Ignition Timing - Convert Degrees BTDC to mm - Digital Ignition 2

I’m installing an Ignitech digital ignition system to my TMKZ10 144cc 2 stroke engine. The supplier has provided me with BTDC value of 10 degrees.

How do I convert/calculate that value into millimetres?

Stroke = 54.43mm
Conrod length = 109.8mm

I believe the late Al Nunley had a formula on this on his famous excel sheet.
Failing that: https://lambretta-images.com/tuningh/port-timing-calculators/degrees-to-mm-timing-calculator/

(Edit, looks like 0.5mm but confirm this :wink: )

10deg BTDC = 0.515mm


Thank you. How did you calculate it?

I’ve written a spreadsheet to do the maths quickly.
But its just trigonometry.

1 Like

Just trigonometry…lol. Can you share the calc sheet?

Not sure if I can append a spreadsheet here, but the formula is:


{ST} = Stroke
{RL} = Rod Length
{BTDC} = Degrees Before Top Dead Center

You can jusy copy that into excel or google sheets :smile:
(It looks way more complicated than it really is when it’s written out like that)

Edit. I can upload an attachment.
timing.xlsx (9.0 KB)


Thank you for sharing.