Well…with anything, there is always a risk. You could throw a turbo onto your KA and it could blow instantly, or it could go for 10 years without a problem. You could swap an SR in and it could blow after a few miles, or it again, could last nearly forever. Your “safest” bet would be to tear your KA apart and check the condition of the internals. If they look fine, throw it back together, or if budget allows, start replacing stuff. At least you know at this point that you’re investing in stuff thats going to last, whereas an SR/RB could be completely torn to bits from some guy overseas doing a little Tokyo drift right into a wall, only after beating the crap out of the engine for months.
Unless you have a lot of money to blow (doesn’t sound like it) you should factor in future repair and maintenance costs and make sure whatever option you choose is affordable not only now but down the road. Thats why I suggested the KA and/or a V8, because they’re North American engines and parts can be found in any wreckers in your local area. The V8s I suggest would be out of Silverados which wreckers have tons of.
Someone mentioned some torque thing…torque is directly related to horsepower, and vice-versa. The equation goes sort of like this: HP = (torque x RPM) / 5252. Thats why high-revving engines always have more HP than torque, and a lot of the low rev engines have higher torque values, since most of their power is made under 5252 rpm. I’m not a technical expert, so I’ll stop there before I say anything too stupid.