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

HI, I have a 22nd series Deluxe Eight with the little peanut plugs, there are AC M-8's in there now. I need to replace them, should I get more M-8's or is there something better to use?

AC M-8s are fine, you could also just go to the local auto parts store and get a set of Autolite #3136 which is also a correct current plug for this engine.

Amen. Have been using AC M-8s for decades. First in my '40 120, now my '47 Super Clipper and they give good service, the heat range seems to be spot on. Friends with '41 Cadillac-ack-ack-ack-ack-ack-acks report the same,
and they have at 7.25:1, slightly higher compression than 1940-47 Packard 8s and Su-8s' 6.41 and 6.85:1 tho' my '47's running a '48 327 head for 7.5:1 my auld mechanic having worked in postwar Packard and Hudson garages, knew about this in the day per an obscure Packard Service Counsellor bulletin.
A friend's run a 288 head in his '42 One-Sixty drophead for decades using M-8s without a hitch. Someone told me long ago that as old stovebolt Chevy 216-ci ohv sixes also use the small 10mm plugs, AC continues to produce these for the South American, etc. markets. I hope they and others continue to do so or we're sunk.

BTW, have oft wondered why Packard didn't go higher, 1942-47, than 6.85 compression from the factory given Clark Street's 7.25 since an inline eight is inherently smoother than a V-8 and would allow a slightly hotter cam in the win-win bargain. Any engineering insight? I know the horsepower race wasn't on 'til the '50s, but Buick got a lot of PR out of the power from their compound carbed 1941-42 320, and Packard did increase 356 compression from 1940-41's 6.41 to 6.85:1 from 1942-47 to match Buick's advertised 165 hp---and not as far from the truth as most makes' claims, Packard's among them, according to Flint engineeers tests of all makes at the GM Proving Grounds.

Cadillac complained about Buick's corporate oneupmanship, tho' part of that was Flint's cheek in marketing a few Brunn catalogue customs for 1941.

NO interest in what ifs, coulda, woulda, shoulda Monday morning quarterbacking. And please don't tell me Packard didn't care about such, because i've got a '47 Super Clipper ad crowing about "....the most powerful eight-cylinder engine ever cradled in a production car." The extremely limited production Duesenberg J and blown '37 Cord 812s notwithstanding, that was true regarding torque, but the compound carbed 1941-42 Buick did trump Packard 356's hp and yes we know a 356 with twin carbs would be 190 or so blah, blah, blah.

The point is, Packard cared, so why didn't they boost compression a wee more? The flathead Cadillacs didn't ping
at 7.25, my '47 doesn't at 7.5, nor does my friend's 42 160 ragtop at 8:1, and you know Packard engineering ran all manner of tests, war work or not.


? Anyone?

As regards Inline vs V Motors, OHV vs Flathead, and compression, that long crankshaft saps power. The long stroke is also a limiting variable. Supposedly up to 40% of an engine's power output is used up by the compression stroke. The flathead compression is limited due to higher carbon build up than an OHV motor. The 359 is pretty much at the limit and the aluminum head made smooth to fight carbon build up. Once I serviced a 41 160 with the opitonal HC (high compression/high carbon) cylinder head for knocking. Even with the 6.85 (probably more due to past milling) it was loaded with carbon. The owner was happy that all it needed was to have the 1/16th inch of carbon scraped out. It sounded like it had bad rod bearings.

So that's about it. The lighter parts in a V-8 use up less power to make it go.

Hope this helps

Thanks, Cardinal Cole, but my question wasn't about ohv vs. L-head, only why Packard didn't raise the compression of their valve-en-bloc 356 to the Cadillac valve-en-bloc 346's 7.25:1 or higher, given Packard's own Service Counsellor bulletin suggesting the 327 head be used as soon as it came out in the late summer of '47 for 356 wanting a little more oomph, and that providing an instant 7.5:1 compression sans milling.

Long stroke isn't an issue in THIS comparo as the 356's stroke is only 1/8th of an inch longer than the Cad 346's 4 1/2 inches.

That's the question. We know all things being equal, an ohv engine can handle a full number higher compression than a sidevalve engine. The fact remains that Packard increased the 356's compression for 1942 to counter that Buick advertised for their 320--- which was closer to the truth than most makes to begin with going back to single-carbed 1940 Flintmobile dyno tests GM engineers did including all the other makes of the day.

The question involved 356 and 346; both flatheads nearly the same displacement and stroke. Some friction losses in the 356's additional six main bearings, but again, inline eights (and inline sixes) have inherent balance that no V-8 had or has.

So .... since Packard had an inherent edge on smoothness,
why didn't they make the cam a trace livelier and boost the compression on all 356s even as their '47 Service Bulletin suggested?