Understanding Cometic Head Gaskets and the 50–100 HP Potential

Cometic head gaskets are engineered for high-performance applications where standard OEM gaskets become a weak link. Manufactured from multi-layer steel (MLS) and often coated with a specialized sealing compound, Cometic gaskets provide superior clamping force, thermal stability, and resistance to blowout under high cylinder pressures. For forced induction, nitrous, or high-compression builds, the upgrade can unlock 50–100 horsepower simply by allowing you to run more boost or a tighter quench without risking gasket failure. However, a gasket alone won’t add power — it’s the supporting modifications (boost raise, timing advance, fuel tuning) that realize the gain. This guide walks you through a professional-grade installation that ensures the gasket performs as intended.

Tools, Materials, and Workspace Preparation

Essential Tools

  • Cometic MLS head gasket set (confirm part number for your block and head)
  • Precision torque wrench (ft-lb and in-lb ranges; calibrated within the last year)
  • Deep socket set (including hex/Allen for head bolts if needed)
  • Engine degreaser and lint-free shop towels
  • Plastic or brass gasket scraper (avoid steel on aluminum surfaces)
  • Straightedge (machinist’s quality) and feeler gauges – to check deck flatness
  • Thread chaser or tap & die set (for cleaning bolt holes)
  • Assembly lube (recommended for head bolt threads)
  • Permatex copper spray or Cometic’s recommended sealant (check instructions)
  • Rubber mallet (for gentle head alignment)

Preparation Steps

Work on a cool, clean engine. Disconnect the battery negative terminal. Drain coolant and engine oil (you’ll be changing oil after reassembly anyway). Remove the intake manifold, exhaust manifolds/headers, valve covers, timing components as needed, and any wiring or hoses blocking head access. Label connectors with painters tape. This is also the time to inspect the timing chain/belt and consider replacement if due.

Removing the Cylinder Head and Old Gasket

Bolt Loosening Sequence

Cylinder heads can warp if bolts are removed haphazardly. Always follow the reverse of the factory torque sequence (typically working from the outer bolts inward in a cross pattern). Use a breaker bar or ratchet; do not impact. Loosen each bolt one half-turn at a time until all are free. Remove bolts and set them aside in order if they are reuseable (some engines require new bolts).

Lifting the Head

With all bolts removed, gently pry the head loose using a plastic trim tool or head lifting tool. Never use a screwdriver between mating surfaces. Lift the head straight up and place it on a clean workbench. Immediately remove the old gasket (often a compressed multi-layer that may be stuck). Use a plastic scraper to remove any residue from both the block deck and head surface. Avoid scratching the aluminum – MLS gaskets require a smooth, clean surface.

Surface Preparation – The Key to a Perfect Seal

Cometic MLS gaskets are unforgiving of deck imperfections. Use a machinist straightedge to check the block deck and head surface for flatness. Maximum allowable deviation is typically 0.003″ across the length of the head and 0.0015″ over 6 inches. If warping exceeds spec, the head must be resurfaced (and the block decked if necessary). Clean all oil and debris from bolt holes with compressed air or a thread chaser – oil in the bolt holes can cause bottoming out and false torque readings. Finally, wipe both surfaces with brake cleaner on a lint-free towel. Do not apply any additional sealant unless Cometic specifically recommends it (their gaskets are often pre‑coated; check the product instructions).

Installing the Cometic Head Gasket

Gasket Orientation

Cometic gaskets are marked “THIS SIDE UP” or have a specific front/rear orientation. Some are symmetrical; others have alignment dowels. Place the gasket onto the block dowel pins. Do not use any sealant on the gasket itself unless the instructions say otherwise – many MLS gaskets rely on the coating factory‑applied. If you are using a bare MLS gasket, a light spray of copper sealant can help initial sealing, but follow the manufacturer’s recommendation.

Lowering the Head

Carefully lower the cylinder head onto the block, ensuring the gasket remains in position. Rotate the head slightly if needed to align over the dowels. Do not drag the head across the gasket. Once seated, install the head bolts hand‑tight in the proper sequence to hold the assembly.

Torquing the Head Bolts – Correct Sequences and Values

Torque specifications vary widely by engine platform. Never guess – consult your vehicle’s factory service manual or Cometic’s data sheet. Below is a typical MLS gasket torque procedure (verify for your engine):

Example Three‑Step Procedure (Common for Aftermarket MLS)

  1. Step 1: All bolts to 30–40 ft·lb in the factory tightening sequence.
  2. Step 2: All bolts to 60–70 ft·lb (or the mid‑value) repeating the same sequence.
  3. Step 3: Final angle‑tighten (e.g., 90 degrees) if specified. Many MLS gaskets call for torque‑to‑angle. Use a torque angle gauge or protractor.

If the bolts are reuseable (check manufacturer spec), apply a light coat of assembly lube to threads and under the bolt heads. Clean and dry threads get inconsistent torque. After final torque, wait 10 minutes and re‑check each bolt in order – you may see a slight drop as the gasket compresses.

Reassembly and Component Installation

Upper Engine Assembly

Reinstall the intake manifold with a new gasket set (don’t reuse old ones). Torque to spec in a cross pattern. Reattach exhaust manifolds with new gaskets – exhaust leaks will throw off AFR tuning. Reconnect all coolant hoses, vacuum lines, wiring harnesses, and throttle brackets. If you removed the timing chain or belt, verify timing marks.

Fluids and Initial Checks

  • Fill coolant with the proper mix (distilled water + antifreeze).
  • Add engine oil – you should have drained it before head removal. Use the recommended viscosity.
  • Reconnect the battery.
  • Prime the oil system: crank the engine with the fuel pump relay removed (or disable ignition) for 15–20 seconds until oil pressure registers on the gauge.

First Start, Break‑In, and Tuning

Initial Start Procedure

Start the engine and let it idle, monitoring coolant temp, oil pressure, and for any leaks. Rev to 2000–2500 RPM for about 30 seconds, then let it idle again. Check for coolant leaks at the head gasket seam. If you see bubbles in the radiator immediately shut down and re‑torque the head bolts (retorque is essential for many MLS gaskets after the first heat cycle).

Heat Cycling and Retorque

After the first warm‑up, let the engine cool completely. Retorque the head bolts following the same sequence and final torque values. Some Cometic gaskets may require a second retorque after 50–100 miles. Refer to the included instructions.

Tuning for the HP Gain

A new head gasket alone does not produce 50–100 HP. The gain comes from the ability to run higher cylinder pressure (more boost, higher compression, or advanced timing). You must retune your engine management system – fuel curves, ignition timing, and boost parameters – to take advantage. Consider a chassis dyno session to safely dial in the tune and verify the power increase. Without tuning, you may actually lose power or cause detonation.

Common Pitfalls and How to Avoid Them

  • Dirty bolt threads: Oil in the hole causes the bolt to bottom out, giving false torque. Chase threads and clean thoroughly.
  • Skipping the straightedge check: Even a 0.002″ warp will cause a leak with MLS gaskets. Machine the head if needed.
  • Improper gasket orientation: Flipping the gasket blocks coolant passages. Confirm markings.
  • Over‑torquing: Strips threads or deforms the head. Use a calibrated torque wrench.
  • Reusing old head bolts on torque‑to‑angle applications: Stretch bolts lose clamping force. Replace with new if required.
  • Failing to retorque after heat cycle: MLS gaskets compress further once hot. Retorque is mandatory.

Verifying the Power Gain: Dyno and Road Testing

After 500 miles of break‑in (varying load, no sustained full throttle), schedule a dyno session. A proper baseline (before gasket swap) vs. after‑tuning comparison will show the actual HP gain. Many tuners report 40–80 whp on turbocharged engines after raising boost 3–5 psi, and 50–100 hp on high‑compression naturally aspirated builds. Keep in mind that supporting mods (fuel system, intercooler, exhaust) must be adequate to handle the increased output.

Conclusion

Installing Cometic head gaskets is a precision job that rewards attention to detail. Proper surface prep, correct torque procedures, and a careful tune are the foundation of a reliable, high‑powered engine. Follow this guide, consult your service manual for exact specs, and you can confidently expect a measurable horsepower increase – often 50 to 100 HP – while maintaining a leak‑free seal under extreme conditions.

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