4.1 why less boost

[mydesigner]

I was reading a thread that said 4.1 don't handle as much boost, i was wondering why do they not handle as much boost as a 3.8. I didn't think there would really be a difference

 

[Intercooler]

They are an earlier design not intended to be turbocharged thus being weaker. The block isn't reinforced in the lifter valley for one but I don't know how much it really loses there. The big kicker is the decks are 1/8" thinner from jump and the head bolt threads are right in the top of the deck on the 4.1 where on the 3.8 they are anchored down about 2" into the water jacket.