Holley 94 carb jets

[Ggmac]

In our quest for truth in sorting out documented fact from opinion, it would be great if posters would qualify their answers. I have often embarrassed myself by not always having a backup of actually doing the research before posting an answer. Never too late for New Year Resolutions!

As have I made mistakes, many and probably will in the future. But I have furnished the material from Holley as to where I got my drilling response.
Thank God for Keeping books from the 80s .

 

[scicala]

Okay . My post about drilling a jet . Holley jets are chamfered on both inlet and outlet sides . Drilling a standard jet oversize removes portions of this chamfer , thereby lengthening metering passage and increasing amount of flow restriction. When this occurs, a larger diameter drilled jet may actually flow less than a smaller standard jet .

As with any metering orifice the total area of the orifice rather than the diameter of the orifice is the critical factor .

Both the paragraphs were taken from the Holley Carburetor super tuning and modifying book
Page 46 and 44

All of the Holley main jets that I have and have seen are only chamfered at a slight angle on the exit side of the jets only. The entry side is straight with a sharp edge.
Re-drilling the jet would only reduce the length of the orifice by a few thousandths of an inch. I'm taliking about jets no bigger than about a #70.
My documentation is from flowing jets at the old Zenith Carburetor engineering lab before and after re-drilling, and doing 12 years of carb flowing/development work, and 57 years of carburetor repair and rebuilding.
Now if we were working on the space shuttle or brain surgery, I would say what I just stated is inappropriate.

Sal

 

[ford38v8]

Okay . My post about drilling a jet . Holley jets are chamfered on both inlet and outlet sides . Drilling a standard jet oversize removes portions of this chamfer , thereby lengthening metering passage and increasing amount of flow restriction. When this occurs, a larger diameter drilled jet may actually flow less than a smaller standard jet .

As with any metering orifice the total area of the orifice rather than the diameter of the orifice is the critical factor .

Both the paragraphs were taken from the Holley Carburetor super tuning and modifying book
Page 46 and 44

Not having any direct experience in flow engineering myself, I would still agree with the logic, but also consider info from a manufacturer regarding its own products to be …interesting. To be clear though, I do totally agree with the logic, and thank you for the documentation!

 

[Ggmac]

Coming from the Holley book word for word , pages and date of publication. Most jets Ive played with have a chamfer on both sides though one side is usually much more pronounced.
When holley came out with the 3 digit precision jets it was no longer necessary to drill or modify jets that I worked with . Most 2 digit jets have a variable flow of 7% the precision jets IIRC ARE 3% . Aftermarket jets are a complete crap shoot .