The secrets of sky-high engine speeds.
From the June 2013 Issue of Car and Driver
We all need oxygen. Straighter intake runners allow easier breathing, as do variable intake manifolds. The latter allow engineers to tune shorter, straighter intake passages for high rpm, as well as longer ones that better fill the cylinders at lower rpm for more torque. Because a high-rev screamer needs flexibility.
At high rpm, a car’s relatively heavy valves can lose contact with fast-spinning cams. Near redline, the valves may bounce off their lobes, and valves and pistons can collide. Stiffer valve springs can alleviate this “valve float,” but they bring friction and noise. Roller-type cam followers cut the friction, and lighter componentse.g., titanium valves, solid liftersreduce the chance of float.
Overlap (when both intake and exhaust valves are open) helps engines breathe at high rpm. The downside: Overlap can cause a rough, dirty idle. Modern variable-valve-timing hardware facilitates a balance between the two.
Without sufficient oil, engine components wouldn’t live long at 9000 rpm. State-of-the-art synthetic oils better maintain their film strength, ensuring proper lubrication at high rpm and over a wide temperature range. Oil is also vital for cooling, and modern oils are able to withstand higher temperatures. A well-engineered oil sumpwet or dryis also crucial.
Lighter components and shorter strokes reduce crankshaft and connecting-rod stress, allowing for higher rpm. Pushrod valvetrains include more reciprocating components than overhead valvetrains. That’s why pushrod engines seldom rev as high as overhead-cam engines. The LS7 in the C6 Corvette Z06 reached 7000 rpm with ultralight titanium connecting rods and intake valves, but that stuff’s not cheap.
The term “redline” technically refers only to the red hashmarks on a tachometer, but it is synonymous with maximum engine speed. The 9000-rpm Porsche 911 GT3 and Ferraris prove that, even if redlines are dropping with the proliferation of turbocharged and diesel engines, there are still some high achievers out there. In the above illustration of the 458 Italia’s V-8, we’ve highlighted the factors that determine how fast an engine can spin.
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