do you get a vacuum with boost?
Thread Starter
Instructor
Joined: Jan 2007
Posts: 131
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From: Silver Spring MD
do you get a vacuum with boost?
When you blow or boost a car, do the vacuum lines still have vacuum? is it necessary to get an electric vacuum, to retain stock vac. components? which is a better system for handling a boosted car, MAF or MAP?
Safety Car
Joined: Apr 2001
Posts: 3,525
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From: Houston TX
Boosted cars still have vacuum when at idle and under part throttle. Basically, vacuum is anywhere from idle to WOT (0 - <14.7 psia) before the vacuum disapates. Then there is a period at WOT where there is no vacuum and no boost (14.7 psia). This is followed by boost (>14.7 psia).
The requirement for a suplemental vacuum pump will depend on cam and other engine components, but I would highly doubt that one would be required for the builds on these boards. I run a large solid roller and the car still pulls ~14"Hg at idle and cruising will pull in excess of 18" Hg. This is sufficient for power brakes, etc.
MAF or MAP? Depends on whether it is a stock or aftermarket ECM. Stock ECM and fairly mild build, I find that MAF is the better route. Highly modified combo, and an aftermarket ECM, certainly MAP is the route to take.
Aaron
The requirement for a suplemental vacuum pump will depend on cam and other engine components, but I would highly doubt that one would be required for the builds on these boards. I run a large solid roller and the car still pulls ~14"Hg at idle and cruising will pull in excess of 18" Hg. This is sufficient for power brakes, etc.
MAF or MAP? Depends on whether it is a stock or aftermarket ECM. Stock ECM and fairly mild build, I find that MAF is the better route. Highly modified combo, and an aftermarket ECM, certainly MAP is the route to take.
Aaron
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Supporting Vendor
Joined: Oct 2004
Posts: 761
Likes: 68
Hey Guys,
Aaron's explanation of the transistion from vacuum to boost is perfect. Let me add that the vehicle's HVAC controls are fed from a vacuum cannister. The vacuum cannister connection to the intake manifold is thru a checkvalve. The idea is that at WOT (with or without a blower or turbo) the HVAC vacuum actuated 'doors' continue to operate. Without the checkvalve the 'doors' would return to their resting position while accelerating. So with or without a blower it's a good idea to verify the operation of the checkvalve and vacuum cannister. 20 year rubber tubing may need replacing and make sure no one has removed or by-passed the GM checkvalve.
The brake booster also has a checkvalve which should be checked and sometimes I add an in-line heavy duty checkvalve to protect the booster with high boost applications. Remember while braking your foot is typically off the throttle anyway providing maximum vacuum. So even with a big cam there is plenty of vacuum while the engine is deaccelerating.
Best regards, Greg
Aaron's explanation of the transistion from vacuum to boost is perfect. Let me add that the vehicle's HVAC controls are fed from a vacuum cannister. The vacuum cannister connection to the intake manifold is thru a checkvalve. The idea is that at WOT (with or without a blower or turbo) the HVAC vacuum actuated 'doors' continue to operate. Without the checkvalve the 'doors' would return to their resting position while accelerating. So with or without a blower it's a good idea to verify the operation of the checkvalve and vacuum cannister. 20 year rubber tubing may need replacing and make sure no one has removed or by-passed the GM checkvalve.
The brake booster also has a checkvalve which should be checked and sometimes I add an in-line heavy duty checkvalve to protect the booster with high boost applications. Remember while braking your foot is typically off the throttle anyway providing maximum vacuum. So even with a big cam there is plenty of vacuum while the engine is deaccelerating.
Best regards, Greg
