AFAIK, the round-Britain fuel economy record is now held by the VW Lupo TDI (the "3-litre car"). Certainly this has the best "official" fuel consumption figures of any production car ever. It's not very popular, though, since it costs around £1500 more than the petrol model. That's the point - the public would like more economical cars, but the known technology to deliver this costs hundreds of pounds even at cost price. (And here is the reason, I suspect, why the Daihatsu diesel is no longer with us). Hence a "gismo" that delivers it for £50 should have all car makers beating a path to the inventor's door.
Just about every modern engine uses some kind of swirl technology, to a lesser or greater extent. Most modern engines already have close to the optimum swirl level and would only gain 2 or 3% economy by adding more swirl - even assuming that leaking a bit of air into the inlet manifold would deliver this. The new Vauxhall Twinport engine switches swirl level according to load and speed, but even that only claims about a 2% improvement.
Nick, I'd be interested to know what time period your fuel measurements covered. Fuel consumption varies significantly between summer and winter so this could be having an influence (see section 4 of
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I'd also be fascinated to know what happens if you take it off (orat least disable it) for a bit. BTW, according to my calculation you'dsave 8% of fuel by driving just 3 mph slower on the motorway... Of course, it could be that the Ecotek is leaning the mixture off a bit, and perhaps marginally improving atomisation, since this is (with the greatest respect) not the world's most modern or sophisticated engine. 1993 is exactly the point when cats became compulsory so I guess your car should have a lambda sensor, but it may be one of the last that didn't, or indeed the sensor may not be working correctly since on-board diagnostics didn't come in in Europe until 2000. If it is leaning the mixture you may get a small economy improvement, especially if a 70mph cruise is around the point where the engine starts to run slightly rich for power purposes. 8% still seems implausible, though.
The improved torque must be an illusion, since the valve is shut at wide-open throttle and so can't have any influence.
(replace "nospam" with "fuel" to reply)