106 | Converting an Engine to EFI
If you’re faced with converting an engine that uses a carburettor and distributor to run electronic fuel injection there are a range of considerations you need to make. In this webinar we’ll cover what you need to know about your fuel system, what options you have to provide trigger information to the ECU, and what options are available to upgrade your ignition system.
- Hi, it's Andre from the High Performance Academy, and welcome this webinar. In this webinar, we're going to be discussing what's required if we are going to be converting a carbureted engine to run on EFI. Now, this is something that's been done probably for almost as long as EFI has been in existence, but it is still an area where there's a little bit of confusion, and perhaps some misunderstanding. And today, with the easy access of both sensors, trigger systems, and affordable ECUs, it's becoming increasingly popular to convert some of the older engines out there to run on EFI. So, we're simply going to go through why we would want to do this in the first place, and what our considerations are going to be.
What are we going to need to focus on to make sure that we're going to get as good a job as possible? And in my career of 15 years tuning all sorts of cars, this was one of the areas I saw the most trouble. When the cars were brought to me that had been converted from carburetor to fuel injection, and often these had been done by hobbyists at home. And while on the face of it, it is a relatively straightforward task, obviously it still needs to be taken care of correctly. And when we're custom-making a lot of the components, custom-fitting a lot of the components, this entails that there's more room for error than if we're simply adding a programmable ECU and maybe some custom wiring to an engine that is already running an existing EFI system. And one of the biggest areas, which we will be focusing on in detail, for this, one of the reasons why this is the case, is because when we're customising or starting from scratch with this sort of system, it's very easy to end up making mistakes or creating problems with our trigger system, and this becomes the key input for the ECU to be able to do its job.
So if that isn't right, then we can expect no end of trouble, whereas if we're dealing with an existing EFI engine, then it'll already have an existing trigger system that the OE has designed, and should understandably be quite effective for that particular application. So let's-- I'll just mention before we do get started, as usual, we will be having some questions and answers at the end of this webinar. This webinar's probably a little bit shorter than our usual, so please make sure that you ask any questions while I'm talking. Punch those into the chat box, and Colin will transfer those through to me so I can deal with them at the end. So, let's start with why, exactly, we may want to convert to EFI.
And I'm hoping the very fact that you're involved with High Performance Academy, you're a gold member and you're watching these webinars, that you should already be able to answer that very well. However, I'll just touch on these, what should be relatively obvious points. First of all, the carburetor, it's getting a little bit long in the tooth now. These were never, even when they were brand-new, never very good at creating a reliable and consistent tune that was going to be the same from one day to the next. Perhaps if you drove from sea level up a mountain, all of the very reasons why EFI has come into existence, the same reasons why we may want to convert an older, carbureted engine to run on electronic fuel injection.
We're going to have much easier tuneability. We're going to have much more accurate control over both our fuel as well as our ignition. And this is going to potentially give an older engine a new lease of life. Hopefully, it may result in additional amount of power on the wide-open throttle, although I will touch on that briefly, because there is quite a, sort of a misunderstanding, I guess, that there's going to be an instant gain in power, swapping from carburetors to EFI. And the actual reality is that a properly set up and properly tuned carburetor actually can do quite an exceptionally good job of delivering fuel to the engine.
And really, when we're talking about EFI or carburetors in a conventional ignition system, what we're talking about is getting the right amount of fuel into the engine, and igniting it at the right point in the engine cycle. And if we can do that with a carbureted system, then it's still going to produce the correct amount of power, the amount of power that engine was designed to develop. What open-throttle, though, unless we're a drag racer, is actually a really narrow area of our engine's operation, and where we generally see really large improvements in EFI is in the part-throttle response, the mid-throttle torque and driveability, and of course, fuel economy. I'll add that if it's tuned correctly, we should also be getting a reduction in our emissions at the tailpipe, and again, this is really one of the key drivers that resulted in the end of the carburetor era, with all of the OE manufacturers swapping to EFI in the first place. Okay, so with that touched on, we'll go over what we actually need to consider if we're going to be converting from carburetors to EFI.
And I like to break it up into six key areas that we can focus on. I'll just detail those, and then we'll go into each of them individually. So we're going to be talking about fuel system, we're going to be talking about fuel injection system, then we're going to move on, talk about the ignition system. We'll talk about the trigger system, which is key to the ECU knowing what the engine's speed and position is. And then we're going to talk about additional sensors that we may want to add, in order for the ECU to be able to do the best job possible.
Finally, I'll just briefly touch on ECU selection, as well, or what ECU is going to be suitable for your particular task. So that's the six areas we're going to be focusing on. Let's go back, and we're going to start with the fuel system, and this is one of the key areas that a lot of people overlook when converting from carburetors to EFI. When I'm talking about the fuel system, here I'm talking about the physical fuel delivery system, so the fuel tank, and the fuel pumps, and the fuel lines, now, also, the way the fuel pressure is regulated. So, this is a key difference, because with a carbureted system, we're talking about a low-pressure fuel system, and we may be talking somewhere in the region of perhaps two to six PSI of fuel pressure, so very, very low.
The other thing that we need to consider with the carburetor is, the carburetor itself contains a float bowl, which is filled with fuel. So the float level is maintained, the float bowl level is maintained. So, we always have that reservoir of fuel inside the float bowl. Now, what this means is that if the pick-up or fuel supply from the fuel tank is momentarily interrupted, in a carbureted system, this isn't too big a issue, because the fuel is already there, up in the engine bay, in the float bowl of the carburetor, ready to be delivered into the engine. Conversely, if we're looking at a fuel injection system, electronic fuel injection system, we're talking here about port fuel injection, not direct injection.
And these systems typically will run somewhere between 43.5 PSI and 58 PSI. So, the fuel pressures are much higher, and the fuel pumps that may be suitable for carbureted fuel pressures simply won't be able to cope with the sort of pressures that we're going to need with an electronic fuel injection system. The other aspect that can trip you up here is that, unlike the carburetor with the float bowl that has that steady supply of fuel right there at the engine, the electronic fuel injection system requires and demands a constant, high-pressure fuel, high fuel pressure, is always maintained right up to the fuel injectors. And what this means is that if we're going to use the existing fuel tank, typically a carbureted fuel tank won't have any surge tank fitted inside it. And this means that it may work fine, if the car's sitting stationary, or if it's driving in a straight line at modest speed.
It may even work okay out on a racetrack, when the fuel tank is topped right up to the brim. Where we're going to see problems, however, is when that fuel level starts to drop. That's when it gets down to about half-tank. We're likely to see the fuel slosh and surge away from the pick-up under hard acceleration or hard cornering, even hard braking. And as soon as it moves away from the pick-up, that's going to mean that the fuel pump is going to pick up air, and it's going to interrupt that high-pressure, high-pressure fuel supply to the injectors.
This is instantly going to result in fuel starvation, and our engine's going to hesitate and miss. And at first of all, it can interrupt power being delivered. Obviously, the engine momentarily loses power when it uses that fuel supply. This can upset the car if you're cornering really hard, and can actually be quite dangerous. Even beyond that, though, it's obviously a real frustration if the driver's constantly having the car stutter and hesitate, but the worst aspect of it is that under these conditions, the engine is momentarily running lean, and of course if you have an engine that is producing a lot of power and turned right on the edge, this can be dangerous, which can actually result in doing damage.
So we need to consider our fuel system. Let's just have a quick look at my laptop here, and I've got a diagram here that I simply grabbed off the Internet. There's no real need here for me to recreate the system. It's a fairly well-understood and well-known style of fuel system, and I'll just talk you through what we've got here. First of all, we have our fuel tank.
So, in this situation, we were converting from a carbureted system to EFI. It's quite possible to retain the factory fuel tank, unmodified, and we can even retain, provided it can cope with the fuel requirements, we can even sometimes retain the low-pressure carbureted fuel pump, and we'll use it as a lift pump to pump fuel from the main tank into a surge tank. So, this is our surge tank here. This is generally quite a lot smaller in capacity, perhaps one and a half, two litres. And it'd also be quite tall and narrow, and what this means is that it makes it very hard for the fuel to slosh away from the pick-up at the bottom.
And we can see, from the bottom of our surge tank, we have our high-pressure fuel pump, finally, that runs into a fuel filter, and then it runs forward to our fuel rail, where our fuel injectors are fitted. Now remember, we're talking about the injectors separately. Now, finally, after the fuel rail, it moves into the fuel pressure regulator, and it's the regulator's job to maintain a consistent fuel pressure. We can choose here to even the reference this fuel pressure regulator to the intake manifold, or we can leave it vented to atmosphere, and run at a constant fuel pressure. I'm not going to go into that style, the differences there're between a constant fuel pressure and a manifold reference fuel pressure system, in too much more detail.
If you want to have a more thorough understanding of the fuel system that I'm talking about here, and the differences between a return-style fuel system and a non-return fuel system, check out our webinar archive. And if you look at 'fuel system' in the search box there, you'll find a previous webinar we've already run that goes into this in much more detail. Here, we're only looking at an overview. So, from our fuel pressure regulator, which would typically be mounted up in the engine bay, you can see that we then have our fuel return line that-- Whoops, I'll just draw this right out-- Our fuel return line that then returns fuel back into the surge tank. So, the idea behind this is that the actual low-pressure pump only needs to supply the amount of fuel that the engine is using, and the return fuel will simply go back into the surge tank to keep it topped up.
And then any overflow will simply go back down the return line, into the fuel tank. So, in this way, it's actually quite easy to convert a carbureted fuel system to run EFI. This is probably the most common technique. If you don't want to clutter your boot or your underbody with a surge tank and an external fuel pump, it is possible, although it's a lot more work to physically open up a factory-carbureted fuel cell and weld in a surge tank system or a surge component from a factory EFI fuel tank. And that's going to keep your whole system looking a lot more factory.
You're not going to have all of those components to mount though the car. Okay, I'll just jump back to my notes now. So, once we've got our fuel tank and our fuel system set up and configured to work correctly, we can then move forward and talk about our actual fuel injection system. Actually, before I do that, I will just touch on, I've mentioned that it is possible to use the carbureted low-pressure pump as a lift pump. I'll just reiterate there, that we do need to be a little bit careful.
Quite often when we're converting from carburetor to EFI, this may also involve some serious modifications to the engine that may, hopefully, have the engine producing more power than it did when it was running on a carburetor. And we need to consider this, and it's quite possible we're going to now be consuming more fuel than the factory lift pump, the factory low-pressure pump, could support. So, in that case, we need to understand that, and we may need to upgrade to a higher-flowing, low-pressure pump as well. Okay, so moving forward to our injection system. So, here we need to fit the engine with some injectors to physically get the fuel into the intake ports, and there's a few considerations here.
First of all, is the actual injectors that you're going to be using, and we need to make sure that the injectors are physically large enough in order to be able to support however much power our engine is going to be making. Again, the webinar that I've just referenced goes into this in detail, and it will give you a formula so you can figure out what size injectors your engine is going to need for a given amount of power and a specific type of fuel. Obviously, this is also going to depend on how many injectors are are going to be fitting. When we're talking about the injectors, we need to understand the difference between high-impedance and low-impedance injectors. This is becoming a lot less problematic these days, as most of the modern crop of injectors that we're seeing on the market, most of them are based around the Bosch EV14-style injector, which is a high-impedance injector.
So, back in the earlier days, we were seeing a lot of low-impedance injectors. The reason this is important is, that we need to make sure that the type of injector we're using is able to be supported by the ECU that we're using on our project, and also that we've wired the ECU correctly. So, the caveat is that a low-impedance injector, and then typically when I say, "Low-impedance," that'll typically measure with a multi-meter, somewhere between about 0.5 and roundabout five ohms, if we go across the two terminals of the injector. A high-impedance injector, on the other hand, would be somewhere between about eight ohms and about 14 ohms, so that's just how you can tell which type of injector you've got. So, a low-impedance injector either needs to be used with an ECU that has a peak-and-hold injector driver, that's able to control the current supply to the injector.
Alternatively, if the ECU uses the more common, saturated drive injector, which is really designed to be used with a high-impedance injector, we can still use low-impedance injectors with a saturated injector drive, but we do need to use a ballast resistor pack and line, and if we don't get that right, it is possible to damage the injector drives in the ECU, so it is important to understand this. So once we've got our injectors and we know that they're compatible with our ECU, we need a way of physically mounting them in the engine. And this is a little bit complex, because there's no single answer here. What we need is a way of mounting them in the intake manifold, positioning them in a way so that they're pointing directly at the intake portal, the back of the intake valve, so that when they open, the fuel is going to be supplied into the engine, and it's not going to be simply wetting out the port wall. And this is one of the key areas, if we look at the key areas to consider.
If we look at a factory EFI engine, there's a lot of development goes into this aspect by the OE manufacturer. Now, they're choosing an injector location, and they're also choosing an injector angle, to make sure that their particular aims are met with where the fuel is going to be delivered. And really, what we're trying to do here, is make sure the fuel gets into the engine in a nice, finely-atomized form that's really easy to combust. It's really quite common with an OE engine to purposely aim the fuel injectors to wet out the back of the intake valve. That's going to get very hot during operation, and what we find is that the fuel will vaporise off the back of the intake valve, and that makes it very easy to combust when it's drawn into the combustion chamber, on the next intake stroke.
So it's a little bit more difficult for us in the aftermarket to achieve that, and some compromise needs to be made here. With the OEs, obviously they've got a budget that's much larger than ours, and they'll even go as far as to choose and modify the injector spray pattern, and to target exactly where they want that fuel to be delivered. So, in our circumstances, we're going to have to accept some compromise. Now, the first system for mounting our injectors, and this may be relatively uncommon, there are some engines out there in the industry that were delivered in both carburetor as well as electronic fuel injection form. Now, this makes it really simple for us, if we've got that particular style of engine.
It's as simple as unbolting the carburetor intake manifold, finding a second-hand EFI-style intake manifold, and then fitting the injectors to that. That's a really easy way of getting a nice, seamless, and also factory-looking integration of our EFI system. Probably in my experience, that situation's pretty rare, probably covers less than a few percent of the applications we were actually going to be converting from carburetor to EFI, so there's some other options available for the rest of us. Let's just jump back to my laptop, and we'll go through some of the common ones here. So, for most of the popular engines that people are modifying, there are adapter manifolds too.
Weber, Delotto, carburetor stud patterns, or bolt patterns, I should say. And there's a large industry out there, of these EFI-style throttle bodies, which share the Weber Delotto-style bolt pattern, and these can be really easily adapted to the original carburetor adapter manifold. So, in the background here, we can actually see this is the carburetor adapter manifold. So this bolts physically to the cylinder head, and then we simply bolt the throttle bodies, the electronic fuel injection throttle bodies, onto our carburetor adapter. These are available in a variety of different sizes and fitments, and a lot of these companies have just simply chosen EFI hardware.
Here is a nice example. They offer kits for a lot of the popular engines out there in the market right now, that are being modified. So this makes it very, very easy for you to add the fuel injectors onto your engine. The other advantage with us as well is, you can see the blue intake trumpets here. And if we are using an ITB or individual throttle body-style intake, there's a lot of tuning that we can do with the length of these trumpets, and generally as a rule here, as we go to a shorter trumpet, this is going to improve the bottom end torque.
As we go to a-- Sorry, I've said that around the wrong way. A shorter trumpet generally tends to improve torque at higher RPM, whereas a longer trumpet tends to improve torque at low RPM. I've done a fair amount of experimenting on various engines with this, over my career, though, and it's always easiest to have a range of sizes, or better still, an ability to vary the electronic trumpet infinitely while we're on the dynam. And then we can simply test and see what's going to give us the best sort of results for what we are trying to get. Now, one of the downsides here, as I've mentioned, we can see that the injectors on this manifold are mounted quite close to where the ITBs bolt up to the carburetor adapter manifold.
Now, what this does is it places them quite a distance away from the intake valve. So, certainly much further away than what we would end up with in an OE EFI intake manifold. So, this is what I was talking about with our injector placement. We're likely to see some compromise there. We're likely to see a lot more port wetting.
And this may affect, in particular, low airspeed performance, in comparison to a proper, factory-style fitment. Now, of course, that's not to say you can't go and make your own manifolds. Obviously, the sky's the limit, and really it's going to depend on how much money you want to sink into a project, and also to a degree, your own level of skill. But certainly, fitting the injectors up near the intake valves is going to help get the fuel, in particular at low air speeds, at a nice atomized form. The flip side of this, though, is at high RPM, wide-open throttle, we can actually see some advantage for moving the injectors back further away from the intake valves.
And this is why, in a number of highly-developed, naturally-aspirated racing engines, we often see them equipped with two sets of injectors, one quite close up to the intake valve that work at low air speed, low RPM, and then the ECU would stage out to another set of injectors, often even mounted outside of the intake trumpets, which were used at wide-open throttle and high RPM to aid atomization and mixing of that fuel with the air. So, that's just a consideration there. We'll move along, and what we're going to do is look at another common option here. Actually, I'm going to jump ahead a little bit. These have popped up, these sort of, I call them a fake carburetor.
These are designed to look like a conventional carburetor, and they'll adapt up to a conventional carburetor manifold, so this makes it really easy, particularly for V8 engines, which have already been running on perhaps a four-barrel carburetor, to really easily add fuel injection. Now, some of them also incorporate everything you need in the one unit. Even I'm pretty confident in saying there are a couple now on the market where the ECU, the electronics, are actually incorporated inside this fake throttle body as well. Now, while yes, it is a way of getting EFI onto your V8 engine, is it the best way? Probably not. This is going to give you a lot of the compromises that we see with a carbureted system, in terms of the fuel and the air distribution into the existing intake manifold, as well as all of the complication, or some of the complications, of adding EFI.
So, in my eyes, this is really such a compromised system that it would only suit those who really just wanted to be able to go to EFI, didn't really want to get all of the advantages of a fuel injection system, and wanted to limit the efforts in terms of what they physically needed to do, as well as how much money they wanted to spend. The real, biggest advantage for these systems, other than their ease of installation, though, is that they will retain the carbureted look. And obviously, that is important for some people. You can still bolt on your existing intake air filter as well, and once that's on there, probably not too many people will be much wiser about the fact that your engine's now running on EFI. My preferred system, if we can't find a factory EFI intake manifold, is to use something similar to this.
These are, again, available from a huge range of manufacturers. When we moved to a multi-point injection system, again, you can see that this sort of system moves the injectors right down near the intake valves, and now we have an injector mounted in each intake port. So this is, in my opinion, a better solution to getting the fuel delivered. The system still can give a very carbureted look, by the time you've got a large air filter mounted on the top of that four-barrel throttle body here. Again, it covers most of the fuel rails and the injectors.
Obviously, we could choose a slightly more stealth colour for the fuel rails rather than the bright red anodized, and that's going to help everything sort of blend in. This sort of system, as I've said will get-- Do a better job of delivering the fuel and metering that out per cylinder. Generally, the air flow, because we're still basing it on a carbureted four-barrel-style intake manifold, often the air distribution won't be quite as good as what we normally see with a modern EFI system. Which if we look at factory LS engines, for example, LS V8, we see a plenum of the single throttle-body that's front-facing, and that seems to do a better job of giving even air distribution. And then we get both even air and even fuel distribution to the engine.
So, that's covers off the main, the common ways of getting fuel injectors physically fitted to the engine. Let's go back to my notes for a second, and we'll move on in to cover our next topic, which is our ignition system. Now, really, when it comes to the ignition system, we're talking here about getting spark into the engine. And it depends, exactly, what your existing ignition system was. If we're talking about an older-style carbureted engine, we're probably going to be talking about a distributor-style ignition system with mechanical, advance weights inside the distributor to give it some kind of curve so that the ignition timing advances as the engine RPM increases.
Now, what we're going to do here is really going to depend on the look you want. Obviously, if you're looking for something that still looks stock, we're going to want to keep that distributor. It's also going to depend on the complexity of the system we're putting together. If we want to get the best possible performance, then we're looking at moving to an individual coil-on-plug system, that's going to dictate the type of trigger system we're going to need to add, which we're talking about next. So, in the simplest system, what we can do is physically remove the distributor.
With popular V8 engines, we can buy off-the-shelf replacement distributors already set up for EFI. It's also possible to mechanically lock up the advance mechanism, so that the advance is fixed. And then we're going to be using the ECU to trigger a coil, an external coil, and then we have control of the ignition advance through the ECU, just like we would with any EFI system. Obviously, beyond the distributor system, which has its downsides, we can then look at systems such as waste spark and direct fire, although they require a little bit more hardware, and they also require a little bit more consideration, as I've touched on with our trigger system. The trigger system, as I said at the start, this is one of the areas where I see the most room for error, because we are really starting here with an absolute clean slate, so it's possible to get system installation really, really wrong.
If you do want more information on this, I'm going to be covering the basics here, but if you do want more detail, please check our webinar archive and look for the webinar we've done recently on trigger systems. It's going to give you a lot more detailed information than I'll be able to cover off of here in this webinar. So, really, there's just two main systems that we can use. The simplest would be to fit a trigger system into the existing distributor. There's, again, there's off-the-shelf systems available for popular engines that make this incredibly easy, and we can simply take a trigger system out of the trigger input from the distributor, and feed it straight into our ECU.
And one of the simplest types of trigger input there is what's known as tooth per TDC, or basically, the ECU receives a trigger input, or a tooth edge, every time a cylinder passes or is ready to fire. So, really, all the ECU is getting there is data about the engine RPM, and it doesn't specifically know which particular cylinder is firing at any time. Now, that's okay for a distributor ignition system, but it's also going to have some implications on our fuel injection strategy, because if the ECU doesn't know whereabouts in the engine cycle it is at any time, it's impossible to use full sequential fuel injection, where the fuel injector is timed to the intake stroke of each particular cylinder. So, it's a very basic strategy, certainly not my favourite strategy. The next option that I would look at is going to a crank-style trigger system.
Actually, before I touch on that, one other aspect that's a consideration. If you're going to derive your trigger input solely from the distributor, is particularly with older carburetor cars, it's quite common that we'll find a little bit of slack in the drive mechanism for the distributor. And what this can result in, is certain regions in the RPM range where the distributor will essentially oscillate, and this can result in some timing instability, if we really want to be fussy about rock-solid timing. So, my preference there to fix that particular issue as well as allow some more flexibility, with our particular installation, is to move to a crank trigger system. As its name implies, this is where the trigger input, where at least one of the trigger inputs is being derived straight from the crankshaft.
And really, that's the aspect that we're interested in. We don't really want to know so much what the distributor's doing. We want to know exactly where the piston is in its cycle, and we can tell that if we know whereabouts the location of the crankshaft, as well the rotation of the crankshaft. Now, again, for common systems, if we'll just pop to my laptop again, for common engines, I should say, there are often easy, bolt-on trigger kits available. Now, this one here comes from Holley.
It includes all of the parts that you need to achieve a really rock-solid trigger system. And this is one of the important aspects here. We've got this mount system here, which is used to mount this reluctor-style pickup. A reluctor-style pickup looks at this tooth wheel that will go on the front of the crankshaft or a harmonic dampener, or the like. The reason I bring your attention to this mount bolt is one of the really important points is to make sure that our crank trigger pickup is mounted really solidly.
It's quite common to get some really nasty harmonics and vibrations being transferred through the engine at certain RPMs, and what those can do, is if your trigger mount is, or your pickup mount is not particularly rigid, this can result in the reluctor pickup, or whatever pickup you're using, actually vibrating and moving quite a lot more than you'd give it credit for. And I've seen this result in the trigger input contacting the toothed wheel, and obviously that's not a great solution if you want to ensure that your trigger system is reliable and lasts for a long time. So, it's quite possible to create your own trigger system. Obviously, if you've got an engine that has great after-market support, then often it's quicker, easier, and more cost-effective to choose a reliable, after-market trigger system that you can simply bolt onto the engine, and start from there. Well, we'll just jump back into my notes again.
Now, when we're talking about these systems as well, if we go to crank trigger, we have a couple of options here. Again, this comes down to what sort of data our ECU needs. Now, on the simplest system, we can run what's known as a missing tooth-style wheel. Let's actually just jump back to that photo, just briefly, sorry, before we move on. And we can see that that's exactly what the style of wheel is.
Now, the missing tooth, the old missing teeth, what that does is, the ECU can detect this gap in the regular teeth spacing, and it knows every time that that gap has gone past the reluctor pick-up. So, this gives it some information about whereabouts in the engine cycle, the engine is. However, because there are 720 degrees, or two full revolutions of the crankshaft, to one engine cycle. While it will know, for example, if number one cylinder is at TDC, it won't know if it's at TDC on the compression stroke or on TDC on the exhaust stroke. So, this will allow us to run, for example, waste spark.
We have a little bit more flexibility with our injection system. We still can't run full-sequential, because the ECU doesn't know if the intake valve is open, or the exhaust valve is open, for example. Sorry, the intake valve is open on the intake stroke, or if it's closed. It can't tell where it is. So in order to get that data, we still need one more input, and this needs to, this is what's referred to as a synchronisation input.
And if we want to run a crank-trigger system like the one we've just looked at in conjunction with a single pick-up from our distributor, the distributor, remember, is rotating at half-engine speed, so it takes two full revolutions of our crankshaft for the distributor to do a single, full revolution. This pick-up, if we've got a single tooth pick-up in our distributor, this combined with our crank trigger, gives the ECU all of the data it needs to know both what the engine RPM is, as well as exactly whereabouts in the engine cycle it is. And this is my preferred system. It allows us to run full, direct fire spark as well as full-sequential injection. It gives us all of those advantages of electronic fuel injection.
My personal opinion is that if you're going to go to the trouble of converting from carburetor to EFI, we might as well spend the extra time and cash and make sure that we're going to be getting all of the advantages that this sort of system can offer us. Well, I'll just jump back into my notes. And we're getting down to the last couple of steps. I'll just mention here, if you do have any questions, this is a great time to ask those questions in the chat box. Okay, so we've got our basics covered.
We've got a fuel system that can provide consistent, high-pressure fuel. We've got our injectors mounted to supply that fuel into the engine. We've got a trigger system to supply data to the ECU. And, of course, we've got an ignition system set up. And if we want to get the most out of our EFI system, we are going to need to add some additional sensors.
And, well, there's an unlimited number of sensors that we can add. The basics will include an intake air temperature and engine coolant temperature sensor, so this is going to allow the ECU to account for changes in our engine temperature for the likes of cold-start performance. We can then use the ECU also to trigger a fan relay, and control our engine cooling fan. On the intake air temperature side of things, we're going to be using their input, either directly in the fuel model to account for air temperature and hence, air density. This is going to help account for changes in air density and keep our air-fuel ratio consistent, as the air density changes.
Or, in some ECUs, we're going to be manually making those corrections to the fueling, based on air temperature. We can also use those corrections, obviously, to change aspects such as our ignition time, as well. We're going to have more control over that. We're also going to have the ability to add a manifold absolute pressure sensor. Now, this is going to be a critical sensor if we're going to run the speed density system, particularly if we're using a single-throttle body and plenum-style intake manifold.
This is the common system that aftermarket ECUs will be using. We want to use a manifold pressure sensor to measure the pressure in our inlet manifold. It's one of the key inputs to the speed density calculation. I'll just add here that if we are running individual throttle bodies, then this gets a little bit more complex. With ITBs, the manifold pressure signal is no longer a good indication of engine load.
And in this sort of system, we will typically set up our fuel and ignition tables with throttle position as the load excess, and this is known as Alpha-N, or referred to as Alpha-N. Now, in those systems, I still generally like to include manifold pressure where possible. This gets a little bit more complex, because we now need to drill and tap our intake manifold after each of our throttle plates, and then we need to run a balance tube. So what we're doing is combining the manifold pressure signal from each of our intake runners after the throttle plate, combining them into a vacuum tube, or a balance bar, so that we're getting the average manifold pressure across all of our cylinders. Now, I'm not going to use this as a load input, but what we can do is use this in a background calculation, even though we're using Alpha-N or throttle position as our main load input.
We can still use manifold pressure as a background calculation to modify our fueling, and we'll find that this is going to give us much more consistent fueling when we're out in the road, and we're holding a consistent throttle position, but we're moving up and down hills, for example. This will result in the same throttle position, same RPM, but a varying manifold pressure, and those can affect our fueling ECI if your ratio move rich and lean, if we're not using that manifold pressure in the background to help with our fuel calculation. This also brings me to our throttle position, since I've just touched on this with Alpha-N, but throttle position is another key input that we need if we're running an EFI system. If we're running Alpha-N, obviously it's critical because our fuel and ignition scheduling is based off throttle position. Even if we're using manifold absolute pressure, though, it's an advantage to have a throttle position sensor because we can use that throttle position sensor for aspects such as transient or acceleration enrichment.
We can also use that throttle position sensor to trigger aspects such as idle speed control, so really important to have that sensor. Now, that seguways nicely into the idle speed control system, and if we're converting to EFI, we may also choose to add a idle speed control solenoid that'll bypass air around the throttle plates. And if we're going to use that, we need a way of triggering it, telling the ECU we need to go into auto-speed control, which is why we need our throttle position sensor. And then we can tune the idle speed control solenoid opening, to control and achieve really nice, stable idle control. This is, again, an area where carbureted engines don't do quite as good a job as a modern EFI system.
Again, I mentioned we can really have as many sensors as we like. I'm going to add one more there, that I generally like to include, which is a wide-band oxygen sensor. Now, this is useful for tuning. We can use the input directly into our ECU to help the tuning process and speed up tuning the fuel mapping. However, also, in some ECUs we have the ability, then, to use the wide band lambda sensor to help run closed-loop fuel control.
So this is going to help us maintain stable air-fuel ratios if our atmospheric conditions change, or something ends up just affecting at your fuel ratio slightly, so it's able to give us really, really accurate and fine control over our air-fuel ratio. Okay, our last section that I was going to just touch on, and this will be very brief, so we'll move into questions shortly, is our ECU selection. Now, this is a question that pops up regularly, and I'm going to give the answer here that I always give. There is no one best solution that's going to suit everyone when it comes to choosing an ECU. What I always suggest is, the best ECU for your particular application is the one that your tuner is most familiar with.
They're going to know the system inside and out, and they're going to be able to get the best out of that system really quickly. It's gonna give you, probably, a better tune in less time, and hopefully that's going to mean that it's going to save you money. Now of course, you guys watching these webinars, a lot of you are tuning yourselves, so that puts you in a unique position, because you may not already have an affinity to a particular brand, and that gives you the ability to choose just about any system. Now, here's the strategy that I go through when I'm choosing an ECU, and this is what I recommend. First of all, we want to make sure that the ECU is physically capable of controlling our engine.
On the basics, what we want to look for is that the ECU has sufficient ignition channels, and sufficient injector channels to drive the number of ignition coils and injectors that we physically need. We also need to make sure that's going to be compatible with the trigger system that we've got on our engine, although when we're converting like this, it's less of an issue. The common systems that we'll use during an EFI conversion are almost certainly going to be supported by just about any after-market ECU. So, there's obviously going to be a huge range of ECUs that are going to fit the bill at this point. Next, we're going to consider our budget, because everyone has a budget, and there's likely to be a few ECUs that will still fit within your particular budget.
Once you've narrowed your selection down to a few ECUs, the next option, the next aspect I would suggest, is that you consider local support in your particular area. Particularly when you're learning or just getting started, it's always easiest if you're able to pick up the phone and physically talk to either the ECU manufacturer or one of their representatives, that knows that system inside and out, and get quick answers to your technical questions. So, for those reasons, always easiest to choose, or best to choose, an ECU that is well-supported in your area or your country. That's gonna get you the best results. Finally, if there's still a couple of ECUs that will tick all of your boxes at this point, this is the position where I would try and find a few customers that have used each of the brands, and get their own personal feedback on what they liked and they didn't like.
You do need to be really careful when you're asking for advice on a particular ECU, because what I find is that experiences on a particular platform dramatically vary. So you need to find out if there's a particular reason why someone is speaking really badly of a particular ECU, when everyone else that you talk to has had great experiences with that particular brand. All right, so hopefully that's given you some insight into the six considerations that we need to keep in mind when we're converting from carburetors to EFI. Let's jump into the questions now. We'll see what we've got.
Our first question comes from Arun Kafar, I'm sorry if I've pronounced that wrong, who said, "If you're using a crank trigger "for an RPM and a pick-up in the distributor "for position in the cycle, is the distributor "accurate enough? "No issues with backlash in the gear drives, "or with timing chains?" Okay, that's a really good question there. And one of the considerations here is, if we are using that system, the actual trigger input, the position information, is coming directly from the crankshaft. So it's going to be rock-solid and reliable. All we need from the distributor pick-up is one pulse per engine cycle, to tell the ECU whereabouts in the engine cycle it is. And the only considerations we have here is, we want to make sure that the signal from the distributor is reliable enough that it's going to occur between two of the pulses from the crank-trigger system.
And in fact, in some instances, particularly if we are using a missing-tooth-style trigger wheel, the one we looked at there, in fact that's really easy, the resolution is great, because all we want to do is make sure that the trigger input from the distributor occurs anywhere except that gap where those missing teeth are. So it gives us a huge, basically a 350 degrees of the crankshaft rotation, where the synchronisation pulse can come from the distributor without any chance of the ECU getting confused. So, it's one of the cleanest ways of getting both a reference and a synchronisation input into the ECU. Again, I'll recommend our webinar on trigger systems, because it goes into a lot more detail there. Barry G.
has asked, "Hall Effect, or Reluctor? "Which is better?" Great question, and I think there's always going to be two schools of thought on this, and probably no firm agreement. Personally, I've always been a fan of the Hall sensor. The reason for this, in my mind, was it's a nice, clean, digital signal. However, they can also be problematic, particularly the very popular GT101 Hall sensors. These don't work very well with very high-frequency, high-tooth-count inputs, and they actually start providing false data to the ECU.
So really, it's a case of horses for courses. One of the advantages with the reluctor-style pick-up is that it creates its own voltage output, as the trigger wheel passes the reluctor input. This can help the ECU still receive trigger data, if the cranking voltage or the system voltage gets very low during cranking. But essentially, properly-configured, properly-selected, and well-installed, either system can do an exceptionally good job. I can't say that there is one that you must use.
Next question comes from Wren Kafer, who's asked for unusual applications, V8 in his case, with no four-valve manifolds. "No four-valve manifolds are available. "What should I use for a throttle body?" Okay, that's really going to come down to your own level of ingenuity there, and what you want to create. Not being 100% aware of your exact application, it's a little bit hard to sort of advise too thoroughly there. If you want some more details, I'm happy if you want to post in the forum, and maybe some photos, and we could give you a little bit more personalised advice.
But really, it comes down to how involved you want to get, and how much money you want to spend. It's possible to customise a factory-intake and manifold on a V8, to include injectors mounted down near the ports, and then adapt just about any manner of throttle body that you could consider or could conceive. It's common on a centrally-mounted, four-barrel-style throttle body, to adapt that with a 90-degree angle, and then bolt on a single throttle body, and that gives you access to just about any throttle body you could imagine. I recently saw just exactly that style of application, with an LS V8, where an two, it was using a carburetor-style intake manifold that had been converted to fuel injection, and then a 90-degree adapter had been bolted to the top of the down-drive style intake manifold, and that had been adapted to an three drive-by wire throttle body. So, really, there's no limitations there on what you can do, but some photos of what you've got there, in the forum will probably help, let me help you a little more thoroughly.
Okay, that's got us to the end of our questions, and as usual, if you do have any more questions, please ask those in the forum, and I'll be happy to answer them there. Thanks for joining us today, and I hope you enjoyed today's webinar. Look forward to seeing everyone next week!