well it further hinders the exhaust from exiting the cylinders efficiently.

The front cylinders have about a foot of travel before the collector, whereas the rear cylinder has about 4". Those rear cylinders HAVE to be hotter than the front ones.

 

I would not think they would be much hotter ...maybe 7 to 10C, I dont know for sure ..... I just dont feel that the exhaust manifold design on the 5.4 is something to "point at" as a cause for detonation...or major contributor.


"hot exhaust"

the exhaust manifold being the same with the natural 5.4 and the SC 5.4 will have the same mass it will simple move at a different speed and density....its at a higher density and higher pressure. But does it come out faster? Or just at a similar speed maintaining high pressure? With the 5.4 SC motor its prolly exiting faster coming out of the engine through the same sized holes (valves)......into the exhaust manifold. On the same motor the speed would slow with a bigger (say LT's) to exit into with the upper cats gone.(upper cats=bottleneck)
Its an interesting thought you have going here but if shorties dont help our 5.4 (power wise) its probably because of no change in exhaust reversion/ back pressure until you get rid of the cats,.....so I bet Wydopnthrtl could tell us at what H.P. level the 5.4 exhuast manifolds fail to keep up......or are they really not the restriction....do you just gut the cat and all is well... or add those Bassani high flow cats to the stock exhaust system and your good to go.

 

Right, I'm not an engineer... just throwing out ideas.

I also got rid of the stock "midpipe" and added hi-flow cats (2 total)