Why is the top speed so slow on these cars? The 1930’s and 1960’s cars have a lot faster top speed in a straight line by nearly 50 miles per hour! For example, the Auto Union 1939 car can go 220 miles per hour at Le Mans and the 1960’s Lotus can do that as well, while the 1976 Lotus can’t go past 170 miles per hour! I know some of the wings create drag but surely the more powerful engines of the 1970’s could make up for some of it? Just to be clear, I’m talking about everything stock, no upgrades.
Can you change the gear ratios and reduce the downforce?
This.
Even modern F1 cars top out ‘only’ 180mph on tracks like Monaco, where they run huge downforce.
You’ve already answered your own question, you just can’t bring yourself to believe it. On almost any track, downforce gains you more in lap time than you lose on the straights. Hard data on 1976 F1 car top speeds is hard to find, and would have varied from track to track based on aerodynamics and gearing, but I’ve seen one source claim a top speed of 180 mph for the Ferrari 312 T2, and also I’ve seen it reported that Mario Andretti and Gunnar Nilsson critized the Lotus 77 for having poor straight-line speed. So 170 for the Lotus sounds plausible. A more recent case would be Red Bull Racing from 2010-2013; for most of their four championship-winning years, RBR had one of the slowest top speeds, but the fastest lap times, because they excelled in the area of aerodynamic downforce.
Many don’t notice it but downforce aids with acceleration up to a certain point, you can exit corners faster and you just go way faster. You’ll find that on most tracks, P and X class cars run high if not full downforce. Same with these cars.
The cosworth dfv powered cars of the 70s were not any more powerful than the likes of the auto union but typically carried considerably more drag. That much is obvious just looking at them, the cigar auto union versus the bewinged M23.
The auto union had two superchargers and 4 extra cylinders, the dfv was a very small and compact naturally aspirated V8. They actually made similar power thanks to technological advances on the dfv but as you can see aerodynamic differences can make a huge difference to top speeds.
A few reasons.
Lack of power (500hp)
Massive tyres creating drag.
Aerodynamic efficiency-They added downforce with wings but also added drag.
A car like the Lotus 49 with a similar Cosworth DFV would probably be 10mph faster in a staight line.Not much drag.