I think the amount of benefit you get out of CHEAP bolt on engine mods to a D-series is not that high per dollar spent.
If you want the car to sound better just take the resonator box out, run a piece of heat poof pipe from the front bar to the bottom of the stock airbox, and just change the panel filter to something like a K&N. As I said before though this won't really do much for power but at least this will minimise heat soak from a poorly designed short RAM intake.
I think your money is better spent on improving the handling of the car with an upgraded pair of springs/shocks or coilovers, A light weight pair of rims and tyres to reduce rotational mass, and a lightweight flywheel and clutch combination.
If power is your sole aim then as above swap a B16a/B18c in
read through the build threads there are ALOT of people who seem to agree that although the K is awsome its not all that and besides the amount of added supporting mods needed to get the most out of the k is crazy when u start doing the maths, unless max power is your goal the b18c is an awsome powerplant and plenty of get up and go for the real world
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