I’m beginning to figure out how much more static compression I have to have to get this engine to respond better. I decided to pull engine this spring for new seals, fresh paint, transmission freshening, and firewall metal & paint work.

Using this on line [url=http://www.wallaceracing.com/dynamic-cr.php]calculator[/url], and entering the following values:

6 cyl
Bore= 3.430â€￾
Stroke=4.125â€￾
Rod length= 6.698â€￾ FSM (6.697â€￾ to 6.701â€￾)
Static compression ratio= 9.53:1 (with FelPro head gasket)
Intake close @ ABDC= 283 degrees (measured from degree wheel)
Boost=0
Altitude = 200ft

Your dynamic compression ratio is 6.83:1 .
Your dynamic cranking pressure is 129.24 PSI.

(Compression test shows 150, 151, 160, 145, 150, 149 PSI with 5 compression strokes.)

I think I have a ring problem. Head is 44cc each.
Dose this above result seem reasonable? If so:

Cutting Peanut head an additional 0.025â€￾ for a total cut of 0.100â€￾, using stock steel head gasket I get a caculated static compression ratio of 10.53:1, and the following calculated dynamic compression ratio per caculator:

Your dynamic compression ratio is 7.53:1 .
Your dynamic cranking pressure is 146.93 PSI.

Will this engine run on pump gas?

Bill

_________________
67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

This does not seem right. ( unless the calculator has special rules about the intake close number you use)
Most IC points I see (and use) are between 35 & 85 degrees ABDC.
DD

I ran your numbers on 2 different calculators both come up close to what you got, that 283 degrees intake closing is probably 77 degrees, using ether number gives you the same compression numbers on the calculators.
You should have no problem with pump gas

Doc:
[quote]This does not seem right. ( unless the calculator has special rules about the intake close number you use)
Most IC points I see (and use) are between 35 & 85 degrees ABDC.
DD[/quote]


I have to confess I’m still deep in the weeds with the degree wheel with its disjointed partial duel degree scales seemingly unrelated to one another; in my mind anyway. Recalling while plotting graph, this cam tended to overlap the nice defined events painted on wheel adding to confusion.

I plotted out both exhaust & intake event in what I’ll call real time in a 720 degree graph, or two rotations of crankshaft. I realize that cam turns two revolutions per crank and perhaps this is where my head explodes following degree wheel. At any rate, both events are plotted on a two rotation or 720* graph showing exhaust on left, and intake on right. I suspect graph is out of phase by some multiple of 90* not allowing my world to play nice with degree wheel world. I realize that every technical procedure has its conventions particular to application, it’s just I’m not fluent in, and have trouble thinking in the vernacular. I’m sure that if one could look over another’s learned shoulder for three minutes this would all make perfect sense.

Out of excuse mode:
As drawn, intake closing event is at 638* or better part of two crank rotations or 283* of one rotation, and I see how 77 degrees is arrived at. 360* – 283* = 77* before end of full revolution. I plotted exhaust event first than intake so their overlap is shown in middle of plot.

From beginning of opening to full closed, intake is open 356* at zero lift, and 316* at 0.006â€￾ lift, overlap of exhaust is 142* at zero lift, at 0.006â€￾ lift overlap is 101*.

Once engine is out of car, I’ll revisit degree wheel.

DI:
[quote]44 cc chamber, on a peanut head is starting to get close to the 'wedge'/shelf of the chamber, I had a head like this and asked to cut a little more off...now I have a 38.5 cc chamber...once the cut approaches this area the .0066 per 1cc is no longer appropriate so double check how much 'cylinder' you have before the cut goes too far.[/quote]

Thanks for the heads up… LOL

More questions:
If successful in raising compression ratio to 10.5 static or 7.5 dynamic, will this increase or help steady vacuum reading at idle, and provide better vacuum signal to carburetor?

How much would a broken ring contribute to wagging vacuum gage needle at idle such as 0 to 6 in Hg. Where the two weak cylinders take a few more strokes than their siblings to top out pressure gage 15 psi lower than the others, and a few squirts of oil in the plug hole brings big increase in pressure, say 180 psi, with only two or three stokes, I’m suspecting some sort of ring malady. Your thoughts.

_________________
67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

Okay I am going to ask a question that may sound stupid but if you are running at a consistent rpm IE 500 shouldn't your degrees be equal?
If you take this information and divide the 638 by 2 you get 319 not 283. if you take 283 and multiple by 2 you get 566. Looks like to me some sort of creeping issue. Based on what you have provided you can assume the next rotation would be 948 if not further.

_________________
2006 Jeep Commander
2013 Chrysler 200

1964 Valiant 4 Door
1965 Plymouth Barracuda
1967 Chevy Camaro

No, intake close event takes place at same degree every two crank rotations. (4 cycle) Nothing is slipping, and rpm has nothing to do with static opening and closing events. The only way to change cam to crank relation is to have a lot of slack in timing chain so there is some give and take between cam and crank rotation. This engine has a slop free chain.

Once engine is running, spark light-off can be moved ahead, or retarded within valve event by base timing setting, and mechanical and vacuum advance impute, but camshaft position in relation to crankshaft always stays the same in these engines.

_________________
67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

I just used this calculator on my new '64 Dart motor and got 8.9:1 dynamic CR @ 800 ft elev. Sounds right based on my experience.

10.6:1 static
intake valve closes 55 deg ABDC (257 @ 0.050" cam, 100 centerline)
7" rods, 3.445" bore

Should work great on pump premium and idle pretty well. Hoping for around 275 reliable crank HP.

6.83 sounds crippling, and a smaller cam or higher static CR is needed.

Lou

_________________
Home of Slant6-powered fun machines since 1988

Bill,

Now that I responded to your PM and looked at your numbers again, you are probably in good shape with your CR. The 150 psi cranking numbers are a clue that you are about there. You could go another 0.025-0.040" mill and would be fine too on pump gas (prolly premium).

I would guess that either your timing curve is not right (not enough initial - need 15 or a bit more, then 28-30 deg total - DI build one for you?) or your carb is just junk. This should all work pretty well together. It will not be a smooth idle, EVER, but should not be choppy.

Lou

_________________
Home of Slant6-powered fun machines since 1988