Thorough investigation/mapping of Holley 4180's...

[Walking-Tall]

Don,

The short answer for blow-thru turbo/super charging is to get yourself a double pumper...

There's no easy or effective way I have seen or know of to do what I know would be necessary for normal secondary opening function...
... which would be to somehow seal off the rectangular hole out the bottom of the vacuum secondary housing and onto the diaphragm rod, with a clamped on bellows boot or something, that would allow the secondary diaphragm and rod to freely move up when airflow through the carburetor signaled it to do so and according to the opening spring rate, and then boost-reference the underside of the vacuum secondary housing/diaphragm... and probably some experimentation with some variable restrictions added to either/both above and below the secondary diaphragm... blow-thru as is, without some sort of modifications like above, would boost pressurize the passage/s that lead to the vacuum secondary upper housing and diaphragm, and blow shut and/or keep the secondary throttles shut, obviously not allowing them to open under boost...

[dynodon64]

Mike thanks for that reply. I never even gave the vacuum secondaries a thought. I have always run double pumpers and am not use to a vacuum secondary. I give the idea some more thought.

Thanks again, Don

[mrriggs]

You could enclose the entire carburetor in a box like the old Paxton supercharger kits used.

[FB71]

Looking forward to when you can return to this project, Mike! Life called for me as well, just beginning to get back to my Foxes...

[Walking-Tall]

Me too, Jim. The 4180 is still all here, and has been and is sleeping in a box. Things came up... looks like 2+ years ago since I've signed in here... and things got real busy remedying a good number and variety of hot rods and oldies. I had a look into the forum at least once weekly over the time, and didn't see opportunity to contribute.

My own (Fox) has been working real good, with probably 3000 miles on the freshened 306.

[xctasy]

Hey Brian, thanks. I recently finished sorting out, re-calibrating (based on a fellow's mild 351W), and rebuilding a LIST-4779-2 750 double pumper. Here are some modification detail pictures and what all I put into it based on the engine combination, that should work very well... the bravery to "molest" and dial these suckers in really is worth it and rewarding with how surprisingly well they'll work, both for rock'n'roll power production and better fuel efficiency than imagined possible.


Primary metering block idle feed restrictions drilled out and tapped for adjustable 6-32 brass set screws drilled for feed restriction size, and primary power valve channel restrictions drilled and tapped for adjustable 8-32 brass set screws drilled for feed restriction size ...



Primary idle air bleeds drilled and tapped for adjustable 8-32 brass set screws drilled for bleed restriction size ...




Primary idle feed and power valve channel restrictions in place...


New cup plugs up top after all mods of block and wells cleared of any potential debris or drilling nicks into wells...




New sized and adjustable primary idle air bleeds in place...




... and it's good baseline calibration (better suited than factory Holley calibration, for a stock/mild street engine/vehicle) for starters...



.

Hey Walking Tall, welcome back, where do you get 3/8 " cup plugs from, Just via Quickfuel on line, or is there another better place?

[85MUSTANGTGT]

Hi Xctasy, I'm not Mike, but these are what I got from Holley. They're smaller that 3/8", measure closer to 1/4". Quickfuel may offer an equivalent. Not sure if there is a generic source for 1/4" brass cup plugs.

[qikgts]

Here's another source.

https://allcarbs.com/product/meterin...ley-qft-demon/

[xctasy]

Thanks Guys

[Walking-Tall]

Yes, factory common Holley metering block cup plugs are 1/4". At some point I still have to source some 5/16" cup plugs that the Holley 4180's take...

[WilliamCapri]

It looks like www.freezeplugfactory.com or www.goodson.com have 5/16” plugs.