Holley Single-Stage Power Valve, Standard Flow 4.5 in. Hg including gasket

Holley Single-Stage Power Valve - Part #125-45

Ensure optimal fuel enrichment during acceleration with this genuine Holley 4.5 in. Hg power valve. This critical component operates vacuum-controlled enrichment in your carburetor's power circuit, opening at 4.5 inches of mercury to deliver additional fuel during heavy acceleration and full-throttle operation, preventing lean conditions and hesitation. Designed for moderate to aggressive performance engines with lower idle vacuum. Includes gasket for complete installation.

What's Included:

• 1x power valve (4.5 in. Hg rating)
• 1x gasket

Key Features:

• 4.5 in. Hg Rating: Opens at 4.5 inches of mercury vacuum for moderate-performance engine applications
• Single-Stage Design: Standard flow for performance applications
• Vacuum Operated: Automatically responds to engine load conditions
• Genuine Holley Quality: OEM-grade component for reliable performance
• Standard Flow: Balanced enrichment for performance engines
• Gasket Included: Complete installation kit for leak-free operation

Performance Benefits:

• Prevents lean conditions during acceleration and heavy load
• Eliminates hesitation and bogging under throttle
• Provides smooth, consistent power delivery
• Automatically enriches fuel mixture when engine vacuum drops
• Essential for proper carburetor performance on modified engines
• Prevents power valve from opening at idle on lower-vacuum engines

Understanding Power Valves:

• Function: Adds fuel to the main circuit when engine vacuum drops below the valve's rating
• Vacuum Rating: The point (in inches of mercury) at which the valve opens
• Selection Rule: Typically use a valve rated at half your idle vacuum reading
• Common Ratings: Range from 2.5 to 10.5 in. Hg for different applications
• 4.5 Rating: Ideal for engines with 9-10 in. Hg idle vacuum (moderate to aggressive cams)

Ideal Applications:

• Performance engines with moderate to aggressive camshafts
• Engines with 9-10 in. Hg idle vacuum (use half of idle vacuum)
• Street/strip combinations with performance camshafts
• Modified engines with lower idle vacuum than stock
• Replacing failed or damaged power valves
• Carburetor rebuilds on performance engines

When to Replace:

• During carburetor rebuild or overhaul
• If experiencing hesitation or stumbling during acceleration
• After engine backfire (can rupture power valve diaphragm)
• When changing camshafts or engine modifications affect idle vacuum
• If fuel leaks from the power valve area
• If current power valve rating is too high for lower-vacuum engine

Selection Tips:

• Measure idle vacuum with engine fully warmed and in gear (automatic) or neutral (manual)
• Divide idle vacuum reading by 2 to determine proper power valve rating
• Example: 9 in. Hg idle vacuum ÷ 2 = 4.5 in. Hg power valve
• Lower vacuum engines (moderate to big cams) need lower-rated valves (2.5-4.5 in. Hg)
• Using too high a rating on lower-vacuum engines causes rich idle and poor fuel economy

Technical Specifications:

• Part Number: 125-45
• Vacuum Rating: 4.5 inches of mercury (in. Hg)
• Type: Single-stage power valve
• Flow: Standard
• Includes: Gasket
• Application: Holley performance carburetors with power valve circuits
• Common Use: Engines with 9-10 in. Hg idle vacuum (moderate to aggressive cams)

Fast dispatch from our Perth warehouse. In-store pickup available for local customers.