The problem with this motor is the head, cam and fuel/ignition system.
The head is restrictive, the cam tops out at redline, and the fuel system is barely adequate. Then ignition, cuts you off just as you peak.
What all this means is, most mild mods (bolt ons) will only net you little gains, if anything.
Which means you need internal work to really get anything out of it.
You have 2 or 3 options.
Get a fully modded head from Metric Mechanic, Like Febi has. This includes springs, cams, retainers, thinner valves, new buckets... A custom chip able to rev to to about 7500.
Expect to spend about $3500 (guestimate) for the head and cams, another grand for the custom chip.
Should get you about 170. Give or take a a few.
Do not expect it to last.
The bottom end needs work to handle those revs. Specifically the bearings. Lighter rods and pistons will also help.
Done properly, expect to spend $5500-$6000.
You can go to a 1.9 by boring it, which will get you around 180hp, thats probably another $500.
Or go all out and stroke it as well for 2.1 liters for 210 hp. Price, expect a couple grand more.
All just estimates.
The only alternative, is to do a bore and stroke without the top end, meaning no extra revs. This will get you what you are after, though porting still may be necessary, as will a cam most likely, which also means a custom chip. All said and done, you are again, looking at a few grand.
The other alternative is an engine swap.
This is tricky.
A heavy motor will upset the handling, the M3 motor IS heavier, plus requires lots of maintenance. The 6 is much heavier and longer, a double wammy. You need a light weight, 4 or 6. The only things that come to mind is the Ecotec from Gm.
