The 89 cars where faster than 88 cars 'cause Turbo in 1988 was under resticted power rules. 88 cars wheres slower than 87.
Also they reduced the Gas tank for turbo cars in 88 so they couldn't got with the boost on maximun all the time. That's why Prost letted Berger pass in Adelaide, 'cause he knew he was gonna be all power all the time and probably won't have enought fuel to end the race (Gherard had told that in the morning to Alain when they were having breakfas, it was the last turbo race so Gherard wanted to fell the power all the way to the last time). But he spun and didn't ended the race anyway.
I remeber something like in 86 that Renault had a bi-turbo engine just for qualify but just Ayrton Senna could run with it, they didn't trusted the car to Johnny Dumfries. I just remember this from that time, but I never read something on magazines about it. Will check my old newspapers and magazines to confirm it.
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Rocker