'Mountain' enhanced boost chips for the Elan

Introduction

My interest in tinkering with the Elan's engine management programming started back when I wrote ElanScan. Understanding the ALDL (assembly line diagnostic link) required much raking around websites with information concerning the modification of GM P4 ECUs. It is possible to download the contents of the Elan's 32kb PROM 63 bytes at a time via an ALDL command and so an algorithm was written into ElanScan to do this.

After lot of work reverse engineering the PROM the boost control code was been identified and the ability to reprogram the boost control system acquired.

Boost from the turbo is limited by a wastegate, when this is open exhaust gases bypass the turbo so drive is removed from it. The wastegate is opened by an actuator that operates when the pressure in the output side of the turbo exceeds around 0.5bar (curiously a bit higher than the 0.4bar quoted in the Lotus manuals). In the Elan the ECU can actively control the boost above the passive limit, up to 0.65 in factory configuration. The extra boost is gained by limiting the pressure the wastegate actuator receives. A solenoid valve is installed in the wastegate acuator's feed line and by varying the proportion of time the valve is open (the duty cycle) the size of the leak, and therefore the boost achieved, can be varied. The ECU looks up a target boost, the value of which depends on engine RPM and throttle opening and varies the duty cycle of the solenoid valve to meet the target.

In this upgrade the tables have been modified to allow higher boost values to be employed – up to 0.9 bar. Two boost maps are offered here.

The Chips

A few characteristics of the chip are different to the original. First and foremost the boost targets are higher.
Boost map comparison

The chip's primary characteristics are listed here:

Stock Turbo Elan

Maximum programmed boost 0.65bar

Fuel cut limit 0.92bar

Boost pickup rate quite slow (boost lags behind target value under heavy throttle)

Nominal power 165bhp (flywheel)

Kilimanjaro

Maximum programmed boost 0.8bar

Fuel cut limit 0.96bar

Boost pickup rate enhanced

Dyno power 180bhp (flywheel estimated)

Everest

Maximum programmed boost 0.9bar

Fuel cut limit 0.98bar

Boost pickup rate enhanced

Dyno power 200bhp (flywheel estimated)

The ECU solution leaves all the safety features enabled:

Boost is limited to 0.5bar when:

the coolant temperature is below 50°C

any fault code is set

The boost is progressively reduced if knock retardation exceeds 5°

Why not use a cheap MBC (with optional FCD) or an Expensive BBR kit (MBC+BBR)?

An MBC puts a fixed leak in the air line to the wastegate this increases the pressure required to open the wastegate and gives higher boost as a result. Its primitive but it works with a few caveats:

With an MBC the leak is always on so the engine will be exposed to high boost even when the engine is cold or faults are detected.

An MBC cannot react to changes in atmospheric pressure - maximum absolute pressure will vary by 0.1bar depending on the weather. This can mean overboost fuel cut some days but not others.

With an MBC the knock control strategy in the ECU functions only partially, spark retardation remains but boost reduction (via the BSV) is disabled.

The boost attained varies with RPM (due to changes in turbo & wastegate efficiency with RPM) so the boost will vary over the rev range, the peak boost will occur at around 4500RPM.

An FCD removes all the protection against uncontrolled boost caused by a stuck wastegate.

An FCD fools ECU into believing the boost is lower than it actually is and all table lookups that use manifold pressure (mixture & spark advance included) are compromised as a result - for example the engine will run progressively leaner and more advanced than programmed in the ECU above the clipping threshold (generally around 0.75-0.8bar). Good for power, bad for engine life. Its a good thing the ECU also includes knock control!

Money back if you don't like it

If you send an undamaged kit back within 30 days, for any reason, you'll get a full refund minus postage & packing costs. All UK orders are sent recorded delivery.

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