The biggest problem with all straight sixes is that with central fuel distribution, it doesn't distribute equally to the 6 runners. The fuel drops tend to go more to the center cylinders (rich) and the outers run leaner. TBI can give a finer spray which should distribute better, but still not as good as MPFI. Of course, MPFI controls assume all the injectors are balanced. There were after-market intakes which probably distribute better, like the long Hurricane runners or the dual carb one.
