old vs new

inteva6184 said:

my 80 supposedly peaks at 4.5 these new 80 bikesare almost 4 times that power.

Click to expand...

probably different type of engines... racing and street engines have different states of tune. modern simple two stroke road going 80cc engines may not have any more than 10 hp...
a racing mx 80cc from the '80s may have the same power as modern 85's.

even in road engines there is a huge variation. tzr 125 yamaha engine (yamaha, not minarelli) is power valved electronically with stepped motor with more or less modern technology and puts 20 hp (great smooth engine BTW with a big, large, flat torque curve). aprilia rs 125 engine (rotax) is mechanically power valved (although the solenoid is controlled electronically) but with a on-off actuation, puts almosy 30 hp...
they both are very similar on tech but the reeds of the yamaha goes on the crankcase and the aprilia goes on the cylinder.

small things does the most gain!

Ditto on the powervalves. That is huge.

Also, if your older bike is a modestly tuned trail bike, it is going to have much less power than a race bike from the same era. For example, a '78 YZ80 is going to have way more power than a '78 GT80.

The little race bikes have much more aggressive porting, higher compression, better tuned exhaust systems, bigger carbs, single ring piston vs. two rings, etc... It all works together, but the cylinder porting and power valves are the big difference maker, IMO.