Well from the way I think TBIs work is they are not an on demand per barrel fuel delivery like a carburetor is. SO intakes that draw air from all 4 barrels for each cylinder (single plane) work better because fuel from the TBI is delivered equally to each barrel. If a cylinder is only drawing from one or two barrels then its fuel mixture is going to be screwy at lower rpms, because part of the fuel it needs is being delivered to barrels not being used at that point. It all averages out in the end, but it isn't as efficient at lower rpms.