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

Hi
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 )

10deg BTDC = 0.515mm

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Thank you. How did you calculate it?

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

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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
(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)

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Thank you for sharing.