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kencombs

milled head . chamber work/size Compression ratio

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I had my head milled, more than normal (.060) because I wanted to do some chamber work. 

I marked the gasket edge on the head and ground the area near the exhaust valves back closer to the gasket edge to unshroud the valves and did a little smoothing.  Checked the resulting size and arrived at 70cc.  I measured the head gasket that will be used and estimated (guessed) its' compressed thickness at .040 so it should add 8cc or so.

 

Compression ratio = (cylinder displacement+chamber volume+head gasket volume) / (Chamber volume+head gasket volume)

 

My numbers, all in cc's ,  (628+70+8) / (70+8 

 

That puts me at 9.05:1.  Close to maximum I think for a flathead.  Probably be a premium fuel burner.

 

Now the questions.  How do those numbers compare to any measurements you folks have taken?

Does the calculation above make sense to the collective wisdom here?

 

There is a  more smoothing that could be done to gain a few cc's if needed.

 

edit to add:  This is a 56 Plymouth 230 head.  These were advertised originally at 8 or 8.1:1.  With the .060 I removed they must have been way under the spec'ed ratio from the factory as the amount removed in the chamber work was not all that much.

Edited by kencombs

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Almost 100 views and no comments.  I figured there would be some discussion (cussing?) of my formulas or faulty math.  Or at least, 9 to 1 will blow that old thing up!

 

I probably should have started with .040 off the head, but didn't want to pay again to take more off if that wasn't enough.

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I thought ya had started with some good information supplied by Tony a few weeks ago and kinda wondered why another thread was started but I'm more interested in the information rather than strict presentation rules.  I have rebuilt a few flatheads, but that was before I knew anything about boosting the CR to squeeze some more horsepower out of the dinosaur juice.  The late '50s car flathead production have interested me as a performance target because the engines were effectively the same as the late '40s, but with about 25% more power, and that's the kind of reliablity I'm interested in, no need to make my buggy run like a scalded dog, but a little more oomph to get up the hills would be nice.  Studying that chart, I'd be leaning towards achieving a CR of 8.8-9.0, anything more than that is getting into excess of the safety margin originally used for these engines.  I have read that the rule of thumb for head gasket compression is about 75% of original thickness, dunno if that's how ya figured that thickness but .040 seems kinda thin...but, increasing this volume will still result in a CR around 9.

 

I suppose running premium fuel during engine break-in wouldn't hurt, beyond that it may take some experimentation to determine if there is any performance change in octane.  I only did one experiment with octane, on a '99 Ranger with a 3.0 V6, as it was a work truck that I was racking up 3k a month driving to projects.  Within a year, I could tell that little truck ran slightly better on 89 octane (especially in the hot summer months), not much better with 91.  I have driven other ppl's modern cars, and would shock them by making their buggy come alive simply by putting 91 octane in the tank, just like the label says on the fuel door, but those engines were specifically designed to run on premium for maximum power generation...other older cars, never could see the improvement by switching to premium because the engines were designed to run on lower octanes...

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32 minutes ago, JBNeal said:

I thought ya had started with some good information supplied by Tony a few weeks ago and kinda wondered why another thread was started but I'm more interested in the information rather than strict presentation rules.  I have rebuilt a few flatheads, but that was before I knew anything about boosting the CR to squeeze some more horsepower out of the dinosaur juice.  The late '50s car flathead production have interested me as a performance target because the engines were effectively the same as the late '40s, but with about 25% more power, and that's the kind of reliablity I'm interested in, no need to make my buggy run like a scalded dog, but a little more oomph to get up the hills would be nice.  Studying that chart, I'd be leaning towards achieving a CR of 8.8-9.0, anything more than that is getting into excess of the safety margin originally used for these engines.  I have read that the rule of thumb for head gasket compression is about 75% of original thickness, dunno if that's how ya figured that thickness but .040 seems kinda thin...but, increasing this volume will still result in a CR around 9.

 

I suppose running premium fuel during engine break-in wouldn't hurt, beyond that it may take some experimentation to determine if there is any performance change in octane.  I only did one experiment with octane, on a '99 Ranger with a 3.0 V6, as it was a work truck that I was racking up 3k a month driving to projects.  Within a year, I could tell that little truck ran slightly better on 89 octane (especially in the hot summer months), not much better with 91.  I have driven other ppl's modern cars, and would shock them by making their buggy come alive simply by putting 91 octane in the tank, just like the label says on the fuel door, but those engines were specifically designed to run on premium for maximum power generation...other older cars, never could see the improvement by switching to premium because the engines were designed to run on lower octanes...

Not so much thinking of a performance increase on premium as I am concerned about spark knock.  These old chamber shapes are more prone to that than the newer ones with ‘squish area’ over the piston.  I got some of that back with the deep milling but it may still ping more than an overhead valve of the same compression. 
as you say, experimentation will tell the tale.  I want enough octane to allow decent spark advance which helps with hp output. But no more than enough.  87,89 91 93...whatever it takes. Fortunately I have those available locally in e10 and e0..  and e85 if I want to really experiment. 

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1 hour ago, JBNeal said:

 There are a couple of easy ways to check valve to head clearance on flat heads.  Solder would surely work if you pick the right diameter solder.  There are lots of them.  I prefer play dough.  Kids toy. But works. 
 

or quick and dirty, lay the head In place no gasket or bolts then turn the engine over slowly while watching the valve side.  No movement means you have space. And it will increase when a gasket is installed.  If it there is interference move on to play dough, modeling clay or solder with a gasket
 

I cced mine because of all the charts out there that list safe numbers to remove but None of them match. One says 30 another 50 or something. Plus there is no way to know if you are dealing with  a virgin head. 

Edited by kencombs

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On 12/28/2019 at 12:03 PM, kencombs said:

edit to add:  This is a 56 Plymouth 230 head.  These were advertised originally at 8 or 8.1:1.  With the .060 I removed they must have been way under the spec'ed ratio from the factory as the amount removed in the chamber work was not all that much.

Are you taking into account that the piston probably doesn't come all the way to the top (0 deck)?

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3 hours ago, Adam H P15 D30 said:

Are you taking into account that the piston probably doesn't come all the way to the top (0 deck)?

 

Not in my formula, but will be when I get the crank, rods and pistons in.

 

I thought of that  the original post, but decided to leave that out of the discussion until I get further along.  But, I'm sure there will be enough there there to get me well below 9:1. 

 

Right now I'm looking for a local cam grinder.

 

Odd thing happened.  I've heard all my life about cams or cranks warping in improperly stored but have seen hundreds just laid with no regard to that..  Anyway, when the new cam bearings went in the cam wouldn't turn easily.  Everything measures ok, and it is fine with only two bearing/journals engaged,but as soon as all the of them are engaged it is really tight.  Looking a #2 bearing there is a mark that looks like the journal is not in line with 1 and 3.  Got a spare cam off the shelf and it is fine, goes in with no drag and turns freely.

 

I don't have a good set of v blocks to confirm, but I think the original is bent/warped.   Bad thing is I kept the lifters in a storage board in order so I could reuse the cam and lifters as originally installed.  If I change cams, it and the lifters will need to be resurfaced. 

 

So looking for some cheap vblocks, Maybe, just maybe, I can straighten in the press.  If not, off the the grinder.

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