compression causes the stock chrome plating to flake, so here's a quick primer on compression
for easy math, lets assume a 66cc with a 6cc head and 1.2:1 crankcase compression. basically a stock engine with a fred head
while the exhaust port is open, the piston isn't compressing anything, so any displacement below the top of the exhaust port isn't relevant to our calculations yet. lets say, again for easy math, you have 50cc of compressible space. to calculate your compression you find the ratio of compressible space to combustion space. in this case it'll round to 8.3:1. assuming you're at sea level and everything seals good, that means if you multiply (8.3*14.7)*1.2 you'll get your compression in PSI. in this case, that'll be 146.4 PSI. not too bad. the problem is when you get on the pipe, that cranking pressure spikes, ideally to 176.4 PSI in this case. this is because the expansion chamber effectively works to seal off that exhaust port.
176 is already sounding nasty, but then you gotta remember we're just talking cranking pressures, not combustion pressures. combustion pressure works on a logarithmic scale, at least to a certain point. a 10 PSI increase in cranking pressure can mean a 1000 PSI increase in combustion pressure. there's no easy way to determine what the exact combustion pressure is, but it could easily be a difference of 20,000 PSI in the cylinder. as you can imagine, that's not easy on these cheap plated cylinders.
in my opinion, if you want to cram a ton of compression in these, you need to either get them replated by a company with employees that are paid more than 10 cents an hour, get them sleeved, or simply be prepared to replace the top ends every few hundred miles.
if I remember right, last I checked my engine was turning 204 PSI. I get away with it thanks to the help of a replated cylinder and bushings instead of rod bearings. plus a little bit of avgas.
the CDI isn't going to help you with RPM either, but jaguar CDIs are tested to 11000 if I recall. if you want more RPM, that's in the port timing. personally, I use a stock CDI with an adjustable magnet, just have the timing retarded for the whole rev range. when I built my bike jag CDIs weren't yet capable of my RPM requirements and I've been stubborn about switching.
