Use this exhaust diameter calculator to determine the optimal size of an exhaust pipe for a vehicle’s engine using formula D = √(CC ÷ (RPM ÷ 88.6)).
Exhaust Diameter Calculator
| Engine Displacement | Max RPM | Calculated Diameter | Recommended Diameter |
|---|---|---|---|
| 1500cc (1.5L) | 6000 | 1.94 inches | 2.0 inches |
| 2000cc (2.0L) | 7000 | 1.98 inches | 2.25 inches |
| 2500cc (2.5L) | 6500 | 2.25 inches | 2.5 inches |
| 3000cc (3.0L) | 6500 | 2.52 inches | 2.5 inches |
| 3500cc (3.5L) | 6000 | 2.85 inches | 3.0 inches |
| 4000cc (4.0L) | 5500 | 3.16 inches | 3.0 inches |
| 4500cc (4.5L) | 7000 | 3.50 inches | 3.5 inches |
| 5000cc (5.0L) | 5000 | 3.69 inches | 3.5 inches |
| 6000cc (6.0L) | 6000 | 4.00 inches | 4.0 inches |
| 7000cc (7.0L) | 7000 | 4.50 inches | 4.5 inches |
| 800cc (0.8L) | 5000 | 1.45 inches | 1.5 inches |
| 1200cc (1.2L) | 6000 | 1.75 inches | 1.75 inches |
| 1800cc (1.8L) | 6500 | 2.05 inches | 2.25 inches |
| 2200cc (2.2L) | 7000 | 2.30 inches | 2.5 inches |
| 3200cc (3.2L) | 7500 | 3.00 inches | 3.25 inches |
Exhaust Diameter Chart
| Horsepower | Exhaust Diameter |
|---|---|
| 100-150 HP | 1.75 – 2.0 inches |
| 150-200 HP | 2.0 – 2.25 inches |
| 200-250 HP | 2.25 – 2.5 inches |
| 250-300 HP | 2.5 – 2.75 inches |
| 300-350 HP | 2.75 – 3.0 inches |
| 350-400 HP | 3.0 – 3.25 inches |
| 400-450 HP | 3.25 – 3.5 inches |
| 450-500 HP | 3.5 – 3.75 inches |
| 500-550 HP | 3.75 – 4.0 inches |
| 550-600 HP | 4.0 – 4.25 inches |
| 600-650 HP | 4.25 – 4.5 inches |
| 650-700 HP | 4.5 – 4.75 inches |
| 700-750 HP | 4.75 – 5.0 inches |
| 750-800 HP | 5.0 – 5.25 inches |
| 800-850 HP | 5.25 – 5.5 inches |
| 850-900 HP | 5.5 – 5.75 inches |
| 900+ HP | 5.75+ inches |
Exhaust Diameter Formula
D = √(CC ÷ (RPM ÷ 88.6))Where:
- D = Exhaust pipe diameter in inches
- CC = Engine displacement in cubic centimeters
- RPM = Maximum engine speed in revolutions per minute
Suppose we have a 2.5-liter (2500cc) engine with a maximum RPM of 6500.
D = √(2500 ÷ (6500 ÷ 88.6))
D = √(2500 ÷ 73.36)
D = √34.08
D ≈ 5.84 cm or 2.3 inches
This calculation suggests an exhaust diameter of approximately 2.3 inches would be suitable for this engine.
How to Measure Exhaust Diameter
Follow these steps:
- Locate the measurement point: Usually, this is at the exhaust manifold outlet or just after the catalytic converter.
- Clean the area: Ensure the pipe is free from debris or rust for an accurate measurement.
- Use a caliper: A digital caliper is ideal for precise measurements.
- Measure the outside diameter (OD): Place the caliper around the widest part of the pipe.
- Measure the inside diameter (ID): If possible, measure the inner diameter as well.
- Record measurements: Note down both OD and ID in inches or millimeters.
Let’s say you measure an exhaust pipe and find:
- OD: 2.5 inches (63.5 mm)
- ID: 2.25 inches (57.15 mm)
What Size Exhaust for 200 HP?
For an engine producing 200 horsepower, a general recommendation would be an exhaust diameter between 2.25 and 2.5 inches.
Consider a naturally aspirated 2.0-liter (2000cc) engine tuned to produce 200 hp at 7000 RPM. Using our earlier formula:
D = √(2000 ÷ (7000 ÷ 88.6))
D = √(2000 ÷ 79.01)
D = √25.31
D ≈ 5.03 cm or 1.98 inches
Rounding up to the nearest standard size would suggest a 2-inch exhaust diameter. However, given the 200 hp output, opting for a slightly larger 2.25-inch diameter might provide better flow characteristics and room for future power increases.
How Do I Choose an Exhaust Pipe Diameter?
Selecting the appropriate exhaust pipe diameter involves considering several factors:
Engine power output: Higher horsepower generally requires larger diameter pipes.
Engine displacement: Larger engines need bigger exhausts to handle increased gas volume.
Intended use: Street cars may benefit from smaller diameters for better low-end torque, while race cars often use larger diameters for maximum top-end power.
Turbocharging: Forced induction systems typically require larger exhaust diameters than naturally aspirated engines of similar power.
You’re upgrading a turbocharged 1.8-liter engine that’s been modified to produce 300 hp at 6500 RPM.
Using our formula:
D = √(1800 ÷ (6500 ÷ 88.6))
D = √(1800 ÷ 73.36)
D = √24.54
D ≈ 4.95 cm or 1.95 inchesHow Do You Calculate the Volume of the Exhaust Muffler?
For a cylindrical muffler:
V = πr²hWhere:
- V = Volume
- r = Radius of the muffler
- h = Length of the muffler
Let’s say we have a cylindrical muffler with a diameter of 6 inches (radius = 3 inches) and a length of 14 inches.
V = π (3 inches)² 14 inches
V = π 9 14
V ≈ 395.84 cubic inches (or approximately 6.49 liters)Related Tools:
