Why the GSXS-1000?
The Rush SR uses a drive-by-wire 1.0 liter motor from the 2022+ GSXS-1000, which produces just over 150whp. There are several reasons that we selected this engine for use in the RUSH SR over other engines that have typically been used for bike-engine cars (BECs).
Long-Term Engine Parity
In any spec series, parity between engines are a critical issue. Keeping the power output of all engines within a few horsepower of each other is essential if a series is to be widely accepted as a true spec series.
While the GSXR engines (and select others on the market) produce more power, these engines are used in motorcycle race applications and go through a redesign every 3-4 years. This would make long-term parity difficult to maintain.
The GSXS engine was developed in 2017 for the street bike. Suzuki have stated that this engine will be used for at least 10 years. The GSXS is a refresh of one of their best engines ever built: the K-5 / K-6, which was used in the 2005 and 2006 GSXR motorcycles.
Engine Reliability
Many people have asked why we did not go with the GSXR. After all, in stock form, it makes 204hp at the wheel.
There are many reasons! We think that 200hp in the very light Rush SR would require a very different skill-level of driver than the mass market it is trying to reach. Significantly more aero and wider tires would be required to make it drivable. The GSXR engine also hits the rev limiter at 15,400rpm instead of the 11,400 of the GSXS, so engine wear is greatly increased when used in the powerband constantly.
This translates directly to rebuild costs. GSXR-powered cars need rebuilds every 40-80 hours, and cost $10,000-$15,000 to rebuild. Conversely, the GSXS-1000 as used in the Rush SR requires a rebuild every 160+ hours, and costs approximately $3,500 to rebuild.
Engine Oil System & Cost Considerations
The GSXR and most engines people fit to BECs are motorcycle race engines! They are designed to be ridden at high angles of inclination. To keep the bike fast, they want the CG as low as possible. When the bike is at an angle, the forces on the bike are pushing the oil into the sump. This means manufacturers can use a small and shallow sump, which allows them to get the engine as low as possible in the frame. The GSXS, however, is a street bike. Although it banks in the corners, it is driven at a far milder angle than the race bikes.
Subsequently, the manufacturers raise the engine and use a larger, deeper oil sump. This is very beneficial to us, as most people who are familiar with BEC’s know that oil starvation can be an issue. Indeed, if we used a GSXR engine, it would be necessary to add a dry sump system, which would add nearly $10,000 to the build cost. This is why most GSXR-powered cars are at least $90,000!
The sump on the GSXS engine is almost 3 times deeper, 3 times the length, and has a steep sidewall. This prevents the oil from moving out of the sump when the engine is in a constant horizontal position and is subject to high lateral loads. Our testing has confirmed this, and we have had no oil starvation scenarios observed during skidpad testing or in series racing.
Pictured are the sump diagrams of the GSXR (left) and GSXS (right) engines, and the difference in the size and shape of the sump can be clearly seen.
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