This exhaust diameter calculator helps you find the optimal pipe size for your engine’s exhaust system.
What exactly is this diameter? Imagine exhaust gases flowing from your engine through a pipe. If you install a pipe that’s too narrow, the gases become restricted and create backpressure that chokes your engine’s performance.
If you choose a pipe that’s too wide, the gas velocity drops and you lose the scavenging effect needed for efficient operation.
Continue reading if you want to learn how to calculate exhaust diameter and have the sizing principles explained in detail.
Exhaust Diameter Calculator
Inputs (CID Method)
Real-World Applications of Exhaust Diameter Calculation
| Application | Why it Matters |
|---|---|
| Performance Cars | Right diameter boosts horsepower and torque. |
| Motorcycles | Ensures smooth exhaust flow and better acceleration. |
| Trucks | Helps in towing efficiency and fuel economy. |
| Racing Engines | Critical for maximizing exhaust scavenging effect. |
Example 1 (CID Method)
Problem: A car engine has 350 CID displacement with a single exhaust system. Find the recommended exhaust diameter.
Solution:
- Step 1 (Given Data): CID = 350, Exhaust = Single
- Step 2 (Formula): D = √(CID / 1000)
- Step 3 (Substitute): D = √(350 / 1000) = √0.35
- Step 4 (Result): D ≈ 0.59 inches
Example 2 (HP Method)
Problem: An engine produces 60 HP per cylinder. Find the recommended primary tube diameter.
Solution:
- Step 1 (Given Data): HP = 60
- Step 2 (Formula): D = √(HP × 2.1) / 1000
- Step 3 (Substitute): D = √(60 × 2.1) / 1000 = √126 / 1000
- Step 4 (Result): D ≈ 0.011 inches
Reference Table for CID Method
| Engine Displacement (CID) | Single Exhaust Diameter (inches) | Dual Exhaust Diameter (inches) |
|---|---|---|
| 200 | 0.45 | 0.32 |
| 300 | 0.55 | 0.39 |
| 400 | 0.63 | 0.45 |
| 500 | 0.71 | 0.50 |
| 600 | 0.77 | 0.55 |
*Values are approximate and should be used as a guideline for selecting exhaust pipe diameter.
Reference Table for HP Method
| Horsepower per Cylinder (HP) | Recommended Tube Diameter (inches) |
|---|---|
| 40 | 0.009 |
| 50 | 0.010 |
| 60 | 0.011 |
| 70 | 0.012 |
| 80 | 0.013 |
| 100 | 0.014 |
*These values are based on the formula D = √(HP × 2.1) / 1000. Small variations may occur in practice.
FAQs
Why is exhaust diameter important?
The exhaust diameter decides how smoothly gases exit the engine. The right size improves performance, fuel efficiency, and overall engine life.
Which method should I use – CID or HP?
Both methods are correct. CID method works best when you know the engine displacement, while HP method is useful when you know the horsepower per cylinder.
What happens if I use the wrong exhaust size?
If the pipe is too small, the engine can’t breathe properly. If it’s too big, you lose back pressure. Both cases reduce performance.
Can I use this calculator for bikes and cars?
Yes! This calculator works for motorcycles, cars, trucks, and even racing engines – as long as you know the input values.