Building a Mitsubishi 4G63 engine for over 600 horsepower demands more than just a big turbo and aggressive fuel maps. One of the most critical weak points on any high-boost 4G63 is the factory head bolt setup. The stock bolts simply aren't designed to withstand the extreme cylinder pressure generated by 30+ psi of boost. Replacing them with ARP head studs is a non-negotiable upgrade for anyone serious about reliable power. This guide walks you through the complete installation process, from tool selection and block preparation to final torque and reassembly. Whether you're rebuilding a 6-bolt 4G63 or working on a 7-bolt, these steps will help you lock the head down for consistent, high-horsepower operation.

Why ARP Head Studs Over Bolts?

Factory head bolts are torque-to-yield fasteners designed for low-budget mass production. Once torqued, they stretch and lose clamping force over time. Under high cylinder pressure, the head can lift even slightly, blowing the head gasket and causing catastrophic coolant and compression loss. ARP head studs, by contrast, are made from high-tensile 8740 chromoly steel, heat-treated to 200,000 psi tensile strength. They do not stretch like factory bolts. Studs also provide more uniform clamping force because the nut rotates against a fixed stud rather than twisting the fastener shank. This reduces friction and gives you more accurate torque readings. For 600+ horsepower, the added clamping load and stability of studs are essential.

Tools and Materials Needed

Before starting, gather everything you need. A proper installation depends on using the correct tools and following ARP's specifications. Do not cut corners on torque wrenches or lubricants.

  • ARP head stud kit (part #203-4204 for 6-bolt 4G63; confirm fitment for 7-bolt models)
  • Torque wrench capable of 0–150 ft-lbs, preferably a beam or click-type that is recently calibrated
  • Socket set with deep sockets (12mm and 14mm for nuts and studs)
  • Ratchet and extensions
  • ARP Ultra-Torque fastener lubricant or high-quality engine oil (do not use anti-seize unless specified)
  • Thread sealant (Loctite 567 or similar PTFE paste if sealing blind holes into water jackets)
  • Thread chaser kit (M12 x 1.5 for 4G63 block threads)
  • Gasket scraper and razor blade
  • 100-grit sandpaper or a flat file for cleaning block and head surfaces
  • Straightedge (12-inch precision ruler) and feeler gauges to check head and block flatness
  • Clean rags and brake cleaner
  • Safety goggles and gloves
  • Engine stand (if rebuilding) or jack stands and chocks (if working in-chassis)

Optional but highly recommended: a torque angle gauge if using ARP's recommended three-step method without angle specifications. Many high-builds also perform a final retorque after a few heat cycles, so keep the wrench handy.

Preparation Steps

A clean, flat sealing surface is absolutely critical for 600+ hp. The 4G63 is known for having a closed-deck block that can handle power, but any imperfection in the deck or head will compromise the head gasket seal. Follow these steps carefully.

Engine Condition and Access

  • Ensure the engine is fully disassembled to the short block if doing a full build. For a stud install with the head already removed, you must remove the cylinder head completely.
  • Disconnect the battery and drain coolant if the head is still on the vehicle.
  • Remove intake manifold, exhaust manifold, valve cover, and timing belt components. If the head is off the car, degrease it thoroughly.

Head and Block Cleaning

  • Use a gasket scraper and razor blade to remove all old gasket material from the block deck and head surface. Be careful not to gouge the aluminum head or iron block.
  • Lightly sand the deck with 100-grit sandpaper on a flat block to remove any high spots or corrosion. Wipe clean with brake cleaner.
  • Check flatness using a straightedge placed diagonally, lengthwise, and across the head and block. Maximum allowable warp is 0.002 inches per 6 inches. If you see more than 0.004 inches overall, have the deck resurfaced at a machine shop.
  • Inspect head bolt holes in the block. For 4G63, the holes are M12 x 1.5 thread. Chase each thread carefully with a tap or thread chaser to remove any oil, carbon, or debris. Do not cut new threads.
  • Clean the bolt holes thoroughly with brake cleaner and compressed air. Any trapped oil will hydrolock and prevent proper stud seating.

Choosing the Head Gasket

For over 600 hp, a stock composite gasket is insufficient. Use a multi-layer steel (MLS) gasket from Cometic or a factory Mitsubishi MLS from later 4G63 models (if you have a 6-bolt, you may need to machine the block for the MLS fire ring). Follow the gasket manufacturer's surface finish requirements. Typically, an MLS gasket needs a RA (roughness average) between 40 and 60 microinches. Stock surfaces are often too smooth. Have the deck machined if switching from composite to MLS.

Installing ARP Head Studs

With the block and head clean and flat, you are ready to install the studs. ARP supplies the studs, hardened washers, and nuts. Do not mix them with hardware from other kits.

Step 1: Lubricate and Seal the Studs

  • Apply a light coat of ARP Ultra-Torque (or engine oil) to the lower threads of each stud that will thread into the block. This ensures accurate torque when installing the studs themselves — some builders skip this but it can affect preload.
  • If the bolt holes on your 4G63 block go into the water jacket (this is common on the outer row of holes on a 6-bolt), apply a small amount of thread sealant to the bottom 3-4 threads of each stud. Use a non-hardening PTFE sealant like Loctite 567. This prevents coolant from weeping up the threads and contaminating the oil.
  • Do not get sealant on the upper threads where the nut will go.

Step 2: Install the Studs into the Block

  • Thread each stud into the block hand-tight only. Do not use a tool to tighten them. ARP studs are designed to be installed with the factory bolt holes’ bottom as the seat. You want the studs to bottom out gently and then back off 1/4 turn if they are too tight. The studs should stand equally proud; use a ruler to verify height consistency.
  • Ensure the studs are straight. If one is crooked, remove and clean the threads again.
  • Allow the sealant to cure for the manufacturer's recommended time (usually 30 minutes to 1 hour) before placing the head gasket and cylinder head.

Step 3: Place the Head Gasket and Cylinder Head

  • Set the new MLS head gasket onto the block, aligning the dowel pins. Do not use any additional sealant on an MLS gasket unless specified by the manufacturer.
  • Carefully lower the cylinder head over the studs. Use a guide tool if needed to avoid damaging the gasket or stud threads.
  • Install the ARP hardened washers and nuts. The washers must be placed with the chamfered side facing the nut. Hand-tighten the nuts in the sequence until they are snug against the washer.

Step 4: Torque the Nuts

Follow the torque sequence below. The factory torque sequence for the 4G63 is a specific cross pattern. ARP recommends the same pattern used by Mitsubishi: start at the center and work outward in a spiral.

Torque Sequence (number head bolt positions from front to rear, driver side = 1-5, passenger side = 6-10):
Torque sequence diagramRefer to the ARP instructions for the exact numbered pattern. A common sequence for 6-bolt 4G63 is: 1-2-3-4-5-6-7-8-9-10 starting from center (positions 4 and 5? )

  1. Stage 1: Tighten all nuts in sequence to 30 ft-lbs using a torque wrench with the ARP moly lube.
  2. Stage 2: Tighten all nuts in sequence to 60 ft-lbs.
  3. Stage 3: Tighten all nuts in sequence to 90 ft-lbs for 6-bolt engines with ARP studs using moly lube. For 7-bolt, ARP often recommends 70-75 ft-lbs with moly lube. Confirm the specific instructions that came with your kit. If using engine oil as lubricant, reduce final torque by 15-20% (around 75 ft-lbs for 6-bolt) because oil has higher friction than moly lube.
  4. After the final pass, go back and check each nut one more time in sequence. Do not back off any nut to retorque; if one is slightly below, tighten it to spec.

Important: Do not overtighten. ARP studs are strong but the block threads can strip. Stopping at 90 ft-lbs is safe for most builds. Some extreme setups go to 100 ft-lbs with ARP studs and MLS gaskets, but that requires a perfectly clean and strong block. Stick to ARP's numbers.

Reassembly and Post-Installation Steps

With the head torqued, finish assembling the engine. Pay careful attention to cam cap bolts, timing belt tension, and valve lash if the head was disassembled.

Reinstall Valve Train and Timing

  • If you removed cams, torque the cap bolts in a progressive cross pattern to 20 ft-lbs (or manufacturer spec). Reinstall lifters, rockers, and valve lash adjusters.
  • Set the engine to Top Dead Center (TDC) on cylinder #1. Install the timing belt, ensuring the tensioner is set correctly. For 4G63, the belt tension specification is 40-44 lbs on the long span (check your service manual).
  • Rotate the engine by hand two full revolutions and recheck the cam timing marks. If correct, proceed.

Reassemble Intake, Exhaust, and Accessories

  • Install valve cover with a new gasket. Use a small amount of RTV at the 90-degree corners of the semi-circle plug on the head.
  • Reattach intake manifold, exhaust manifold, and turbo. Use new gaskets on all surfaces.
  • Reconnect coolant lines, vacuum hoses, and electrical connectors. Fill with coolant and engine oil (after priming oil system).

Initial Startup and Retorque Procedure

  • Start the engine and let it idle for 15-20 minutes to reach operating temperature. Watch for coolant leaks at the head gasket area. Listen for abnormal mechanical noise.
  • Shut the engine off and let it cool completely (at least 4-6 hours).
  • Loosen each head nut one at a time (in sequence) and retorque to final specification. Never loosen all nuts at once. This step accounts for gasket compression and thermal expansion. For high-boost builds, a retorque after the first heat cycle is critical for long-term seal.
  • After retorque, start the engine again and verify no leaks. A compression test and leak-down test are highly recommended to confirm head gasket integrity.

Torque Specifications Reference

Always verify with your specific ARP kit instructions. The values below are common for the 4G63 platform using ARP Ultra-Torque lubricant:

  • 6-bolt 4G63: 30/60/90 ft-lbs (final)
  • 7-bolt 4G63: 30/55/75 ft-lbs (final) — check because some 7-bolt blocks have weaker bolt holes near the water jacket.
  • If using engine oil instead of ARP moly: reduce final torque by 10-15% (e.g., 80 ft-lbs for 6-bolt).

If you have a modified 4G63 with o-ringing or copper gasket, consult the gasket manufacturer for torque specs. Some race builds use 100+ ft-lbs but risk thread damage.

Additional Considerations for Over 600 HP

Head studs are just one component of a reliable high-horsepower 4G63. For sustained 600+ wheel horsepower, consider these complementary upgrades:

  • Main studs: ARP main studs keep the bottom end rigid and prevent bearing movement under high cylinder pressure.
  • Deck surface prep: Have the block deck and head surface checked by a machine shop for flatness and finish. An MLS gasket requires 50 RA or better.
  • Gasket selection: Cometic MLS gaskets in 0.030” or 0.040” thickness are proven for 700+ hp. For even higher boost, consider a copper gasket with receiver grooves.
  • Coolant system: Air pockets near rear cylinders can cause localized hot spots and gasket failure. Use a coolant system bleeder or install a drilled thermostat.
  • Use ARP Ultra-Torque: It is specifically designed to provide consistent clamping force. Do not substitute generic anti-seize.

External Resources

For further reading and official specifications, refer to these resources:

Conclusion

Installing ARP head studs on your Mitsubishi 4G63 is a straightforward DIY job that pays off every time you make a full pass at 30+ psi. By following the proper cleaning, lubrication, torque sequence, and retorque procedure, you can eliminate head lift and gasket failures as a limiting factor. The 4G63 platform is legendary for its ability to handle power, but only when the foundation is correctly assembled. Take your time, use the right tools, and reference manufacturer instructions. With the head studs locked down, your engine will be ready to push well beyond the 600-horsepower mark with confidence.