After several years of development and testing, Eagle has introduced our 4th generation design (4D) H-Beam rods. Racers are making more power now than ever before and the bottom end has got to be up to the task! Eagle 4D rods are designed to handle all the power you can make without breaking the bank. Design advancements include thicker webbing and thicker beam to improve tensile and compressive strength by as much as 20% in some applications! The big end of the rod also sees several design improvements. Material has been added at the parting line to improve size consistency at higher bolt clamping loads. The bolt head engagement area is strengthened. The "shoulder" area of the rod is also thickened between the webbing of the beam. The webbing on the cap is significantly strengthened. All of this adds up to a tremendous improvement in big end strength and rigidity. This is important because under very high loads, the big end of the rod can become distorted ("egg-shaped") causing a loss in oil film consistency along the rod journal surface eventually leading to a breakdown in support at the bearing. This will often result in the "spinning" of a rod bearing. Adding material in these areas solves this issue in very high power applications. All Eagle 4D rods come standard with 7/16" ARP 2000 bolts - even 4 and 6 cylinder applications! This is a 36% increase in bolt strength alone for those applications! All Eagle 4D rods are 100% CNC machined - every surface! This provides unrivaled consistency in manufacturing that is unmatched by any large-scale manufactured rod. Finally, Eagle 4D rods are forged from a steel that has been 30 years in development. "4340" is an alloy formula conceived by The American Iron and Steel Institute (AISI) and adopted by the Society of Automotive Engineers (SAE) and the American Society of Mechanical Engineers (ASME). It is the material of choice for connecting rods and crankshafts and a mainstay in the high-performance industry. Eagle has spent the last 35 years establishing a very good relationship with our steel foundry of choice and when you buy as much steel as we do, they will start listening to special requests. While 4340 is very good standard to start with, like everything, it can always be improved upon. Not just in sheer strength, but modulus of elasticity, area reduction under stress, fatigue strength, and other properties. While we won't go into too much detail, know that Eagle has been constantly tinkering with the alloying "formula" and heat-treatment process that goes into our steel to try to improve the performance. We are thankful that our foundry has entertained our requests and we are very pleased with the result. The steel we use in our 4D rods exceeds ASME 4340 in several areas: tensile strength is higher than typical 4340 steel, fatigue strength due to cyclical loading is improved, modulus of elasticity is improved significantly as is area reduction under stress. The specifics concerning all of this is obviously a very closely guarded secret. Gone are the days of "off the shelf 4340". We haven't named our proprietary alloy yet - the results were more important than the marketing. We are confident the results will speak for themselves. Eagle 4D rods will prove themselves to be the strongest rods on the market - at ANY price! Eagle 4D rods are available along side Eagle 3D rods as well as our I-Beam options. With so many choices, it may be a bit confusing. If you need help, please call us and we help recommend what's right for your engine. Eagle H-Beam rods are not legal for use in pollution-controlled vehicles.