Re: Spark Plugs

Posted by su8overdrive On 2013/3/12 2:40:54

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?