Those of us who have modified our cars for more performance for two or three decades know that in some respects the "good old days" really weren't all that good. There were some great aspects: cruising was actually semi-respectable, an occasional street race wasn't regarded as a grossly antisocial act, old Chevys were inexpensive and easy to work on, and 100-octane gas cost less than half a buck a gallon!
There weren't smog laws to worry about, but a lot of the modifications made in the name of more power made our cars run slower, use more gas, and occasionally ruined their driveability. A big part of the problem was that not many people really had a clue as to what worked and what didn't. If, for instance, you were fortunate enough to own a '61 Corvette with the base 230hp engine and you wanted to pump up the power output, you could be pretty sure that by utilizing the factory dual-quad intake and carburetors, and factory 270-horse cam, you'd end up with something roughly equivalent to a 270-horse 283. That was because you were, for the most part, re-creating a higher horsepower, factory-engineered package.
On the other hand, if you bought parts from the local speed merchant, the process was kind of like going to a Chinese restaurant and ordering one item from column A, two from column B, and one from column C; sometimes the combo tasted great, and sometimes it wasn't fit to eat. Using our hypothetical '61 Corvette with the 230-horse engine, you might luck out with a combination of parts, usually from a number of different manufacturers, that actually improved the old 283's performance. You could just as easily wind up spending a lot of your hard-earned dollars to get a setup that was an over-carbed and over-cammed, barely driveable eight-cylinder disaster that guzzled gas like a wino on cheap port, and couldn't outrun a six-cylinder '55 Ford.
The problem was an assemblage of parts that wouldn't-or couldn't-work together harmoniously. It could be caused by either the buyer or seller's pure ignorance-or both. Maybe the blame could be pinned only on the speed shop owner's greed; sell the customer the most expensive parts available, and who cares if the end result works. Lots of speed shop customers believed the old adage that if a little was good, more had to be better, and a whole lot would be just about perfect. Thinking along the lines of, "If a 230-horse 283 uses one four-barrel and a 270-horse has two small 'fours' on a low-rise manifold, then I'm gonna get a lot more power if I slap two big fours on a tunnel ram." Or, "A Duntov cam has more lift and duration than the 230-horse engine's cam, so if I get a cam with gazillion degrees of duration and a couple feet of lift, I'm gonna get way more power than with the Duntov." Yeah, right!
That's not to say that the individual parts were no good; they just weren't right together. The key to a good-running modified engine is the right blend or combination of components-not a random selection of items that may not work well together.
One of the greatest performance developments in recent years is the engineered performance packages that eliminate the old "by guess or by golly" approach to buying high-performance parts for your classic Bow-Tie. Engineered packages are the result of a manufacturer designing and testing cams, intake manifolds, even cylinder heads to work together as optimized assemblies. These "packages" may be listed as individual components that are engineered to work well together or as an essentially complete system that can be ordered under a single part number. Best of all, many of these are 50-state smog legal. If aftermarket performance parts can get the blessing of the California Air Resources Board, they have to be good, at least from the environmental standpoint. And for said aftermarket performance parts to be environmentally friendly enough to satisfy the Golden State's clean air cops, you can bet they've been carefully and well engineered.
The best way to describe a performance engine system is as a total air and fuel management system. Cylinder heads, intake manifold, and camshaft are all designed and engineered to work well together. The heads are crafted to optimize the airflow ratios between the intake and exhaust runners, and airflow characteristics of the heads and intake are matched as closely as possible. A camshaft is configured so its lift and duration work harmoniously with the heads and intake to provide a powerband that's appropriate for the intended use of the system. A well-engineered street system should return better gas mileage (assuming the driver can keep from slamming the pedal to the floorboards too often) than stock.