Packard Forum Index » Post-War (1946-54)

I am trying to figure out what compression ratio my car has now. This '54 Pacific came with a long-gone aluminum head,with a 8.7 CR, but now wears a "327 Thunderbolt" cast iron head. Can anyone here inform me how I can ascertain the year of this 327 head?

They had different compression ratios in different years, and maybe measuring the thickness of the cast iron head might reveal the compression ratio if I can't ascertain its year of manufacture. It might have been shaved before being placed on the 359 block with the 4 bl manifold.

Is there an easy way to ascertain that the block IS a 359 block? I confess I am a newbie with Packards, being an olde tyme Chrysler product fan who has recently found this awesome Pacific in great rebuildable condition. Thanks.

On the block check the motor number on a pad just below the head and above the starter. The 359 will start M6xxxxx. If the number starts any other way it is a different engine or year. Here is a portion of the engine serial number chart which is available for download in the literature section.

On the heads I don't know if anyone has a dimension to measure and as you said, they could have been milled anyway. AFAIK, the different heads for the various sizes were the same thruout the years of production so YOM should not make any difference. There is an article explaining different head and compression ratio changes for the 327/288 and 356 engines but don't believe there ever was an option to swap heads on the 359 to have official factory info. Here is what they said about the other engines. I don't know if you can extrapolate the 356 info to get close enough to the 359 to be meaningful.

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There is usually a date cast in the head right near the water outlet, though it is fairly often unreadable. All uncut cast iron heads are 1.87" (will doublecheck this tomorrow). Changes in compression ratio were always done in the pattern before casting and not by milling the heads thinner. If you have the head off, you can tell it has not been cut as the machining marks on the bottom will be straight lines as the heads were broached and not rotary milled. Any head milled by any normal machine shop will have tool marks that curve.

A 53 or 54 cast iron head will give too much compression and make a very fussy pinging engine. My choice for a 359 is a 1950-52 327 stick shift head. That puts your compression ratio in the low eights and the engine will not be fussy.

HH56 and Ross, your replies were spot-on and of great assistance to me and my mechanic. I thank you both for taking the time and effort to share your knowledge about these awesome time machines.I wish I had learned to enjoy them sooner, but am blessed to do so at this late time. May God bless you both!

EDIT: My M6XXXX engine is correct for 1954 (a 359cid), but I still don't know what 327 head I have. See below:

I checked the 327 cast iron head near the thermostat and believe the numbers stamped there are "35 5". Does that look like a head or date (May, 1935?) number to anyone? I'm trying to find out which head is on it because the 327 heads were not the same compression ratio each and every year; they varied as to CR.

The car was parked for a long time in an airplane hanger and has now been cranked and has run for about an hour. It smokes enough to kill swamp mosquitoes in Louisiana, but hopefully the smoking may stop after it has been run awhile without Marvel Mystery oil poured into it. It is pretty smooth running considering one of the pistons has not found compression yet. We're trying to baby it until it wakes up.

I would image there should be a longer casting number on the head somewhere.


I keep saying that we need to build a list of casting numbers to head IDs. Then it would make it easy to ID what head is on the motor and see if it's correct or not.

I just don't have access to enough heads to create that list.

Looking back through my unfinished projects, I did come across this Excel file (attached as a PDF for easy viewing). But I would just need to add the casting numbers to it for a complete reference. This was compiled from the Parts List:

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Bigkev, thank you for the information you have sent. I have yet to learn what year 327 Thunderbolt head is on my car, finding only the numbers "35-5" near the water outlet.

Perhaps you could answer a corollary question by email to my personal address: I have no experience or knowledge about EMI (Empire Motors, Inc.) in El Paso, but have had the pleasure of speaking to the owner, manager, who is very knowledgeable.Do you know of anyone who has purchased an aluminum "Edmunds" knockoff head who actually installed and used such a head on a 359 or other Packard engine? If so, I would love to know how the head performed.

I realize the head cannot be shaved, or should not be, but not knowing the CR on the 327 head, I am concerned about having too low compression. I plan to DRIVE the car if and when it gets restored because it has or will have every accessory needed for comfortable traveling: It has power seat, p/s, p/b, 3 speed with O.D., Add-on Vintage A/C, radio and heater.

I also ask you your opinion of the value of the car with the "wrong" 327 head vs. a repro Edmunds head which is readily identified as a repro by the wider ("better") fins on the head? That seems also to be a "wrong" head unless an indistinguishable repro head can be custom-made by EMI at a custom cost of $3,150. I can send EMI a series of pics of my unusable original aluminum head for him to use in reproducing the aluminum head, but I can't guess how accurate and indistinguishable such a knock-off would be, or how that would affect the value of my car. Any ideas on this?

Kev, another question is what to do about the valve seats: Do I use a lead substitute, or what can I do to prevent burning the valves/seats?

A poster on another site was recently offering an Edmunds-type cylinder head (brand new) and he also had a dual carburetor manifold. Can't recall the site, but you might want to look on the AACA and Packard Club sites. I'll look too and let you know if I find it again. It was not too long ago, maybe a week or so back that I saw his posting.

(o[]o)

This thread on the AACA Website.