Product successfully added to your shopping cart
Quantity
Total
There are 0 items in your cart. There is 1 item in your cart.
Total products
Total shipping To be determined
Total
2.5L 24v - M50B25 (without vanos)
Manufacturers
2.5L 24v - M50B25 (without vanos)
Warning: Last items in stock!
New product
Set of 6 forged 4340-steel connecting rods for BMW 6-cylinder, 135 mm center-to-center.
BMW built a long line of inline-six engines sharing the same connecting-rod length: a 135 mm center-to-center distance. This common base links the SOHC M20 “small six” (launched in 1977) to the modern twin-cam, four-valve-per-cylinder M50, M52 and M54 families. From one generation to the next the architecture evolves (24 valves, VANOS, aluminium block), but the rod geometry stays compatible, so a single set of forged rods covers a very wide range.
Renowned for their smoothness and durability, these engines power the 3, 5 and 7 Series as well as the Z3, Z4, X3 and X5, and form the basis of many builds. Their bottom end copes well with power, but the original rods become the limiting link as soon as torque or rpm rise significantly.
Machined from high-strength 4340 steel and then heat-treated, these forged connecting rods replace the original rods to withstand the higher revs and cylinder pressures of a build without flinching. Forging aligns the metal’s grain flow and removes casting porosity: the result is markedly higher fatigue strength and the safety margin that becomes essential as soon as power climbs.
Each set is inspected and balanced, then supplied with high-performance ARP bolts sized for the target torque. Paired with forged pistons, these rods form the basis of a reinforced bottom end, able to endure intensive use and competition.
| Reference | Brand | Profile | Bolts | Pin diameter OEM 22 mm | Small-end width | Big-end diameter OEM 48 mm | Big-end width | Center-to-center OEM 135 mm | Weight per rod |
|---|---|---|---|---|---|---|---|---|---|
| R-BMW-006-I | ZRP | I-Beam | ARP 2000-3/8"-38mm | 22 mm | 48 mm | 21.9 mm | 135 mm | 499 g | |
| R-BMW-006-I-L19 | ZRP | I-Beam | ARP L19-3/8"-38mm | 22 mm | 48 mm | 21.9 mm | 135 mm | 499 g |
| Connecting rod | Bolts | Tightening torque | Recommended stretch |
|---|---|---|---|
| ZRP (R-BMW-006-I) | ARP 2000 | 61 N·m | 0.140 – 0.152 mm |
| ZRP (R-BMW-006-I-L19) | ARP L19 | 67.8 N·m | 0.152 – 0.165 mm |
Manufacturers recommend the bolt-stretch method (stretch gauge) as the reference: the instructions supplied with the kit always take precedence. The quoted torque figures are for assembly with ARP lubricant.
| 4340 steel is a nickel-chromium-molybdenum alloy steel used in aerospace and motorsport alike. Forged then heat-treated (quench and temper), it offers excellent tensile strength, high fatigue resistance and real ductility. Compared with an original rod (often sintered/powder metal, optimised for series-production cost), a 4340 forged rod shows roughly +19% higher yield strength, +8% higher tensile strength and above all +19% to +37% higher fatigue strength, i.e. a fatigue life under cyclic loading several times longer. This is what makes forged 4340 the reference material as soon as boost and rpm climb. |
 | I-Beam profile. With its slimmer central section, the I-beam rod favours light weight and an excellent stiffness-to-mass ratio. It is the most common profile, perfectly suited to builds of the BMW inline-six engines with a 135 mm rod, from a reinforced engine to high power levels. |
The rod bolt is one of the most heavily stressed parts in the engine. The key is to match the ARP grade to the real use of the build, then to strictly follow the assembly torque and stretch.
 | ARP 2000 (tensile strength ~220,000 psi, i.e. ~1,517 MPa) is the high-performance standard. Suited to builds up to 150 hp per cylinder with 5/16" bolts or 200 hp per cylinder with 3/8" bolts, and up to 8,500 rpm, it is the most common grade in circuit, track days, drift, rally, drag and hillclimb, recognised for its strength, reliability and versatility, with no particular storage constraints. |
 | L19 (tensile strength ~260,000 psi, i.e. ~1,793 MPa) is designed for engines pushed to the extreme, up to 200 hp per cylinder with 5/16" bolts or 250 hp per cylinder with 3/8" bolts, and up to 10,000 rpm: very high boost pressure, sustained high rpm and high cylinder pressure. It is the choice for big-power builds: drag racing, drift, rally and circuit use. Caution: sensitive to corrosion and hydrogen embrittlement, it must always be stored and fitted oiled, away from moisture. |
In addition to torque tightening, measuring rod-bolt stretch is the most reliable check for optimal preload. The check is done with the bolt fitted: place the gauge (dial indicator) on the two ends of the bolt and read its actual stretch, which must match the recommended value (see the torque & stretch table above). This method removes the friction variations inherent in torque tightening and secures the assembly on heavily stressed engines. |
 | ZRP, a Greek brand of high-performance forged connecting rods, designed by Alex Drakos in Athens. Each rod is forged from 4340 steel, precision-machined and balanced to ±1 g to stay reliable at high rpm. Available in I-beam or H-beam profile with ARP 2000, L19 or Custom Age 625+ bolts, they are designed and inspected in Greece, and proven in rally, on circuit and in drift. |
 | 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 |
These forged connecting rods fit all BMW inline-six engines whose rod shares a 135 mm center-to-center length. The table below lists the engines, models (with chassis code), power and model years:
| Make | Model (chassis) | Engine code | Power | Years |
|---|---|---|---|---|
| BMW | 325i / 325iX (E30) | M20B25 | 170–192 hp | 1983–1993 |
| BMW | Z1 Roadster | M20B25 | 170 hp | 1988–1991 |
| BMW | 525i (E34) | M20B25 | 170 hp | 1988–1990 |
| ALPINA | C1 / C2 (E30) | M20B25 | 185–190 hp | 1985–1988 |
| BMW | 325i (E36) | M50B25 | 192 hp | 1990–1995 |
| BMW | 525i 24V / 525iX 24V (E34) | M50B25 | 192 hp | 1990–1996 |
| BMW | 323i / 323ti (E36) | M52B25 | 170 hp | 1995–2000 |
| BMW | 323i / 323Ci (E46) | M52B25 | 170 hp | 1998–2000 |
| BMW | 523i (E39) | M52B25 | 170 hp | 1995–2000 |
| BMW | Z3 2.5 (E36) | M52B25 | 170 hp | 1998–2000 |
| BMW | 328i (E36) | M52B28 | 193 hp | 1995–1999 |
| BMW | 328i (E46) | M52B28 | 193 hp | 1998–2000 |
| BMW | 528i (E39) | M52B28 | 193 hp | 1995–2000 |
| BMW | 728i / 728iL (E38) | M52B28 | 193 hp | 1995–2001 |
| BMW | Z3 2.8i (E36) | M52B28 | 193 hp | 1996–2000 |
| BMW | M3 3.2 (E36) | M52B32 | 243 hp | 1996–2000 |
| BMW | Z3 M (E36) | M52B32 | 239–243 hp | 1998–2000 |
| BMW | 330i / 330Ci / 330xi (E46) | M54B30 | 228–231 hp | 2000–2006 |
| BMW | 530i (E39) | M54B30 | 228–231 hp | 2000–2003 |
| BMW | 530i (E60) | M54B30 | 231 hp | 2001–2005 |
| BMW | 730i / 730Li (E65/E66) | M54B30 | 231 hp | 2003–2008 |
| BMW | X3 3.0i (E83) | M54B30 | 228–231 hp | 2003–2006 |
| BMW | X5 3.0i (E53) | M54B30 | 228–231 hp | 2000–2006 |
| BMW | Z3 3.0i (E36) | M54B30 | 228–231 hp | 2000–2003 |
| BMW | Z4 3.0i (E85) | M54B30 | 231 hp | 2002–2005 |
OEM references (per engine): M20B25 11 24 1 288 386 ; M50B25 11 24 1 730 420 ; M52B25 11 24 1 739 725 ; M52B28 11 24 1 744 315 ; M52B32 11 24 1 247 175 ; M54B30 11 24 1 437 210.
On these now-classic inline-sixes, replacing a tired original rod with a new genuine part is expensive and offers no extra margin against a power increase.
For a comparable budget, fitting 4340 forged connecting rods changes everything: the part is new, stronger than the original and built to handle torque and rpm. A lasting investment rather than a like-for-like repair.
For the same budget: more reliability, more potential and real peace of mind to drive hard. That’s the whole point of reinforcing these engines with forged rods as soon as the bottom end is opened up.
