Re: 356 CI Compression Ratio

Posted by Scott On 2023/12/31 10:57:20

The '49 Golden Anniversary Std 8 (288) w/OD I used to own gave me up to 20mpg but that was on long trips that were all freeway. Mixed it was around 16-18mpg. I had rebuilt the engine (it had low compression prior to) and custom made a set of leaner metering rods for the carburetor and ignition was set not by spec but by ear (which was more advanced than book but that's why they had the "octane adjuster" Vernier scale on the distributor). Interestingly it actually did better at 70mph than at 55-60mph and that's where I would get the 20mpg. Packard offered different metering rods for the Carter carbs to enrich or lean from stock and I had managed to find the specs on them. One can change the metering jets but that changes the entire range whereas the optional rods had different profiles, not just fatter. In this way one can for example keep acceleration about the same but lean cruise.

My '48 Custom 356 w/OD is more like 13mpg in mixed driving (mostly freeway). I haven't messed with the metering rods in it yet but am contemplating bumping the CR before experimenting with mixture and ignition.