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Location: At my Bar drinking and wrenching in Lafayette Colorado
There is quite a range of Holley 4150 series carbs. The HP series 4150s have pretty much the same features as the Demon, and the two carbs will perform virtually identically. They both have 4-corner idle systems and replaceable bleeds. If you compare the Demon to the entry-level 4150, the Demon will have more tunable features, but that's comparing apples to oranges.
I have used both on my 430hp 355 in a 69' convertible - in both 650 and 750 sizes. My favorite so far has been the 650 Mighty Demon. Far superior idle quality and amazing high rpm performance. More expensivie, but much higher quality parts. I have spent less time messing with the Mightly Demon then the 4150. I used the Holley for years and had to rebuild it every year. I have been using the Mighty Demon for two years with no rebuilds (knock on wood).
I have a couple more questions I forgot to ask when I originally posted this. I've heard that Demon carbs flow better than the same rated Holley because Demon carbs are wet tested, and Holley carbs are dry tested. Is this true? What's the difference between wet and dry flow testing? What would a 750 cfm Demon carb rate if it were measured on the Holley scale?
Also, what does tuning an emulsion circuit do? I was reading that one of the main differences between the Mighty Demon and the Race Demon was that the Race Demon had adjustable emulsion circuits.
Your correct on the differences in rating methods between BG and Holley. Basically, BG copied and improved upon the 4150 Holleys, then the originator Holley copied BG to come out with their pricey HP series. After doing some research between the 2, I'll be getting a Mighty Demon for my engine
Not sure about the emulsion circuits
Modified 1974 Corvette
388 big bore/ short stroke Dart SBC, TT II's, 4pt rollbar, Tremec TKO
the holleys will come with cast metering block and base plate, the metering block is the piece between the bowls and the main body of the carb. they are well known to be porous and cause internal leaks. this is also where your emulsion circuits are. kinda like a bunch of little jets, that can be tweaked. you can purchase billet metering blocks, but why not spend the cash on something better to begin with. the holleys are tried and true, but i think the demons are a little more advanced