Deciding Which VOES to Use

Since most VOES are sold as 'fixed-trigger-point' switches, the only real decision is, figuring out which 'strength' unit to purchase. Luckily, only one variable influences the VOES: vacuum, so the decision is fairly straightforward.

The basic VOES units which are best suited to our engines come pre-set to the following pressures:

• 3" Hg*
• 4" Hg*
• 5" Hg*

Note: For those who love to tinker, there is also an adjustable unit that allows you change the 'trigger point'. It is nearly double the cost of the basic units, however.

Here's how to calculate which VOES you need. This information is based on input from engine experts and experienced tuners I consulted:

3" Hg*, Drag Specialty# 2101-0007. For engines with:

• Stock pistons
• High performance carburetor
• VOES vacuum attached to carb

4" Hg*, Drag Specialty# 2101-0009. For engines with:

• Stock bore (engine displacement)
• High compression pistons
• High performance carburetor
• VOES vacuum attached to carb

5" Hg*, Drag Specialty# 2101-0010. For engines with:

• Larger bore than stock (big-bore)
• High compression pistons
• High performance carburetor
• VOES vacuum attached to carb

Tip: Go up one size if attaching a VOES to the intake manifold instead of the carb.

*Note: Hg is the standard, chemical notation for mercury, which is commonly used in measuring pressure--like a blood-pressure meter or a barometer.