speed or lake of
well... here are some numbers for you which you may not like:
72 base motor does 0-60 in 7.6 (brand new)
My little sisters Escort zx2 does 0-60 in 7.6 seconds (brand new)
1/4 mile is mid to high 15's...
Not great but it gets worse!
If you read some old Motor Trends and Road and Tracks you'll find similar numbers for the older engines as well as the big blocks!
Except for very rare, very expensive cars i haven't seen one that does 0-60 in less than 7 seconds. (with the original motor) The faster the car was stock, the more $$ its worth too.
I don't know what you're looking for performance wise, but you'll probably be disappointed with stock C3's if you compare them to late model cars.
My thinking is this... If you want a fast car, buy a fast car. You'll save a ton of money and heartache!
For instance:
I'm not going for a "fast" car but I did have a ZZ4 put in my 72 coupe. The car is very powerful and a blast to drive. The problem? It doesn't beat a stock 98 Trans Am.
The car is still very low tech in spite of the 355hp motor. The Muncie four speed has a long hard throw, and the car is hard to launch properly. Too much gas and you lose control, too little and you bog down. After that its a blast!
My Trans-am owning friend only has to floor his car when the light turns green. (he has an auto) Unless the pavement is slick, his car hooks up and goes everytime.
As for your question about slugish 72's... no its not much different than a 70. Real horsepower difference is slight. A 454 or LT-1 would have more power but would cost you several thousand dollars too. 255hp (net) for the LT-1. 270hp for the big block + 300lbs or so. On the plus side the LT-1 and 454 are more collectable than the base engine.
I guess you'll have to test drive them and see. All the above engines still don't get you below 14.5 in the quarter mile.
To me a C3 is a classic sports car, with "classic" being the key word. Any year Corvette is the best performing GM car of its time.
Like I said, if you want to go fast you'd be better off with a Trans-am, Mustang, or late model Corvette. For that matter if you racing in a straight line, I don't think the Corvette is the best car for that. You'd be better off with a late model Camaro. You could spend the extra $$ on parts.
-Gooney0