1.use sparkiv to browse vehicles.img and replace the files, rebuild and save the archive.
 
2.browse EFLC/common/data/headling  open the following files with texteditor, replace the lines for the car you replace with these one :

Headling :FXT 	     2500.0  0.00  85	0.0 0.04 -0.28 		0.37 5  0.148 1.0 350.0	0.22 0.570 0.44 35.0		1.25 1.08 12.2 0.15 0.4828		2.6  0.8  0.9  0.10 -0.14 0.0  0.50  		1.0 0.6 1.2 1.5 	0.0  55000 		440010		0				0

HAVE fun !!