This is a highly subjective topic. When the Slingshot was first introduced, the 2.4L GM Ecotec engine was a very important factor for many owners since parts were pretty much available anywhere. The 2.4L Ecotec has a long service history and a pretty good reputation for bullet-proof reliability. Those were important factors in my purchase decision. I have a 2015 Base model Slingshot (later called the S model) and added a Hahn Stage 2 Turbo kit once my factory 2-year warranty expired. I now have over 62000 miles (with over 25000 miles with the turbo).
The new 2.0L Polaris engine is a totally new engine and, IIRC, is also Polaris' first 4-cylinder in-house-designed engine. As such, its reliability and suitability for boosted performance are unknowns when compared to the same factors for the GM 2.4L engine.
Remember that the Slingshot is built and sold as a unique motorcycle. As such, it is common for motorcycle engines to be higher-revving that conventional car engines such as the GM 2.4L engine. The 2.4L Ecotec motor is rated at 173 HP @ 6200 rpm and 166 Ft Lbs Torque @ 4700 rpm and redlines at 6500 rpm, IIRC. The new 2.0L Slingshot motor is available in 2 versions, with the R model engine rated at 203 HP @ 8250 rpm and 144 Ft Lbs Torque @ 6500 rpm with a redline of 8500 rpm, IIRC. The detuned motor in the S & SL models is rated at 178 HP @ 8500 rpm (redline) with 144 Ft Lbs Torque @ 5500 rpm. While the new 2.0L motor is rated at higher HP than the old 2.4L motor, the 2.0L motor also produces far less Torque in either version than the old 2.4L. The 2.0L Slingshots are still geared to produce acceleration numbers similar to or exceeding those for the old 2.4L-equipped models.
Performance enhancements for the 2.4L motor is pretty much limited to adding a turbo or supercharger which generally boost HP to higher levels than is currently available in the 2.0L motor. I am unaware of any TC or SC kits being available yet for the 2.0L motors, although I assume the aftermarket suppliers are developing them. At the same time, now that the S model is available with a manual or AutoDrive transmission at the detuned power levels, a Performance Tune is available for under $1000, IIRC, that restores the higher level outputs of the R model motor, offering a significantly cheaper route to more performance that also lacks the higher levels of risk for motor damage that comes from adding a TC or SC to a motor that may or may not have been meant to be boosted. The 2.4L motor risks engine damage when performance is raised above 300 HP w/o rebuilding with strengthened internal parts such as piston rods, etc. Long-term reliability of the Polaris 2.0L motor is also an unknown at this time, especially as power is increased, but I have read posts where the 2.0L motor has been tuned to performance levels higher then the stock 203HP/144 Ft Lbs Torque numbers. Once TC or SC kits start appearing, experience from the initial adopters will allow us to start getting an idea as to how well the 2.0L motor will hopefully hold up under higher performance conditions.
The AutoDrive software has been reworked for 2021 and now produces smoother performance.The new software can be reflashed in the 2020 models and Polaris has added a Paddle Shifter option that fits the 2020 as well as the 2021 models. If the paddle Shifters work anywhere as smoothly as Paddle shifters in regular sporty cars, the AutoDrive may really prove itself to be an excellent choice. The improved AutoDrive in the 2021 model has received glowing praise in at least one review I've read.
The 2.0L motor needs to driven more like a high-revving motorcycle engine to match the performance levels of the 2.4L motor and I feel the higher-revving 2.0L motor will provide a more enhanced motorcycle experience compared tot he lower-revving 2.4L motor, but that is a highly subjective feel/opinion.
Just my 2 cents, well more like 4 cents!
p.s. - I didn't make a choice in the poll since I feel both engines have their advantages and disadvantages.
