Engine Building

Cylinder Overbore Calculator

Calculate displacement gain from cylinder overboring. See how boring your engine block increases cubic inches and potential horsepower.

Quick Presets

Results

Enter engine specs to calculate displacement gain

Why Overbore?

Cleanup: Remove scoring, restore roundness
Performance: Increase displacement
Rebuild: Install oversized pistons

How to Use

Enter original bore diameter in mm
Enter stroke length in mm
Select number of cylinders
Enter desired overbore amount

FAQs

How much can I safely overbore?

Most cast iron blocks can handle 1.0-1.5mm. Aluminum blocks typically max out at 0.5-1.0mm. Always sonic test cylinder wall thickness before deciding.

What's a sonic test?

Ultrasonic testing measures cylinder wall thickness at multiple points. It reveals casting variations and helps determine safe maximum overbore. Costs ~$50-100.

Do I need new pistons?

Yes. Overbored cylinders require matching oversized pistons. Common sizes are +0.5mm, +1.0mm, +1.5mm. Custom pistons available for unusual sizes.

Will overboring make more power?

Displacement increases proportionally with bore area. However, gains are modest (1-3%). The real benefit is allowing oversized pistons for a proper rebuild.

Limitations

Does not measure actual wall thickness
HP gain is a rough estimate only
Some blocks have thinner walls in spots
Always sonic test before machining

Engine Specifications

Quick Presets

Results

Displacement