Nitrous oxide is widely used in drag racing in applications, from your standard street car to a 5-second Pro Mod. You can spray as much nitrous as you want as long as your engine is up to the task, and if you’re going to use a big shot of giggle juice you better think about upgrading your connecting rods. We talk with Tom Lieb from SCAT to learn the basics of nitrous connecting rods.
When you spray nitrous into an engine you’re generating a reaction that creates a much bigger bang, and that means more horsepower. That horsepower doesn’t come on gradually, though…it’s instant, and that can be pretty rough on the parts inside your engine, especially the connecting rods. So if you plan on really spraying a lot of nitrous you need to have connecting rods that can deal with the abuse.
“The impact you get with the rod is pretty violent, which means the beam is going to be taking on all the stress. You want a connecting rod that’s relatively heavy on the beam side because of all the compression forces it’s exposed to,” Lieb explains. “In a forced induction application, you’re building up pressure, and the rod is pressing against it. The stress builds gradually with boost; it doesn’t have the shock factor that nitrous does. Nitrous pressure is built by ignition, so the speed of the ignition, and impact just beats the rods up.”
A standard I-beam connecting rod isn’t going to get the job done in a high-horsepower nitrous application. The rods need to be made of a material that can survive the violent environment a nitrous engine creates.
“You need something made of 4340 chromoly type material for the rod. The H-beam rod would be your best choice. You can typically tell how strong a rod is based on the amount of material that’s in it. Now, you can have a rod that’s plenty heavy, but the material is around the big end and not around the beam, that’s not what you want for a nitrous application. The beam needs to have a thicker cross-section. In our HPS rods, you can see the groove around the H-beam, and it has a large radius at the bottom that strengthens the beam dramatically,” Lieb says.
You need to look for connecting rods that have extra material in the beam that’s been strategically added. This is something that SCAT does specifically with its connecting rods that are made for nitrous applications.
“You really see the difference when you have two similar rods on a scale, but one is made for a nitrous application. You can see where the material has been moved and added to a nitrous rod so it can deal with the shock and compression the nitrous applies. We drill a hole towards the big end of our nitrous rods and move that material to the beam of the rod. That allows us to redistribute the weight to the best spot for a nitrous application and makes balancing the rod easier,” Lieb states.
To learn more about nitrous rods and see what works best for your build check out SCAT’s website right here.