Atomic Billet Conrods
Atomic billet steel conrods were designed from scratch with one principle in mind; useing aerospace quality materials and sophisticated manufacturing processes to produce an extremely strong, light (722g) and durable connecting rod for the popular inline 6 cylinder Ford SOHC/DOHC engines, at an affordable price.
The Superleggera conrods are our lighter rod. Great for 1000hp and NA motors because even though they're light, they're strong as Truck. They come standard with CA625 bolts that will happily take more RPM than other bolts. They're also the only Barra rods that we know of to have an oiling hole that runs up the centre of the rod to provide oil to the wrist pin and piston. No one has broken these rods since we started selling them in 2004 as far as we know.
The Design and Evaluation Process
The Atomic engineering team set out to address these parameters by designing what many performance engine builders are now calling the finest conrod on the market for the Ford DOHC 6 cylinder engine. Extensive CAD/CAM computer modelling was employed and produced a H-Beam design, which has an extremely high stiffness-to-mass ratio.
H-Beam is superior in strength to a I-Beam, plus the thicker cross section allows us to include piston crown cooling and pressurized feeds to the gudgeon pins.
Refer to the pictures of the Cosworth F1 titanium conrods below – they are also a H-beam design, showing the superiority of this design in the ultimate test of engine output, Formula One.
Next came FEA modelling (Finite element analysis) to simulate stresses on the conrods. This entailed weighing every piston, gudgeon pin and ring set on the market and loading this information, plus various strokes, rotating and reciprocating conrod values into our computer modelling software to calculate the stresses.
The greatest load exerted on a conrod in a boosted Barra engine comes not from the force of normal combustion blasting down the piston but from the tensile force exerted by the piston/reciprocating mass at top dead centre (TDC).
At only 5250 RPM the piston exerts a tensile load on the conrod of 1908 g’s (-1693 kgs) at split overlap TDC reversal. This exceeds combustion loading by approximately 65%.
If you increase maximum engine speed by only 1000 RPM to 6250 RPM, the TDC tensile load rises by 50.4% to 2870 g’s. At 7500 RPM the tensile loading increases to 4132 g’s, clearly demonstrating Atomic’s design strength of 8000 g’s means it has plenty in reserve.
Excessive loads at TDC are brought about by a high reciprocating mass and/or by increasing engine RPM, so it is essential to design reciprocating engine components with the lowest mass possible to minimize premature lower bearing shell bearing failure. This is particularly relevant to our customers who are turning their engines to 8500RPM+
What about the Bolts?
We started by using ARP2000 bolts but now use our own custom CA625 bolts as standard for no extra cost. That means a lot higher RPM capability than other bolts.
We avoid a 7/16”bolt in these applications as material needs to be removed from the conrod to accept a bolt larger than is required, thereby weakening the conrod unnecessarily.
Accuracy of Machining
Finally, sophisticated computer controlled manufacturing techniques were employed to finish the critical dimensions such as big end bore, pin bore and centre to centre length on specialist CNC equipment. Shot peeing in the final step in manufacturing what we believe are the best conrods on the market for the Barra, bar none.
Even Stronger Conrods - the “FatRod” was born.
Having great success with the then 698kW rated Superleggera conrod was rewarding but we weren’t going to rest on our laurels. We believed power levels of the Turbo Ford were going to be pushed beyond the 150kW per cylinder design parameter of our original design, so we had only one alternative - go back to the drawing board and come up with another design that could handle 200 Kw per cylinder and beyond. Some people told us we were mad - who needs a conrod that strong? But we believed there would be a need so after 7 months of blood, sweat and tears the FatRod was born.
“This is a serious bit of kit”. The design brief was to ensure it could cope with the enormous combustion shock loads associated with 2000HP+ flywheel figures, so the tough H-Beam construction was retained, as it has a higher stiffness-to-mass ratio than an I-Beam design. It also allows us to retain piston crown cooling and pressurized feeds to the gudgeon pins, features that are absolutely imperative in big boost Barras – features that simply cannot be included in inferior I-beam conrod designs.
We gave it the biggest beam we could fit inside the piston and coupled it to the largest size bearing tunnel that could physically fit inside the Ford crankcase.
The minimum cross section has been increased by a whopping 34%, the beam is 13% wider, 14% thicker and the small end of the rod can accommodate a .927” Chev diameter gudgeon pin, if required. Serious conrods for serious power.
Refining and upgrading our conrods is an ongoing process.
We don’t stand still at Atomic and for 2008 we developed some innovative features to our range of conrods. Firstly, we beefed up the Superleggera conrod by increasing the cross section of the beam, bumping up the power rating to 698.
Secondly we added pressure oil feed to the gudgeon pins on both Superleggera and the FatRod and thirdly, we engineered piston crown cooling as part of the conrod design.
Pressure fed gudgeon pins is an Atomic innovation, borrowed from diesel engine technology. We redesigned our conrods to provide a direct pressure feed of engine oil to the load side of the gudgeon pin bush, thereby providing oil directly to the gudgeon pins and bushes. As turbo/supercharged engines make more power than their normally aspirated cousins, the forces of combustion are far greater which in turn place much greater loads on gudgeon pins, leading to excessive pin/bush wear. Providing pressurised oil feed to the pins increases life of the engine considerably.
Piston crown cooling is not new either but has not been available for the Ford 6 cyl engine previously. This feature helps remove heat from the piston by spraying oil onto the underside. It is common practice in many high performance engines, such as the Nissan “Godzilla” 2.6Ltr engine, Sierra Cosworth, Turbo Porsches, etc who employ this method of internal thermal management. This feature will help to “detonation proof” our engines by drawing heat from the piston in much the same way a rich air/fuel mixture is cooler than stoichiometric.
Atomic innovation at work
- First Hi-Kw H-Beam conrod in 2004
- First manufacturer to offer 698 Kw rated conrods in 2008
- First to offer piston crown cooling for Barra engines in 2010
- First to offer pressurized gudgeon pin oiling in 2010
- We have NEVER HAD A SINGLE failure of a H-Beam conrod, ever!!!!!
Atomic conrods are the most technologically advanced conrod on the market... accept no substitutes!
Please note: Big end tunnels in #306200 and #306201 conrods are finished to 2.2394” (bottom size) and the small ends are left at .866” so final clearancing can be done by the engine builder to provide the correct clearance to suit the gudgeon pins. We do this as we have found some gudgeon pins come as a finished (Metric) size of 22.00mm (.8665”) (eg Cosworth, Mahle, etc) whereas other pins (predominately US made such as JE, etc) are finished to an Imperial measurement of .866”.
For Installation instructions click here
