Here is a spec that surprises people the first time they see it: the Honda K20 is a perfectly square engine — 86 mm bore, 86 mm stroke, a bore/stroke ratio of exactly 1.00. That is not a coincidence; it is Honda deliberately splitting the difference between revs and torque. Load the K20 preset above and the panel flags it as square. This calculator carries the whole B- and K-series with verified geometry so you can see each engine's character, not just its size.
The B and K families, side by side
What separates these engines is mostly stroke, and the geometry tells the story of each one's personality:
| Engine | Bore mm | Stroke mm | cc | B/S | Geometry | Marketed |
|---|---|---|---|---|---|---|
| B16A | 81.0 | 77.4 | 1595 | 1.05 | square | 1.6 L VTEC |
| B18C | 81.0 | 87.2 | 1797 | 0.93 | undersquare | 1.8 L GSR |
| B20B | 84.0 | 89.0 | 1973 | 0.94 | undersquare | 2.0 L |
| K20A | 86.0 | 86.0 | 1998 | 1.00 | square | 2.0 L square |
| K24A | 87.0 | 99.0 | 2354 | 0.88 | undersquare | 2.4 L |
| F20C | 87.0 | 84.0 | 1997 | 1.04 | square | 2.0 L S2000 |
The B16A is 81 mm × 77.4 mm — oversquare, high-revving, 1,595 cc. The B18C keeps the bore and lengthens the stroke to 87.2 mm for more torque at about 1,797 cc. The K24 stretches the stroke to 99 mm and trades some RPM for a torquey 2,354 cc. Bore is nearly constant; stroke does the character work.
Why the badges round down
A "1.6" B16A is really 1,595 cc; a "2.0" K20 is 1,998 cc. As everywhere, the badge is a rounded class number and the geometry lands just under it — which is worth knowing when you are checking that a swapped engine is what the seller claims.
The F20C outlier
The S2000's F20C shows how far Honda pushed the oversquare idea for RPM: an 87 mm bore against an 84 mm stroke, about 1,997 cc, built to chase one of the highest redlines of any road four. Enter it and the panel reports the oversquare geometry that makes that redline possible.
Modelling a swap or a build
B- and K-series engines get mixed and matched constantly — B20 blocks under VTEC heads, big-bore sleeves, different cranks. Because the families share dimensions but differ in stroke, the only reliable way to know what you have is to measure bore and stroke and calculate. Load the nearest preset, edit the numbers to match your parts, and read the displacement, per-cylinder volume and geometry together.
Confirming a used engine's identity
If a listing says GSR but the stroke measures 77.4 mm, it is a B16, not a B18C. The calculator plus the closest-engine hint turns a tape-measure reading into an identification, which is a lot more reliable than a sticker on the cam cover.
References & standards
- NIST SP 811 — Guide for the use of the SI, including the exact inch and unit-conversion factors.
Frequently asked questions
What are the B16A bore and stroke?
81 mm bore and 77.4 mm stroke across four cylinders, giving about 1595 cc — the high-revving 1.6 VTEC.
How do I calculate a K20's displacement?
Enter its 86 mm bore and 86 mm stroke; four cylinders give about 1998 cc, and because bore equals stroke it is a perfectly square engine.
What makes a K24 bigger than a K20?
A longer 99 mm stroke against the same-ish bore. At 87 mm × 99 mm it reaches about 2354 cc, trading some RPM for extra torque.
Why is the B18C stroked versus the B16?
It keeps the 81 mm bore but lengthens the stroke to 87.2 mm, lifting displacement to about 1797 cc — more torque while staying a high-revver.
Is a K20 really square?
Yes — 86 mm bore and 86 mm stroke give a bore/stroke ratio of exactly 1.00, a deliberate balance between RPM and torque that the panel flags as square.
What is a B20 'frankenstein' build?
A B20 block (84 mm bore, 89 mm stroke, about 1973 cc) paired with a VTEC head — enter the B20 bore and stroke to see the displacement that setup starts from.
How do I confirm a swapped Honda engine's size?
Measure bore and stroke and calculate, since B- and K-series share families but differ in stroke. The result plus the closest-engine hint helps identify what you actually have.
What bore and stroke make an F20C?
The S2000's F20C uses an 87 mm bore and 84 mm stroke for about 1997 cc, oversquare to chase its famously high redline.
Are Honda engines usually oversquare?
The sporty ones lean oversquare or square for RPM — the B16 and F20C especially — while longer-stroke variants like the K24 shift undersquare for torque.
Can I model a de-stroked or big-bore Honda?
Yes. Load a preset, then change bore or stroke to reflect a big-bore sleeve or a different crank and read the new cc and per-cylinder volume.
Why does my B16 read 1595, not 1600?
Because 1600 is the rounded badge. The real 81 mm × 77.4 mm geometry gives 1595 cc, just under the round number, as with most 'nominal' sizes.
Which preset fits a GSR versus a Type R?
The B18C covers the GSR-family 1.8; edit stroke or bore for specific Type R variants, then confirm the displacement against the panel's figure.
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