Following the demise of my engine in October 2004, an engine rebuild was obviously on the cards, however I decided to go a little further than that...
These pictures were taken in Summer 2005, during the rebuild. Click on a picture to enlarge it.
I wanted the GT-R to be essentially a track car, and so the modifications were aimed towards this while still keeping it road legal. The interior was completely stripped, and all sound deadening removed, then an OMP Roll Cage welded in place.
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After spending many hours searching the internet for ideas and parts, I discovered that the later post '99 Miata / MX5 was fitted with a different style 'BP4W' head, which had the intake ports angled down into the combustion chamber, greatly improving flow. All the web sites I found said the head would not fit on a 323, but none seemed to explain why not? I decided the best option was to source a head and find out why not for myself!
I tracked down a complete '99 MX5 engine via ebay, and brought it home.After removing the head, it was obvious that all the head studs, water and oil gallerys were the same, and so were the exhaust ports. The only difference was that the intake ports had been moved up the head by around 10mm, and so the fuel rail was also different. Since the flange on the GT-R intake manifold was quite large in the areas required, I was simply able to redrill the mounting holes, and mount the GT-R manifold to the BP4W head. A blanking plate was made for the MX5 thermostat and radiator pipes, and the GT-R thermostat housing refitted. The world first GT-R (and probably BG shape 323!) with a BP4W head was created!
Whist the head was off, I carried out a minor porting job to further improve the flow. The head also benefits from solid lifters and more agressive cams, and I sourced some uprated cams from Japan to improve breathing even further.
The bottom end was rebuilt with Wiseco 83.5mm forged pistons and ARP studs throughout. The main bearing support plate needed modifying to clear the studs. The crank was reground, new bearings fitted and clearance checked, then new water pump oil pump and all seals and gaskets were fitted.
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To keep the temperatures undercontrol, I fitted an engine oil cooler, and also the gearbox was modified to fit a cooler system.
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I also decided to replace the factory ECU and wiring loom with a DTA E48XP unit and custom made loom and sensors. This meant I could remove the Airflow Meter.
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Finally, the whole car was back together in August 2005, nearly 12 months later! To save weight even further, all the glass except the front windscreen was replaced with perspex.
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