the defaults around, even if you do no more than highlighting the entire table when you're doing ramp runs, and adjusting it up 50 or 100 degrees, and adjusting it down 50 or 100 degrees, just to see the magnitude of change, if any, that you're seeing. And that'll give you a really good guide on that particular engine if further investigation and fine tuning is worth your time.

Often, you'll see little to no change, in which case, hey, may as well just leave it where it is and be done with it. BarryG has asked, could there be any negative effects to the motor by having the injection timing too far out from optimum? No negative effects to the engine in terms of, there's no chance of doing mechanical damage, nothing particularly nasty like that. I have had some instances where I've spent a lot of time optimising the injection timing on the dyno, seeing gains on the dyno in terms of torque, or air/fuel ratio, but also when I've actually road tested that car, found that it is given a detrimental effect to something such as a transient acceleration enrichment. So it's something to watch there, sometimes the numbers on the dyno chasing maximum torque, maximum power, may actually cause you some other issues in terms of drivability further down the line, and sometimes that trumps a couple of percent of additional torque here and there. So it's something to keep in mind.

You really have to focus your tuning efforts on the big picture, and if it's causing you issues in another area it may very well be that giving away that 1% of additional torque might be worth it for improved acceleration enrichment. Bellotech’s asked, any wide open throttle ramp run tuning on this table? I think I've touched on that, yeah absolutely, once we've done some steady state tuning we can switch across to ramp run tuning, and when I'm doing that I will tend to treat it very much like an ignition table. Highlight the entire table, increase it, decrease it, see how the engine responds, use the magnitude of change to help guide you on the direction that you need to go with that table and how far you need to go. TheStig asked, is there any engines that you see a much larger increase in power changes? Very, very, very dependent on the specific situation. I guess the few engines that I have tuned, naturally aspirated engines on individual throttle bodies where the injectors were mounted outside of the throttle plates in the intake trumpets.

That's probably the situation where this will really pay the biggest dividends. You've got the quite a long transport time between the injection event and the intake valve itself, and moving it around in this situation can actually show a bigger increase than what we've seen here with our 350Z. While it's not specifically related to today's webinar, there is another webinar in our archive where we cover the same aspects on our Toyota 86 fitted with the MoTeC M1. Not specific to the M1, but that does show the magnitude of torque change when moving direct injector injector timing around. That is quite a lot more significant than port injection timing.

Which probably should go without saying, but I'll just mention it here as well. TheStig has also asked, do you see differences with fuel types? No, not specifically. Nothing I can think there. What I would mention is, if you're going from perhaps a pump fuel to E85 or perhaps methanol, where there is a much larger volume of fuel being delivered so, for example if we move from petrol to E85, we're probably going to typically be injecting 35 to 40% more fuel volume to match the same amount of air, provided we're sticking to the same set of injectors. By necessity, that means our injection pulse width is going to expand, so that may have some effect on the ideal injection timing.

Again, if we are focusing our injection timing on end of injection, my gut says that it's probably going to be a minimal to insignificant change there anyway. Okay, that's brought us to the end of our questions. Thank you for joining us today for the webinar and I hope that that has helped your understanding of injection timing, you've got a more complete view now, and hopefully also a process that you can try applying in your own tuning and start seeing the effect of injection timing in your own tuning. As usual, if you do have any further questions, please ask those in the forum and I'll be happy to answer them there. Also, if you haven't already left us a testimonial review on our Facebook page we'd really appreciate that.

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