Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version nyu B notes v1.5 12/10/84; site acf4.UUCP Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!mhuxt!houxm!whuxl!whuxlm!akgua!mcnc!philabs!cmcl2!acf4!hkr4627 From: hkr4627@acf4.UUCP (Hedley K. J. Rainnie) Newsgroups: net.auto Subject: Speed, H.P., and Corvettes Message-ID: <330035@acf4.UUCP> Date: Fri, 19-Apr-85 16:13:00 EST Article-I.D.: acf4.330035 Posted: Fri Apr 19 16:13:00 1985 Date-Received: Mon, 22-Apr-85 02:23:58 EST Organization: New York University Lines: 93 Reply to Chris Kay's question: "Why is the new Corvette so fast and how fast were the older Vettes?" There are major three things to consider when one talks top speed. Horsepower, aerodynamics and gearing. The new Corvette excells in the latter two. Weight is more important for accelleration and handling than top speed, assuming all other things equal. In any case, the new Corvette standard (read loaded) weighs about the same as a standard late 60's Vette. You need a tall top gear so as to be able to cruise at a high speed without exceeding the redline of the motor. A five speed gearbox is nice with a high final drive in that you are still permitted to have a relatively low first gear to facilitate acceleration. The new Corvette has both the high final drive (3.07) and the 7 speed transmission (however you like to count gears). At the top speed, the amount of horsepower you need is determined by the quality of your aero specs. Since drag runs something like the cube of your speed, good aero specs can count for a lot of horsepower. The Corvette has an exceedingly low coefficient of drag. Now, onto the qeustion of yesteryear's Corvettes. First of all, aero-wise, they weren't so bad. In fact, I read that the aero figures for a 82 Corvette (which is the same body as the late 60's Vettes with some aero-mods stuck on) has about the same coefficient of drag as a 928! Boat racer Gale Banks and friends took a stock bodied 69 Vette a few years back, stuffed it with a twin turboed big-block and broke 220 mph at Daytona. So the aero figures aren't that bad at all. In fact, the 1963 Stingray is, to the best of my knowledge, one of the first if not the first American car to be designed with the aid of a wind tunnel. Using a 3/8 miniature of the experimental Stingray, GM rented wind tunnel time and a couple of fellows from M.I.T. to study the behavior of the body at wind velocities up to 160 mph. Gearing is a problem. Back then, almost all Corvettes were tested with final drive ratios like 3.70 or 4.11, making for truly hairy acceleration but redline-limiting their top speeds. We're looking at 120-130 mph here. On the other hand, the engines back then wound up a bit higher than engine nowadays: we're talking 6400 rpm for the 427 and 6500 rpm for the 327, as compared with around 6000 rpm for today's 350. Look at the rpm's for the top speed of the new Vette: 4100 rpm at 149 mph. The engine is not powerful enough to redline with that steep top gear. (If it could, you'd find yourself going 218 mph). Between the gearing and the engines, I've ever seen a test of an older Vette where it was unable to redline in all gears. Also, back then, there was a choice of two gearboxes, a close-ratio with a first gear of 2.20 and a wide ratio with a ratio of 2.52. Neither of these is close to today's 2.88 gearbox. The closer-ratio boxes of back then allowed you to keep the engine running at peak rpm's and made shifting nicer. Today, the point is to keep rpm's as low as possible for good milage in normal driving, but also holding a low first gear for quick acceleration. Thus the ultra wide ratio box. This allows a high (numerically low)* final drive ratio without killing accelleration--and thus a higher top speed. NOW, to the question of top speeds of older Vettes. With the right gearing (say 3.08) an older Vette could easily hit 150 or so well under 6000 rpm and probably faster. Without some sort of aero aid, it might well start flying at this speed, however, and the tires back then would probably give up. So as far as the standard, everyday Vettes go, top speeds haven't changed that much, for the reasons we've outlined. BUT back then, you didn't have to remain content with an everyday Vette. You could factory-order engine options to make for a super Vette for $1000-$3000 over the standard high performance option. The fastest Vette from Chevy has to be the ZL-1 aluminum Can-Am engine Corvette of 1969. Rated way under peak at a low 430 hp, they were very rare. Zora Arkus-Duntov, considered the 'father' of the Corvette, had one around the GM test track at 185 mph. The somewhat more common L-88's would make about 180 mph with the right gearing. Both of these are with open exhausts-- the factory exhaust was designed for you to throw it away--but otherwise stock cars. We've been talking a lot about top speed, and I've kept saying that the cars of that time were meant for acceleration. What kind of acceleration you wonder? Well, the pedestrian 435-hp big blocks were good for 0-60 in 5-1/2 seconds but the L-88 with the proper gearing was a real screamer: 0-60 in 4.2 sec, 0-100 in 8 sec. 0-140 in 17 sec., 1/4 mile in 11 @ 120mph. sources: Road & Track various issues from Oct 62- Sept 70 Road & Track 1985 Buyer's Guide Corvette: America's Star-Spangled Sportscar by Karl Ludvigsen Vette magazine: Nov 84, Mar 85 (signed) Speed Racer * 'low' gearing implies a high numerical ratio (engine to wheel): low gear or first has the highest ratio, over 2:1, while high gear has the lowest ratio (1:1).