After driving the car for a while, my head became full of all sorts of strange ideas about forced induction systems.
When trying to sleep at night my mind would plan out all sorts of exciting power possibilities like a notebook that writes itself and is out of control...
The first option that popped into my head was to use an Eaton M112 rootes type compressor from a Jag that i have had lying in the workshop for some time, and as i can't remember what i payed for it originally i see it as 'free' in terms of cost. But it would require a lot of good fabrication work to make up a new inlet manifold to mount it inbetween the cylinder banks, new injector mountings, intercoolers (air/air or air/water) and drive belt system. With maximum 1:2 gearing it could give a theoretical 12psi boost although 9-10psi would be more sensible. And the compression ratio would need dropping to around 9:1, knock detection would be handy as well (the M60 has 4 knock sensors as standard). Forged pistons would be a good idea for over 7psi boost i'm guessing.
The main amount of work involved for any high-boost forced induction system on this engine is lowering the compression ratio, either with custom 2.5mm thick solid copper gaskets, opening out the combustion chambers, or by using custom dished pistons. The standard M60 pistons have a large amount of material on the crown and could probably take a 2mm deep dish without adverse affects.
The more popular way of adding forced induction these days seems to be the highly overdriven centrifugal blower. This avoids the physical mounting problems of the large rootes blower, and in the case of the M60 it could avoid fabricating a new inlet manifold.
German tuning outfits have fitted large Vortech centrifugal blowers on the M60 and M62 without intercooling and seem to make impressive dyno figures. But if there is space for an intercooler (as there is in the nose of the Capri) then it seems prudent to lower the charge temperature and lessen the point at which detonation will occur.
ESS Tuning's kit for the 540i uses a Vortech V3 without intercooling with larger injectors and a new ECU chip to create 411bhp peak on a 7psi boost. Which is quite an impressive peak power figure for this amount of boost, and demonstrates the M60's ability to flow large volumes of air very well without any internal modifications.
But because centrifugal blowers develop boost exponentially, a system geared for 7psi @ 6000rpm will only deliver 2.5psi @3000rpm, some see this as a blessing because it means that lowering the compression ratio is often unnecesary. But a Rootes or Lysholm blower will give a much larger torque increase at the 1500-4500rpm range that most everyday driving is done.
Then there is the turbo-route, twin TD04s could work well (and they're cheap because Subaru WRX owners are always replacing them with something bigger). Some Lexus 1UZFE V8 tuners have had good results with them, apparently creating a relatively lag-free installation. The main problem with twin turbos is just finding space under the bonnet for everything without it becoming an entangled nightmare to work on.
Large single Holset and Schwitzer truck turbos have been used to good effect on some pretty crazy drag racing installations. And they're cheap. But accurate information on their flow capability (or more importantly if they'll spool too late) is difficult to find. There are quite a few variable geometry truck turbos around nowadays which could work very nicely to reduce lag on a large installation, but without available flow maps it would be a case of just measuring the turbine and compressor sizes and then making a rough comparison with a similar sized Garrett frame turbo for flow.
For a proper large single turbo installation, the Garrett GT35 or GT40 frame with appropriate trim compressor and A/R turbine housing would be an exciting (but fairly costly) proposition.
At the moment i'm still keen on the Eaton M112 idea due to it's small dent in the wallet. Having created an Eaton supercharged hybrid in the past, i was impressed with the extra torque at low rpm which gave an instant response even with 5-7psi. For fun A and B-road driving it was superb.
But at the moment it must all remain a long-off fantasy. The rest of the car needs improving before it can handle more power...
