Like some of you here, I closely follow what's going on on the US (global) RX8 owner's forum. I'm particularly interested in the different developments that have started on forced induction kit for our lovely RX8.
There are some interesting, and less interesting stuff going on. Here are a few examples :
- Richard Paul is developping an axial supercharger (working along the same principle as a jet engines compressor). He's still only working on the development of the compressor itself, and not yet on the RX8 kit. A lot of people have criticised Paul's idea of an axial supercharger. Most say it's not applicable to automotive use or that it will 'stall'. However, it looks like he knows what he's doing. And a spinning rotor with blades would be a good feature for a rotor only engine like the RX8's. However, we're not going to see anything we can fit on our cars for a long time.
http://www.rx8club.com/showthread.php?t=29778- There are a few kits released and even for sale on the internet (like the Speed Force Racing turbo kit). Unfortunately, usually, once the piping is made, and the bits and bobs are put together, most of them have struggled to deal with the hard part of the job : the engine management modification to cope with the extra, forced induced air into the combustion chamber. So you can indeed buy the system, but it seems thay haven't got around to sort theis out! However, for someone with sufficient engine knowledge, it is a hardware base to start with.
However, I would not expect a single turbo to be flexible enough to give a good performance improvement both at low and high RPMs! Look at the RX7 (redline at what? 7500 / 8000 RPM), it needs 2 sequantial turbos to cover the complete engine speed range.
http://www.rx8club.com/showthread.php?t=34604 (SFR turbo kit) Most of the other threads have disappeared into oblivion!!
- Word is too that a turbo version of the 8 is in development at Mazda, based on a single electrically assisted turbo (a regular turbocompressor hlped by an electric motor). This kind of device reduces lag and widens the operating range of the turbo. But it won't be offered as a kit!
- Hymee, in Australia, has started to work on the development of a Supercharger kit too. I must admit is highly professional, step by step, approach seduced me and I offered him my help to test it in Europe too, before becoming his 'agent' here.
http://www.rx8club.com/showthread.php?t=36376The kit will be based on a Opcon Autorotor twin screw superchager that has a very high adiabatic efficiency (low heat release for a given amount of compression work), better than a Roots type blower (like Eaton's). Roots and Twin-screw are both positive displacement, belt-driven superchargers. Their advantages over a turbo are:
- a wide operating enveloppe
- no thermal constraints (compared with turbo's turbine side)
- no modification of the exhaust system
- no lag
However, they might cost a bit more although the price of a kit based on such superchargers would still be competitive as you don't need to integrate it into the exhaust system, like a turbo. Another plus for the turbo, is the fact they recover some of the heat lost in the exhaust to generate compression work.
- Personally, I've always been interested in another type of device : an electrical compressor. Imagine a turbo, with its compressor linked to the turbine. Now take the turbine off and replace it by an electric motor. Now the compressor is not driven by the exhaust gases in the turbine, but by the electric motor. Nothing radically new here either. Some companies have been working on such a concept since the late 90's with mixed results. But some are available from very big automotive companies, like Visteon's Torque Enhancer System. It's power is limited to 2 kW, and the whole kit, only available for main car manufacturers ordering huge quantities, include a battery (separated from the car's main battery), a re-inforced alternator and also a by-pass valve enabling the air to feed the engine without going through the compressor. The compressor only works for short durations, under acceleration. And it's low power can only give additional power for smaller engine, hence the name of Torque Enhancer System : it usually gives better low down torque (koppel) than high engine speed power!
As I mentionned, that technology is unfortunately not available for aftermarket applications. So with a design engineer (ex-Sauber) I know, we're seriously thinking about creating such an electric compressor, of about 3 kW for engines up to 2,0 l. However, if we go ahead, sure I will test it on my Std Power RX8 to see if it brings any torque advantage. If it does, I might distribute a kit too, cheaper than a full supercharger/turbo kit, as it would give less performance improvement.
It is however a big challenge as some issues need to be sorted out :
- sourcing an electric motor that spins fast and is powerful -> Brushless DC motor?
- expensive electric motor controler
- sourcing a high quality, low cost, high duty, small and light battery.
But we only started last month. Tertou also offered his help.
So when there is something new in this field, I'll let you know. I'll try to post some pics too.
Next post will be about the problem of adapting the engine management for forced induction.