‘ The YPVS had the best mo­tor’

Motorcycle News (UK) - - Feature -

“The YPVS is my favourite two-stroke mo­tor. It’s a won­der­ful en­gine and is the last in a long line of Yamaha par­al­lel-twins that started air­cooled way back in the 1950s and cul­mi­nated with the liq­uid­cooled RD350 YPVS in 1983.

“Be­fore the pow­er­valve, two-stroke mo­tors were get­ting peakier and peakier as en­gi­neers squeezed more power from them, but when the YPVS ar­rived you sud­denly had a lovely spread of power on a two-stroke thanks to that pow­er­valve.

“Pow­er­valves were around in so­phis­ti­cated race en­gines be­fore, but Yamaha used it on a road bike to cre­ate a broader spread of power. On a two-stroke the pow­er­valve low­ers the top of the ex­haust port by about 10mm, which gives more mid-range, be­fore open­ing and rais­ing the top of the ex­haust port, giv­ing a topend boost, too.

“And in­stead of an on/off sys­tem like its ri­vals had, the YPVS did this pro­gres­sively by work­ing off sen­sors in the en­gine and set­ting the valve’s po­si­tion to cer­tain revs, giv­ing an el­e­gant and re­fined power de­liv­ery. It was bomb-proof, too – which some of its ri­vals cer­tainly weren’t.

“It re­ally is a fan­tas­tic mo­tor and my favourite two-stroke en­gine ever built.”

Pow­er­valve gave im­proved flex­i­bil­ity

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