Holden HQ HJ HX HZ WB 283-400 Small Block Chev Pacemaker Competition Headers PH5325

Pacemaker PH5325 Competition headers (extractors) are designed for Holden HQ, HJ, HX, HZ and WB applications fitted with Small Block Chevrolet V8 engines.

Pacemaker lists PH5325 for 283, 302, 305, 307, 327, 350 and 400 Small Block Chevrolet V8 engines. The tuned 4-into-1 Competition design uses 44mm (1¾") primary pipes and large 76mm (3") outlets, providing increased exhaust-flow capacity for performance Small Block Chev combinations.

PH5325 is the larger-primary Competition option in this Pacemaker HQ-WB Small Block Chev range, combining 1¾" primaries with a 3" collector outlet.

IMPORTANT – PH5325 will fit slant-plug cylinder heads but will NOT fit raised-port cylinder heads.

Will NOT fit factory air conditioning, Powerglide automatic or column-shift automatic applications.

Correct engine mounting spacers are required. RH spacer is 1¾" high and LH spacer is 1¼" high.

Please check availability and current lead time before ordering.

Key Features

• Competition performance header
• Tuned 4-into-1 design
• 44mm (1¾") primary pipes
• 76mm (3") outlets
• Suits 283-400 Small Block Chevrolet V8 engines
• Will fit slant-plug cylinder heads
• Power steering compatible
• Manual and selected automatic transmission compatible
• Designed for Holden HQ-WB Small Block Chev applications

Construction

Pacemaker PH5325 uses a tuned 4-into-1 Competition configuration with 44mm (1¾") primary pipes feeding into large 76mm (3") outlets.

The standard Pacemaker finish uses the distinctive Pacemaker Blue heat-resistant coating, designed to withstand temperatures up to approximately 800°C.

Additional Options

Ceramic Coating: PHC30 ceramic coating may be available for improved heat management and corrosion resistance. Please contact Best Mufflers for current availability.

DSF9: Replacement cylinder-head exhaust gaskets are available separately.

PEMP350: Pacemaker engine mounting spacers are available where the original correct engine spacers are not fitted.

Vehicle Fitment

• Holden HQ: Small Block Chevrolet V8
• Holden HJ: Small Block Chevrolet V8
• Holden HX: Small Block Chevrolet V8
• Holden HZ: Small Block Chevrolet V8
• Holden WB: Small Block Chevrolet V8 application
• Engine: 283 / 302 / 305 / 307 / 327 / 350 / 400 Small Block Chevrolet V8
• Transmission: Manual / selected automatic applications
• Power Steering: Yes
• Air Conditioning: No

Pacemaker lists PH5325 as an HQ-WB 1971-1985 application. Engine availability varied between models and years, so the engine list represents PH5325 header compatibility rather than factory engine availability in every HQ-WB model.

Header Specifications

• Part Number: PH5325 L/R
• Brand: Pacemaker
• Design: Tuned 4-into-1 Competition
• Primary Pipe: 44mm (1¾")
• Secondary Pipe: N/A
• Outlet: 76mm (3")
• Power Steering: Yes
• Air Conditioning: No
• Oxygen Sensor: N/A
• EGR: N/A
• Replacement Gasket: DSF9
• Approximate Fitting Time: 2 hours

Fitment Notes

Slant-Plug Heads: PH5325 will fit slant-plug cylinder heads.

Raised-Port Heads: PH5325 will not fit raised-port cylinder heads.

Air Conditioning: PH5325 will not fit with factory air conditioning.

Column Automatic: PH5325 will not fit column-shift automatic applications.

Turbo 400: Pacemaker confirms PH5325 will fit Turbo 400 automatic.

Turbo 350: Current Australian application information also lists PH5325 as compatible with TH350 automatic.

Powerglide: PH5325 will not fit Powerglide automatic.

Engine Mounting Spacers: PH5325 will only fit with the original engine mounting spacers or Pacemaker PEMP350 spacers. The spacers must be installed on the correct side:

• RH spacer: 1¾" high
• LH spacer: 1¼" high

Protect painted surfaces during trial fitting and check steering, starter motor, transmission, engine mounts and exhaust clearances before final tightening.

What's Included

• Pacemaker PH5325 left-side header assembly
• Pacemaker PH5325 right-side header assembly

Header bolts, reducing cones, gaskets and other installation hardware should not be assumed to be included unless specifically confirmed with the current kit before ordering.

Recommended With

• DSF9 exhaust manifold/header gaskets
• Pacemaker PEMP350 engine mounting spacers where required
• Suitable 3" intermediate pipes, joiners or exhaust adaptors

PH5325 vs PH5320

PH5325: Tuned 4-into-1 Competition design with 44mm (1¾") primary pipes and 76mm (3") outlets. Will fit slant-plug heads, but does not suit factory air conditioning, Powerglide or column automatic.

PH5320: Tri-Y design with 44mm (1¾") primary pipes, 51mm (2") secondary pipes and 57mm (2¼") outlets. Suits factory air conditioning and Powerglide, but does not suit slant-plug heads.

Both headers use the same 44mm primary pipe diameter, but their collector design, outlet size and fitment requirements are different.

Why Good Headers & Exhaust Systems Matter

At 4,000 rpm, a 350ci (5.7L) Small Block Chevrolet V8 theoretically draws approximately 11,400 litres of intake air per minute at 100% volumetric efficiency and expels around 34,200 litres of hot exhaust gas per minute at approximately 600°C.

Actual airflow varies with engine capacity, RPM, volumetric efficiency, camshaft, cylinder heads, induction system and engine specification.

A well-designed header and exhaust system helps manage this high gas flow efficiently, reducing restriction and improving exhaust scavenging, torque, throttle response and engine performance.

Installation Tips

Before ordering, identify the cylinder-head configuration and confirm that the vehicle does not require compatibility with raised-port heads, factory air conditioning, Powerglide or a column-shift automatic.

Check that the correct engine mounting spacers are fitted. Pacemaker specifies a 1¾" RH spacer and 1¼" LH spacer, or the corresponding Pacemaker PEMP350 spacer kit.

Because PH5325 uses a large 3" outlet, confirm the downstream exhaust configuration before installation.

Professional installation is recommended.

Warranty & Compliance

Pacemaker headers are covered against manufacturing defects subject to Pacemaker's current warranty terms and conditions.

Installation must comply with applicable Australian state or territory requirements relating to exhaust noise, emissions and vehicle modifications.

FAQ

What vehicles do PH5325 headers suit?
Pacemaker lists PH5325 for Holden HQ-WB Small Block Chevrolet V8 applications, covering the 1971-1985 platform.

What engines do PH5325 headers suit?
Pacemaker lists 283, 302, 305, 307, 327, 350 and 400 Small Block Chevrolet V8 engines.

Are PH5325 headers Tri-Y?
No. PH5325 is a tuned 4-into-1 Competition header.

What size are PH5325 headers?
They use 44mm (1¾") primary pipes and 76mm (3") outlets.

Will PH5325 fit slant-plug heads?
Yes. Pacemaker specifically lists PH5325 as compatible with slant-plug cylinder heads.

Will PH5325 fit raised-port heads?
No. Pacemaker states PH5325 will not fit raised-port cylinder heads.

Will PH5325 fit with air conditioning?
No. Pacemaker lists PH5325 as not compatible with air conditioning.

Will PH5325 fit with power steering?
Yes. Pacemaker lists PH5325 as power-steering compatible.

Will PH5325 fit a Turbo 400 automatic?
Yes. Pacemaker specifically confirms Turbo 400 compatibility.

Will PH5325 fit a Turbo 350 automatic?
Current Australian application information lists PH5325 as compatible with the TH350 automatic.

Will PH5325 fit a Powerglide?
No. Pacemaker specifically states PH5325 will not fit Powerglide automatic.

Will PH5325 fit a column automatic?
No. Pacemaker's current specification states PH5325 will not fit a column automatic.

What engine mounting spacers are required?
PH5325 requires the original correct engine mounting spacers or Pacemaker PEMP350 spacers. Pacemaker specifies RH 1¾" high and LH 1¼" high.

What gasket suits PH5325?
Pacemaker specifies DSF9.

Can I pick up from the store?
Yes. Pick up is available but must be pre-arranged before collection.

How much is freight?
Freight varies depending on your delivery location and where stock is available. Please contact us for freight charges before ordering. Where possible, we can arrange dispatch from the nearest available product location to help reduce freight costs and delivery times.

Do you ship to the USA?
Yes. Best Mufflers regularly ships exhaust systems and exhaust parts to customers throughout the United States.

Please note that import duties, tariffs, taxes, and customs clearance fees are not included in the product or shipping price. Once your order is processed and the applicable charges are calculated, we will send you a secure payment link to finalise the import duties and tariff charges before dispatch.

Customer Support

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