Yamaha scavenging research - 1999

[casal-fan]

Interesting document I found while freeing some Mbs in my laptop. Thought I´d lost it.
Just a drop from the monsoon wich is analysing scavenging behaviour... but anyway, interesting.

To make it easyer, the real focus is in the terms:
*RFC (reduced flow coeficient) wich is the coeficient between incoming flow from transfers and losses through the exh. port (a higher number is good).
*TF (total flow, more interesting TF16, meaning flow mesured in liters/second in an horizontal plane 16mm below the top of the bore (again, a higher number is good)

Many may consider this research as a waist of time as it leaves out the single most important element on a 2stroke engine, the pipe, wich affects everything.
Anyway... this research is from 1999. In 2000 yamaha wins the 250GP championship, and also in 2000 pushes ahead with a new 250cc production racer, the 5KE wich offers significant power advantages over its predecendent the 4DP.

knock yourselfs out
http://ledob86.free.fr/NouveauSite/Documentations/porting.pdf

[EEKNOWS]

No doubts the Jante tests Yamaha did revealed (to them at least) how far they were behind the mark. Over at Aprilia Jan Thiel has his pulsed flow bench working for at least 2 or 3 years. They never found the real key to it all which Jan knew from the 60's. Getting flow to cling to the piston and cool it. In the new millenium Aprilia Corse was beginning with Laser Doppler Anometrey which is a level up from this testing.
The testing is only concerned with basic flow numbers, as Aprilia found the secret was the turbulence out of the ports, less turbulence meant less mixing of spent and fresh charges, better cylinder filling and piston cooling.Which is just as important was the pipe,
The interesting finding is that if scavenging was better plugging was worse and vice versa.
Think the 5KE jumped in performance more due to the long long overdue switching to 54 X54.5mm configuration.