Holley 94 carb jets

F

fsacht

Member
Where can I learn about jets and size applications for the Holley carbs.
I have recently cleaned and replaced gaskets on two spares I have. One carb set is stamped.47 and the other .51. What does the 47 or 51 indicate and what source will give proper size and what determines one's choice of size.

My manuals don't tell me.
 
I have a few 94s and often they have 51s in them. I don't know if any factory application had 47s. 50 or 51 is a good size to start with.

Mart.
 
fsacht said:
Where can I learn about jets and size applications for the Holley carbs.
I have recently cleaned and replaced gaskets on two spares I have. One carb set is stamped.47 and the other .51. What does the 47 or 51 indicate and what source will give proper size and what determines one's choice of size.

My manuals don't tell me.
Click to expand...


There are several Holley paper back books that will answer all your Holley carb questions.
 
This might help.

The decimal numbers correspond to make of carb. Stromberg for .97 and Ford for .94. Those numbers are the venturi sizes, too.

Jets where hanged for altitude so, if the carb was in CO, it would probably be jetted different than CA.

Frank
 

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The number refers to the hole size. The bigger the number, the larger the hole. Jets should NOT be drilled to get a larger hole. Buy the appropriate jet.
 
The .51 jet would be for use at sea level to about 4000 ft. Above that altitude, .50 or .49 jets would likely run better. Trial and error, going by spark plug color. The .47 you have was likely used in a dual carb application.
 
The venturi size, is how the 97 Stromberg and 94 Chandler/Grove (aka Holley and Ford) carbs where named.
 
Ford38v8,
Thanks. That's the kind of information I am looking for. One of my cars is said to have come from Colorado.
 
ford38v8 said:
The .51 jet would be for use at sea level to about 4000 ft. Above that altitude, .50 or .49 jets would likely run better. Trial and error, going by spark plug color. The .47 you have was likely used in a dual carb application.
Click to expand...

OK, so question: what is the size of a 51 jet? decimal .051 or 51 drill size .067
 
A Holley main jet size is close to the inch measurement (#51 jet = approx. .051") As sizes get larger, the inch measurement gets further from the number size. I'm pretty certain the jet # is determined by how much fuel flows through it at a specific head pressure. I believe for example a #51 jet flows 51cc at that given head pressure over a specific duration. When I worked at Zenith Carburetor in Detroit, that's how they did it.


Sal
 
rustedorrotting said:
Gentlemen, jet size is the numbered drill size of the hole in the jet. The higher the number, the smaller the hole or jet.
Click to expand...

No. bigger number = bigger jet size.

Smaller numbers approximate size in thou, then the numbers drift as they get bigger.

509392
 

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Not only size of hole but the chamfer and depth are figured into the flow . Thats why they say not to drill a jet . It may not flow like a factory comparable sized jet . Iirc .
 
Using an AF meter will help. However, backin the old days we'd brig the engine upto a fast idel. Runyouy hand over the carb an if the engine increased it was lean, decrees could be rich or OK. Drop a jet size and try again.
Gramps
PS in tis day and age the AF meter can lean an engine out in cruise, but now you have to richen it out in power, This is done by the power valve. However the PV is just an on and off valve and the jet size is a small hole in the carb and must be drilled out. Be carful here, you can't mak it smaller.
 
What Mart said is 100% correct. Good info.
Also, redrilling a jet does not chage the length of the orifice.
Good info from Ol' Ron too.

Sal
 
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!
 
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
 
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