Polaris SlingShot Octane Question?
That said, as Slingshot’s GM engine is of relatively high compression, in this case 10.4:1, 91 or higher octane fuel is called out by GM and Polaris for the best performance. It’s a good recommendation and should be followed, especially if you drive that Sling hard.
There is another potential darkside to using lower octane than 91: knock sensor issues. This is a recurring problem with a number of Slingshots that is generally treated as a sensor issue, when in fact it is typically a driving habits issue. 2015-2019 Slingshot with the GM Ecotec engine already has two strikes against it where this is concerned, even if using 91 or 93 octane:
1. It possesses very tall gearing, which increases load on the engine. Final drive gearing on Slingshot is in the 3.20:1 range, which is considerably taller than the automotive applications of this engine, which are typically in the high 3's/low 4's. Polaris apparently chose such tall gearing to help suppress wheelspin, which as the Slingshot only has about 600-some pounds on the rear wheel is an evident issue. Taller gearing helps reduce wheelspin, but it comes at a cost in terms of the engine's ability to resist spark knock, already somewhat exacerbated by the Ecotec's relatively high 10.4:1 compression ratio.
2. It is about as aerodynamic as a barn door. Slingshot's looks are very appealing, but are horribly poor in the aero department. At higher speeds, this drag makes for even more load on the engine, further worsening the effect of the tall gearing.
How to best deal with these aspects? Don't "lug" the engine, especially at higher speeds. Ecotec produces voluminous torque by design, but that torque comes at a price in terms of load. Rev it! When it's time to accelerate, downshift. Don't just mash the gas at low RPM without downshifting. Grab a gear down and let it rev. It will not only accelerate better, it's easier on the engine and will remove the tendency to spark knock from the above described aspects.- Bill Hahn Jr.