Vacuum issues...anyone? D/C pumps?
Thread Starter
Racer
Joined: Oct 2005
Posts: 469
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From: West Slope of the Sierras California
Vacuum issues...anyone? D/C pumps?
Ever since I've owned this car I've had some issues with vacuum, be it the headlights, or heat/a/c controls.
There is a 383 stroker in it with a 486 lift cam and I'm aware that bigger cams take away vacuum, but...down to 9"???
I've checked for leaks and none, it holds at 9". I also know that you SHOULD have a min. 15-18" for proper operation of the power brakes but they have seemed to work fine for me. The heat controls another story. They don't work for squat! Headlights are a bit slow but worked..until now and it's just the actuator seals need replacing...again! Guess my main question is...has anyone gone with vacuum pumps to get around the low manifold vacuum issue? Thanks ahead for any assistance.
Randy
There is a 383 stroker in it with a 486 lift cam and I'm aware that bigger cams take away vacuum, but...down to 9"???
I've checked for leaks and none, it holds at 9". I also know that you SHOULD have a min. 15-18" for proper operation of the power brakes but they have seemed to work fine for me. The heat controls another story. They don't work for squat! Headlights are a bit slow but worked..until now and it's just the actuator seals need replacing...again! Guess my main question is...has anyone gone with vacuum pumps to get around the low manifold vacuum issue? Thanks ahead for any assistance.
Randy
Race Director
Joined: Dec 1999
Posts: 19,610
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From: Forked River NJ
I have run my headlights for years with 9" of vacuum with no trouble. I would not try to run vacuum brakes with it though. It sounds like you have other problems with your vacuum system. A .486 lift cam usually does not have much duration it sounds like there are other issues with the motor. I run a 252/260 @ .050 duration cam and idle at 8.5 inches of vacuum. If your cam is around the 230s @ .050 you should be pulling 12 to 14 inches at idle.
Drifting
Joined: Dec 1999
Posts: 1,462
Likes: 1
From: Reno nevada
I have a 238/248 Crane solid lifter cam. I increased the idle vacuum by recurving the distributer advance to allow about 18 deg. at idle and still only have 38 total with VA plugged.
Dialing in the idle mixture screws to also get max vacuum.
My head lights are a little slow. Brakes are great. But the problem is all those little tiny control lines under the dash and console crack and break over the years. I don't think my defrost vents work anymore
Dialing in the idle mixture screws to also get max vacuum.
My head lights are a little slow. Brakes are great. But the problem is all those little tiny control lines under the dash and console crack and break over the years. I don't think my defrost vents work anymore
Race Director
Joined: Dec 2007
Posts: 14,345
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From: Hartselle AL
St. Jude Donor '09
Interesting thread.
Here's a question for the experts....
How difficult and/or practical would it be to segregate the different "sections" of the vacuum system with check valves and a redesigned vacuum line system? Specifically, as long as your engine is producing decent vacuum, have a vacuum "manifold" with check valves that would keep good vacuum to the various sub-systems (brakes, headlights, climate control) regardless if a different sub-system has problems.
Am not the expert but as far as I recall, only the line to the brakes has a check valve.
Am I missing something here or experiencing late in the day fuzzy thinking?
Here's a question for the experts....
How difficult and/or practical would it be to segregate the different "sections" of the vacuum system with check valves and a redesigned vacuum line system? Specifically, as long as your engine is producing decent vacuum, have a vacuum "manifold" with check valves that would keep good vacuum to the various sub-systems (brakes, headlights, climate control) regardless if a different sub-system has problems.
Am not the expert but as far as I recall, only the line to the brakes has a check valve.
Am I missing something here or experiencing late in the day fuzzy thinking?
Thread Starter
Racer
Joined: Oct 2005
Posts: 469
Likes: 0
From: West Slope of the Sierras California
Thanks to all for some interesting info. I did have the car dynoed some time back and would have figured they would have kept the vacuum in mind while tuning, but who knows?! Idle mixture? There is another issue, just turned up, in cold starting, it's not wanting to 'idle up' on the auto choke. Maybe time to go back to the dyno shop? BTW...carb is a Holley SA 670.
