'18 is the closest to an RS and we all know it. It is more powerful than a 21 and requires even less snipping of wires than a '21.

'21 is the common mans NSR, but this does mean you can also get all the common man parts for your very common '21.

'28 I guess is the coolest but you buy one because it does look good not because it goes well.
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If I have to take the carbs off once more...