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) !

[nditiz1]

I want to say when I was calculating DH on my 2056 rebuild I had a shop mill the bottom part of the cylinder effectively bringing the heads closer to the top of the piston, lowering my deck height number.

[Superhawk996]

I want to say when I was calculating DH on my 2056 rebuild I had a shop mill the bottom part of the cylinder effectively bringing the heads closer to the top of the piston, lowering my deck height number.

Yup, that would do the trick too!

Always more than one way to skin a cat!

[jaredmcginness]

I want to say when I was calculating DH on my 2056 rebuild I had a shop mill the bottom part of the cylinder effectively bringing the heads closer to the top of the piston, lowering my deck height number.

Yup, that would do the trick too!

Always more than one way to skin a cat!

If my deck height is .076 and I mill .020 off the base of the jugs on the Bridgeport at work... My DH is now .056 thou, and we are good to go?
No changes in the connecting rods or anything like that.

No necessity to port.

Thank you guys for helping my grasp this.

[Superhawk996]

I want to say when I was calculating DH on my 2056 rebuild I had a shop mill the bottom part of the cylinder effectively bringing the heads closer to the top of the piston, lowering my deck height number.

Yup, that would do the trick too!

Always more than one way to skin a cat!

If my deck height is .076 and I mill .020 off the base of the jugs on the Bridgeport at work... My DH is now .056 thou, and we are good to go?
No changes in the connecting rods or anything like that.

No necessity to port.

Thank you guys for helping my grasp this.

Before you cut anything make sure you're evaluating your Compression Ratio at that new deck height target of 0.056" and make sure it's where you want it.

Per your OP

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

Estimating: if you put the deck height at .056 you're going to be around a 8.95 (let's round to 9:1) with a 50cc head.

If you want an 8.5:1 CR you're still going to have to remove about 2-3cc worth of head material.