Any specific reason you want a V6? I would be inclined to turbocharge your car instead, unless the engine is knackerd.
If you do go for a V6 it would be more of a pain but well worth making it mid engined.
You need'nt stick to Renault though, there are tons of v6 engines which would be better, what about a 2.9 cosworth cologne V6 out of a scorpio with ready available turbo technics forced induction kits at reasonable prices. They are also gear timed so no f**king cambelt to faf with / worry about and it's a ford so parts are cheap. If I had the money it's what I'd love to do.
Take no notice of BHP figures from big engines though there usually not too imressive ie; 2.8 capris had less bhp than the latest clio RS but it wasnt a slouch, 0-60 - 7.9 and they were big heavy cars.
Look for the amount of torque you'll get, it's that you will find makes the car quick and in something light like a clio, basicly it'll pull like a train and have punch in every gear at most speeds even from low revs.
Or a Rover V8 3500, more scope for power without f.i. and lightweight alloy and cheap, 10 years ago my mate dropped one of these (bored out, lightened, ballenced, ported heads....) in an MGB Roadster and it went like an AC Cobra and sounded mental, you could pull away in fourth gear it had so much tourque.
