Lotus Esprit V8 A'pexi AVC-R Variable Boost Controller Upgrade - By Ian

You may or may not have read yet, our write-ups on Water Injection and Turbine Bypass Valves.  Well, the reason for those upgrades is because we originally conceived and installed this one.  The Variable Boost Controller.

Also a MANDATORY addition to your instrumentation should be an Air/Fuel gauge. This installs very easily on to one of your Lambda/Oxygen Sensors (we use the pre-cat sensor). This gauge tells you, usually in the form of a bar code whether your Air/Fuel mixture is in a danger Zone.  Air/Fuel gauges are available from your local performance super store.

Lotus fresh from the factory limits turbo boost to approximately 0.6 - 0.7 bar. (8 - 10psi).  We have enhanced that to include incremental and fully adjustable turbo boost pressures of 0.35 bar and 1.2 bar respectively.

Why those specific pressures you may wonder? The main reasons are:

1. The standard waste gates are adjusted mechanically to 0.35 bar. We decided to leave these as is and make it the lower limit, as it really is an insignificant boost pressure. And, an added benefit of this low is; while cruising in a fuel conservation mode with no boost enhancement, we get up to 350 miles to a tank full of fuel.  Calculate those MPG statistics for 16 gallon tanks!
2. The other number is a little ambiguous, the ECM (Electronic Control Module, or the computer) takes readings from the MAP (Manifold Absolute Pressure) sensor to measure and hence limit the boost at the top end.  Lotus cunningly fitted only a 2 bar MAP sensor to the car.  Lotus also uses an atmospheric sensor as a reference device.  Given that absolute pressure is 1 bar, and also, given (or perhaps assumed) a 10% tolerance for the MAP sensor, we come up with a MAXIMUM allowable boost pressure of 1.2 bar. (Even though the controller can provide up to 2 bar!) The ECM compensates for higher boost by putting more fuel into the cylinders assuring the undesirable LEAN MIXTURE CONDITION does not occur.  The Boost controller (A'PEXI AVC-R) monitors injector duty cycle and we can see the injectors efficiency in the cockpit of the car at all times. And remember, the Lotus Esprit V8 employs 10 fuel injectors, 8 in each cylinder and 2 auxiliary injectors on each side of the plenum.   We performed a lot of tests, and our injectors never increased beyond an 80% duty at 1.2 bar. Saying that 1.2 bar is a little impractical as the wheels spin between gears with even a modest driver (Me!). So we limit our car to a max of 1.1 bar.
3. Lotus states in the manual that prolonged periods of over 1 atmosphere of boost (14.7psi) will trigger the computer to shut down the injectors.  IT DOES NOT HAPPEN ON OUR '98! So be real careful not to exceed 1.1 bar of boost at any time, while closely monitoring your Air/Fuel Gauge.
4. And now the disclaimer yet again, we do not assume or accept any responsibility for any damage to your engine caused by irresponsible operation of the boost controller. WATCH THAT AIR/FUEL ratio.  And take care of your precious gearbox, especially that 2nd to third gear shifting.

All items listed assume the person(s) doing the modifications have a complete set of up to date Lotus workshop Manuals.

The steps we performed are as follows:

This procedure is very simple in comparison to some of the other upgrades we have completed.

• Open the tailgate as far as it will go without disconnecting the struts and support it. (we used a rope to the roof of the garage through the rear wing)

• Disconnect the battery.

• A'PEXI provide a super precision vacuum solenoid.. This has to be mounted somewhere in or around the engine bay in a cool spot, within close proximity to the standard Boost solenoid.This proved to be quite a task. Remove the right hand bulkhead trim from the rear of the car.  (this is the same trim you have to remove if removing or changing the ECM or fuel pump) This is actually harder than it seems, it is a bitch to wiggle out after all the screws are removed.  But it does come out eventually.

• Remove the right  hand flexible hose connecting the air intake to the air filter box.  This is simple, undo the clamps and you are done.

• Now, mount the solenoid in the cavity in a vacant spot on the wooden ancillary mounting shelf that covers the right hand fuel tank.  There are all sorts of things screwed to this  shelf; the ECM, Pressure Reference Sensor, Boost Gauge Transducer (pre '98 cars), Alarm immobilization module etc.  We mounted ours close to the firewall towards the center of the car.  There is adequate room and actual physical location is not really that important providing it is relatively cool.  It is not a good idea to put it into the engine compartment.

• Once the solenoid is mounted. Locate the original ECM controlled solenoid. This is mounted on the right rear firewall. DO NOT DISCONNECT THE ECM cable or your fault light will activate.  Simply remove the vacuum tubes from it.  One goes to the wastegates on the turbo chargers, the other comes from the vacuum supply from the FRONT right hand side of the plenum (this also provides the boost gauge transducer with a reference on pre '98 cars).  Follow the instructions in the AVC-R's instruction book for the solenoid vacuum connections. Effectively what you are doing is replacing the stock solenoid with the one controlled by the AVC-R.

Stock boost solenoid, notice the RED vacuum tube is now re-directed into the right hand cavity

• Now that the piping is complete, the electrical wiring needs to be installed.  Remove the excuse for an inside glove compartment that is mounted to rear firewall of the driver's compartment. There are 4 screws, 2 on each side under the carpet.

  

  Cockpit center glove box

  • Remove the small front center console switch cover. There are 2 screws in the front. This lifts off quite easily.

  • Remove the large rear center console cover. Be careful as these are all fine leather and can be damaged if not treated with care.

  

  Large center console

  • We drilled a 3/4" hole in the firewall (this is also used for the Aquamist MF2 wiring as mentioned in the Water Injection text) at the lowest point we could find, this was emotionally harder than physically, as drilling any holes in the fiber panels of a Lotus can be a stressful activity.  The panel was double skinned so effectively 2 holes were actually drilled at the same time. A large tapered grommet was inserted both sided after it was drilled. These were hard to find. We ended up using 2 from a parts store that were  normally intended for use for mounting EGR valves into valve covers. It took quite a few trips to the store and a  lot of guesswork. Also, laying across the engine, probing blindly in the engine compartment, feeling ones way around proved quite interesting. the wiring loom was fed from the inside of the car into the engine compartment, and and up through the right hand side firewall into the cavity where the solenoid was located.  All wires were also covered with a spiral protecting cover for extra protection.

  • Now for the fun part.  Installing the Fuel Injector Duty Cycle wire. We removed the ECM connector, removed the cover and unwrapped the loom to about 4 inches back from the connector. Locate ECU Pin 1 and splice in the wire from the AVC-R control unit. Then re-wrap the ECM wiring loom with the existing and additional wiring tape if needed. (You can get old fashioned wiring tape from Home Depot or Home Base) Appropriate quantities of black tie wraps were used throughout to tie wires and pipes out of harms way. It should look as if nothing was tampered with when you are complete.

  • Inside the cockpit, mount the AVC-R wherever you are most comfortable.   We did not want to damage any of the cars interior, so we fed the AVC-R's wiring loom under the center console (we had to extend some of the wires, but this was easy using similar colour wires from your local Radio Shack) through to the left of the steering wheel.  We finally mounted the unit on the left of the driver under AC vent using the double sided tape provided.

  

  Boost controller location,

• The AVC-R was set up exactly as the manual suggested. We set a solenoid percentage ratio of 60% for "A" (0.75bar) and 80% for "B" (1.1Bar) and all worked fine first time.

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