Hi,
Induction Manifold length influences both torque and economy, usual practice is that the longer the intake the more torque generated at a particular rpm. Also the economy is increased. BMW did this in the late 80's with an engine for the 5 series, which they simply put longer induction manifolds on, changed the valve timing and cam lift so that most "power" was generated at lower rpm
Though most european engines went through some form of emmisions control in the 70's and 80's it was never as radical as the requirements for the US market, such as air pumps, exhaust recirculation and of course the dreaded catalyst. In fact at the time most european manufactures, MB, BMW etc etc were developing "lean burn" engines which met all the proposed requirements without catalysts, pumps etc, but they were "killed off" for political reasons, mainly because the big three in the USA were so far behind in the technology race at the time the only way they could met the US standards were with all the smog control junk. Hence the US goverment decision to insist that catalyst technology was used.
Malc
Scotland