340 HP's vs headers
I have the Hedman Tight Tubes for my Duster, they install easy enough but good luck getting the exhaust hooked up; I had to fab my own downpipes that snaked down off the flanges, up over the steering linkage, then back down to the rest of the exhaust. Very time consuming, and in the end it still looks like you have headers in your car lol.
Manifolds suck because the exhaust pulses from each cylinder smack into the adjacent ones, on stock engines it doesn't matter because the cam overlap is too short for it to make a difference but put any kind of performance cam in it and the engine is basically working against itself trying to push the exhaust out, instead of it being scavenged out by individual header tubes.