ENGINE
A wide variety of engine modifications are available. Everything from a simple boost upgrade to complete replacement engines with larger turbochargers and full aftermarket engine management systems. Internal modifications can include re-profiled camshafts, enlarged inlet and exhaust valves, lower compression pistons, lightened and balanced conrods and flywheels. The main limiting factor is the same as most other engines... Money!
ATMO (2849cc)
Tuning the existing engine:
The oddfire normally aspirated engine has a standard output of 160bhp. This can be increased to 200bhp by combining all of the following modifications:
(i) Replacing the standard Solex carburettor setup with either 2 triple or 3 double downdraft carburettors. Neither of these conversions usually include a choke mechanism so they are best suited to track rather than everyday use. Both conversions are expensive and fuel economy will suffer.
(ii) Fitting higher lift camshafts
(iii) Fitting replacement 3 into 1 tubular manifolds and a performance exhaust system.
This effectively produces an engine equivalent to the GT pack A310 conversion offered by the factory. The main problem as stated above is the fuel economy. Even a standard GT atmo is usually only good for around 20mpg. These mods will reduce consumption to as little as 12mpg when driven hard. A high price to pay for relatively low power output by modern standards.
Replacing the engine:
A much better approach is to replace the engine with one of the more modern evenfire versions of the PRV engine:
(i) Use the 12V fuel injected evenfire PRV engine from a Laguna or Safrane. These engines are still only 12V but have potential for 210bhp with a freeflow exhaust system. They also have the benefit of a balance shaft which helps to reduce vibration from the offset crank. It is also possible to use the engine from a late Renault 25 which is similar but lacks the balance shaft.
(ii) If you want a little more power then the 24V engine from the Peugeot 605 or Citroen XM can also be used. This was the most powerful version of the PRV engine producing 200bhp in standard normally aspirated form (the same output as the GTA turbo). A GTA installation normally produces around 240bhp with a performance exhaust and decent engine management.
In both cases when the donor car is front wheel drive you will need to change the crankcase and sump to fit the engine in a GTA. Both engines will still return over 30mpg on a long run and are suitable for everyday use. It is also possible to turbocharge or supercharge either of these engines for more power. Venturi did this and achieved over 400hp in the 400GT.
A recent trend is to replace the 6 cylinder engine with the 4 cylinder engine from the R21 turbo which is lighter, relatively easy to tune and best of all bolts straight in without a crankcase change. The factory also built a few cars in this configuration and you will find photos of the installation in the gallery.
TURBO (2450 or 2458cc GTA. 2975 or 2963cc A610)
The standard output of the turbo engine is 200bhp. However many older cars with tired turbos and faulty sensors will produce considerably less. It pays to make sure that your turbo is in good condition and sensors are all working before you start tuning, otherwise your best efforts may result in achieving less than the manufacturers standard output!
(i) Boost Upgrade
It is possible to run 14psi on the standard management with a simple piggy back chip or module which bypasses the factory boost cut out. An otherwise standard engine with a freeflow replacement exhaust will produce around 230-240bhp.
Running a larger turbo and more boost will give more power but don't expect Nissan Skyline type outputs. The 12V PRV engine is an old design and does not respond that well to increased boost. The exhaust manifolds are particularly restrictive and we have yet to see more than 280bhp for a UK 2.5 litre car on standard manifolds regardless of boost.
(ii) ECU Upgrade
The standard ECU is primitive by modern standards and it is not possible to remap this unit. The exception to this rule are the very last cars fitted with a catalytic convertor and the A610 which in theory have re-mapable ECUs.
The best solution is to fit aftermarket engine management and this is essential if you are looking for in excess of 280bhp. This can be of the 'plug-in' type which will retain the standard engine bay wiring loom and as many sensors as possible or the 'stand-alone' type which will require a new loom (or extensively modified original) and sensors.
Of course if you want to run more than one bar of boost you will have to replace the standard MAP sensor.
(iii) Capacity Increase
The standard GTA turbo has a capacity of 2450 or 2458cc. This can be increased to 2975 or 2963cc by using a low compression engine from a Laguna or Safrane. This effectively creates an A610 engine and you will have to use an A610 inlet manifold as the spacing between the heads is different. An A610 spec engine should produce a minimum of 250bhp.
(iv) Twin Turbo
Theoretically the best conversion for the GTA engine due to the restrictive standard exhaust manifolds. European A610 spec engines running twin turbos regularly achieve over 400BHP. Two UK cars are currently known to be in development.
(v) Combination of the above
A proven 300BHP has recently been obtained from a UK GTA with an A610 spec engine running a T4 spec turbo and aftermarket management.
TRANSMISSION
The UN1 gearbox is strong and can reputedly handle a 100% increase in power. The Atmo and Turbo gearboxes are identical apart from shorter 4th and 5th ratios in the normally aspirated version. Many prefer the closer spaced ratios of the Atmo box at the expense of maximum speed.
The clutch however is not so resilient and will begin to slip when output approaches 250bhp. (NB While the Atmo clutch is still available the Turbo clutch is fitted routinely to all cars). The simplest upgrade is to fit the A610 clutch which should be good for 300bhp+. The original A610 installation includes a helper spring but the pedal operation pressure is still acceptable without this in a GTA.
For higher outputs reinforced "SACHS" clutch kits are also available but these are expensive.
BACKGROUND
Searching the forum will provide plenty of up to date information on individual owners projects.
There is some interesting background regarding the PRV engine and the GTA on the Delorean website: PRV FEATURE
EXAMPLE PHOTOS
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