I remember racing my SL70 against several GT80s back in about 1976 & 77 they all had yz80 top ends on them & were rocket fast down the straights, even with my SL70 being 82cc with motoplat ignition, roller cam 22mm carby, frogmod pipe, cr125 forks & custom swingam with the shock forward mounted for a whole 7 inches of travel, it was near impossible to keep up with the GTs. in 1978 i bought a worked xl75 off another racer & it was able to beat the GTs everynow & then. Karston Jorgenson, Glen Watson, Rodney Meekins, Chris Cavanagh all had these GT80 rocket back in the day & racing with them & the other guys on 4strokes was awesome.
back then my SL could hold its own against the average 125 play racer on an MX track but guys that raced regularly would leave an 80 for dead