Brake venturi in supercharged engine
06-05-2017, 11:58 AM
#31
Just to make it clear, even with no vacuum to the booster at all you will still have full braking ability... It will just require more pedal force for the same braking effect. So for those saying you will not be able to stop if you lose vacuum to the booster, that is simply false in every respect.
99% of all cars out there, including plenty of race and performance cars just run straight manifold vacuum to the brake booster with perfectly acceptable booster performance in all situations.
and to j.kenzie, I have full power from the booster immediately on starting the car, as should you if you run manifold vacuum to the booster. My car for whatever reason has never had the high idle function work when starting a cold engine however, I always get about 800rpms when I first start it, no matter the temperature.
99% of all cars out there, including plenty of race and performance cars just run straight manifold vacuum to the brake booster with perfectly acceptable booster performance in all situations.
and to j.kenzie, I have full power from the booster immediately on starting the car, as should you if you run manifold vacuum to the booster. My car for whatever reason has never had the high idle function work when starting a cold engine however, I always get about 800rpms when I first start it, no matter the temperature.
06-05-2017, 12:37 PM
#32
Administrator - "Tyson"
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I disagree with your statement that if you loose booster vacuum, let's say at 65-80 MPhil freeway speeds , if traffic were to come to a sudden stop you would also stop after you hit the car in front you, booster fails your brakes are like wood, and I'm speaking from experience. Yeah you still have braking ability of a model That. Until it has failed on you don't talk like you know everything, that kind of info is dangerous,NO VACUUM BOOST ON A CAR THAT IS SUPPOSE TO HAVE IT, AS PER YOUR BOOSTER FAILING OR LOOSING VACUUM , BRAKES DON'T STOP IN HALF THE DISTANCE AND FURTHER NOTE ADVERSE PRESSURE ON THE MASTER CAN CAUSE THE SEAL TO BE ROLLED AND THE MUSHY PEDAL, TURNING WRENCHES FOR OVER 25YRS.
If the booster is bad when you start off, it's not a big deal. And yes I'm speaking from experience. My 80 had a leaking booster when I bought it, no power brakes. My wife and i drove it without power brakes for the remainder of the summer / fall since I didn't feel like doing a full brake overhaul until winter.
"Adverse pressure on the master" - this is a false statement. The amount of pressure on the master doesn't change with or without the booster working. All the booster does is lower the effort on your foot pushing on the pedal.
06-05-2017, 12:55 PM
#33
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I think that the original statement from kombatrok needs more emphasis on "It will just require more pedal force for the same braking effect." Such pedal force is not available in my car.
True, but not the salient point here. That same 99% of cars out there do not anticipate extended full-load operation with inlet manifold pressure at or above atmospheric pressure. Most cars depend on the "reserve" of vacuum in the booster can, and the sudden low manifold pressure that happens when you unload the engine to maintain that vacuum in the booster. Some empirical evidence from Dave shows that there's more assist available with the Venturi eductor in place even in normal street driving. In a separate thread, mrspencer shares that static readings at idle show lower pressure ("more vacuum") at the booster end of the hose than at the source port on the intake manifold alone.
In my limited experience, I find that there aren't a lot of extra parts like this thrown on to the engine without a reason. We've identified the benefit of the improved braking performance, and maintaining availability of cruise and HVAC functions at extended full-load operation. Either alone is worthy of maintaining the system as designed, especially when integrated with a supercharged or turbocharged engine. I believe that was the original question.
99% of all cars out there, including plenty of race and performance cars just run straight manifold vacuum to the brake booster with perfectly acceptable booster performance in all situations.
In my limited experience, I find that there aren't a lot of extra parts like this thrown on to the engine without a reason. We've identified the benefit of the improved braking performance, and maintaining availability of cruise and HVAC functions at extended full-load operation. Either alone is worthy of maintaining the system as designed, especially when integrated with a supercharged or turbocharged engine. I believe that was the original question.
06-05-2017, 01:10 PM
#34
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Remember guys, in this thread I was talking about hooking the brake booster directly to the manifold, and eliminating the venturi mechanism. I ended up going back to the venturi because of some of the concerns raised here. I was never going to go without vacuum to the brakes except the potential scenario of prolonged WOT and sudden braking before vacuum builds up again.
Thanks ,
Dave
Thanks ,
Dave