The Need For Speed, Inside and Out
The sound of any good ol’ American V8 moving up the RPM band is music to a motorhead. There is little doubt that the popularity of NASCAR and fuel-burning drag racing can be attributed to that roar of performance (compared to the high-pitch whine of open-wheel type cars). As technology evolves in
classes like Super Stock and Pro Stock, big inch gas-burners have moved higher and higher in their RPM bands – spinning seven to nine liters (that’s 425-500 cubic inches for us rednecks) at 9500 rpm or greater is no small feat.
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For instance, modern valvetrain technology is a far cry from putting in a bigger cam and springs. In the hardcore arena, it sometimes means moving the camshaft physically higher up in the block to lessen the severe strain out on valvetrain parts. In Super Stock Hemi racing, where this is not legal, builders are using the largest cam journals possible to get maximum lift out of the cam (rumor has put some of these as high as .900+ inches) and very sophisticated value gear (such as rollers, rockers, valves, etc.) The cam blank, reportedly based on a big block Ford version, is custom ground to get the engine both WAY up in the RPM range and move an enormous amount of fuel into the cylinders. This is only possible due to the lighter space-age materials now available, as static weight in the valvetrain (as well as the reciprocating assembly) will drag on potential RPM levels.
Of course, this action results in some attendant complications with piston-to valve clearance, not to mention harmonic issues. Harmonics is an inherent vibration in the
 The 1968 Charger’s rear window styling was cool, but created some real problems when NASCAR driver got it up into the higher speed levels. Air working across the surface and trapped by the ‘wings’ on the sides would make the car’s rear end very dangerously loose. |
actual metal composition the part is made of. Valvesprings, which move at extremely rapid rates of expansion and contraction, are probably among the most susceptible to this, which results in breakage. The OEM and aftermarket has addressed this with unique alloys and proprietary casting and construction techniques, and there is usually a learning curve associated with making new inroads.
It can get expensive to solve these problems. I remember once seeing a couple of race engineers in Auburn Hills trying to sort out a NASCAR truck engine problem with a high-speed camera; at a particular RPM level, in slow motion, the spring would begin to visually oscillate and then break. Now it became the job of the metallurgists to figure what composition of materials would be needed to fix the issue, to get a supplier to fabricate some springs at those specs, and then the testing would start again.