I have a 1966 383 4bbl engine automatic. Does anyone know what the stick compression ratio is? With this discussion I went out to look at my heads they are 2406516 which I guess you call 516 and this motor is a 65 not the original for my 66. So is the compression 9.0/1 or 10.0/1 ???? <span class='smallblacktext'>[ Edited ]</span>
Joined: Mon Oct 31 2005, 12:48PM
Location: Bakersfield, California
Posts: 1755
It all depends on how far that stick will bend before it breaks!
Oh, you mean stock.
I will have to check with the books at home, but I would guess between 150-175 pounds p.s.i.
D'oh! I just reread your question, you were talking ratio. A stock 440 was 10.0-1, perhaps 10.5-1. The 383 had to be in the same area. Again I will have to check. I am sure someone else will tell you before I get back to this site.
Joined: Mon Jan 16 2006, 02:52AM
Location: Vantaa,Finland
Posts: 379
The advertised compression ratios may be far from the truth. Typical mopar open chamber heads have 88-90cc chambers. If you calculate the CR with that chamber size, use NHRA Stock accepted pistons for a '68 383 that have 1.920" compression height and assume that the factory steel shim gasket is about 4.5cc's, you'll end up with just a tad over 9:1 compression ratio.
Joined: Mon Oct 10 2005, 10:29AM
Location: Metamora, MI 48455
Posts: 43
IIRC, Mopar was still using the 516 head on std. fare motors with the coveted 915s (?) being reserved for 440s. Maybe I'm wrong on that. In any case, even my -346 heads that have been worked over are still only @ 76cc which would bump up the comp. ratio to a closer ballpark to what MaMopar quoted.
Joined: Mon Jan 16 2006, 02:52AM
Location: Vantaa,Finland
Posts: 379
383's with closed chamber heads had lower compression height pistons than '68 & up. If I remeber, I can check what my '67 factory manual says about them.