The k series can be a solid engine. We've built many for rallying. We always fit a cometic gasket and use arp bolts. the K uses very long head bolts ( reaches right down to the crank web) and these can stretch. Given the engines propensity to overheat, it does not take much for the head to lift and blow that silly little pink rubber seal. then your engine cooks and the head warps. The head can be fixed. you mill it flat again, re-cc your combustion chambers, re-cut your valve seats and since it's in bits, open out the ports a little. Yea, just get a fresh head. Even then, you might want to gas flow it while it's in bits, bigger vales, etc... You can alter the alter the water flow by fitting an interference fit plug in the water way and drilling it out, which can force water in a different direction, but one problem is the thermostat, fit an 82 degree instead of an 88, or lower.
They do respond well to wider duration and bigger lift, especially if you go down the bigger valve route. Not difficult to achieve 100 hp per litre. I don't know how "Programmable" the OEM ecu is, on K series I've built for rally cars, like Mk II escorts, we obviously have to go to aftermarket ECU.
For big revs from a standard K you're gonna wanna replace your rods and pistons for forged, not nasty cast, but the lotus variant must have some decent internals already, so probably cams and a minor remap could yield good performance improvements...
There is more. If you have the thing on the bench, then you can deck the block to suit your head gasket and desired compression ratio, though to increase compression, you will really need to CC the combustion chambers and check the piston heights. Then you need to check your valve heights, which means a dry assemble with some plasticine ( don't use blu tak) on the pistons, so you can measure the piston to valve clearance. It's important that you don't go for a a cam with more lift than your valve diameter will support ( roughly 1/4 dia in lift, though often you might want to exceed that slightly to allow for the inviscid layer) also, a must is three angle valve seats and don't over lap in your valves. Just a thin pencil line touch is all that is required or you defeat the object. We prefer a gentle recut, with a minimal final lap, to get the seal.
Now, to increase your compression ration, you're gonna have to change the timing, and this is best done on a dyno, but a rule of thumb I go by, is start at 32 degrees and if it det's, retard it. Also, you're cams will need a refuelling, and again, that level of change is a dyno job. Start with more fuel than you need, weak will burn holes in your pistons when you pull on it. We use DTA (ecu) quite a lot and have some standard maps for the engines we build.
Oh, and if you've decked the block, CC'd the head and fit cams ( or any combination) your timing marks will be for shit, so get a crank degree wheel ( Kent cams provide them) and some verniers and dial in your timing on lift. If you're lifting the rev range, valve springs will come in to play and TBH anything above 7.5k I like to use solid lifters, though some hydraulic will work into 8K, I don't like to risk it. when you're smashing up and down the revs in and out of corners you don't want fluctuations in oil pressure messing with your valve train. You need a consistent supply to the crank and big ends.
Finally, dry sumps do wonders for reducing internal engine component drag and ensuring a consistent oil pressure...
