I know this isnt an 8v example, but on the 3.0 we have found with 2.5" exhaust, heavily ported plenum and boltons, that the 58mm
tb (unported, so its not really 58) doesnt make more power in back to back tests compared to the 52mm.
Anyways, in australia RPW built a custom log intake to replace the stock intake for mitsubishi applications. The stock sohc mitsubishi
tb is like 60mm so its already bigger then what the chrysler 3.0 likes for a
tb.
On back to back dyno's the custom intake with 75mm
tb took the car from 152 peak WHP to 183 peak WHP on a basically stock (just an intake) car with stock exhaust. The car also made more power throughout the whole rev range by 15-30 whp. I think they put it on a car with exhaust and it made even more power (195ish) but they didnt do back to back tests. I think thats pretty amazing for a sohc since bone stock 24v
dohc 3.0's only make 170-180whp and 180-190 with boltons and exhaust.
Anyways, the point is that when you see a powergain that huge and the entire power curve increasing, then you know the intake was successful and its not just a bigger
tb (which does nothing on a stock intake). The fact that a bigger
TB makes a new intake manifold even better, doesnt mean its not a fair comparision. If the stock intake doesnt see gains from using a bigger
TB then thats not the fault of the better manifold.