Minimum vacuum expected
Thread Starter
Burning Brakes
Joined: Jul 2018
Posts: 979
Likes: 258
From: Maryland
Minimum vacuum expected
Just curious: was there ever a guide as to what is the minimum amount of vacuum expected (for the system to properly work) at different points in the C3 vaccum wiper and headlight system?
Drifting
Joined: Aug 2009
Posts: 1,346
Likes: 160
From: new iberia la
My stroker has only 6-7 in hg vacuum at idle.. The headlights would open but only one at a time and take about 30 seconds .. BUT I HAD ZERO BRAKES... after installing an electric vacuum pump producing 18-20 in hg constant vacuum, to have power brakes, I then connected the Headlights to it.. They both pop right up.
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,809
From: Cool Northern Michigan
Even some of the hairiest cams should pull 6-8 inches of Vac. But there are just so many Vac lines going everywhere that you my not have that much vacuum left for the headlights or brakes. With that many Vac connections, there are bound to be some leakage.
As far as minimum for normal operation? IDK. Maybe 10".
If all else, may have to rev it up a bit to get the headlights to operate.
As far as minimum for normal operation? IDK. Maybe 10".
If all else, may have to rev it up a bit to get the headlights to operate.
Drifting
Joined: Aug 2009
Posts: 1,346
Likes: 160
From: new iberia la
Its Stainless Steel Brakes brand.. about $200 if I recall. It runs about 20 seconds when you first turn on key to charge , then shuts off . after you depress brakes 2-3 times it will come on again for 20 seconds .. I cannot hear it after I start the engine .Its about as loud as old style elect fuel pumps were. I ve had it 10 yrs , no issues at all and brakes work great. Simple install. I put it where the charcoal canister used to be under the booster.
Thread Starter
Burning Brakes
Joined: Jul 2018
Posts: 979
Likes: 258
From: Maryland
Reason I asked the minimum vacuum question is that I read 7-9 in Hg vac at idle, and come up to a max of about 20 in Hg vac when accelerating slowly. My wiper door and headlights have been staying open during idle, but close under a slow acceleration. I've changed all the vacuum lines, my wiper door actuator tests ok, and I don't see any vacuum leaks with the mity-vac. Is 7-9 in Hg vac sufficient to close the headlight and wiper doors?
Le Mans Master
Joined: Apr 2011
Posts: 6,284
Likes: 1,170
From: Hermosa
Reason I asked the minimum vacuum question is that I read 7-9 in Hg vac at idle, and come up to a max of about 20 in Hg vac when accelerating slowly. My wiper door and headlights have been staying open during idle, but close under a slow acceleration. I've changed all the vacuum lines, my wiper door actuator tests ok, and I don't see any vacuum leaks with the mity-vac. Is 7-9 in Hg vac sufficient to close the headlight and wiper doors?
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
2027 Corvette vs The World: Every Model vs Closest Competitor
Joe Kucinski
10 Most Common Corvette Problems of the Last 20 Years!
Joe Kucinski
5 MOST and 5 LEAST Popular Corvette Model Years in History!
Joe Kucinski
2027 Corvette Buyer's Guide: Everything You Need to Know!
Joe Kucinski
10 Things C8 Corvette Owners Hate (But Won't Tell You)
Joe Kucinski
10 Best Corvettes Coming to Barrett-Jackson Palm Beach 2026!
Brett Foote
Every Corvette Grand Sport Explained! (C2, C4, C6, C7, & C8)
Joe Kucinski
Grand Sport & Grand Sport X Launch Alongside All-New 535hp LS6 V8!
Michael S. Palmer
5 Reasons Bad Drivers Crash & 5 Ways to Avoid a Costly Mistake!
Joe Kucinski
Le Mans Master
Joined: Oct 2002
Posts: 7,098
Likes: 378
From: Las Vegas - Just stop perpetuating myths please.
Reason I asked the minimum vacuum question is that I read 7-9 in Hg vac at idle, and come up to a max of about 20 in Hg vac when accelerating slowly. My wiper door and headlights have been staying open during idle, but close under a slow acceleration. I've changed all the vacuum lines, my wiper door actuator tests ok, and I don't see any vacuum leaks with the mity-vac. Is 7-9 in Hg vac sufficient to close the headlight and wiper doors?
Min vacuum for good operation of accessories is 12" Hg from what I've read - though many say less than that works.
Hope this helps.
Thread Starter
Burning Brakes
Joined: Jul 2018
Posts: 979
Likes: 258
From: Maryland
That reads like you have the connection on a "ported" vacuum port on the carburetor. Idle vacuum should be at the highest at idle with the throttle blades closed and connected underneath the carburetor (not on a ported vac port).
Min vacuum for good operation of accessories is 12" Hg from what I've read - though many say less than that works.
Hope this helps.
Min vacuum for good operation of accessories is 12" Hg from what I've read - though many say less than that works.
Hope this helps.
did it.
For the vacuum advance, it looks like he used the ported vac. It has never idled that well, and I am thinking maybe to move it to a manifold vac source?
Le Mans Master
Joined: Oct 2002
Posts: 7,098
Likes: 378
From: Las Vegas - Just stop perpetuating myths please.
So with a good manifold vacuum source I expect the headlights should have enough vacuum. It reads like you have them connected to some other source or the vacuum lines are mixed up.
I think you understand now how they should operate and just need to sort the lines out.
I think you understand now how they should operate and just need to sort the lines out.