Originally Posted by
flywilly
Hi Tarquin,
One 'caveat' about the dive test: it only provides an approximate reference point. In other words, you may achieve a positive result for the test, but not have the pipe length optimized.
I am sure you are aware of the new YS 'classic' 60. During testing of the prototypes, the US importer (Rich Verano) was unable to replicate the factory rpm figures (14,000rpm on an 11x9 apc prop). Rich was using the same set-up he had used for his YS .61AR in his Escape and could only achieve about 13,200rpm on the prototype which ran great otherwise. The factory sent their set-up; pre-tuned header and pipe and, voila, Rich could now get 14,000 rpm and the engine ran great in the air. The factory set-up had the pipe length about 1" shorter than Rich's set-up.
I love the OS 'VF' series of engines and still have several in running condition.
Please post some photos of your Subarashii - maybe even the plans!
Regards,
Will
True enough. Except YS is trying to sell engines so reporting a maximum is one way to do that.....The 1" longer set-up probably needed more load and Verano knows that. Back in the day I ran 12x12 and 13x10's on my YS's with longer pipe set-ups. Reliability was the most important parameter driving us, always has. The fact that engines sipped the fuel at the reduced rpm was a nice bonus. And the quiet was deafening
Regardless, the dive test has proven its value over and over. It is an early step in the tuning process, not the final step, but gets one in the ball park quickly and effortlessly