Most articles on the K series have an understandable lean towards going bigger - away from 1.4 towards 1.8. Is there any advantage to taking a 1.4 and doing all the usual mods - forged pistons, multi-point injection, steel head dowels (okay that's a preventative), right-end thermostat (ditto), solid lifters opening out waterways, bigger valves but not increasing capacity?
Ie would the smaller bore be less likely to have liner movement, would the smaller stroke allow higher revs if everything was balanced properly than the 1.8?
Put another way, would a 140 or 150bhp or 160bhp 1.4 be more reliable than a 1.8 with the same power levels? Is there an agreed crossover point in bhp where it's time to upsize?
This isn't about the time cost of swapping out an existing 1.4 engine but starting with no engine and looking at donors.
VVC gives you a very flat torque curve, it actually works very well. My GTM is running a 160vvc and I think it’s a cracking engine. Given the lack of all-up weight it would take a peakier engine without any dramas, but I like the delivery as it is.
If you're wanting 150-160bhp I'd just bolt a stock 1.8 VVC motor in and leave as is. They're all pretty much the same weight so it's the easiest option. A 1.4 making similar power will be just on the cusp of getting a bit harder to live with - I did a 1.6 with a ported VVC head, VVC removed with aftermarket (milder end) road/rally cams, balanced stock bottom end etc and it made about the same bhp as a ZR160 but less torque and wasn't as quick. A 1.4 would need to be even wilder to get those sort of figures, and as (by the sound of it) you're not limited to a capacity class for racing you might as well start with the 1.8 VVC and go from there.
I know someone who was running them in bangers converted to carb and dizzy. He really rated them, tough and used to rev to destruction point. Oddly he didn't have the usual omg head gasket failure problems either.
There are some 2.0 litre versions making over 200hp. Judd built the MG BTCC winning K series engines for WSR these must be making 300, full race though. Brilliant little lightweight engines but you have to keep on top of the cooling obviously.
It might be worth looking into the MG 6 1.8 K series turbo, these have improved block design and all the problems areas fixed, complete engine from a crashed MG6 with all the turbo parts would be an interesting project
I’ve played about with the K series a lot and as said if they’re built right then reliability isn’t an issue. I had (have, it’s still in the garage destined for a friends Chevette) a 1.6 with some bolt on mods, TF135 cams, Jenvey ITB’s and an emerald and that made 140ish bhp which was good fun. Other than that my brm track car runs a solid cammed vvc engine and is over 190bhp and the mgb has a crazily specced 1.8 which is putting out over 220bhp. Just depends how much you want to spend really.
There’s a chap called Lee with a k series turbo in an elise that’s running well over 300 bhp iirc.
There's not much to be gained from balancing them. Based on the three or four I rebuilt when I started rallying with them, they come out of the factory almost perfect. I gave up worrying about it TBH because I was potentially causing more problems taking them apart and rebuilding than leaving the bottom end alone.
I'm sure you already know, but there's a well trodden path for K-series upgrades. Dave Andrews is the man!