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Old 01-28-2023, 10:06 PM
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433lemans 433lemans is offline
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Default Holley Spreadbore Carb 650/800 Difference

I have a spreadbore Holley carb that I purchased some time ago that was advertised as an 800 cfm carb. It is a dual feed double pumper that a previous owner cut the choke tower off of so I can't confirm what it is exactly (that's where the ID is stamped).
My question is, what is the physical difference between a 650 cfm carb and an 800 carb. In other words, there must be some physical way to be able to identify at least the cfm of the carb? Are there internal venturi differences? What makes the carb flow 650 vs. 800?
Bottom line, in order to regain a choke for this carb, can I replace the center section using one from a 650 carb (as these seem to be far more available than 800's) and still have an 800 cfm carb? Or will I have a 650 carb then?


Last edited by 433lemans; 01-28-2023 at 10:21 PM.
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Old 01-28-2023, 10:49 PM
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Bruce Meyer Bruce Meyer is offline
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Take a pic of the secondary boosters and post it. I can then tell you what you have. The 800 have large boosters like a dominator. Also the center section of a 650 can interchange but it will be a 650 then. Although the butterflies are the same for both carbs, the 800 has a larger secondary venturi area.

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Old 01-28-2023, 11:23 PM
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Default Spreadbore

Here's a pic
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Old 01-28-2023, 11:31 PM
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That is an 800. Good find!

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Old 01-28-2023, 11:43 PM
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Thank you! I really, really appreciate your help! Now I need to find the correct center section to restore the choke, and the right rebuild kit. Thank you again!


Last edited by 433lemans; 01-28-2023 at 11:57 PM.
  #6  
Old 01-29-2023, 12:05 AM
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The Metering Blocks for the spread bore carbs would also have the "list #" which could
additionally tell you that you have the correct metering blocks for the carb.

Numbers will be on the top of the block on the right.

Tom V.

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Old 01-29-2023, 10:01 AM
grandam1979 grandam1979 is offline
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That carb is funky looking like it got spray bombed with gold paint?

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Old 01-29-2023, 02:12 PM
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Yup, Painted.
6910 7866 stamped on the other block.
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Old 01-29-2023, 02:23 PM
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General Q: are the fuel bowls and metering block interchangeable or dead-same from 650-800-1050? And 2- and 3-circuit?

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Old 01-29-2023, 09:07 PM
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To answer a question that no one has asked, back in the mid 1980's we were doing dyno pulls with my 455 and the Holley spread bore 800 carb. Paused the testing, milled the choke housing off, and resumed runs finding out that there wasn't any noticeable horsepower gain by loosing the choke tower. I guess the only good news was we didn't loose anything either.

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Old 01-29-2023, 10:42 PM
Joe's Garage Joe's Garage is offline
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Default LIST 6910 is an 800 double pumper.

We've used that one plenty of times. Great carb.

Quote:
Originally Posted by 433lemans View Post
Yup, Painted.
6910 7866 stamped on the other block.

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Old 01-29-2023, 11:49 PM
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Quote:
Originally Posted by Half-Inch Stud View Post
General Q: are the fuel bowls and metering block interchangeable or dead-same from 650-800-1050? And 2- and 3-circuit?
I know the fuel bowls are interchangeable between the 650 and 800 as long as they are the dual feed race bowls. They are not interchangeable with a 4150 bowls unfortunately. Why Holley did that I have no idea. As far as the metering blocks, I don't know. A good question for experts like Tom V.

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