When Polaris introduced the new Prostar 2.0L engine and mentioned the horsepower numbers, they did sound really good, but we did see a pretty good reduction in peak torque from the previous 2.4L Ecotec. We were a little concerned that the new engine might be a little peaky and feel a little gutless while cruising around. However, once the new engine specs were posted on the Polaris website after the reveal, they also posted up the new transmission gear ratios and the new final drive ratios and that's when we started to notice some important changes Polaris made.
Once we saw the changes to the transmission gearing and final drive, it became pretty obvious to us that although the engine would make less torque, we were going to see a faster Slingshot.
To confirm this, we started the comparison by using one of the dyno's of the base 2.4L Ecotec GM has posted over the years that shows peak horsepower/ torque and their RPM's. We put that information into a spreadsheet, then multiplied the engine power by the gear ratios of the transmission, final drive and also factored in the rear tire diameter. We plotted all of those data points, for all 5 gears on a graph below in red lines.
Next we needed to generate the same data for the the new Prostar 2.0L engine, but there is no actual dyno graph of the engine posted yet from Polaris. No problem, Polaris was good enough to give the peak torque/horsepower figure and what RPM's they occur. Knowing both of those figures, it is pretty easy to interpolate between them to make a nice smooth graph for that range. Once we had a graph for the RPM range above peak torque, we had to generate it for below the peak torque figure. This is where we had to do a little bit of estimating and although we did estimate the new engine torque below peak, we feel but came up with something that should be fairly accurate based on how other engines making similar Horsepower and torque behave.
The new Prostar 2.0L engine was plotted on the graph below in black. You will see that each gear is indicated by a different line in black for the 2.0L, same as the Ecotec is graphed in red. Please note this graphs is of the 173HP Ecotec and the 203HP Prostar.
A couple takeaways from the graph data -
- The new engine will not have the same power at the wheel as the current Ecotec in the lower RPM's of 1st, 2nd and 3rd gears. However those are relatively low speeds and under full throttle, the time spent in this area of the graph will be pretty minimal. Also, typically the rear tire can not maintain traction at these speeds in these gears, so even though the Ecotec has more available power in this range, the Slingshot is typically traction limited here. So even though the Ecotec has more power, the rear tire will determine the actual acceleration in those first coupe gears. In 3rd gear a lot of Slingshots do have traction and the power at the wheels is very similar between the 2 engines once in 3rd gear.
- Once the 2.4L Ecotec reaches peak torque and starts to drop off in power, the new engine keeps accelerating. Not a big surprise here since the new engine seems to be designed to make its power more in the upper RPM range.
- Once the Slingshot is in 4th or 5th gear, because of the new transmission and final drive ratio's, the new Slingshot will out accelerate the Ecotec. Even with the engine making less torque, because of the gear multiplication, there is more power available at the actual tire than before, especially while cruising in 4th or 5th gear.
- The new Slingshot will be electrically limited to 125mph from Polaris, but it will also have a lower actual top speed also because of the shorter gearing of around 185mph at the stock redline, compared to well over 200mph with the older gearing. Not that this really matters for most everyone, but thought it was fun to note.
It will be interesting once we get some time behind the wheel of the new 2020 Slingshot how it actually performs.