gentlemen, i see mucu confusion in comparing the mini to the junior, so let me try to put some clarity to the topic:
the first difference between the two is the engine, the mini is 660cc naturally aspirated or turbo, this small engine comes with 20 valves and DOHC thus enabling it to take out around 50hp, however pls note that due to its small cc, this little engine has to work really hard to keep up with the normal road traffic, due to this the normal wear and tear of the engine would be higher...(running on high RPMs), this engine is mainly for the domestic japanese market where the kei (max 660 cc) class cars get special rebate on tax and therefore running them on roads where there is normally no speed limit and bigger engine cars run puts a lot of strain on the little engine.
Meanwhile the junior was produced for the European markets and therefore it came with an 1100cc engine, due to the bigger enhgine the gear and differential ratios are also better and if you know what i mean, you can feel that the engine is much more relaxed than a mini's while driving on similar speeds. the Junior's stock tyre size is wider than the mini's, the juniors stock ground clearance and suspension width is also more than the mini's apart from this the body of a junior comes equipped with a sporty kit this making it even look bigger than the mini even though the body shell size is the same.
pls note that there is no alteration required for swapping a minis engine with a junior engine, however to get the true junior performance u will also have to change the gear and the differentials so that the ratios match...
the above are some of the main differences between the mini and the junior (and yes even the brakes are larger on the junior)...
I hope i have been able to answer some of your queries
