Forged connecting rods Honda K20 2.0 16V i-VTEC 135.5 mm center-to-center (stroker build) for forged pistons

The Honda K20 engine (2.0 16V i-VTEC)

A 2.0 L (1998 cc) four-cylinder from the K family, the K20 combines sixteen valves, twin cams and i-VTEC variable timing acting on both valve lift and phasing. In its most accomplished naturally aspirated forms (K20A2, K20Z1, K20A3) it spins to around 8,400 rpm and makes 160 to 220 hp, which made it the engine of the Civic Type R EP3 and Acura RSX Type-S. As soon as its stroke, compression height or ratio is altered, typically in a stroker build, the rotating-assembly geometry changes and the factory sintered rod no longer fits. It then becomes the weak point of the assembly, unable to cope durably with the new cylinder pressures and inertia loads. Fitting forged rods of the chosen length, weight-matched, is the foundation of a lastingly reliable stroker K20.

The forged connecting rods (135.5 mm length)

These ZRP rods stand out through their short 135.5 mm center-to-center length, below the K20's factory dimension: they are designed for modified-geometry builds (stroker, revised compression height) and not for a like-for-like swap. Drop-forged then precision-machined, they tolerate compression, bending and fatigue loads far beyond the factory sintered rods. They suit every demanding use: circuit, time attack, drift, drag, rally and hillclimb, on a hard naturally aspirated K20 as on a Stage 2, Stage 3 or Stage 4 turbo or supercharger conversion. Supplied as a complete weight-matched set of 4, they keep the K20's 22 mm piston pin while requiring, because of their length, pistons with adapted compression height.

	H profile: H-beam by ZRP; its two flat flanks give excellent bending stiffness for a controlled weight, a versatile, proven choice for most naturally aspirated or lightly boosted stroker K20 builds.
	I-HD profile: reinforced I-beam (Heavy Duty) by ZRP; it combines lightness and strength and favours compression resistance, tailored to a heavily loaded stroker K20, notably under boost.

The 135.5 mm range is limited to two ZRP profiles: the versatile H and the reinforced I-HD (Heavy Duty), more at ease under high load. The specification table details, for each reference, the center-to-center length, big-end diameter and width and the weight, to choose by the power and rpm target of the stroker build.

Technical specifications of the K20 rods (22 mm pin, 135.5 mm center-to-center)

Forged rods technical guide

4340 forged steel

The beam is forged from 4340 low-alloy nickel-chromium-molybdenum steel, the benchmark alloy for race rods. Forged, quenched then tempered, it keeps a continuous grain flow that gives high tensile strength and outstanding fatigue life, two decisive assets on a stroker K20 stressed high and long. Compared with a factory sintered rod, designed above all for series production cost, a forged 4340 rod offers about +19% yield strength, +8% tensile strength and +19 to +37% fatigue endurance. This mechanical reserve absorbs, without breaking, the pressure peaks and inertia loads of a K20 whose stroke has been lengthened.

The rod profile

The 135.5 mm range is limited to two ZRP profiles: the versatile H and the reinforced I-HD (Heavy Duty), more at ease under high load. The specification table details, for each reference, the center-to-center length, big-end diameter and width and the weight, to choose by the power and rpm target of the stroker build.

How to choose your rod bolts?

	ARP 2000: the all-round benchmark alloy, with a tensile strength of about 220,000 psi (1,517 MPa). Offered here in 3/8" diameter, it covers the vast majority of stroker K20 builds, up to about 200 hp per cylinder, at speeds reaching 9,000 rpm. It is the default choice for an engine made reliable for sustained sporting use.
	ARP L19: a very-high-strength steel (approx. 260,000 psi / 1,793 MPa), stiffer, reserved for the most heavily stressed stroker K20s, up to about 250 hp per cylinder and the highest engine speeds. In 3/8" diameter it markedly raises the safety margin (note: corrosion-sensitive, it requires careful storage).

Measuring bolt stretch

Discover the ARP stretch gauge

The brand offered

ZRP

This 135.5 mm range is made by ZRP, a race forged-rod maker known for its price/performance ratio. Both H and I-HD profiles are forged from the same 4340 steel and supplied as a complete set of 4, each with its dedicated ARP bolts.

Vehicle compatibility

Alternative-length rods (135.5 mm): these are not drop-in replacement rods. Shorter than the K20's factory dimension, they are intended for specific-geometry setups and stroker builds on the K20A2, K20Z1 and K20A3 engines below, and require pistons with adapted compression height:

Tightening torque and stretch

On these rods, tightening is controlled by bolt stretch, measured with a gauge, rather than by torque alone. The values below are a guide: always follow the bolt maker's instructions.

Glossary

1) Small end 2) Small-end diameter 3) Rod beam 4) Rod bolt 5) Big end 6) Rod nut / bolt 7) Rod cap 8) Big-end diameter 9) Center-to-center

Why is it the most economical solution?

A set of forged rods costs vastly less than a blown engine: on a stroker K20 pushed in rpm or load, an unsuitable rod that lets go takes out the block, the crankshaft and often the head. By choosing the right forged-rod length, weight-matched, from the outset, you make your build reliable for the long term and spare yourself a full rebuild, for a negligible extra cost next to a new engine.