A look Inside GRP's Con-Rod Manufacturing

Spare the rod, spoil the motor – Connecting rods are a critical part of any high performance build, but how much do you really know about how they’re made? A look at GRP Connecting Rods’ manufacturing process reveals some interesting details. GRP starts with a special aluminum alloy plate stock that’s selected for material strength, good resistance to fatigue crack propagation, and high fracture toughness; all very important qualities in a part that will experience vibration, compression, tension and inertia loads, all at more or less the same time. From there, the raw alloy is CNC machined, but GRP takes a different approach to design in that every rod is custom built around the actual center to center distance rather than arbitrary coordinates. That means that custom rod lengths are as easy as inserting a new center to center distance in the program.

For more on the GRP machining process, check out their website.

The rods are then honed to size, and held to a +/- 0.0002″ tolerance, which is important because the center-to-center distance is final-cut from that bore to a +/- 0.0002 tolerance as well. From there, a high-energy finishing machine removes stress risers and gives the rods a high sheen. Start to finish, the process takes about two weeks for custom orders, but common sizes are often in stock for immediate shipping, and GRP has been known to turn around custom sets the same day they’re ordered in extreme circumstances.

Understanding the breakdown of the GRP product line is easy:

Small block rods – 1000-1500

1000 – Lightweight for NHRA Super Stock
1100 – Middleweight, for nitrous and bracket racing applications
1200 – Heavyweight design developed for Top Alcohol Dragster
1300 – Middleweight design for heavy duty applications – developed from the Pro 2100
1400 – Reduced reciprocating weight design for “Honda” style 1.888″ crank journals
1500 – Similar to the 1000 series, but designed for a 2.000″ crank journal

Pro Series – 2000-2200

2000 – GRP’s original 500ci Pro Stock rod as used in Dick Maskin’s 96-97 program
2100 – The 2000 series, lightened by 10 grams. Adopted by Maskin for 1998
2200 – The lightest Pro Stock rod on the market. Can also be used for small block applications with a .990″ wrist pin

HEMI rods – 3000-3500

3000 – Designed for N/A, nitrous, and light blower applications
3100 – Similar to the 3000, but designed for a 2.325″ Chevy-style bore
3300 – New generation HEMI design tailored for blown alcohol classes
3400/3500 – Top Fuel rods, with pin widths up to 1.400″ (3400) and 1.600″ (3500)

Big block rods – 5000-5400