Racing Fuel Systems

Something spotted today that has me curious. Picked up a Holley era 850 Mighty Demon, when they started putting the full part number on the air cleaner ring. For the most part a better quality carb than the latter days of Barry Grant, some aspects by a long shot. Machining is the standout. I noticed Holley made some changes to the metering blocks and it’s got me thinking is it just cheaper manufacturing techniques or is there something behind the changes. First was the newer blocks are a little thicker by .025”. No big deal, it might affect plumbing depending on type of fittings used. Most apparent thought was separate primary and secondary blocks. No ability to use power valve on the secondary block. That would be an economic decision. The next apparent change is the vertical idle channel. Holley has made it wider yet shallower (see pic below. Holley on right). Would this be an improvement fuel delivery wise or just a more efficient way to machine that channel? Also the idle feed hole that is where lower IFR is usually located is larger than the Grant era model on the Holley era. Again, any advantage fuel metering wise or just a manufacturing method? Lastly and most curious is the secondary emulsion holes. They look quite large and when pinned they are for the most part. Top and middle a .033” drill fits snug. Bottom hole.035”. But these don’t go all the way through to the main well. It takes .031” and .033” respectively to pass all the way through to the well. Would this be due to manufacturing techniques or by design? Primary metering block emulsion holes are same size all the way through to main well as would be expected. Sizes are .031” top & middle, .033” bottom hole for primary. Has Holley weaved some magic and made some tweaks to improve as a fuel metering device or have they just found changes to boost profit?

Holley is mostly overseas now, my brand new Holley logo valve covers and $300ish intake say right on the box Made in China.

Back when I got into tuning carb metering blocks I bought some Quickfuel 3e hole(2 sets). And when I bought some BLP later it was apparent that they machined their blocks different. The Quickfuel are like those pictured and have a gasket lip, they CNC the gasket surface and it's not entirely flat like the BLP were they don't bother with a lip prob cause it's easier to get a good flat surface. A couple of the QF blocks had spots that I'm betting leaked internally if you didn't use a new gasket, seemed that way to me and I no longer plan to use the QF 3e lip blocks. There are other differences between BLP & QF that were also pointed out as better to me but I'll let someone else go into that.

Here is my mainbody vlog where I show the metering blocks differences somewhat. https://youtu.be/iyLQCWCN1NI