Since fitting the mapped ignition to my RH7, I have been very satisfied with the improved running of the engine, instant starting and clean idle. The perfection of the ignition has helped show up some anomalies in the carburation, especially when the engine is hot. The DCO/SPs while giving sterling service have been difficult to get spot on for progression, or maybe I'm just a nitpicker, when the engine was hot they would fluff a little on progression, weaker idle jets cured the fluffing but gave a little hiccough when flooring the throttle. The EMERALD M3D unit that controls the mapped ignition also supports fuel injection and I had always planned to go this route. Before I knew where I was pound signs began circling my head and I started thinking about fitting injection.
I had a long chat with a friend, Peter Jones who runs Jondel Race Engines and he told me that an engine he had recently built with an almost identical spec. to mine but running injection was the most flexible race unit he had ever seen; apparently the throttle could be stood on at 1500RPM (it's running 300 degree cams) and the engine would simply pull like a steam train. The reason for this is the reduction in standoff resulting from going to injection, and the extra advance that could be used. While my engine was fairly flexible considering it's specification, it would only pull on a very light throttle when below 4000RPM, Milton Keynes being full of roundabouts (160!!) and me being lazy, the idea of a very tractable engine appealed greatly.
Being an inveterate fiddler and PC fanatic the idea of playing PCs while dialling in the power seemed like Nirvana, so I decided to look at the costs and practical considerations of converting to fuel injection using the M3D. The original fuel injection systems such as 'K' Jetronic and similar as fitted to the XR3i and Golf GTI use mechanically controlled injection, so the fuelling requirements are fixed and cannot be varied without a lot of messing about. Later systems such as 'L' Jetronic and Motronic use computer controlled injection which is eminently programmable, this makes it easier to change fuelling requirements both for the manufacturer and the after market 'chip-tuner'. The M3D falls into this later category. It is only since the introduction of these computer controlled management systems that the technique known as 'chipping' has evolved. Chipping merely means changing the map of ignition and fuelling settings to give maximum power and flexibility. The manufacturers settings are often a compromise between economy and power, and need to cope with poor fuel and extremes of circumstances. Because of this they often do not give best performance.
The M3D makes all this very easy by giving straightforward access to the ignition and fuelling maps so that they can be tailored to exactly suit requirements, in fact without this functionality it would not work at all. To program the M3D you attach a notepad PC via a null modem cable that comes with the unit. You may then alter the maps, download new ones, or even change the fuelling and ignition settings while the engine is running, this is often the best way to perfect things as the engine can be run under real life conditions. The enterprising can even alter the settings while driving down the road! The system gives feedback on current speed and load, ignition advance and fuelling, together with air and water temperature. In the near future, a Lambda reading will be incorporated (mixture strength), from a Lambda sensor in the exhaust. I already have such a sensor fitted to my exhaust.
These modern fuel injection systems use a technique called pulse width modulation, what this actually means is very simple. Each cylinder has its own injector that is basically a solenoid valve. In its normal condition the solenoid valve is closed, fuel is supplied to these injectors at a known and regulated pressure. When fuel is required, usually once per revolution the solenoids are triggered for a pre-determined time (pulse width) by the engine management computer and fuel is squirted into the inlet. When more fuel is required, the pulse width is increased and the injector is open for longer allowing more fuel. This system has many advantages, fuel can be monitored and supplied in a very exacting manner, airflow is not required to draw the fuel in (as with carbs) so at low RPM with large throttle openings fuelling is much improved. Feedback can be given to the control unit on temperature, engine speed, load and acceleration with the control system varying the fuelling to suit. This gives very precise monitoring under all conditions. Since no venturi is required to help draw the fuel into the airstream, the inlet tract can be made obstruction free. The precise fuelling requirements for all these circumstances are stored in a fuelling map within the ECU (in this case the EMERALD M3D). The disadvantage is that whereas a carburettor is a passive device and will increase fuel according to airflow, an injection system has to be told for every engine speed, at every engine load exactly how much fuel to supply, which can be time consuming.
In order to fit an injection system you need
somewhere to mount the injectors and also a throttle regulating mechanism of some kind
(like the butterflies in a carb). The beasts that perform this trick are known as throttle
bodies and are just like carbs but with no float chambers, jets etc. and with
provision for mounting the injectors and fuel supply rails. I looked at various
manufacturers bodies (ooo-err), and the Lumenition ones looked best, however they were
expensive at 500 pounds a pair. A quick call to my pal Peter Jones confirmed that the
Lumenition throttle bodies were re-badged Jenvey bodies, which were available at 307
pounds a pair direct (a new pair of DCO/SPs is 520 pounds!). With throttle linkage and all
necessary bits including fuel rails and air horns they cost 430, which I considered good
value and they are a direct fit onto the carb manifold.
I was lucky enough to trade an old NatAsp Cosworth exhaust manifold I had in the loft for a set of standard Cosworth yellow injectors (good for 270BHP). A Cosworth pump and pressure regulator were donated by Peter Jones in return for building him a PC and installing some software.
He also had an example ignition map and fuel map from this other engine, and although it was from a different engine management system, it was useful to establish maximum fuelling values and the shape of the fuel curve. Because the injectors fire once per revolution in both systems, the fuelling should be similar where torque values are similar, so a glance at the fuel map showed where the peaks were on the torque curve.
A trip to the scrapyard was called for next to obtain some wiring bits and pieces, an injection harness from an old Vauxhall Carlton supplied the snap on connectors for the injectors and the wiring behind them. I attached the throttle bodies to a dummy manifold (piece of angle iron!) so that I could make the injector wiring harness and connect the throttle linkages in advance. I then sent the M3D ECU back to Emeralds for a firmware upgrade to support the injection. The wiring loom was simplicity itself, all the injectors are pulsed together, so they were wired in parallel via a two wire connection, a single feed from a switched supply and a lead to the M3D box which will trigger to earth in order to fire them when necessary.
The injection system uses a very high fuel pressure, around 57PSI, so the normal FACIT fuel pump I had which supplied the Webers was unsuitable (only just bought the bastard!). I used a Bosch pump from a Cosworth (the XR3i/Golf GTI pump is also suitable). Injection pumps have to be gravity fed and run horizontally, so I had to modify the fuel tank with a large take-off on the bottom of the tank on the nearside rear. I laid in a new fuel line from this take off to the fuel pump mounted on the inner wing just below tank level. The old fuel line could then be used as a return from the pressure regulator when converting.
The injectors fitted no problem to the Jenvey throttle bodies, but the studs on the inlet manifold were too long for the bodies to mount cleanly, so I used Jenveys stud kit which incidentally was M8 thread (the manifold was tapped UNC). This caused some serious aggro when actually fitting the throttle bodies at Emeralds. The Jenvey bodies have provision for fitment of a throttle potentiometer that is vital to feed back information on load to the M3D and the one from the DCO/SPs fitted with little difficulty.
The fuel supply comes in at one end of the fuel rail; the two rails are connected at the centre, with the fuel regulator hanging off the other end of the rail from which excess fuel returns to the tank. At idle more than 80% of the fuel supplied pumps straight back to the tank.
The injection system also needs sensors to determine coolant and air temperature, in order that it can supply extra fuelling for cold starts etc., these were connected ready. I booked an appointment on Emeralds Rolling Road and when the day came I despatched myself down to Southwark.
I arrived in plenty of time for breakfast at the local Cafe and then installed the car inside Walkers Workshop where his new rolling road with all it's attached systems lurked nearby. The first job at hand was to disconnect the carbs and fit the throttle bodies, no easy task because the old manifold studs were too long and the new ones were the wrong thread - oops. After an hour of careful re-tapping, the bodies were attached and bolted in place, followed by the throttle linkages. An hour later all the electrical connections were made to the new pump, the injector loom etc.
We spent another hour and a half remaking the fuel connections at the rear, where the existing pump was bypassed and the new one piped in to the fuel supply.
The M3D firmware had recently been upgraded from 8 load sites to 16, and Dave Walker was keen to install this new firmware and software in my car. This meant removing the unit (3 times in all) which is not easy as it is placed awkwardly in the footwell. It also meant re-processing the ignition and fuel maps to suit the new 16 load sites, this took a good 40 minutes to do. I have since written a software utility to do this automatically for existing M3D owners who want to upgrade.
3pm arrived and the engine was ready to start, and start she did, but MEGA rich. We found out then that the fuelling values I had used from the dyno engine were exactly twice what was required, so Dave decided to start from scratch. This was the first time he had mapped an engine with 16 load sites and such an extended rev range. It basically meant mapping 256 load sites, this mapping took a long time and nearly asphyxiated us both with exhaust fumes. We managed to match the power output from the carbs no problem, and then set about re-fuelling at high RPM. At 8000 RPM we found another 25BHP where previously the power had been dropping off, this was achieved by weakening off the mixture considerably. Holding the engine at these sort of revs brings your heart to your mouth but gave another 1000RPM or so of usable power at the top end. The fuelling at the bottom end was much more controllable and enabled us to 'dial out' a lot of the intractability felt at low RPM cleaning up the progression no end. I finally got away from Emeralds at about 1.30AM and arrived at home around 3AM - a truly gobsmacking day.
On the way home I discovered that my fuel tank would need baffling to avoid fuel surge, every time I negotiated a left hand bend or corner with the tank less than half full the engine would cut-out, due to fuel surge in the tank! A new tank has been designed and is awaiting welding on the bench at home
The mapping was by no means finished and I made another appointment to finish it off mainly in the area of progression and low RPM. Another visit was made to Emeralds, this time in the pouring rain with the car stalling every time I stopped because the idle mapping was not correct. This proved to be a serious problem on the journey down, as I was travelling down through North London on the A5. The car stalled at every set of traffic lights; continued restarting (lights on because it was 6.30AM) proved too much for the battery and it went flat. This was perhaps my most embarrassing moment in the car (other than when the brakes stuck on the M1).
A quick call to the AA, and a 15 minute wait in the p*ssing rain saw the arrival of a very nice man who supplied some jump leads. He was absolutely fascinated as I plugged in my laptop PC and dialled in improved fuelling and advance settings, and watched as the idle transformed from leaden to crisp and reliable. He dolled out a cup of tea for us both and remarked that he had done very little, and it was the easiest call all week, although when he had heard from his control centre that it was a kit car he had feared the worst.
I made my way down through London past Buck House and Tony's posing parlour all the way to Emeralds where breakfast was once again in progress. After another long session (mainly spent tweaking the advance curve) I took the car out for a test drive on a damp road and promptly nearly ran into the back of a delivery van. I made the mistake of nailing the throttle at 2000RPM which before would have caused the engine to growl and very little else. Instead it lurched forward with stomach churning torque, with the back end snaking away! To say that the tractability had been improved was definitely an understatement. The engine felt more like a steam engine at low RPM!
When I looked at the ignition map and rolling road readings I was surprised at how much advance was being used at relatively low RPM, but the engine loved it. The torque available between 1500 and 3000 RPM on a full throttle had virtually doubled; this explained the improved tractability. The car is now very easy to drive off the line and bends and roundabouts can be negotiated without having to stir the gear lever.
After the mapping was finished Dave Walker very kindly corner weighted the car, and checked all the suspension geometry with the electronic kit he has available. He offers a very good healthcheck service for suspension and geometry and the kit is excellent. This showed up a problem with the castor on one side of the car that has appeared after fitting the tie bars.
Was it worth it?
Yes!! Following a very wet journey home and a couple of days 'testing', I can see just how flexible the engine is, sure there is still a point at which the cams come in, but the engine is much better behaved when below this threshold, and is far easier to drive. The net result is vastly improved tractability, the engine is transformed. Roll on summer!