Converting to Annular Boostres on Holley 80513 Carb

[CDN]

Holley classic HP 1000 80513 1.56 venturi carb with downleg stepped boosters ..........475ci BBC 650hp 9.8 cr

for street use would it be worthwhile to convert it to Annular boosters like the 80514 carb ??
I realize would have to jet downand adjust MAB otherwise could I keep my idle IFR and IAB tune the same ?
AirGap dual plane intake 8-9hg idle at 1000rpm
appreciate any and all input

[Duh]

In my opinion you should be able to use the down leg on your motor. The only time I use annular is on a combination that might need extra sensitive booster or if you have a less than optimal intake.

Is you 80513 Zink or Aluminum. Are you having issue with it?

[CDN]

[Duh]

I personally think it's the main body for 1.56 venturi HP style. I believe your main body is the same as the 850TW I have. The entrance to the venturi sits lower and makes a sharp ridge. The first photo is the aluminum main body's I have now. The second picture is a Zink 80513. I'm thinking of getting a different brand 1.56 main body just to test my theories.

[Duh]

[CDN]

My main body

IMG_3477 (1).jpg (32.62 KiB) Viewed 2257 times

Here is mine


Y , the lower of two of your pictures does that have annular boosters?

I have been told the very early 850DP main body had the best designs but not sure why or what boosters or venturi size
I might consider changing main body too

[Duh]

Yous looks to be the old style Zink. My current one is the new aluminum. I ran the same carburetor on my old motor, no issues. Yours has down leg stepped boosters. Allstate Carburetor has a kit to make boosters changeable. https://allcarbs.com/product/threaded-annular-booster/

[CDN]

Yes mine has downleg stepped boosters ........ at least 10 yrs old but not the very early gold dichromate color
I see now the difference in venturi shape

[rgalajda]

A 1.56 venturi Holley carb with Annular boosters would be an advantage for a street car.
The bigger the venturi , the more air bypasses the booster. Generally any Holley carb with larger than 1.4 venturi will benefit from a Annular booster. Especially when using an unheated intake manifold , meaning no exhaust crossover.
On a light race car that launches at say 4500 rpm and up, the downleg booster will be adequate in a 1.56 venturi.
An annular booster has a larger inside diameter ( excluding mini annualars ) which forces more air flow through the booster, improving the signal. Plus will have multiple discharge holes for better fuel atomization.

For a street car that has to deal with a wide working rpm range, the 1.56” Venturi and a downleg booster will be poor at low main -venturi speeds. The signal drops by a sizable margin compared to a 1.4 venturi. This is where a high gain booster to amplify the main venturi signal is needed.

When converting your carb to Annular boosters the IFR can stay the same size. The IAB , maybe?

I converted my Holley carb primary boosters to annular last fall. Although I didn’t have time to finish the testing before the season turned cold, the initial tests showed better throttle response at lower rpm. And that was a 1.4 venturi carb. I used 8 hole aprox .072” boosters. Primary jet dropped 4 sizes. Also fuel mileage improved. 800 cfm carb pictured below.

[CDN]

Yes thats what I was thinking the Annular would be better with unheated intake
,not sure if will help will low rpm fuel distribution in my dual plane but Im thinking Im going to try it cant see any downside

Any specific annular booster I should use ??