Obtaining the proper compression ratio

K

kirkallen143

Famous Member
OK, fellers need y'all to refresh my memory, please.

I have:
--'68 200 block w/ 0.040" overbore and 0.010" milled deck.

--'75 stock log head milled 0.025" and using a Felpro gasket.

What I need/want:
Approx. CR of 9.2:1.

So I would need to mill the head 0.050" to achieve my goal, or more?

I remember that 0.010" milling of the head equates to @ 2cc reduction in chamber size, and from there my mind goes blank.

Thanks for any and all responses.

Kirk
 
Probably best have a machinist measure the block/cc the head, etc., and project what needs to be done to get to your desired cr especially since some mill work, boring etc., has already been done to both.
 
You are correct. That's why I was asking because of the previous work done.
I just cc'd the combustion chambers and came up with @ 62 - 64cc's as the average. The headwork done with the oversized valves are the answer for those figures eventhough the head was milled 0.025" is what I am guessing. Thanks.

Kirk
 
JackFish":1lm815d2 said:
62 to 64 seems kind of high for a head that was shaved, doesn't it? :unsure::
Click to expand...

But I had larger intakes installed: 1.75" was the reason I was guessing. I did the ATF fluid and syringe method to measure and used right at 63cc of tranny fluid.

I did the calculations and came up with as of now 7.64:1 CR.

Doing the math with what I have current I would have to mill the combustion chambers down .080" or to 48cc to get 9.13:1 CR. Is that feasable? Somewhere I remember reading that 44cc was acceptable and I think it was "Horsing Around With the Mustang Six" and AK Miller.

Kirk
 
Have you cc'd the block? On mine I came up with that 7:1 thing with the larger head. It appears to be due to some odd piston combo someone put in mine at some point in history. At least when they did that they worked on the head to get back to the 8.5:1 area. I did not want to mess with the bottom so I ended up fixing the original head instead of using the 'better' late one.
 
I did mine with a syringe and atf too, and with my head ('78)being shaved .050 I got a volume of around 54cc, +/- a bit.
 
I did my block and head(s) at home myself then had the shop do it when I took the head in to be worked on. I was 1 cc off from what they got.
 
Thats what I'll do too and have the machine shop double check what I did. I read that article again and AK Miller achieved 10.5:1 with the steel shim H.G. and 44cc combustion chambers and said it ran like a top and still kept that smooth inline six feel.

So it looks like 48cc for me and the 9.2:1 CR. And I sure do appreciate y'alls input, thanks.

Kirk
 
Don't forget that cutting the head or block that much to arrive at your projected compression will require you to replace the pushrods with custom length ones to restore the correct geometry to the valve train. Just in case you haven't thought that far ahead....Also, since your making the valves come a lot closer to the piston as well, checking P/V should be done, regardless of which cam you use just to be on the safe side.
 
Appreciate the heads up. I do have adjustable rockers and hydralic lifters, I think that would/should make up for the difference in milling. I have heard of putting 1/2" washers under the rocker pedistals to account for the difference.
I am staying with the stock '68 cam (.372 lift, but that's with 1.6 rockers so add @ .030 to that).

I don't think I will have any problems, but I will make sure that my calculations are backed by the machine shop.

I am trying to achieve the same comp. ratio as a stock '65 200.

Kirk
 
Reading thru a whole lot of older threads I found out that hyd lifters can soak up to 0.125", I'm safe plus the adj rockers.

This is what I plan on for this combo:
victor head gasket 0.044"
mill head to 46cc
3.72" bore x 3.126" stroke
7cc dished pistons
deck height 0.025" (measured)

-This should give me a 9.5:1 CR which I will run on 93 pump gas with @36 - 38 degrees total timing and using ported vacuum.
-I'll have headers, 1.6 ratio rockers, stock cam (@ 0.402" lift, that w/ the 1.6 rckrs).
-Holley 350cfm direct mount, 1.75" int valves w/ 1.38" ex valves that are backcut, 3 angle valve job, & mild port/polish.
-4 speed tranny w/ 4:10 gears and 33" tires.

I think it ought to run OK ;) .

Kirk
 
kirkallen143":4gbqe2eb said:
Reading thru a whole lot of older threads I found out that hyd lifters can soak up to 0.125", I'm safe plus the adj rockers.

This is what I plan on for this combo:
victor head gasket 0.044"
mill head to 46cc
3.72" bore x 3.126" stroke
7cc dished pistons
deck height 0.025" (measured)

-This should give me a 9.5:1 CR which I will run on 93 pump gas with @36 - 38 degrees total timing and using ported vacuum.
-I'll have headers, 1.6 ratio rockers, stock cam (@ 0.402" lift, that w/ the 1.6 rckrs).
-Holley 350cfm direct mount, 1.75" int valves w/ 1.38" ex valves that are backcut, 3 angle valve job, & mild port/polish.
-4 speed tranny w/ 4:10 gears and 33" tires.

I think it ought to run OK ;) .

Kirk
Click to expand...

Kirk,

I see no mention of a turbo here :unsure: What happened? :)

My old D8 log head was shaved .080 and the motor was decked .020 and I had no problems to report as long as I used the adjustable rocker arms.

Later,
 
Mustang_Geezer":3s9tr7kc said:
kirkallen143":3s9tr7kc said:
Reading thru a whole lot of older threads I found out that hyd lifters can soak up to 0.125", I'm safe plus the adj rockers.

This is what I plan on for this combo:
victor head gasket 0.044"
mill head to 46cc
3.72" bore x 3.126" stroke
7cc dished pistons
deck height 0.025" (measured)

-This should give me a 9.5:1 CR which I will run on 93 pump gas with @36 - 38 degrees total timing and using ported vacuum.
-I'll have headers, 1.6 ratio rockers, stock cam (@ 0.402" lift, that w/ the 1.6 rckrs).
-Holley 350cfm direct mount, 1.75" int valves w/ 1.38" ex valves that are backcut, 3 angle valve job, & mild port/polish.
-4 speed tranny w/ 4:10 gears and 33" tires.

I think it ought to run OK ;) .

Kirk
Click to expand...

Kirk,

I see no mention of a turbo here :unsure: What happened? :)

My old D8 log head was shaved .080 and the motor was decked .020 and I had no problems to report as long as I used the adjustable rocker arms.

Later,
Click to expand...

Thanks for the insite Doug. Oh yeah the turbo is off, just wanting to try something different for a change. And I really, really like the sound of headers with dual exhaust and a crossover/h-pipe. Anyways, the V8 broncos got tired of me beating them in the sand drags ;) .

Kirk
 
Well got the head milled yesterday for a total of 0.090", 0.025" the first time around and 0.065" this time. (I made a mistake and had the wrong cc of the head last time, it was really 59cc and not 62cc. Like reading the wrong side of a ruler, I did the same with the syringe)

This 0.090" mill almost got into the water jackets but didn't. I am right at 47cc chamber which give me a compression ratio of 9.2 to 1 by the calculations.
Only thing is that I found a hair-line crack that goes from the corner of #3 and #4 exhaust port to top of the intake log. I checked inside of the intake and it only looks like it is on the outside, hopefully. Well, I am going to run it anyways and once it breaks or cracks more, there will be another of Mike's aluminum heads on a 200 six. For now i'll smear some jb weld on top of it and put it back together and run it tell it gives out. Knowing the reputation of these sixes and how they last, I might not even be buying one of Mike's aluminum heads :LOL: . Just thought I let y'all know.

Kirk
 
kirkallen143":1knc9w2e said:
Mustang_Geezer":1knc9w2e said:
kirkallen143":1knc9w2e said:
Reading thru a whole lot of older threads I found out that hyd lifters can soak up to 0.125", I'm safe plus the adj rockers.

This is what I plan on for this combo:
victor head gasket 0.044"
mill head to 46cc
3.72" bore x 3.126" stroke
7cc dished pistons
deck height 0.025" (measured)

-This should give me a 9.5:1 CR which I will run on 93 pump gas with @36 - 38 degrees total timing and using ported vacuum.
-I'll have headers, 1.6 ratio rockers, stock cam (@ 0.402" lift, that w/ the 1.6 rckrs).
-Holley 350cfm direct mount, 1.75" int valves w/ 1.38" ex valves that are backcut, 3 angle valve job, & mild port/polish.
-4 speed tranny w/ 4:10 gears and 33" tires.

I think it ought to run OK ;) .

Kirk
Click to expand...

Kirk,

I see no mention of a turbo here :unsure: What happened? :)

My old D8 log head was shaved .080 and the motor was decked .020 and I had no problems to report as long as I used the adjustable rocker arms.

Later,
Click to expand...

Thanks for the insite Doug. Oh yeah the turbo is off, just wanting to try something different for a change. And I really, really like the sound of headers with dual exhaust and a crossover/h-pipe. Anyways, the V8 broncos got tired of me beating them in the sand drags ;) .

Kirk
Click to expand...

Okay....I understand now! ;) When do you plan on getting it up and runnin?

JB weld oughta work...it dont get that hot there on the log.

Later,
 
I'll have the head on this evening and get it torque'd down and do a cold adj. of the valves and put everything else back and then wait for Mike's header to come in...So hopefully, not too long.

Kirk
 
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