273 Commando Rebuild Or Not?
Shot oil in the low cylinders and the compression rose indicating ring sealing issues.
The engine supposedly sat for a long time. Back three cylinders are obviously low. The manual says 130-165 psi and + or - 25 psi between cylinders.
actually
the passenger side 2-4-6-8 is all low, and
the driver side 1-3-5-7 is all a little higher; My guess is that one head or headgasket is different
The point remains, to get a "stock" ;
>"high compression 273", DOWN to 145psi will take a really late Ica, or
>"lo-compression 273", with a stock Ica of 48*, DOWN to 145 will take an Scr of about 8.3
I'm not arguing what your engine is or is not.
After all these years, there is no telling what's inside it.
I'm suggesting that the truth will require more investigation.
Furthermore;
As regards the FSM pressure guidelines;
That factory range which you quoted only reflects the quality of the factory builds, in the environment of the real world, and reflects the normal-wear changing values. Numbers like that are NOT a good target. Numbers like that just keep the warranty claims down.
At 130psi, the 273 will be gutless.
At 165psi, it will be as strong as it can ever be and still run on pumpgas.
At +/- 25psi from 145, that translates to a total of 34%; which IMO indicates a serious problem. In my world, if an engine has a pressure spread of more than 10%, something is wrong. My target is 4%.
Furthermore, no matter which engine you're working with, the low-rpm performance, at 145psi average, will be sadly lacking in anything but a lightweight early-A.
For comparison, 140psi is the pressure typical of an 8.0- 318 at 100ft elevation. In the heavier A's of the mid 70s, those were the most lackluster 318s of all time.
My point is this;
if that was my engine, and it was not a numbers matching engine, I would replace it with something bigger.
But if I just had to have a 273, then first I'd check why the one head is down on pressure. The factory 020 gaskets are no longer available and so, if it's just a fat gasket, then I would have a decision to make. Cuz if I put a matching gasket on the other side, it too will have the low numbers, and so the question becomes, can I live with ~140psi?
But if it's NOT a gasket mismatch, then I gotta go hunting, and depending on what I find, that will determine in which direction I gotta go.
Happy HotRodding