Thinking out loud - 1911, Found my deck height. All good? Options

[jaredmcginness]

See update and actual numbers on the added reply.


Sorry for the novel!!

Hey guys,

I'm building a 1911. I want to make sure that I have my thoughts in the right place.

-96 Bore x 66 stroke. Fresh rebuilt 1.7 heads with a 105mm fly cut register. Stock valves

-Running a .495 lift cam, lifters to match, HD springs + counter bore .630 (IIRC) extended.

I need to CC my heads first, get the volume, then determine my deck height and compression ratio? Stock 1.7 heads are 50cc. I assume mine will end up a tad larger, maybe 52cc. (will the fly cut alter the size?) But I might be off.

Is 8.5:1 a good target ratio? Ive read a few threads and this seems to be the middle ground compression. A good target DH is .045-.065? With a minimum of 0.040 to avoid contact.

A few examples - per a CR calculator:

50cc, 0.065 = 8.7:1
50cc, 0.045 = 9.2:1

53cc, 0.065 = 8.4:1
53cc, 0.045 = 8.8:1

This in mind, depending on my head volume it should be easy to narrow down where I need to be.

Am I on the right track? New to this and been digging into some old books.

Whats a good compression ratio, that should be safe for a mild carbed (dual 36) motor and mild cam. Want this thing to last more than a summer! I dont really have a target CR, because I dont know the difference of a few decimal points!

Happy 4th (IMG:style_emoticons/default/beerchug.gif) !

[VaccaRabite]

A 9:1 CR will give you more power, but also more heat that you will need to shed.

On my first 2056 iteration my CR was 9.2:1. This was before I even knew about setting CR, and just made my deck height .040 and ran with it. I did so many wrong things with that first build! Engine was really zippy but it was a bitch to keep cool. There were other contributing factors as well.

When I redid that engine to its current config I set the CR at 8.7ish:1 (I don't remember off hand, but I have it on a note somewhere.)

Zach