Hi Shell,
I can assure you that 'tuning for economy' is not an option available on these motors.


You can add after market components to make the most out of the fuel but for what it costs you would need to use the car for long journeys only, and be prepared to wait two to three years before getting your money back in return for component/economy.
Driven carefully, a GTO T.T. can return around 28 m.p.g. on a run. Around Town is another ball game. The problem is actually driving one with enough boredom to return any decent fuel economy, it just doesn't happen.
Get out on an open road and drive like a granny ! Yeah right.
Redex ? No ! Have the injectors serviced properly and be done with it. We have had stock injectors flow tested and they can be out by as much as 25%, they need proper servicing. If we rebuild a customers standard engine the injectors are always serviced as part of the rebuild. They should even be included in the major 54,000 mile service.
Good examples of these cars still sell for a decent price, but they must be in top order. E-bay has decimated the market in many ways because most of the GTO's sold on there are complete and utter trash ready for the scrapyard. What happens then is that someone upgrades from a Corsa/other chav mobile, because they think they're getting a bargain, a 150 + m.p.h. car for £1500/£2500. The reality is that they are buying a car that someone else hasn't been able to afford to maintain and they will most likely be following in the same footsteps.
Good parts for these cars are not cheap, cheap parts don't work. £99 brakes don't stop a 1.75 tonne supercar at 150 m.p.h. Worn suspension won't get it round the bend properly, over £1K's worth will. Cheap tyres won't keep it on the road, expensive ones will. Cheap oil will crucify the engine, Silkolene Pro-S 10/50 won't. The list is endless but i see people invest their savings into heaps of junk every week, some realise their mistake, others ignore advice on what parts to replace and the car ends up on e-bay yet again

.
What happens then is that someone will test drive it and say that it doesn't stop, doesn't handle etc and the whole GTO marque is crap, this extends to the pub and various other pubs and lo and behold, GTO's aren't worth buying.
If you keep it, do the right bits, spend on the right bits but doing it cheap, it will never ever happen.
By the way, the above wasn't aimed at you, it's a generalisation of how i see this car and why it's undervalued in the market.
Good luck with your deciscion. CB/mark@sumiyaka