Your perception of the importance of camshaft wear is on the mark
as far as the exhaust valve is concerned. But a loss in valve spring tension would cause a similar degradation on the intake valve side.To some degree, camshaft wear is compensated for by valve seat wear. There are some camshaft grinders out there that "harden" their product by the simple process of "carburizing" or flame hardening by heating the lobes with a torch. I have seen some really soft cams provided as OEM replacements, too. Usually the purchaser of a cam from a speedshop doesn't expect longevity from the engine,since performance is the focus at the time the cam is selected. I didn't replace the camshafts in the last engine I modified to take advantage of the pulsing. It is a four valve per cylinder double overhead cam design. I looked at the camshafts and saw that the pattern of oil deposits indicated that the rocker arms were hardly even touching the cam lobes at some points. This was because the valve springs had a low spring rate. If the engine is not run for a few weeks, the valves will not seat properly at first, and it will spit back through the carburetors until the springs regain their memory. So there are the three factors, camshaft hardness, valve seat wear, and spring tension, that will affect the longevity of the valve timing. A manufacturer would have to be able to certify that his engine will meet the EPA's emission requirements for 50,000 miles. And to be able to certify the engine, I would expect that it would be run on a dyno for an equivalent number of operating hours If there was any degradation in performance due to wear, it would be noted. Generally nowadays, engines from Japan are hardly broken in at 50,000 miles, though. When I did my engine mods,
the information I was using was available in the magazines about
that facet of motorsports, which has evolved since to add yet another
resonant vessel to the process. This is the tuned airbox. It works the same way as the pulse tuning in the intake and exhaust systems
works. The machine I modified had such an airbox, but I removed it.
It was fed though a rubber venturi called a "snorkel". If the snorkel
was removed, and the airbox was fed through the hole where the
snorkel had been, the engine suffered a serious degradation in performance. Well, I put the standard K & N filters on each carburetor,
and left the airbox off entirely. Japanese manufacturers have been
setting up these airboxes to work with ram tuning at high speed.
This is called the "pressurized air box", and it helps performance in
two ways: the air is cooler, and therefore, denser; and ramming the
air into the box adds 0.3 psi to the pressure in the box. This is enough
for about 10 horsepower. BAT did not use an air box under the hood
of the BAT Super Car. There was no room. They used a K & N
type filter instead. |
