All filters, air, fuel, spark plugs, stock induction piping ON (Makes major difference i'm afraid, like frank said before though, optimised for grunt inc economy.)
I recon 400 miles out of a full tank should be easy, and i've been revving the nuts off her today, with not so big fuel drops (New spark plugs after 11 years, but the old ones where NGK-R's, and still in great condition when i fully clean them!!)
13-14 inch wheels, could these make a difference, weight and turning power may help here!
Eco driving tip: No electronics or anything on during cold start, use the car very gently until temperature gage is half! Then start using heating etc, i found this somewhat impacted me quite a bit, but i have whiny pulleys so resistance could be issue for me
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