CR -> Octane

[mysavioreigns]

I want to know if I can figure out what my compression ratio is. I know the block is a '66 200, and the head is a '70 170, but I don't know how much he decked it. It's bored .010 as well. Any tips on how to guess?

 

[Bort62]

Well, it is going to vary widely depending on how much the head was surfaced, so I'm not sure how you could reasonable guess...

 

[CZLN6]

Howdy MSR:

I'll hazard a guess after making some assumptions.
Let's see a '70 head will likely be a C9xx or a D0xx. The 1970 170 was rated by FoMoCo at 9:1 so I'm guessing it had a 52 cc chamber volume initially. The head was at least skimmed .010" while doing a valve job in the rebuild so, I'll figure 50 ccs currently. Since it is obvioulsy not original it will likely have an aftermarket headgasket at about .050" thick. The .010" overbore is a helpful fact.

Given the above assumptions my guess is 8.7:1. Turning the assumptions into factual measurements could change this guess to anything in a range of 8.5:1 to 8.9:1.

I hope that is helpful.

Adois, David