oldbmwfan
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Yep, especially turbo cars which had positive manifold pressure a lot of the time. My '86 Saab 900 turbo had a vacuum canister behind one fender.I'll whip the horse one more time.
Shut your engine off. Push the brake pedal a few times. Does it get hard? Now start your car, Does the pedal go back to normal?
Long straight at WOT and OP is using brakes a few times, at WOT there is virtually 0 engine vacuum, so it is like the engine is off. When at the end of the straight there is not enough vacuum to operate the brake booster, = hard pedal. When he lets off the throttle for 1 or 2 seconds before the end of the straight the engine vacuum replenishes the booster and the brakes work as normal.
Walk around the pits and I guarantee every large cam V8, non VVT with power brakes has a vacuum can, or a vacuum pump.
In the 70's and early 80's lots of factory cars came with vacuum cans due to all the vacuum operated accessories.
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