USRA Technical Bulletin: USRA B-Mod Engines

The USRA B-Mod division has grown dramatically in popularity in recent years. The requirement for a stamped rocker arm in our standard engine package has been discussed thoroughly and has had its share of controversy. The reason this rule exists is to limit the valve train of this engine.

The rule book is a set of limitations for what the racer is permitted to do with the race car, including the engine with has limitations cubic inches, compression, rod type, crank type, head numbers, intake numbers and more. The valve train has very few limitations other than the rocker arm.

A stamped rocker arm will withstand only so much stress before it fails and the racer has to build a valve train within that tolerance. What is happening more frequently is that racers are willing to exceed that limitation to gain a performance advantage with the risk of a part failure, which is usually the rocker arm.

One of the areas they are exceeding that limitation is the valve spring pressure. Low quality rocker arms and the flat tappet cam quality declining has added to this dilemma. We have noticed these parts are failing from excessively aggressive valve trains being too much stress on the rocker arms, and from simply poor quality.

Because of these issues we feel that we need to implement a valve spring rule. This will reduce the need to stress parts for performance and lessen the potential of these parts from failing due to poor quality. Since we will now have a controlled spring rule then we can remove the limitation of the required stamped rocker arm and allow a full roller rocker arm with the standard engine.

Effective January 1, 2023, if you choose to utilize a full roller rocker arm then you will have to adhere to the new valve spring rule, or you can stay with the current stamped rocker arm rule and the current spring rule will be permitted. However, the new spring rule will be enforced with all standard engines beginning in 2024.

See Rules 13.7.12 and 13.8.12 for amendments to these rules. You can download rules for all USRA classes at

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