Compression ratio?

[sabre67]

ok thanks for your help time to teardown and see what im dealing with,

 

[33 IMP]

Good idea. The more info you have, the better your decisions will be.

 

[That_Tall_Dude]

It was the 383 I rebuilt for this car:
View attachment 1077900

I had first planned to hone the cylinders and rebuild the 383 with the stock pistons. They sat .076 in the hole though. THis put me about a point under the goal.
I ended up going .030 over and using Speed Pro pistons that sat .025 below deck, then decked the block to get them at .014. I was aiming to be in the 9.25 CR. The heads I have were milled before I got them and when I checked the volume, they came in at either 83 or 84 ccs. My final CR was something like 9.2 or close to that....right where I was hoping to be.
I'm fuzzy on the details but I wrote about it in my build thread titled....
https://www.forbbodiesonly.com/moparforum/threads/lookie-what-5000-buys-you.178346/page-37

starting reading that a bit ago; haven’t got through it yet

That says you have 480/.474 purple in it yeah?

 

[Kern Dog]

Close, the Mopar Performance 280/474.

 

[66Satellite47]

I love Mopar more than any other, but I've had damn near every make out there. The 351 Mach 1 was a slug off the line.
It had a Cleveland which couldn't get out of it's own way unless 3.73 or steeper gears and high revs. The 2bbl heads came w 2.02 intakes and 4bbl came w 2.19's. They were for top end high rev light cars. Now the Windsor was great on the bottom end and could get a 4,200lb pig moving pretty easy.

The Mach 1's I raced against were 351W I'm sure. Not many 351 Cleveland's around. Worked with a guy that had a '70 Mustang 351C & 3 spd manual. Very fast car. Knew another with a '71 Boss 351 Mustang. Very, very fast.

 

[ka0mek]

No matter what the factory service manual states, it is bullshit. They seemed to LOVE to overestimate the ratios.
My 1970 383 was rated at 8.7 to one but when I tore it down and measured everything, it came in at 8.12 to 1. It was an original piston, standard bore, UNrebuilt 383.would i be the same for a 68 838 2 barrel 383??

 

[33 IMP]

It seems to me that mopars compression specs might be for a Blueprinted engine (read stock eliminator engine).
Add a few production line tolerances like .020 or .030 higher than blueprint deck height, and 4 or 5 cc larger combustion chambers, and boom! minus at least half a point of compression.
Not all that bad, when gasoline octane took a **** in the seventies.

 

[BSB67]

The part that is funny about Mopar’s rated compression ratios is that the don’t represent the rated factory production CR, nor the blueprint spec.

As we know, the advertised CR is always higher than actual, but will vary to close, to not close at all.

Usually blueprinting will put you above the rated CR. Again, some more than others.