Belt Length Calculator: L Pitch

To determine the number of teeth on the belt required you will have to know four bits of information:

  1. Number of teeth on the vacuum pump pulley.
  2. Number of teeth on the crankshaft/drive pulley.
  3. The center distance between the vacuum pump shaft and the crankshaft with the pump slid or rotated as close to the crankshaft/drive shaft center as the slot will allow.
  4. The center distance between the vacuum pump shaft and the crankshaft with the pump slid or rotated as far away from the crankshaft/drive shaft center as the slot will allow.

Once you have these bits of information and entered them in the calculator there will be 3 outputs:

  1. The minimum number of teeth on the belt.
  2. The maximum number of teeth on the belt.
  3. The Center of Adjustment. Which is the average of these two numbers.

The Center of Adjustment should place the pump in a position where the belt can be tensioned or removed without bottoming out the bolts in the bracket slots. Use the number of teeth displayed in the Center of Adjustment to search for a matching belt. There are a limited number of belt lengths/teeth available. The number of teeth in the Center of Adjustment may not be available, in this case you will have to go up or down one tooth to find the belt available.

Input





(in inches)


(in inches)

Output




Pitch Belt Length Calculator: 8MM (HTD)

To determine the number of teeth on the belt required you will have to know four bits of information:

  1. Number of teeth on the vacuum pump pulley.
  2. Number of teeth on the crankshaft/drive pulley.
  3. The center distance between the vacuum pump shaft and the crankshaft with the pump slid or rotated as close to the crankshaft/drive shaft center as the slot will allow.
  4. The center distance between the vacuum pump shaft and the crankshaft with the pump slid or rotated as far away from the crankshaft/drive shaft center as the slot will allow.

Once you have these bits of information and entered them in the calculator there will be 3 outputs:

  1. The minimum number of teeth on the belt.
  2. The maximum number of teeth on the belt.
  3. The Center of Adjustment. Which is the average of these two numbers.

The Center of Adjustment should place the pump in a position where the belt can be tensioned or removed without bottoming out the bolts in the bracket slots. Use the number of teeth displayed in the Center of Adjustment to search for a matching belt. There are a limited number of belt lengths/teeth available. The number of teeth in the Center of Adjustment may not be available, in this case you will have to go up or down one tooth to find the belt available.

Input





(in inches)


(in inches)

Output




FAQ

Star Machine specializes in high-performance vacuum pumps and components for race cars. Our pumps are engineered for optimal performance, durability, and efficiency, supporting various racing applications.

Choosing the right vacuum pump depends on several factors, including your vehicle’s engine specifications and intended race use. If you’re unsure, our team of experts is here to help you make the proper selection. Contact us, and we’ll guide you based on your needs.

Our vacuum pumps are designed with over 20 years of experience in high-performance pump technology. We prioritize precision engineering, reliability, and ease of installation, ensuring that our products deliver maximum performance for competitive racing.

Yes! Our vacuum pumps are designed for easy installation, and we provide detailed instructions for a straightforward setup. If you need assistance or have any questions during installation, our team is available to help.

Regular maintenance is key to maximizing the lifespan of your vacuum pump. We recommend following our maintenance guidelines, which include checking for leaks, cleaning the pump, and ensuring that all components are securely fastened. Detailed maintenance instructions will be provided with each product.

Our lead times vary depending on product availability and order volume. Once your order is placed, we will provide an estimated shipping timeline. We strive to fulfill orders as quickly as possible without compromising on quality.

Yes! We offer customization options for certain components. If you have specific needs for your race car, contact our team, and we’ll discuss how we can tailor our products to meet your requirements.

Yes, we ship worldwide. Shipping fees and delivery times vary by location. Please get in touch with us for more specific shipping details and customs requirements for international orders.

Vacuum pumps are rated by their airflow capacity (CFM), which affects the vacuum level (measured in inches of Mercury). The right pump size depends on your engine’s displacement, blow-by levels, and power adders like turbochargers or nitrous. Smaller engines typically require less vacuum, but modifications like low-tension rings or forced induction increase crankcase pressure, requiring a larger or faster-spinning pump. While increasing pump RPM can boost vacuum, excessive speed (over 5000 RPM) may reduce efficiency. An oversized pump can also drain horsepower due to increased parasitic loss. For optimal performance, refer to our sizing guide or contact our team for recommendations.

Most racing engines perform best at 10-15 inches of vacuum, with high-performance applications benefiting from up to 18 inches. In wet sump drag racing setups without wrist pin oiling, we recommend staying below 15 inches. Our in-house testing shows that beyond 12 inches, horsepower gains are minimal—typically only 3-10 HP between 10 and 15 inches. For the best results, consult your engine builder for any specific requirements.

Excessive vacuum can reduce oil mist in the crankcase, potentially leading to wrist pin lubrication issues. Some engine builders also report fluctuations in oil pressure above 12 inches of vacuum. High air velocity through oil return passages may also restrict oil flow back to the pan. To help balance the crankcase vacuum, modifications such as an air line from the fuel block-off plate to the valve cover can be beneficial.

A vacuum control valve helps regulate vacuum levels to prevent excessive pressure, ensuring consistent lubrication and performance.

For high output power adder engines, we highly recommend using a data logger to monitor vacuum levels down track. In general, vacuum should increase the longer the engine runs and as the engine’s RPM climbs. If piston rings start to have problems, such as engine timing being excessive, a loss of vacuum tends to occur due to the increased blow-by when the ring seal is compromised. You may find a benefit to not running a vacuum relief valve at low levels in this situation if you want to observe this occurring, as a relief valve may mask this early warning signal that may be caught by a data logger of ring seal issues. In all out competition where engines are running on the edge, closely setting pump RPM to limit vacuum to the level desired may be preferable to limiting vacuum with a relief valve to help observe ring seal problems. This should be discussed with your engine builder and/or tuner.

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