By the 70s, Gordini was a badge added to the high performance model in a line-up. The engines were still good, even better than Gordini made them. The 807-12/13/20 was the hot engines. 12s and 13s were emission compliant, 20s not so much. Renault also sold crate racing engines. The 807G is a high performance version of the 807 at about 140 or so HP. Alpine made larger and hotter versions for their rally cars.
Gordini himself was a self-taught "magician" who did amazing things with poorly designed (performance-wise) stock engines. When engine design became a science, he was left behind. A similar thing happened to Cooper race cars in F1.
Here's an example. High compression ratios in hemispherical engines result in large thin combustion chambers. This leads to long burn times. Many competition engines were "twin plugged" to speed up the burn time so you could run less ignition lead. The engines made more power and ran cooler as well. Fitting a second plug is not easy. Here was Gordini's solution:
http://www.2040-parts.com/_content/items/images/66/1231266/001.jpgThe spark plug is almost completely shielded. This, needless to say, made things worse. Combined with lots of other mods, however, you might not realize it was creating a problem. My favourite example of this is the tuner of Mike Hailwood's TT winning Ducati twin. He spent hours on the track dialling in the engines for a nice fat mid-range hit. Now modern testing equipment reveals he actually dialled in a flat spot to get his mid-range hit!
Seat of the pants tuning only gets you so far.
