Holley & Motorcraft Carburetor Power Valve 8.5Hg

Power valves used to blow out anytime an engine back fired, but today's power valves are designed to last.

Under normal circumstances the power valve size in our carburetor kits are the correct size.

Under not so normal circumstances such as a built up engine, multiple carburetors the vacuum will be reduced and will require a power valve that opens up quicker.

IDENTIFYING CURRENT VALVE SIZE

How to read the HG on our power valves. Look at the face of the power valve (the shiny surface). Turn the valve so the number reads correctly and is on the right side. Example 8. Read the number at the bottom. Example 5. You have a power valve with 8.5HG.

The power valve stays closed until it reaches it's rated HG. In the example above the power valve won't open until the vacuum drops to 8.5HG.

TESTING VACUUM TO DETERMINE SIZE

Determine your power valve size by connecting a vacuum gauge to the manifold and read the HG under power (hold the break on and power up) and divide by 2 and round to the next .5 For example a reading of 15 HG would require a power valve size of 7.5 HG.