Need some help figuring CR

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moparshwick94

Mopar on the brain....always
Joined
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Hello all,
Due to health reasons I've been unable to post or chime in since 2009. I've sold off many of my Mopar to pay for medical and related expenses...it saddened me quite a bit. But im back from the near death grips..
I'm building a date code 9/11/65 440 with 516 heads. Just got the short block and heads back from machine shop. Was a really low mileage 440 that sat in a field for 30 years. I decided to keep the stock pistons, honed the block and fresh rings and bearings.
The pistons sit .084 down in the hole, and I cc checked the heads at 78cc using a cc kit.
The heads have just been resurfaced and ill be using a 0.020 steel shim head gasket.
My question is...would it be safe to say, that I'll be right around stock compression? And I believe stock CR was 9.5.1..please correct me if I'm wrong. MAN It's good to be back and working on a Mopar AGAIN...Thank you guys and gals!
 
moparshwick94 said:
I've been there and tried that page. There's information that I don't know, like "top ring down" and since the rotating assembly is in already, I can't just measure it. But thank you anyway.
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Just plugged in all your info and used 3/16 to top ring
and come up with 9.6:1. Are the pistons flat top?
 
cudascott said:
Just plugged in all your info and used 3/16 to top ring
and come up with 9.6:1. Are the pistons flat top?
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Well I certainly appreciate you doing the homework, thank you! The pistons are stock cast flat tops, no dish, no dome. Thanks again for doing that..
 
Kendog 170 said:
Glad to hear your back. What's it going in ?
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I dont have anything to put either of these engines in lol! I'm just building em..ive got my eye on a couple of Dusters and a B body tho. I guess I'm just bored. Figured I'd approach this differently this time around.
Before I would have a car and work on whatever it came with, now I'm building the drive train first, honestly idk what I'm doing
 
moparshwick94 said:
When I use these compression calculators, I get a different number every time. I plug in the same numbers, and each time, each different calculator gives me a different number. This is why I asked for some help, to maybe get second opinions.
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Yeah, Same here . I think my SB is 10.5 to 1 and BB 10.8 to1 but I may never know.
 
moparshwick94 said:
When I use these compression calculators, I get a different number every time. I plug in the same numbers, and each time, each different calculator gives me a different number. This is why I asked for some help, to maybe get second opinions.
Click to expand...

Just stick with the Summit Calc and you'll be close. I use the KB one usually myself as that will do "dynamic". The more info the calc requires, the more accurate it'll be but there's more places to enter bad info.
 
80fbody said:
Just stick with the Summit Calc and you'll be close. I use the KB one usually myself as that will do "dynamic". The more info the calc requires, the more accurate it'll be but there's more places to enter bad info.
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So this is the problem here, especially with the Summit Calc, it gives me the lowest CR equation out of them all. Gives me an 8.3:1, and when using original cast flats, same compressed head gasket, and losing just a hair of material by resurfacing decks and heads, the CR numbers should be at stock, or even a slight bit higher...and that's going based off of factory CR at 9.5:1...so I'm confused..
 
moparshwick94 said:
So this is the problem here, especially with the Summit Calc, it gives me the lowest CR equation out of them all. Gives me an 8.3:1, and when using original cast flats, same compressed head gasket, and losing just a hair of material by resurfacing decks and heads, the CR numbers should be at stock, or even a slight bit higher...and that's going based off of factory CR at 9.5:1...so I'm confused..
Click to expand...

Factory compression ratios were bs for the most part. Ignore that in my opinion as alot of motors had the pistons much further down in the hole than the "blueprint" number. If your numbers are correct, that calc will be close. The other calcs simply take more data to "tighten" up the calc. I would guess thou it'd be less than 0.2 of a point.
 
By the way, I had a 360 with TRW forged flats (no reliefs - old school) that ran like a beast. We tore it down and were just going to "re-ring". By the time I got thru the math, it was less than 8:1. Not one of us believed it based on how well the car ran around town with a big cam. Ended up getting new pistons and upping the compression to 10.12:1 I believe with heavily cut "J" heads.
 
80fbody said:
By the way, I had a 360 with TRW forged flats (no reliefs - old school) that ran like a beast. We tore it down and were just going to "re-ring". By the time I got thru the math, it was less than 8:1. Not one of us believed it based on how well the car ran around town with a big cam. Ended up getting new pistons and upping the compression to 10.12:1 I believe with heavily cut "J" heads.
Click to expand...
Ya, im at that point where I'm kicking myself for A. Not zero decking B. Not upgrading pistons C. Not milling heads.
I still have the heads off, and ready for a light port...just might take them back and have them take off .030...assuming the CR Calc is more correct then Chrysler was.
 
80fbody said:
By the way, I had a 360 with TRW forged flats (no reliefs - old school) that ran like a beast. We tore it down and were just going to "re-ring". By the time I got thru the math, it was less than 8:1. Not one of us believed it based on how well the car ran around town with a big cam. Ended up getting new pistons and upping the compression to 10.12:1 I believe with heavily cut "J" heads.
Click to expand...

Soooooo....how did it run with the over 2 point increase in compression? Basically was it worth going from a pump swill engine to a premium fuel engine?
 
moparshwick94 said:
So this is the problem here, especially with the Summit Calc, it gives me the lowest CR equation out of them all. Gives me an 8.3:1, and when using original cast flats, same compressed head gasket, and losing just a hair of material by resurfacing decks and heads, the CR numbers should be at stock, or even a slight bit higher...and that's going based off of factory CR at 9.5:1...so I'm confused..
Click to expand...
Really? I'm confused too. Maybe I'm all screwed up, but I've twice input your numbers into the Summit calculator and I get around 9.7:1 compression.
 
moparshwick94 said:
Ya, im at that point where I'm kicking myself for A. Not zero decking B. Not upgrading pistons C. Not milling heads.
I still have the heads off, and ready for a light port...just might take them back and have them take off .030...assuming the CR Calc is more correct then Chrysler was.
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Honestly, not sure it really felt that much meaner. Damn thing ran pretty good previously. The old 509 Purpleshaft was a pretty good cam apparently.
 
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I come up with about the same CR (9.62) using a different calculator and making some minor assumptions such as head gasket bore and top land thickness.

upload_2021-8-11_9-6-54.png


upload_2021-8-11_9-7-12.png
 
Assuming your measurements are good (no calculator is any good if the measurements are guesses and assumptions),wallace gave me 9.57 . Frankly i was surprised it was that high with the pistons that far down the hole..... then i remembered the steel shim hg, and the closed chamber head.
With a typical 906 head and a composition gasket, thats a high 7 to 1 engine.
 
33IMP said:
Assuming your measurements are good (no calculator is any good if the measurements are guesses and assumptions),wallace gave me 9.57 . Frankly i was surprised it was that high with the pistons that far down the hole..... then i remembered the steel shim hg, and the closed chamber head.
With a typical 906 head and a composition gasket, thats a high 7 to 1 engine.
Click to expand...
You guys are awesome...I appreciate you all. I'm going to go forward with what you all have come up with. I'm obviously inputting something wrong...At those numbers I'm completely satisfied. Thinking about dropping this drive train in a custom hot rod...and just received my Keith Long transmission back for my '88 short bed...I got some work to do. Thank you all!
 
Glad ur all better. Glad to see u back. Sounds like a really nice refresh on the 440. Did u have hardened exhaust valve seats installed? When u do that u can have the larger exhaust valves put in. Thanks. Kim
 
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