a bit more than most would think:
there will be more differences than this but here is a short stab as the differences:
(based on UK models)
cupra has 17" alloys.
R has 18" with larger Brembo brakes. (option in the EU)
rea brakes on
cupra are solid,
on the R are vented.
Cupra has K03s turbo
R has K04 (larger)
R has larger injectors than the
cupra.
R has larger intake and charge pipework and air flow sensor.
Cupra has 1 single side intercooler - located behind the drivers side foglight
R has two intercoolers, (each about 80% of the size of the
cupra). one behind each fog light.
Inlet manifold on the
cupra has its inlet on the drivers side, (so near to the single intercooler)
the R has its inlet on the nearside.
Exhaust manifolds differ,
cupra has single CAT,
R has a twin set up.
Exhaust system on R is larger diameter and has a single oval tailpipe. (
cupra is a singletwin as standard)
Different fog lights, (see different bumper below)
Cupra has
cupra body kit.
R has R body kit. - front and rear bumper are more chunky and angular on the R. Front is also has a spoiler.
i think the R also has a marginally larger upper boot spoiler.
Cupra interior is generally black/dark with white roof lining and pillars.
The R interior including roof lining and pillars is black. (and rear view mirror etc)
Some cupras have leather, (very early standard, but most of the time an option)
R has material seats and had recaro seats as an option. (early ones also had rear recaros as option, later on didnt)
R decals on seats in the R.
R's has small 'R' badges on exterior.
Early Rs have the same steering wheel as the
cupra. Later ones ( i think late 2003 onwards) have a chunkier/nicer steering wheel with red stripe at top.
power:
cupra 180 (remaps to around 205)
R 210 remaps to around 265/270
R 225. remaps to around 265/270 (the 210 /225 engines are in effect the same)
The suspension on the R is a better set up, (think Audi TT)
the anti roll bar on the R connects to the struts, on the
cupra they dont.
I understand the R suspension may have a different ration regards shocks v springs, - (more shock) in my experiences Rs actually drive better, the
cupra can be crashy.
The wishbones on the R are cast so are better than the
cupra
R models have many other subtle differences such as firmer suspension top mounts, wishbone bushes etc.
Cupra R sits 5-10 mm
lower than the
cupra
Cupra R has red decals on the interior vents. purely for show.
overall if you can afford get the R, its a significant improvement.
The
cupra in my opinion drives a little more urgently but runs out of puff early.
The R feels less urgent initially but is much quicker and more within itself as standard.