Black Betty is right. And for the record the mk3 and seat ABF motors use a 50mm manifold but it's not exactly the same as the KR one as they used a single throttle as apossed to the twin progressive on the mk2, corrado etc..
Fine mk1 the lightweight pulleys will give you a huge zero horse power increase. When you lighten your flywheel or pulleys it will make your engine rev up quicker(more responsive) when in nuetral. This is the same as fitting lightweight wheels to your car(same as lightening any part of the drivetrain). So on the dyno I'd expect to see a 1 hp difference or less as they only add a tiny bit to the parasitic power losses. Also as the pulleys are a fraction of the weight of the flywheel don't expect to see many gains, other than the etreme cool factor of having shiny cool pulleys.
Personally if I was building an all out motor I'd get a light flywheel and balance all the other parts as it's easier and cheaper to do that then lightening the pulleys for the same effect.
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