My mom was part German, that's the German spelling for Karl...
340 compression ratio
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My mom was part German, that's the German spelling for Karl...
Brothers from anutha mother? Yer practically twins! Mopar brothers reunited!
That’s what I’ve been told as well. My last name is believed to be German as well.
Claimed compression and actual compression ratios from Mopar varied greatly.
ir3333
Well-Known Member
most find stock early hi comp 340's were around 9.5:1 with 72 cc heads and pistons out of the deck 20 thou or so. Mopar rated them at 10.5:1 so you could blueprint them to 10.5 and be NHRA legal.( cut the decks, cc the heads down to 63-65 cc's etc.)
If your pistons are at zero deck you would be 9 - lo 9's and pistons below the decks like later 340's will give you something in the 8's.
But the only way to be exact would be to measure and calculate.
If your pistons are at zero deck you would be 9 - lo 9's and pistons below the decks like later 340's will give you something in the 8's.
But the only way to be exact would be to measure and calculate.
Couldn’t take it anymore. The pistons have some carbon in the tops of them so figure since I’m that deep, I may as well go ahead and pull them to clean the carbon off. I just pulled one of them today to see if I could get a part number. Looks like a silvolite 1267 .030, that should get me closer. I’ll try and get the heads cc’d this week.
ir3333
Well-Known Member
you don't have to pull them to clean the tops?
are they above,below or even with the deck at tdc?
are they above,below or even with the deck at tdc?
I only pulled one, biggest reason I pulled it was to see if I could find a part number. They are even with deck. How do you like to clean them?
ir3333
Well-Known Member
They can be carefully scraped....
O deck is what most shoot for at around 9:1 ratio depending on valve reliefs,heads and gasket
O deck is what most shoot for at around 9:1 ratio depending on valve reliefs,heads and gasket
Just put them at tdc and run a wire wheel in a drill to clean the carbon off... No need to pull the pistons and put another clamp cycle on the connecting rod nuts...
perfacar
Well-Known Member
the 1267 is a flattop piston, has comp hgt of 1.824, makes it 10.2 comp. the 72 n 73 340, comp ratio will be 9 to 1 if deck block to factory specs, piston down . 054, 64.5 cc head with .036 gasket.
Yes flat tops with 4 valve reliefs, I read that 10.2 on their website, but wouldn’t the heads cc’s and headgasket thickness alter that number?
dibbons
Well-Known Member
So what is the CC size of each of the four valve reliefs in the top of the 1267 piston? I would guess between 1 and 2 cc each for a total of between 4 cc and 8 cc.
I haven’t measured a
I haven’t measured them or the heads yet, but from what I’ve been able to find probably 7-8 cc’s total on the reliefs.
scatpackbee
Well-Known Member
My factory '69 x heads cc'd at 75.
I didn't think it was possible to be so far away from the advertised 63 CCs but Herb McCandless confirmed the fact that x heads were more like 75 CCs on one of his performance seminars.
I milled mine down to get 68 CCs for a true 9.8-1 compression ratio.
I didn't think it was possible to be so far away from the advertised 63 CCs but Herb McCandless confirmed the fact that x heads were more like 75 CCs on one of his performance seminars.
I milled mine down to get 68 CCs for a true 9.8-1 compression ratio.
stixx
Well-Known Member
Tell me your last name and I can tell you whether that sounds german to me.
Easy way to clean them is cook them in a crock pot with a mixture of simple green and water, the carbon will fall off of them.
Where are you in WV?
Thanks sir. I’m in Oak Hill. Where are you located?
Clarksburg,
For the life of me I cannot think of where Oak Hill is located at.
For the life of me I cannot think of where Oak Hill is located at.
Oak hill is is about 10 minutes north of Beckley on RT19 headed towards Summersville.
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FYI
4.06X3.315 is 703.3 swept, and
74 +8.9+12 + zero deck= 94.9 and
(703.3+94.9)/94.9= 8.4 , this is about worst case.
About best case with uncut heads might be
72+6.5+10=88.5 and
(703.3+88.5)/88.5=8.95
Did you do a compression test?
Edit
To get the swept,I assumed .020 overbore, so; 4.04 + .020 =4.06
And so, to get the volume of one cylinder, in ccs, called the swept, I do this;
4.06/2, squared and then multiplied by 3.1416(pi), then times the stroke(3.315), then times the constant 16.387 to get ccs = 703.3
4.06X3.315 is 703.3 swept, and
74 +8.9+12 + zero deck= 94.9 and
(703.3+94.9)/94.9= 8.4 , this is about worst case.
About best case with uncut heads might be
72+6.5+10=88.5 and
(703.3+88.5)/88.5=8.95
Did you do a compression test?
Edit
To get the swept,I assumed .020 overbore, so; 4.04 + .020 =4.06
And so, to get the volume of one cylinder, in ccs, called the swept, I do this;
4.06/2, squared and then multiplied by 3.1416(pi), then times the stroke(3.315), then times the constant 16.387 to get ccs = 703.3
Last edited:
ifishinbc
Active Member
My 340 X heads averaged @ 68 CC, my set of J, 2.02 averaged 73 CC. The vender I bought the J heads from said they were milled .030", doesn't appear they were to me.
uempistons.com has a pretty good compression ratio calculator. It does static, and dynamic.
I cked a few things last night after work. Looks like 75 cc’s on my heads (i had a hard time getting all the air bubbles out), I’m at 0 deck. I contacted silvolite via email and the pistons with the reliefs are 10cc’s with 1.824 compression height. The cylinders are .030 I just used the simple compression calculator on summits website. If I use a .028 headgasket looks like the best I can get is about 8.75. Unfortunately I pulled the valves from one of the heads and the guides are pretty worn. I know the wiggle test is not the way to check them but the wiggle test is all it takes to see these are worn out. So my delima is now to decide what to do. I can buy new heads but that’s a lot of coin for a working man. I’m gonna call our one and only machine shop and check for prices on guides and maybe milling the heads. I’d like to get the compression in the 9’s for the street.
Man I just can’t get that math. I done some measuring last night and used summits “simple” calculator, I posted my findings below. Thanks for the input.
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