rolland beat me to it...

id be interested how those ratios work out with the stock motor. 16/20 with an os18 on my rally was very fast with no real loss in acceleration, i enjoyed it a lot. not sure how the stock motor would have liked it, but the tr4 is different i guess, gearing wise etc, so maybe worth a shot.

i reckon a tr4 with something like an os18tz and 16/20 pinions would really take some beating, but ive never heard of anyone doing that? is there some reason why not? wont a rear exhuast engine fit? it would be a right kick ass underdog if it would work.