Porsche 928 GT – Modified engine
Porsche 928 5Litre 32 Valve Engine
The Porsche 928 V8 was always a favourite of mine. With its 50/50 weight balance, I thought it would make an interesting project for development. However as the GT variant was the last sporting evolution of the model . I thought that it would make a good sound platform to this project, to apply some explorative tuning and modification . The 5 litre 32 valve GT engine is a challenge as there are not many of these particular units around , and thus very limited information regarding development options. I thought if we stuck to the basics , ie camshafts, balancing components , porting etc, Electronic Control Unit mapping, we would see what we could achieve. Of course this is now helped by the ability to modify the base mapping initially with the JDS shark-tuning software, or as, shown in the later stage developments, completely dispensing with the stock electronic control unit and changing to the Adaptronic flagship model, the 1280 which brings together all the nicer modern features which modernisation allows, eg launch control, sequential injection , flat shift etc, along with the advantage of removal of the older style MAF, and configuring for MAP control , this also makes for a simpler and more reliable installation as there are less components to fail. (see the website here www.adaptronic.com.au).
This page will show the evolution of this project from the stock graphs of the GT, to stage 1 and 2 development, along with experimentation from reground cams to custom made units .
To start with the project, I made the point to obtain one of the guaranteed known thicker blocks, the GT block, although extremely rare, all were made with thicker cylinder walls , we were lucky enough to obtain one , through some close contacts, and this will form the sound foundation to base the project. The outlined project which has evolved over 2 years is described below in the following paragraphs.
The stages had developed from a simple desire to extract some more performance from the stock base engine, to then enable it to be successfully tracked, without attracting the potentially catastrophic failures from production engines, that are stressed on the track, (yes even Porsches).
The evolution of the car in stage 2 shows the modifications to the crank oiling system, that is synonymous with production engine oil surge and stock oil control issues. The stock crank is fed from only 1 journal, each in stock form, so using the information available from online communities that actively race these units, and have had known catastrophic failures. I decided to re-drill the crank to allow each of the big ends to be oil fed from 2 points, grooving the bearing shells to supply oil to them. The best solution would be to install a dry sump system, but wanting to keep the GTs stock look and luxury, decided that it would be too hard an install, as well as expensive, and as the car is mostly a street car, the oil modifications should be adequate for reliability along with the correct grade oil, as you can see from the front page we use and recommend Amsoil, in this case the 20w-50.
With the final result on the Dynapack dynometer, with our dynapack when you look at the resultant graphs, I can state that the each of the tuned cells represents an area that I have specifically targeted for optimal performance. Whether that be for economy and drivability or under wide open throttle (WOT) the best torque that can tuned from the ecu mapping. The Dynapack is renowned for this, and I can say that after the first drive the final result is extremely satisfying.
The final tune with the Adaptronic E1280 incorporates VE tuning, this was my first introduction to this style of modification, and I must admit that its simplicity and speed from no map to a running car is very pleasing.
Melding all of the above the final result as I have already stated has been the culmination of many an hours work, fitting it in with our normal business activities (i.e. earning a living), I am hoping that this information contained here will be helpful to anyone who may be contemplating the same journey.
Modifications from the stock 928 GT platform
- ported throttle body (increased 2 mm) and heads – 968 intake valves
- Elgin re ground camshaft – extruder honed manifold
- 944 turbo connecting rods(944 part nos) – balanced assembly
- 180 degree ceramic coated mandrel bent headers and custom exhaust
- JDS modified engine management
- early pistons flat topped giving 11.6 static compression
- I and J windage tray – modified oil galleries
- 944 oil 3 bar oil limiters for the heads as opposed to the stock spring and ball
- ceramic coated ports and piston crowns, cylinder crowns
- Adaptronic 1280 ecu with full sequential management with launch and traction control
- sump spacer – lightweight starter
- modified breather and DR s oil catchment system
- Custom profile camshafts (coming soon)
Custom made camshafts are currently under construction, when delivered should provide some more interesting results, as the stock cams are notoriously mild, it will be interesting to be able to test the results.