A Yamaha dealer will say anything...To sell you a new cart.
I wouldn't even bother asking a Yamaha dealer
I suspect the new quiet muffler will bolt up to the engine in older carts...But not certain.
I own a Yamaha AC electric cart. The noise level in the QuieTech cart is no longer a deal-breaker but I still prefer the smooth and precise throttle response and instant power of the AC motor. I also like that I know I have 60 miles of range every time I leave the house. I don't remember the last time I looked at the fuel gauge.