OK, it's not a popular topic for Rover drivers, but let's talk engine performance.
My D1 has a 4.6 in it with 4.0 intake/exhaust to make it look stock. It has adequate performance off-road, but on the highway is where I'd like a little more. It's just week. It feel like trying to run it over 3000 rpm, say a down-shift to pass or climb a hill, is almost pointless as I get a lot of wheezing noise from the exhaust but little else.
So what are my options to improve the highway performance on these motors? I've heard from Dan somebody does some ECU tuning but don't know who or what. Injectors? Small improvement in cam? Headers? Port match the intake and exhaust (it looks horrible judging from some of the spares I've got)?
The engine itself has less than 40K on it. I suspected the cats might be getting clogged up based on the wheezy noise at higher RPM but a back pressure test by a local shop says no, they're not a restriction (I find this somewhat hard to believe but that's the result). The rest of the exhaust is a single Flowmaster muffler - certainly not a major restriction. I don't have a lot to compare it to and the rest of the truck is so far from stock it's hard to compare with others but I feel like I'm leaving something on the table; that there's more to be had from an otherwise good running 4.6.