This article was written by Andy Warne for "Club Lotus News" in the UK.
Fuel Injecting an Excel
Ever since "downgrading" from a Turbo Esprit to an Excel, (due to an addition to the family requiring a third seat!) I have, as expected, always missed the blinding performance of the Esprit, but apart from the expected deficiency in raw horsepower, the Excel seemed to be very lacking in general responsiveness and "driveability" which was a pity because in all other respects the car is superb. I was becoming irritated by flat spots and hesitating when pulling away and poor mid-range acceleration, although at the top end all was well.
Various people I spoke to, including the Lotus factory confirmed my suspicions that the problem was due to the late model Excel SE cars being "fudged" to conform to emission control regulations and never really worked as they should right from the factory. If ever a car cried out for engine management, this was it. This probably applies equally to the last of the carburettored Esprits, especially the non-turbos.
So I decide to do something about this and fit what the car should have had in the first place, an engine management system. Another future benefit was easily being able to adjust for ever-decreasing fuel quality, including unleaded. Searching for a suitable system was the first step. I decided that I didn't want a system that was tied in to an "approved supplier and installer" for programming and setting up - I wanted to do everything myself including the programming. A few hours of web surfing found what seemed to be an ideal solution, a system called "SDS" which originates from Canada. This system can be seen on this web site: www.sdsefi.com. It's main benefit is that it comes with a small control box with an LCD display, which can be mounted temporarily on the dash, by which all profiling and adjustment is done. I also fitted a mixture meter, mainly to ensure I was not running too lean with associated risk of holed pistons! Using this system it is easily possible to make tweaks to the fuelling and ignition curve while on a journey. (Do NOT while hurtling down the motorway, I meant while standing at red lights etc!). All my research into EFI systems was done on the internet, and I also ordered the system direct via the web as the price when purchased in the UK from a local dealer would have been the same in Pounds as the US Dollar price! Hopefully internet commerce may one day put an end to these rip-off situations.
I chose the top-end system, which includes static ignition with electronic coils, so the notoriously inaccessible distributor won't give any trouble- its now redundant! The main tasks in fitting were:
Fitting 3 magnets to the crank pulley, glued into drilled holes. The pulley, being a skinny alloy affair, only has space for this on the rear face, so I had to work the angles backwards. A sensor has to be fitted. There is a wonderfully convenient bracket on the engine, behind the pulley, which could have been made for the job! No fabrication of special mountings was needed at all and the sensor is not even visible.
Plumbing: This was a real pain. New flow and return lines are needed in high-pressure pipe. I tried to get them down the backbone alongside the original fuel pipe. The problem is that fuel line must be the first part they started with in the factory, and built the car around it! I gave up after trying several different routes. I concluded the only way to do this really neatly and safely would have been to remove the exhaust, diff and propshaft - rather over the top! The problem is ensuring the lines are 100% definitely never going to get anywhere near the propshaft! I could not accomplish this so reverted to routing under the body using 8mm copper pipe running into high pressure hose at the ends. A small surge tank was fitted alongside the main fuel tank in the space below the existing fuel pump, fed by this pump, and this gravity fed into the injection pump mounted in the right hand rear wheel arch. The return pipe feeds into the surge tank and I also fitted a tiny pipe from the top of the surge tank into the main tank to vent any vapour or pressure.
Throttle bodies: I used the Weber units which simply replace the carbs. Easy. They bolt hard up to the manifold so out go those rubber rings and spacers etc. With hindsight I may have used the equivalent Lumenition bodies, being cheaper and having a neater fuel rail arrangement. The injectors plug into the throttle bodies and are standard Bosch units. The injector sizing was calculated at great length using various formulae which all produced different results! In the end I threw all these away and guessed! The result, 300 cc, has proved to be spot on.
Wiring: Not too difficult. Being an electronic engineer helped here! Care has to be taken to get a clean feed from as near the battery as possible and a good earth. The ECU box was hidden under the dash. The injection pump is fed from a fail-safe relay which stops the pump a few seconds after the engine stops for any reason.
Sensors: Water and air temp: easy. Exhaust oxygen sensor: this is not strictly necessary but I needed it for the mixture meter. It can also be used for "closed loop" control but I have never implemented this as it seems unnecessary. The exhaust downpipe had to be removed and a bush welded in to take the sensor.
I fitted everything except the throttle bodies while keeping the car in a driveable state, and then switched over to the engine management for ignition only at first. Much to my surprise it worked first time! I was so surprised I had to double check I had actually switched the plug leads over onto the electronic coils!
Then off with the carbs, on with the throttle bodies and connect fuel flow and return, plug in the injectors and turn the key, not really expecting much to happen first time! It actually started and ran! A bit of playing with the control box and it idled nicely. It took about 2 months of intermittent driving and adjusting to get the profile absolutely spot on. I'm pretty sure a rolling road session would not get it any better, although it would have been much quicker of course.
So was it money well spent? Well it was definitely expensive, about £1800 not including my time for fitting. But to use that old tuning cliché, the car is absolutely transformed! Gone are all the hesitations and flat spots, it just goes! The engine pulls strongly and smoothly from nothing and is enormously flexible. To my surprise there has been a noticeable power increase. This was not an aim and was not expected! I reckon about 15-20% extra. Now I must qualify this by saying that there could well have been something seriously wrong with the previous carb set-up, in addition to the "designed-in" deficiencies although if there was, I could never trace it and neither could a well-known tuning firm. Another benefit has been greatly improved fuel economy, again not an intention but welcome nevertheless!
This exercise has really brought the car into the modern age, the already excellent HC engine now being fed and controlled with an accuracy which brings out it's best. It's really only doing what Lotus would have done with the car had it continued in production for a few more years, as they did indeed do with the Esprit. It's not a modification to be undertaken lightly, not only because of the cost but also the risk of destroying the engine if care is not taken with setting up, not to mention destroying the whole car if that fuel at 40 PSI ever goes astray and catches fire! I found it an interesting and rewarding challenge though and the improvements it produced far exceeded my expectations.