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1.7L 16v - 1750 TBI
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1.7L 16v - 1750 TBI
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Set of 4 forged 4340 steel connecting rods for the Alfa Romeo 1.7 16V Turbo 1750 TBi.
The 1750 TBi (1.75 L, 1742 cc) is Alfa Romeo's direct-injection four-cylinder turbo petrol engine, with 16-valve timing and variable cam phasing. Offered in 200, 235 and 240 hp versions, it powers both the 159 saloon and the 4C sports coupé.
Stressed by forced induction, its factory rotating assembly quickly reaches its limits once tuned. Higher boost pressure, remapping or extra rpm raise the loads on the rods and weaken the bottom end.
Forged from heat-treated 4340 steel, these reinforced connecting rods secure the bottom end as soon as power rises. They become essential when fitting forged pistons, increasing boost pressure or chasing higher rpm.
Designed to absorb the loads of tuned engines, they offer a far greater safety margin than the original part and protect engine longevity over time.
| Reference | Brand | Profile | Bolts | Pin diameter OEM 22 mm | Small-end width | Big-end diameter OEM 51.37 mm | Big-end width | Center-to-center OEM 148.04 mm | Weight per rod |
|---|---|---|---|---|---|---|---|---|---|
| R-ALF-005-I | ZRP | I-HD | ARP 2000-3/8"-38mm | 22 mm | 51.37 mm | 21.94 mm | 148.04 mm | 498 g | |
| R-ALF-005-I-L19 | ZRP | I-HD | ARP L19-3/8"-38mm | 22 mm | 51.37 mm | 21.94 mm | 148.04 mm | 498 g |
| Rod | Bolts | Torque | Recommended stretch |
|---|---|---|---|
| ZRP (R-ALF-005-I) | ARP 2000 | 61 N·m | 0.140 – 0.152 mm |
| ZRP (R-ALF-005-I-L19) | ARP L19 | 67.8 N·m | 0.152 – 0.165 mm |
Manufacturers favour stretch measurement (stretch gauge) over torque alone: it is the most reliable indication of the bolt's actual preload.
| 4340 steel is a nickel-chromium-molybdenum alloy used in both aerospace and motorsport. Forged then heat-treated by quenching and tempering, it develops high mechanical strength, great toughness and excellent fatigue endurance. Compared with an original sintered-metal rod, designed for series-production cost, a forged 4340 rod offers around 19% more yield strength, 8% more tensile strength and 19 to 37% more fatigue resistance, i.e. a service life under cyclic load several times longer. That gain is precisely what makes it the reference material once boost and engine speed climb on a tuned 1750 TBi. |
 | I-HD profile. A reinforced version of the I-beam rod: the central I-section stays light to free up the revs, while the small and big ends are thickened (Heavy Duty) to handle high torque. An excellent lightness / strength compromise on heavily tuned turbo four-cylinders such as the 1750 TBi. |
Connecting-rod bolts are among the most heavily loaded parts of the engine: they keep the cap closed on every revolution. NSB Concept offers these rods with two ARP bolt grades, to choose according to the targeted build.
 | ARP 2000 (tensile strength around 220,000 psi, i.e. ~1,517 MPa) is the high-performance standard. It covers builds up to 150 hp per cylinder in 5/16" or 200 hp per cylinder in 3/8", and up to 8,500 rpm. Versatile and renowned for its ruggedness and reliability, it is used on track, trackday, drift, rally, drag and hill climb, with no particular storage constraints. |
 | ARP L19 (tensile strength around 260,000 psi, i.e. ~1,793 MPa) targets engines pushed to the extreme. It allows up to 200 hp per cylinder in 5/16" or 250 hp per cylinder in 3/8", and up to 10,000 rpm, under high boost pressure and sustained high revs. This steel remains sensitive to corrosion and hydrogen embrittlement: it must be fitted and stored oiled, away from moisture. |
| Beyond torque tightening, checking connecting-rod bolt stretch remains the surest way to obtain a correct, repeatable preload. With the bolt fitted, a dial indicator is set on the two ends of the bolt and its actual stretch is read, which must match the recommended value (see the torque and stretch table above). By freeing itself from the friction scatter inherent in torque tightening alone, this method secures the bottom-end assembly on heavily loaded engines, such as a tuned 1750 TBi. |
 | ZRP is a Greek manufacturer of high-performance forged connecting rods founded by Alex Drakos in Athens. Each rod is forged in 4340 steel, precision-machined and balanced to ±1 g to stay reliable at the highest revs. Designed and inspected in Greece, then proven in rally, on track and in drift, they are offered for the 1750 TBi in I-HD profile with ARP 2000 or ARP L19 bolts. |
 | 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 are compatible with all vehicles fitted with the Alfa Romeo 1750 TBi engine, across every power version:
| Brand | Model (chassis) | Engine code | Power | Years |
|---|---|---|---|---|
| Alfa Romeo | 159 (939) | 939B1000 | 200 hp | 2009–2011 |
| Alfa Romeo | Brera (939) | 939B1000 | 200 hp | 2009–2010 |
| Alfa Romeo | Spider (939) | 939B1000 | 200 hp | 2009–2010 |
| Alfa Romeo | Giulietta QV / Veloce (940) | 940A1000 | 235–240 hp | 2010–2020 |
| Alfa Romeo | 4C (960) | 960A1000 | 240 hp | 2013–2020 |
OEM reference: 5 521 0496 (set of 4 connecting rods).
When a stock bottom end gives out (a broken, bent or scored rod), returning to the factory configuration often means replacing both the rods and the pistons, which are damaged too. The bill climbs quickly for a mere restoration to the original state.
For a comparable budget, sometimes less, pairing forged 4340 steel rods with forged pistons brings far greater reliability and safety margin, plus real potential for power growth. It is the choice European tuners have made for over fifteen years.
For the same budget: more reliability, more potential, more longevity.
