A Couple of Math Questions

Anyone help me to figure this out?

I have a 73 850, well 828, with 40thou oversize pistons and bore.

1) How many cc's do I have now?

2) Anyone remember what the stock compression ratio is on my 73 850? What does the increase of 40thou bore raise my compression ratio to now?

3) I have fitted a Megacycle 5600 cam, a bit more aggressive than the stock 850 cam: Does this cam switch from stock raise the compression at all, and if so how much?

4) with the overbore and new cam, any guess what my compression ratio is now?

just very curious!

Stock C/R is 8.5:1. Depending on tolerances, yours could be a bit higher or lower.

An overbore is unlikely to move the needle in terms of C/R.

An aggressive cam won't affect your static C/R but typically will lower your dynamic C/R. This will typically lower your bottom end power and raise it on the top end - or in other words, "move the power band up the RPM range."

The more technically proficient can no doubt provide a more nuanced and reasoned explanation.

Stock bore plus .40 your New "78 "bore x 89 equates to 850.59 cc and will compress an extra 11cc into each head space,

As Briank says, its known that those who tried to detune a Combat by standard cam only got detonation issues. My 10.5 CR Peel is using a drag only cam to lower effective CR to run on 87 octane if I behave on throttle snaps at low rpm. Seems like I remember a forum post that calc for each .020" bore increase, gives about .1 CR raise. A more aggressive cam/overlap, needs higher CR to be a power adder instead of a power hinderer.