Anybody recognize these 340 pistons?

-
74Dusted

74Dusted

Stock Piler of 340's
Joined
Apr 11, 2011
Messages
1,689
Reaction score
366
Location
Lewistown, PA
These were pulled from a mid-year (July If i remember correctly) '72 340 that I was considering as a platform for a mild boosted engine for my '74 Duster.

Cast inside the skirt is the number "1267" google says it's a 10.5-1 CR (68 - 71) 340 Piston and is supposed to be "Positive Deck", but when I yanked them out, they were below the deck a little bit (at TDC)

I don't believe the 340 in question was ever torn apart prior to me purchasing it, just a wild guess based on the original bearings, original timing chain, 40 years of grease and fossilized gaskets :D

So are these 10.5-1 Pistons or 8.5-1 pistons?

SANY0242.jpg
 
...........Any 10.5 piston i've ever seen only had 2 valve notches.....on ur search did it say the compression distance?......kim.......
 
You need to measure the compression height. The compression height of a 10.5:1 340 piston is about 1.84". Compression height is the distance from the top of the piston to the centerline of the pin. Measure the distance from the top of the piston to the top of the pin bore. It should be about 1.350", give or take a few thousandths. If you're wondering how I came up with this number, it's the compression height (1.84) minus half the diameter of the pin (.984/2 = .492)

As to why the piston were down in the hole - that is common on stock 340s. The block heights are always off by as much as .020".

I would not run cast pistons if you are planning on boost!
 
I forget the Compression distance, it came up as a Keith Black part number for some reason.

They sat pretty far down in the hole. in this picture you can see the #3 at TDC. Somewhere around 3/16" to 1/4" below deck, give or take a bit.

S50004341.jpg


I know someone is going to ask about the Oil Pump Pickup Tube, one of the previous owners ran it in a Dodge Truck (hence the Truck Tube & Oil Pan

The picture up there is old, I tore that engine down over a year ago. Right now the block is inside a crate in my bedroom, and the pistons/rods/cam/lifters/crank/etc are boxed up and labeled/numbered for reassembly.
 
Those are the low compression 72-73 340 pistons 8.5.1 range. they still have steel insert in wrist pin area but and a lower ring land but i would stay below 6 psi or just replace with forged pistons.
 
jay27 said:
Those are the low compression 72-73 340 pistons 8.5.1 range. they still have steel insert in wrist pin area but and a lower ring land but i would stay below 6 psi or just replace with forged pistons.
Click to expand...


Please read the entire thread and links.

Straight off the web site provided above is the following information.

Chrysler
V 8 340 / 5.6L
1968-71


COMPRESSION RATIO(s) 10.2

COMP. HEIGHT 1.824
 
The web site clearly says 68-71 and I have ran in to this before , it is not a 68-71 replacement , have fun trying to find cast 68-71 replacements for that matter, The site is wrong with the info and picture and I did read the thread and link. I am not here to miss inform anyone and have a pretty good knowledge of these engines!
 
74Dusted said:
I was thinking somewhere around 5 - 8 lbs?
Click to expand...

At 5 lbs, you're probably OK. Any higher and you might run into trouble. Whatever you do, make sure that it doesn't go lean or detonate or it will get ugly really fast.
 
jay27 said:
The web site clearly says 68-71 and I have ran in to this before , it is not a 68-71 replacement , have fun trying to find cast 68-71 replacements for that matter, The site is wrong with the info and picture and I did read the thread and link. I am not here to miss inform anyone and have a pretty good knowledge of these engines!
Click to expand...

What is the compression height of these pistons, then?

Without the OP measuring what he has, it's all speculation.
 
They are probably 1.84(that would be best case scenario) 0.60 down the hole with what looks to be a felpro gasket which would put it below 8.5.1. with a 70 cc chamber. Measured alot of this stuff up years ago , silvolite , badger ,ohio etc before kb and others offered other choices and you would be surprized how low everything was. In order to be around 10.5.1(68-71 two valve relief high comp piston) with a j or x head you need to be out of the hole , do alot of milling, replace tulip valves etc. The common 4 valve relief piston (factory or rebuilders) do not offer much for performance
 
jay27 said:
The web site clearly says 68-71 and I have ran in to this before , it is not a 68-71 replacement , have fun trying to find cast 68-71 replacements for that matter, The site is wrong with the info and picture and I did read the thread and link. I am not here to miss inform anyone and have a pretty good knowledge of these engines!
Click to expand...

Wow, they make the pistons and have been in business since 1922 and you know more than they do. R O F L M A O!!

If you look on page 22 of their 2011 catalog you will see that 1267 is still available in seven bores.


I think they know more than you do if they are still making THOSE pistons TODAY.
 
What about the eighth bore? Maybe you meant bore sizes and without looking I would GUESS (only a guess) 5 bore sizes,you obviously have it figured out (its in a book so how could it be wrong??????) I cannot type that fast so explaining this to you would take to much time. And yes i do know!!!!!!! Anyway just wanted to help this person with their Question but feel free to take over from here.
 
You must log in or register to reply here.
-

Back
Top