I've heard some bad reports about Swedish inlets having bad air flow causing uneven air fuel ratios for each cylinder.

I've been looking at other makes of cars that run similar inlets for example evos, they run inlets with the throttle on the side witch looks like it would cause the same sort of issue of uneven afr to each cylinder yet some of the ones I've looked at are 800+bhp.

What's the difference with these manifolds that makes people be able to get good power without running lean on 1 cylinder to another?