Just did 107 highway miles this morning. Car ran great for all of it. Speeds were 70-75 mph for most of it. 70 mph in my car is ~2,550 rpm because of the 2.73 rear gear. I tried to keep my foot out of the secondaries for most of it. At 70 mph the Innovate A/F LM-1 meter is telling me about 16.2:1. A little slower, ~65 mph, the A/F ratio is down in the high 15's.
And the gas mileage result?....(drumroll).....
18mpg on this trip. Hmm. My JET Performance Stage 1 Qjet still holds the record with 20mpg on the same highway run. However, the mechanical secondaries on this Holley 450 make it real fun to drive when you put your foot in it. Even on the highway the acceleration from 65 up to 95 mph or so in 4rth gear is fantastic and you can drop just about anybody with the twitch of a toe. The lean stumble at mid-travel on the primaries is barely noticable now, I believe due to the raised float level. I don't think I'll put too much more time into tuning it in the near future. Probably move onto my disc brake/sway bar swap next.
So, what have we learned?
1) Carbs are fun to mess with!
(Although the wife doesn't much like them disassembled all over the dining room table.
2) A well tuned Holley Economaster 450cfm is a darn good little carb for a mild, small displacement engine like mine. The thing fires on the first whirl and idles smooth as a rock. It does tend to run out of smoke about 5k rpms but that's not much of a problem for the kind of driving I typically do.
3) NO parts are available for Holley Economasters (model 4360) except for a rebuild kit and accelerator pump from Holley, Jegs or Summit. Rebuld kit is Holley p/n 37-1540. Acc pump p/n is 135-1. Search "Holley 37-1540" or "135-1"on their sites.
4) Mechanical secondaries are more responsive and hence more fun to drive than vac secondaries.
5) As much as I like Qjets, the ultimate carb for a mild-street 327 like mine may be a somewhat larger cfm mechanical secondary Holley, maybe somewhere between 500-600cfm but jetted down. I know you can get a 600cfm double pumper, just not sure about smaller. Maybe I'll try that when the a deal comes along. Meanwhile, the Economaster stays for now.