So true! My "355" with it's lopey cam pulls 9 inches of vacuum and the lights work without any extra vacuum tank.
How much vacuum needed for headlights
Thread Starter
Race Director
Joined: Jan 2002
Posts: 11,615
Likes: 350
From: No Where USA
How much vacuum needed for headlights
I just started my 383 and the headlights don't work properly. Everything is new and has been tested. And installed as per the chart. I have about 5-6 inches of vacuum, is that enough to get them working or do I need a vacuum can.
Safety Car
Joined: Oct 2007
Posts: 3,729
Likes: 267
From: Austin Texas
Corvette of the Year Winner 2017
2016 C3 of Year Finalist
No, you need about 9-10" vacuum, for them function in a timely manner.
12-16 is a good engine vacuum with no big cam,
yank that big loppy cam out of there !
check your base vacuum of the engine, with nothing connected to the eng vacuum.
if it is higher with everything dissconnected, you have leaks.
you should also have a vacuum can/tank, to store up vacuum energy.
espicially if you have a big cam = low vacuum.
12-16 is a good engine vacuum with no big cam,
yank that big loppy cam out of there !
check your base vacuum of the engine, with nothing connected to the eng vacuum.
if it is higher with everything dissconnected, you have leaks.
you should also have a vacuum can/tank, to store up vacuum energy.
espicially if you have a big cam = low vacuum.
Last edited by 69Vett; May 12, 2014 at 01:41 PM.
Drifting
Joined: May 2008
Posts: 1,647
Likes: 5
From: Roseville CA
Vacuum is not constant when driving. Try opening them while decelerating (I.E. Engine Braking), they'll pop up fast! As others have said, storing that high vacuum is the purpose of the vacuum can and more importantly the check valve.
Drifting
Joined: May 2005
Posts: 1,968
Likes: 44
From: East TN
I have 6" of vacuum with the cam I have and my headlights need help raising. All new, tested good parts, no leaks, including new vacuum can. If I move my electric vacuum pump from the brakes to the headlights, they work great. Just not enough vacuum from the engine. I have one of the last "Killer Lights" kits before McSpeed stopped making them which I will install when I get the chance and sell off my vacuum parts.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski