It dawned on me the other day why the J. Costa variator provides the tremendous rush of acceleration. While accelerating hard and watching my tach, I realized that the engine immediately climbs to 5500 rpm and holds there. As the Swing's speed increases the rpm still sit at that magical 5500rpm. Why 5500 rpm? After checking several websites, I was able to track down the engine's max torque output. It's 39.1 ft/lbs at, you guessed it, 5500 rpm.
No point spinning the engine faster than 5500rpm, as peak torque is where the engine is most efficient. Even though the engine produces max HP at 7000 rpm, the 5500 rpm mark is the sweet spot. The J.Costa engineers did their homework right in designing their variator to rise to and hold 5500 rpm while accelerating. Good job.

Am I correct in interpreting then that any variator/clutch mod that would rapidly get you to 5500 RPMs would get similar results as the J Costa? Like maybe lightweight Variator Rollers or Sliders combined with upgraded (say Malossi red or yellow) clutch springs?

Tim

Oops!, My mistake. I meant "interpreting". Oh well, it is the start of a holiday weekend.

My J Costa seems to work different from bigbird's.

If I am at a standstill and go WOT, it will hit 6900 or 7000 rpms. It will hold it until about 60 mph at which point it will start to drop a bit as speed continues to increase. It really is close to 7000 rpm, not 5500 rpm, on my scoot. Believe me, I have witnessed it many, many times since installing the J Costa!

I had read an article somewhere that stated that the engine has two horsepower peaks - 5500 and 7000, with 7000 having just a bit more hp.

Not sure why mine would be different - it is the only engine or transmission mod that I have done. Stock size tires (first IRC's then Diablos). Factory clutch.

[quote="bigbird]
The J. Costa not only gets to 5500 rpm, but it stays there under the acceleration conditions. That is as much a function of the sliding pins as the shape of the drive sheave face.

... it's the shape of the sheave that maintains the 5500 rpm spot. This is done by varying the ratio of the front of the belt to hold the 5500 rpm no matter what the road speed of the Swing.[/quote]

So is it the shape (profile) of Ramp Plate and the variator Roller (Slider) Weight tracks --as in the OEM variator assy-- which effects the performance? Or is it the face angle of the belt pulley section of the variator which is changed?

Tim

Tim: I'm no engineer. I believe from my snowmobile experience, which use a similar CVT, that the profile of the ramp plate in conjunction with the slider weights governs the rpm rise and the face angle ultimately determines the gear ratio. These three variables work together. I'm sure the J. Costa engineers did lots of tinkering with the ramp profile against which the sliders push and the face angle which grabs the belt between the sheaves for forward motion.