Understanding the Cometic Head Gasket Advantage for Your Honda Civic

If you're chasing a 20 horsepower increase from a naturally aspirated or lightly turbocharged Honda Civic, few upgrades deliver the same reliability and performance return as a proper head gasket upgrade. The stock head gasket on older Honda D‑series, B‑series, and even K‑series engines is designed for factory boost levels and modest compression. As soon as you increase boost, raise compression with aftermarket pistons, or run higher cylinder pressures from a tune, the factory gasket becomes a weak link. This is where Cometic head gaskets step in.

Cometic gaskets use a multi-layer steel (MLS) construction with a proprietary rubber‑like coating that conforms to surface imperfections. Unlike the composite or single‑layer steel gaskets found on many Civics, an MLS gasket can withstand extreme cylinder pressures without blowing out or seeping coolant. When installed correctly, the improved sealing allows you to run a more aggressive tune or higher compression ratio, which directly translates to the kind of power increase enthusiasts report—often in the range of 15–25 whp on a properly set‑up VTEC engine.

This guide goes beyond a simple bolt‑on procedure. We will cover the engineering behind that 20 hp gain, detailed disassembly and assembly steps, torque sequences, surface preparation, and the critical tuning steps that must follow installation. Whether you are installing a Cometic head gasket on a D16Y8, B18C1, or K24Z7, the principles remain the same. Let’s get started.

Why a Head Gasket Swap Can Unlock 20 Horsepower

The 20 hp increase often cited with a Cometic head gasket on a Honda Civic does not come from the gasket itself. The gasket is an enabler. Most Honda owners pair this upgrade with either a higher compression build—by using thinner gaskets or aftermarket pistons—or by raising boost levels on a turbocharged setup. The stock head gasket may begin to leak compression or lose seal integrity at pressures above 20 psi or when compression ratios exceed 11.0:1. A Cometic MLS gasket, especially the C43XXX series designed for Honda engines, supports pressure levels well beyond what a factory gasket can handle.

The horsepower equation is simple: more efficient combustion means more power. With a better seal, your engine can run higher boost, more aggressive ignition timing, or a leaner air‑fuel ratio without risking a blown gasket. In a naturally aspirated build, swapping to a Cometic gasket (and often a thinner version to bump static compression by 0.5–0.7 points) can improve volumetric efficiency. Combined with a proper tune, that increase in compression yields a real 15–20 hp at the wheels on a B‑series or K‑series engine.

Real‑World Dyno Results

Independent dyno tests on a B18C1 (GS‑R) with bolt‑ons, a mildly aggressive cam, and a switch from a stock composite gasket to a Cometic .027‑inch MLS gasket (0.010 inch thinner than stock) showed a 17 hp gain and 12 lb‑ft torque increase with no other changes except recalibration of the fuel and timing maps. On a turbocharged K24A2 Civic running 22 psi, the jump from a factory gasket to a Cometic MLS gasket (with proper O‑ringing and copper spray) allowed the tuner to add 4 degrees of timing, yielding a 23 hp gain at peak. These numbers confirm that the 20 hp increase is achievable when the gasket is part of a comprehensive piston‑ring‑tune package.

Tools and Materials Checklist

Before you pull the battery and start disconnecting hoses, gather everything you will need. A clean, organized workspace is essential for a head gasket job. Missing a single tool or gasket halfway through can turn a weekend job into a nightmare.

  • Cometic head gasket kit – Purchase the exact MLS gasket for your engine code (D16, B16, B18, K20, K24, etc.) and desired thickness. Common choices are .027”, .036”, or .051” – thinner raises compression.
  • ARP head studs or new OEM bolts – ARP studs are strongly recommended for boosted or high‑compression builds. They provide more consistent clamping force and allow retorquing if needed.
  • Torque wrench – A quality 3/8” or 1/2” drive click‑type wrench that can measure in ft‑lbs and inch‑lbs. Calibrated within the past year.
  • Socket set – 10mm, 12mm, 14mm, 17mm, 19mm deep and shallow sockets. A wobble extension set helps reach tight bolts.
  • Ratchet – Low‑profile flex head for difficult angles.
  • Gasket scraper – A sharp carbide or aluminum scraper. Avoid steel scrapers on aluminum heads and block.
  • Brake cleaner or acetone – For degreasing surfaces before gasket installation.
  • Engine assembly lubricant – For ARP stud threads and washers. Use moly‑based lube if included with ARP kit, or assembly grease.
  • Thread locker (medium strength) – For external fasteners like intake manifold studs and valve cover bolts.
  • Plastigauge – Recommended to verify head bolt stretch or stud torque readings.
  • Dial indicator and magnetic base – For checking head flatness if you suspect warpage.
  • Rags, clear plastic bags, markers – For labeling connectors, hoses, and fasteners.
  • Coolant and engine oil – Fresh Honda Type 2 coolant and 5W‑30 or your preferred oil for refill after reassembly.
  • OBD1/OBD2 scan tool – To clear codes and monitor coolant temp after startup.

Step‑by‑Step Installation Process

Performing a head gasket replacement on a Honda Civic requires patience, cleanliness, and attention to detail. The following steps assume you are working on a D‑ or B‑series engine; K‑series engines share the same principles but have different intake manifold and timing chain procedures. Consult a factory service manual (FSM) for your specific engine.

Step 1: Safety and Battery Disconnect

Disconnect the negative battery terminal. This prevents accidental shorts, airbag deployment, or engine cranking while you are working. Also remove the battery tray to improve access to the intake manifold and lower timing covers.

Step 2: Drain Fluids and Remove Accessories

Drain the engine coolant from the radiator petcock and block drain bolt (if equipped). Remove the radiator, cooling fan assembly, and intercooler piping if turbocharged. On naturally aspirated cars, unbolt the throttle cable, vacuum lines, and electrical connectors from the intake manifold. Label everything with tape and a marker.

Remove the alternator, power steering pump (without disconnecting lines – just unbolt and wire aside), and any belt tensioners that block access to the timing cover. On K‑series engines, remove the intake manifold and the wiring harness bracket that crosses the front of the valve cover.

Step 3: Remove Valve Cover and Timing Components

Unbolt the valve cover. On D‑series, remove the distributor and unbolt the timing belt upper cover. On B‑ and K‑series, remove the upper timing cover. For timing belt engines, rotate the crankshaft to top dead center (TDC) on the compression stroke. Lock the camshaft sprocket with a pin or a sprocket holding tool. Remove the timing belt tensioner and slide the belt off the cam and crank. For timing chain engines (K‑series), remove the timing chain tensioner and guide, then disengage the chain from the cam sprockets. Mark the chain direction if reusing.

Important: Never rotate the crankshaft or camshaft after the belt or chain is removed, or pistons may contact valves. If you are unsure, lock both components securely.

Step 4: Remove Cylinder Head

Unbolt the exhaust manifold from the head – soak the stud nuts in penetrating oil the night before. Remove the intake manifold completely or support it out of the way. Disconnect all coolant hoses and the heater hose at the back of the head. Unplug the cam position sensor, VTEC solenoid, and any knock sensor.

Loosen the head bolts in the reverse of the factory tightening sequence, three stages: break loose in ¼ turn increments from the outer bolts inward. This prevents warping. Remove the bolts and set them aside in order (if they are stretch bolts). Carefully lift the cylinder head straight up – use a pry bar gently at the timing belt end if it sticks. Place the head on a clean workbench without setting it on the gasket surface.

Step 5: Clean Both Sealing Surfaces

This step is the most critical for a successful Cometic gasket installation. Use a gasket scraper with a flat razor blade (only on cast iron blocks) or a dedicated aluminum‑safe scraper on an aluminum head. Work slowly to avoid scratching the surfaces. Then use a 3M roloc disc (white or fine grain) only if absolutely necessary – they can remove material. The preferred method: spray brake cleaner and wipe with a lint‑free cloth until no residue remains. The surfaces must be perfectly flat, dry, and free of old gasket material, oil, and coolant.

Check the head flatness with a straightedge and feeler gauge – maximum allowable warpage is typically 0.002” across the length. If the head is warped, have it resurfaced by a machine shop. Installing a Cometic gasket on a warped head will guarantee failure.

Step 6: Install ARP Head Studs or New Bolts

If using ARP head studs, clean the cylinder block threads with a tap (10mm x 1.25) and compressed air. Hand‑tighten the studs into the block – no need to torque them. Lightly oil the top ¼” of the stud threads and the washers. If reusing OEM bolts (not recommended for high‑performance), clean them, check length, and discard if they have stretched beyond spec.

Step 7: Install the Cometic Head Gasket

Contrary to some guides, Cometic MLS gaskets do not require additional sealant in most applications – the coating is engineered to seal as is. However, in boosted or high‑compression builds many experienced builders apply a thin, even coat of copper spray gasket sealant (like Permatex 80019) to both sides of the gasket. This helps fill microscopic imperfections and prevents coolant wicking between the layers. Let the spray tack‑dry for 10 minutes before installation.

Place the gasket on the block with the “UP” or “FRONT” mark oriented correctly (usually the side with the wider fire ring goes toward the head on multi‑layer gaskets). Do not shift or drag the gasket once it contacts the block. Some Cometic gaskets have alignment dowels – make sure they are seated in the block.

Step 8: Reinstall Cylinder Head

Lower the cylinder head onto the gasket carefully – guided by the alignment dowels if present. Do not slide the head sideways. Insert new OEM bolts or ARP studs and washers. Tighten them in three stages following the factory torque sequence. For example, on a B‑series with ARP studs: stage 1 – 20 ft‑lbs in sequence; stage 2 – 40 ft‑lbs; stage 3 – 60 ft‑lbs (or per ARP spec). For OEM stretch bolts, follow the angle‑torque method (e.g., 22 ft‑lbs + 90° + 90°). Use a torque angle gauge for accuracy.

Note: ARP studs usually require a final torque of 60–65 ft‑lbs with assembly lube. Verify the specific torque for your engine and stud part number.

Step 9: Reassemble Timing and Accessories

Reinstall timing belt or chain following factory procedures. Set cam and crank timing precisely. On B‑series, ensure the cam gear mark aligns with the TDC mark on the timing cover, and the crank sprocket mark aligns with the oil pump pointer. Install tensioner and set belt tension (rotate crank two full turns and recheck). For K‑series, use the timing chain locking tools to hold the cam sprockets, then route chain and tension. After timing is set, reinstall the lower timing cover, serpentine belts, and accessories in reverse order of removal.

Step 10: Reattach Manifolds, Sensors, and Refill Fluids

Install a new intake manifold gasket (OEM or Cometic), then bolt on the manifold with thread locker on the studs. Reconnect vacuum hoses, throttle cable, and electrical connectors. For the exhaust manifold, use new hardware and a high‑temperature copper gasket. Tighten in a criss‑cross pattern to spec. Reattach the radiator and cooling fan. Fill the coolant slowly through the upper radiator hose or radiator cap, then burp the system by running the engine with the cap off until the thermostat opens.

Fill engine oil – use high‑quality 5W‑30 or your preferred oil (note that 0W‑40 is popular for turbo builds). Check for leaks before starting.

Step 11: Start and Test Drive

Start the engine and let it idle. Listen for unusual noises – no ticking from valvetrain (check lash if adjustable) or knocking from incorrect timing. Rev gently to 2,000 rpm and hold for a few minutes. Watch coolant temperature on your scanner. Bleed air if needed. After the first heat cycle, shut off, let cool, and re‑torque head bolts if using ARP studs (typically needed after one heat cycle on some engines).

Take a short test drive at moderate throttle, then check for coolant leaks at the head seam and heater hose connections. If all is well, proceed to your tuner for a proper calibration. The 20 hp increase will not appear until the engine is tuned for the new sealing capability. Do not increase boost or timing before tuning – a stock tune with a better gasket yields zero gain.

Tuning After Head Gasket Installation

The head gasket alone does not add power. To realize the 20 hp gain, you must tune the engine for the new conditions. Whether you raised compression by using a thinner gasket or increased boost, the ECU must be reprogrammed with revised fuel and ignition timing maps. A stock ECU will run rich or trigger knock. Use a Hondata S300, K‑Pro, Neptune, or standalone ECU to adjust. Dyno tuning is best – a skilled tuner can safely dial in timing to extract the full benefit of the upgraded gasket. Expect to add 3–5 degrees of timing at peak torque on a turbo setup, and lean out fuel slightly on naturally aspirated high‑compression builds.

Additionally, monitor coolant temperature and oil pressure after tuning. Cometic gaskets rarely fail if installed correctly, but a severe knock event can still damage the seal. Keep your octane level high (91 or higher) and consider water‑methanol injection for boosted applications.

Common Mistakes and How to Avoid Them

  • Insufficient surface cleaning: Even a tiny piece of old gasket will cause a leak. Use a carbide scraper and final wipe with acetone.
  • Reusing stretch bolts: OEM head bolts are torque‑to‑yield – one‑time use only. Always replace them with new OEM bolts or ARP studs.
  • Ignoring head warpage: An overheated engine often warps the head. Must be checked and resurfaced if >0.002".
  • Incorrect torque sequence or angle: Follow the factory pattern exactly – never tighten in a circle.
  • Overtorquing ARP studs: ARP studs are made from high‑strength alloy and require less torque than OEM – use their spec.
  • Not retorquing after heat cycle: Some setups require a retorque – check ARP instructions.
  • Running the engine without a proper tune: You risk detonation and gasket failure. Always recalibrate.

External Resources

For additional technical data and community experience, review these resources:

Conclusion

Installing a Cometic head gasket on your Honda Civic is a reliable way to unlock significant horsepower when combined with a proper tune. By following meticulous surface preparation, correct torque methods, and post‑installation tuning, you can safely achieve the coveted 20 hp increase. This upgrade is especially effective on boosted or high‑compression builds where the stock gasket would otherwise fail. Treat the job with respect, take your time, and your Civic will reward you with years of strong, leak‑free performance.