In my previous articles on the subject, I’ve explained the Renault Re40 was the first F1 car to blow the diffuser(1983 first year of flat bottoms). I got these pictures today and felt it was worth sharing them along with some insight from the man who brought the idea into F1, Jean Claude Migeot.
This is what Jean Claude Migeot told me about the development
Exhaust blowing was on my menu of aero development during the first year of the flat bottom era (1983) as one possibility to recover some downforce. I was in Renault at the time in charge of aero and, after some checks on the engine bench as we were terrified to face another lag time (!) between throttle movement and downforce creation, I was given the green light to experiment in the tunnel. Exhaust blowing to create a fluid skirt on the side of the car (also tested early 1983) did not worked but blowing the rear diffuser was quite powerful (I remember something like 50 kg on the rear axle at full throttle whatever the speed).
It was introduced at MonteCarlo in 1983 on the RE 40 and stay on it most of the season. It was kept on RE50 the year after (ask Derek Warwick!) and I introduced it also on the F1/86 (Canada 1986) when I worked for Ferrari later.
I remember well that in 1983 we were immediately protested by Brabham and Gordon Murray (on the basis of the exhaust blowing being a movable aero device) but Renault managed to win that case. A pity they did not return the favor to Brabham at the end of the season!!!
Diffuser blowing is specially good for traction out of slow corners but it has its downsides too. It increases balance sensitivity to throttle position which may create problems on high speed corners. Good and bad sides are quite depending on the driving style too: some drivers can take advantage of it more than others. The gas momentum available in the exhaust today is anyway much reduced compared to the turbo era (about 50%).