Originally posted by undertaker55
the muscle cars got like so much horsepower and torque but dont go as fast as the cars today that have less hp and tq?
First of all, most of those old muscle cars were higher in torque, not horsepower. Why? Because they had large V8's and V6's, creating loads of power down low in the rev range, but had a pretty limited top end -- redline at 5,000 rpm, with power falling well before that.
These cars were designed to give the effect of extreme power without having to be technologically complex. The easiest way to do that is to limit the rev range. If the engine isn't spinning too fast, the components in and around it don't have to be all that sophisticated, thus the old pushrod-style V8's. So now you're limited to the lower rev band. Since your HP is never going to be higher than your torque if you never get above 5,000rpm (for why, see: Car Physics at
http://forums.gtplanet.net/showthread.php?threadid=13110), might as well go all out for torque. It'll make a great impression from a standing start!
To do that, they made the cylinders huge (massive gulps of air & fuel), the air intake and exhaust small (to increase the speed of air at low revs), and use plain old iron block engines.
So how does a modern Civic Si give a '68 Mustang a hard time? Gearing (see same thread mentioned above). Gearbox technology wasn't up to modern standards, either. A 3-speed auto and 4-speed manual were pretty standard around 1970. Adding gears added complexity to the gearbox almost geometrically, so there's fewer, taller gears. This made it easier to ride the short wave of torque, but at the cost of total top end power. Speaking of top end power, the fact that since the air intake is so small, the available air is limited at higher rev's, so torque -- and thus HP -- falls off quickly.
Oh, yeah; as mentioned by other people, cars today are generally lighter, more aerodynamic, and have more efficient engine and transmission components (less power loss due to having to move all those heavy bits around).