What the others have said in summary. This is coming from someone with a dedicated track car doing track days regularly.
Some of other reasons why you shouldn't do what you are thinking and you should consider the following feedback:
1. Getting to 270 will not only cost you lots, on top of this you will stress the engine to the point where the risk of going bang when you are consistently asking for 100% on track will be significantly higher. Ask yourself, can you afford an engine rebuild every two or three track days on top of all of the other associated maintenance costs?
2. You said you want to compete with your mates. Why don't you first ask your mates what budgets they are working with to do track days over a whole year, including the cost of car purchase, preparation, maintenance. Then compare with what you have to work with and adjust your expectations accordingly. Lastly track days are not "racing events" therefore TDO's will consistently remind you its NOT a race. Want to race, up your budget and go to "test days"......or go into a one make championship.
3. Most tracks have corners, power to weight is great, but its not the be all end all. More can be gained from a well balanced car and a good driver on most tracks. We regularly get asked about our car when we manage to lap with or quicker than cars with well over 100HP than our car.
4. As above big is not always best. Big means more cost in ALL respects. If budget is not restricted and your ultimate aim is to be the fastest ---> kit cars Caterham R400+ (sub 500Kg) or -----> race cars Radicals++ (sub 500Kg with aero and sequential shifts). Otherwise on a more earthly budget a lightweight Front wheel drive ---> Clio 200 (sub 1000kg), or ideally a RWD BMW E30 318 (sub 1000Kg), would yield best overall results when the driver can reach the limits with such cars.
5. The cost of running a car on a track day on average is around 400-500 quid when you consider the consumables, such as brake discs/pads/liquid, engine maintenance, tyres, fuel, track day costs, etc. The bigger the car and the heavier the car the bigger that number is, none of which includes upgrades, safety additions, etc. The question is can you afford that.... If not, wouldn't it make more sense to buy a dedicated car for track only with a mate and share in the costs as well as the experience of developing it yourselves.
6. My best advice is, buy someone else track toy within your budget. It will cost you roughly twice what the used track car will cost to prepare to a similar level. Ask me how I know
It may seem expensive for a gutted car initially but I can guarantee you it will cost you twice as much if you are starting from a street hack to get to reliable track ready state.
Go on piston heads if you want more specifics about certain cars, but imo these are the best bang for buck in no particular order:
Mazda MX5
Clio 175-200
BMW E30
BMW E36
Keep the Grande as the daily hack and what a nice hack it makes
Humour
