Confessions of an Automationeer, Part 12: The Joy of Six
For eight of the past ten CSR rounds I have entered, my entries were powered by a straight-six engine. Now you may be wondering whether or not I am biased towards this particular engine configuration. In truth, I certainly am not, but have done my homework about the pros and cons of the various engine configurations available in Automation. So, without further ado, here's an example of a (turbocharged) straight-six done right, provided by another user who was willing to share his secrets.
Look at the dyno sheet in the screenshot above and you'll see that the torque curve is very smooth, wide and flat, with minimal lag. For this to occur, small-diameter compressors and turbines have to be used in conjunction with a high AR ratio and low boost pressure. The latter, especially when combined with a high compression ratio, allows for further improvements in efficiency; moreover, the use of a lean air-fuel ratio and conservative ignition timing make this engine even more economical.
On top of that, the low-RPM cam profile is very mild, while the high-RPM cam profile is fairly aggressive. However, due to budget constraints, this engine has a simple air-to-air intercooler and a standard three-way catalytic converter. Installing a water-to-air intercooler (which lowers the engine's minimum required octane number, thereby allowing the compression ratio to be increased even more) would cause efficiency to increase further, while a less restrictive high-flow converter would have a similar effect. So it's not hard to see why four of the eight straight-sixes I made during the past CSR were turbocharged.
But even without turbochargers, straight-sixes are preferable to V6s for several reasons. Whereas a V6 has its cylinders arranged in two banks of three, a straight-six has its cylinders arranged in a straight line. The former needs a bank angle of 120 degrees - too wide for most engine bays - to be inherently balanced, and as such, most V6 engines have either a 90-degree bank angle (which leads to less refinement and more complication, even if the resulting engine was derived from a V8) or a 60-degree bank angle (smoother, but more expensive to develop). Moreover, a straight-six suffers from reduced friction losses compared with an equivalent V6, and also requires fewer components. Finally, it will be easier and cheaper to develop a straight-three or straight-four from a straight-six if they all share the same internal dimensions. The only advantage a V6 has over a straight-six with the same dimensions is its reduced length, and as such, it only makes sense to use one if the engine bay is particularly small.
In short, when budgets are relatively modest and efficiency is key, but a modicum of performance is desired, the sweet spot among engine configurations doesn't always lie with eight cylinders or more, or, for that matter, five or fewer. It can be found in the humble straight-six, and this once-commonplace arrangement looks set to make a comeback. In the next post, I will show a recent build in an attempt to prove that even a supercar (or hypercar, for that matter) can use this relatively humble configuration and still remain competitive in the cutthroat Automation market.
The turbo setup for the winning entry in CSR41
Look at the dyno sheet in the screenshot above and you'll see that the torque curve is very smooth, wide and flat, with minimal lag. For this to occur, small-diameter compressors and turbines have to be used in conjunction with a high AR ratio and low boost pressure. The latter, especially when combined with a high compression ratio, allows for further improvements in efficiency; moreover, the use of a lean air-fuel ratio and conservative ignition timing make this engine even more economical.
On top of that, the low-RPM cam profile is very mild, while the high-RPM cam profile is fairly aggressive. However, due to budget constraints, this engine has a simple air-to-air intercooler and a standard three-way catalytic converter. Installing a water-to-air intercooler (which lowers the engine's minimum required octane number, thereby allowing the compression ratio to be increased even more) would cause efficiency to increase further, while a less restrictive high-flow converter would have a similar effect. So it's not hard to see why four of the eight straight-sixes I made during the past CSR were turbocharged.
But even without turbochargers, straight-sixes are preferable to V6s for several reasons. Whereas a V6 has its cylinders arranged in two banks of three, a straight-six has its cylinders arranged in a straight line. The former needs a bank angle of 120 degrees - too wide for most engine bays - to be inherently balanced, and as such, most V6 engines have either a 90-degree bank angle (which leads to less refinement and more complication, even if the resulting engine was derived from a V8) or a 60-degree bank angle (smoother, but more expensive to develop). Moreover, a straight-six suffers from reduced friction losses compared with an equivalent V6, and also requires fewer components. Finally, it will be easier and cheaper to develop a straight-three or straight-four from a straight-six if they all share the same internal dimensions. The only advantage a V6 has over a straight-six with the same dimensions is its reduced length, and as such, it only makes sense to use one if the engine bay is particularly small.
In short, when budgets are relatively modest and efficiency is key, but a modicum of performance is desired, the sweet spot among engine configurations doesn't always lie with eight cylinders or more, or, for that matter, five or fewer. It can be found in the humble straight-six, and this once-commonplace arrangement looks set to make a comeback. In the next post, I will show a recent build in an attempt to prove that even a supercar (or hypercar, for that matter) can use this relatively humble configuration and still remain competitive in the cutthroat Automation market.
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