#281  
Old 02-24-2018, 11:42 PM
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Last Post with pictures.

In this post I will show some linkage used by Ford and explain a linkage I came up with.

In the first picture you see that Ford Linkage had all of the carb linkage basically on the same side.
You can see the connecting rods with the small slots on the set-up. A slot is on each end carb.
When the slot ends the carb opens just like the Pontiac Tri-Power except that the slot is not on the rod between the
center to rear carb, it is to both the center to rear carb and the center to front carb.

In the second picture you can clearly see the lever arms on the 3 carbs.
What I did was to mount the 65 GTO slotted rod in the normal manner between the center carb top hole and the rear carb top hole
(just like a factory set-up with the slotted rod INSIDE the center and rear carb lever arms.)

If you look closely at the end carb levers you will see that they have a second hole below the upper hole on the end carb arms.
I used a Pontiac passenger side rear to front carb metal rod installed in those two holes but with the rod on the drivers side.

Now all of the carb linkage for the Holley set-up is on one side of the carbs (just like the Ford system) but using the Pontiac
slotted rod and the Pontiac connecting rod. This way you have no throttle plate shaft bending like you would have with the set-ups
in the pics above or a factory Pontiac set-up.

Tom V.
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Last edited by Tom Vaught; 02-24-2018 at 11:54 PM.
  #282  
Old 02-27-2018, 12:07 AM
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Quote:
Originally Posted by Tom Vaught View Post
The Center carb is 355 cfm and the end carbs are 500 cfm each. The center carb has a venturi like a Holley 600 cfm Primary carb and the end carbs have venturis like a 850 cfm 4781 carb. So the real cfm is more like 850 plus 300 or 1150 cfm, not 1350 cfm.
Tom V.

Hey Tom, just wondering if my new found formula has exceptions, 1355 cfm at 1.5" Hg depression converted to a 3" would be 958 cfm right?


Much Thanks,

Frank

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  #283  
Old 02-27-2018, 12:59 AM
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Holley 4 bbl carbs are "sized" and tested at 20.4" of water to flow 850 cfm.

20.39" inches of water is basically 1.5" of mercury.

Holley 4 bbl carbs are "sized" and tested at 20.4" of water to flow 850 cfm.

40.80 inches of water is basically 3.0" of mercury.

so if the cernter carb is rated at 355 cfm at 40.8" of water then the formula goes like this:

355 cfm at 3" divided by 1.414 = cfm at 1.5"
or 251 cfm at the 4 bbl rating.

so if the end carb is rated at 500 cfm at 40.8" of water then the formula goes like this:

500 divided by 1.414 = 353 cfm

353 x 2 for the end carbs = 706 cfm (4 bbl rating)

The center carb we calculated at 251 cfm

251 cfm plus 706 cfm = 951 cfm using real math vs the assumed numbers.

so 951 times 1.414 = 1344 cfm by the 2 bbl rating.

So your number is close. The confusion comes in with how Holley rated them. People say that the ends are 500 in the advertising and 355 for the center carb but the reality is the end carbs are basically the same dimensions as a 850 cfm carb not a 700 cfm carb so the carb rated numbers do not match actual Holley flow numbers which is what my number was based on.

Tom V.

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Last edited by Tom Vaught; 02-27-2018 at 01:05 AM.
  #284  
Old 02-27-2018, 02:19 AM
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Sorry about that and thanks for the correction, I did bunch those together.

I understand now and wondered if that's why you mentioned the size of the venturis.

The more I learn, the more I need to learn.


As always much thanks,

Frank

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  #285  
Old 02-27-2018, 09:16 AM
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This is going to get a bit math intensive but I have included a couple of links to websites that can help with how I got the flow numbers and Holley got their flow numbers.

Post on the PY Board related to flow thru a carb and orifice sizes

Yesterday a very good question was asked about air flow thru a carb vs its advertised number.
And we had a simple discussion and posted a basic formula to get in "the ballpark" (not what "base" the Baseball Runner is actually on during the game, LOL!) That is the point of this discussion, a more Accurate Number.

So, today, I will post up a more accurate formula and explain how it works. Then we will discuss a 750 cfm carb vs a 850 cfm carb vs a 6-pack end carb.

So here is the Formula I use a lot (that came from some posts made by Loren Budzinski (a Pontiac Racer), Myself, and a guy named "Rocco")
Q=0.61*3.14*3.14*2*2/4*[2*32.2*16*62.28/12*0.07484]^1/2 * 60/144

The assumptions in the simple program are:

Gravitational constant = 32.2
Density of air = .07484
Density of water = 62.28 pounds per cubic foot
Orifice diameter is the flow orifice and we want to find out what it flows
Pressure difference (Flow Test Pressure) in inches of water
Discharge coefficient of the orifice: (Sharp edged, nice radius, or perfect radius which = 1.00
Combined coefficients We combine some coefficients because they remain the same in the testing
Orifice area is calculated by the program
Flow is flow cfm thru the orifice at a specified test pressure and the assumed discharge coefficient.

The simple air flow program I used can be downloaded here: http://www.flowbenchtech.com/forum/
You need to be a member to use most of the spreadsheets created by members of the forum but it is a no cost deal unless you want to send the guy a contribution to help run the flow bench site.

If you go to this link in the "FLOW BENCH FORUM:
http://flowbenchtech.com/forum/viewtopic.php?f=14&t=73

You can download the simple excel spreadsheet and play with the calculations.
It will be labeled Flow Bench Calculations" 40kb so a very small excel file.

All that being said as part of the preliminary work to get a REAL carb flow number.

Assumptions:
a) We have a ASSSUMED 750 cfm 4 barrel Holley Double Pumper Carb with four 1.375" Venturis machined by Holley in the carb and a 1-11/16" Throttle Blade baseplate

750 CFM rated carb at 20.4" of water test pressure on Holley's wet flow stand with Stoddard Solvent running thru the flow passages.
We will assume that the Stoddard Solvent running thru the flow passages is a constant.

4 carb venturis ("Barrels" in Hot Rod Terms) with each one flowing as a rough number (750 divided by 4) or 187.5 cfm at 20.4 " of water.
The Throttle Blades as mentioned are 1-11/16" Throttle Blades

But we are trying to compare our 750 cfm 4 carb venturis carb with a similar 2 carb venturis 2-BBL Holley carb.
So the carb venturi size stays the same, (1.375") the formula for the most part stays the same but the test pressure is higher. 40.8 Inches of water vs 20.4 Inches of water.

So we plug the info (from above) into the spreadsheet we get (using the simple calculator) for the 4 bbl rated carb and we get roughly 186.56 cfm per barrel assuming a .999 discharge co-efficient, 20.4" of water test pressure, a 1.375" perfect radius orifice, and the same test conditions for all of our testing.

We get 746.25 cfm for our 750 cfm rated carb divided by 4 and tested at 20.4" of water test pressure = 186.56 cfm

So that says that if we tested out 2 BBL Holley Carb at 20.4" of water test pressure we would actually be flowing 186.56 times 2 or 373 cfm on our 350 cfm advertised 2 bbl center carburetor. So the actual cfm of the center carb is 373 cfm at the 2 bbl test pressure.

If we plug in the numbers for the end carbs at the same 20.4 test pressure we would get 481 cfm for each end carb or 963 cfm for the end carbs and 373 cfm for the center carb or 1336 cfm for the whole 6-pack system.

Two thinks to note here. The end carbs on a 6 pack system have larger venturis vs the 373 cfm 2 bbl carb (750 cfm 4 bbl carb).
The venturis on the end carbs are 1-9/16" or 1.5625" for the venturi size (Same as a 850 cfm Holley carb venturi) but at the higher test pressure would flow more cfm. So that is how I got the 1300+ cfm (4 bbl rated number) vs the other posters number.


Hope that helps out on the actual calculations.

The 1.414 is a good simple conversion though.

Tom V.

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Last edited by Tom Vaught; 02-27-2018 at 09:35 AM.
  #286  
Old 02-27-2018, 05:39 PM
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So did anyone follow what I was trying to explain? or did I screw that deal up. Would not be the first time. LOL!

Tom V.

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  #287  
Old 02-28-2018, 07:42 AM
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Seems I did find a discrepancy in the earlier post, "251 cfm plus 706 cfm = 951 cfm", (corrected = 251 cfm plus 707 cfm = 958 cfm).

355 cfm at 3" divided by 1.414 = cfm at 1.5"
or 251.0 cfm at the 4 bbl rating.

500 cfm at 3" divided by 1.414 = cfm at 1.5"
or 353.6 cfm at the 4 bbl rating.

353.6 x 2 for the end carbs
or 707.2 cfm at the 4 bbl rating.

251 cfm plus 707 cfm = 958 cfm by the 4 bbl rating.

958 cfm by 4 bbl rating x 1.414 = 1354.6 or 1355 by the 2 bbl rating.

As mentioned though the 1.414 is a good conversion, but just gets us in "the ballpark", it does however allow us to avoid the pitch of (Advertised) cfm.


I may be off base here but in the latter equation something doesn't seem right.

So, assuming they used the same method in (Advertised) cfm, and using your formula for each, wouldn't the 850 venturis have at least the same or larger (Actual) difference in cfm than the 750 venturis?

I'm asking because you stated "The venturis on the end carbs are 1-9/16" or 1.5625" for the venturi size (Same as a 850 cfm Holley carb venturi) but at the higher test pressure would flow more cfm."

251 cfm (the 1.414 conversion) vs 373 cfm (the actual calculations) = 24 cfm difference.

958 cfm (the 1.414 conversion) vs 963 cfm (the actual calculations) = 5 cfm difference.

This situation with advertised cfm for carbs is much like the advertised duration of cams, fubar.


Much Thanks,

Frank

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  #288  
Old 02-28-2018, 08:06 AM
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Quote:
Originally Posted by 4zpeed View Post

So, assuming they used the same method in (Advertised) cfm, and using your formula for each, wouldn't the 850 venturis have at least the same or larger (Actual) difference in cfm than the 750 venturis?

THEY DO HAVE MORE CFM, A LOT MORE CFM

I'm asking because you stated "The venturis on the end carbs are 1-9/16" or 1.5625" for the venturi size (Same as a 850 cfm Holley carb venturi) but at the higher test pressure would flow more cfm."

251 cfm (the 1.414 conversion) vs 373 cfm (the actual calculations) = 24 cfm difference.

This situation with advertised cfm for carbs is much like the advertised duration of cams, fubar.


Much Thanks,

Frank
373 CFM - 251 CFM = 122 CFM DIFFERENCE, NOT 24 CFM DIFFERENCE. 24????????

Tom V.

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  #289  
Old 02-28-2018, 04:54 PM
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Surely not the first time I screwed up either.

Back to the question at hand, I don't understand why the actual calculations reflect the differences stated.

Again assuming they used the same method in (Advertised) cfm for the 355 cfm 2 bbl and the 500 cfm 2 bbl, using your formula for each, wouldn't the 850 venturis have at least the same or larger (Actual) difference in cfm than the 750 venturis?

Quote:
Originally Posted by Tom Vaught View Post
"The venturis on the end carbs are 1-9/16" or 1.5625" for the venturi size (Same as a 850 cfm Holley carb venturi) but at the higher test pressure would flow more cfm."
(750 venturis) - (1 x 355 Advertised cfm 2bbl carb) - (251 cfm with the 1.414 conversion) vs (373 cfm with the actual calculations) = 122 cfm difference.

(850 venturis) - (2 x 500 Advertised cfm 2 bbl carbs) - (958 cfm with the 1.414 conversion) vs (963 cfm with the actual calculations) = 5 cfm difference.

Quote:
Originally Posted by Tom Vaught View Post
"THEY DO HAVE MORE CFM, A LOT MORE CFM"
Just wondering why am I not seeing it reflected in the actual calculations?


Thanks,

Frank

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Last edited by 4zpeed; 02-28-2018 at 05:11 PM.
  #290  
Old 02-28-2018, 05:29 PM
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Will try it this way.

Can we agree on this:

Lets stick with Holley Quoted cfm numbers first.
Holley says the center carb flows 356 cfm at its rated point 40.8" inches of water test pressure.

Holley says a outboard 6-pack (end) carb flows 500 cfm at its rated point 40.8" inches of water test pressure. This carb has a 1-9/16" venturi and 1.750" throttle blades.

So simple math 355 + 500 + 500 = what?
1355 cfm, right? at 40.8" of water test pressure.

Ok so we have a second Holley carburetor (that is a 2-BBL carb) It is model 4412 and is called a 500 cfm carb by Holley in all of the advertising
https://www.holley.com/products/fuel.../parts/0-4412C

This carb has a 1-3/8" venturi and 1-11/16" throttle blade. It says it clearly right here (2nd page at the very top).

http://documents.holley.com/techlibr...al_listing.pdf

We have a carb #4782 (center 6-Pack carb) that is rated 355 cfm and we have a #4412 (Circle Track 2 bbl) rated 500 cfm.

So looking at the two carbs internally the #4412n Carb has 1-3/8" venturis and a 1-11/16" throttle blade.

The #4782 center carb on the 6-pack has a 1-3/16" venturi and a 1-1/2" throttle blade so you can easily see the difference in cfm
is caused by the 1-3/16" (.1875") vs the 1/3-8" (1.375") #4412 venturis and the 1-1/2" (1.500") vs the 1-11/16" (1.6875"_ #4412
Throttle Blades.

With me so far? A DIFFERENCE in Venturi Area and a difference in Throttle Blade Area.

Tom V.

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  #291  
Old 02-28-2018, 06:33 PM
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Quote:
Originally Posted by Tom Vaught View Post
Will try it this way.
LOL, ok Tom, thanks for the guidance and patience.

Quote:
Originally Posted by Tom Vaught View Post
Can we agree on this:
We'll see, er uh... I mean yes sir, I am always willing to learn.

As I started to post with a quote this came up,

Edit:
Quote:
Originally Posted by Tom Vaught View Post
A DIFFERENCE in Venturi Area and a difference in Throttle Blade Area.
Quote:
Originally Posted by Tom Vaught View Post
With me so far?
Yes sir, I'm starting to see the light.

Thanks,

Frank

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  #292  
Old 02-28-2018, 08:08 PM
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Now we will compare dimensions on the two "500 CFM" Rated carbs.

#4412 carb has 1.375" venturis and 1.6875" Throttle Blades.
#4783 carb has 1.5625" venturis and 1.750" Throttle Blades.

The venturi size is 1.5625" minus 1.375" or .1875" larger (3/16").
The Throttle Blade size is 1.750" minus 1.6875" or only .0625" larger (1/16").

We know that the venturi size makes a difference in the carb total air flow. The Throttle Blade Size not so much because every double pumper carb from a 650 cfm carb to a 800 cfm carb used the same Throttle base/Throttle Blade size. The air flow difference was due to the venturi changes.

So here is the carb question for you:
If both carb are tested at the same test pressure for a 2-BBL, (40.8" of water) and the Venturi size and Throttle Blade size is quite different, How can they both be Holley 500 CFM Carbs?

The end carbs for the 6-pack set-up are obviously low rated for flow vs their actual flow rating. See my point now.

Chrysler/Holley was playing Carb advertising games with the insurance people and the Racing Organization People. Much lower rated CFM vs what the carbs would really flow on the engine.
You can't miss-advertise up but you can miss-advertise DOWN.

Tom V.

I am working on a Tri-Power Holley carb set-up that uses a 6-Pack End Carb Mainbody (Big Venturi) as the CENTER Carb of my Mechanical Linkage Barry Grant 6-Shooter Ported Intake set-up. Should work great on a 482 cid NA engine.

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  #293  
Old 02-28-2018, 10:19 PM
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Ok, now I understand why the 251 cfm number (1.414 conversion), is so far off, that's what I was initially after.

Quote:
Originally Posted by Tom Vaught View Post
So here is the carb question for you:
If both carb are tested at the same test pressure for a 2-BBL, (40.8" of water) and the Venturi size and Throttle Blade size is quite different, How can they both be Holley 500 CFM Carbs?
Answer: To reiterate again, physics do not change, on the other hand, you can play with numbers...


Much Thanks,

Frank

Edit:
Quote:
Originally Posted by Tom Vaught View Post
I am working on a Tri-Power Holley carb set-up that uses a 6-Pack End Carb Mainbody (Big Venturi) as the CENTER Carb of my Mechanical Linkage Barry Grant 6-Shooter Ported Intake set-up. Should work great on a 482 cid NA engine.
With that setup you should have access to 1400 + cfm, enough to feed the Beast.

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Last edited by 4zpeed; 02-28-2018 at 10:25 PM.
  #294  
Old 02-28-2018, 11:36 PM
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Really GLAD Frank that I finally figured out a way to explain what I was trying to say. Even Holley played games with the flow numbers.
Barry Grant did it with the Test Pressure "bump" (from 20.4" of water to 28" of water to make their normal cfm carbs appear larger
for the guys who just compare cfm "reported" numbers.

I think that you now have a good handle on the formulas and the conversions between the 2-BBL Holleys and the 4-BBL Holley carbs.

Thanks for helping out on the discussion of this topic.

Tom V.

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  #295  
Old 03-01-2018, 07:48 AM
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One comment this morning on the Carb Air Flow number. It is a NUMBER.

How people use that number and what their expectations are means a lot.

I knew people that had perfectly good #4781 850 cfm at 20.4" water test pressure remove that carb and purchase a advertised "950 HP cfm" carb on their engine and not see any performance benefit. Maybe the carb was a bit more responsive but that would be expected with a actual 100 cfm less airflow carb installed.

The situation is the same with the 1000 cfm reported carb that has the 850 cfm dimensions and in reality might be 10 cfm better in airflow (minus the choke airhorn). But people want to brag about their cfm numbers, including me.

The difference is the cfm numbers I reported in this thread in the last couple of posts were under-rated cfm numbers in the advertising.
They were playing games with the Tech Inspectors and the Chebby Guys. They lied too but they lied DOWNWARD. No one got hurt on the deal in the advertising game and spent more money for less cfm air flow.

Barry Grant started that inflated cfm number crap years ago. Well Barry is gone, Holley owns his company and his carbs, and the cow is out of the barn.

Based on the info provided here people can go thru the math and evaluate carbs a bit more carefully. The rule of thumb is:
The only Holley Carbs with a TRUE 950 cfm were the 3-BBL carbs. The only 1050 cfm (850 style carbs, not Dominators) were the Rear tube nozzle 3-BBL carbs.

The early Dominators actually flowed either 1050 cfm or 1150 cfm.

All of this HP1000 (850 carbs) is advertising.

Yes, the carbs do flow 1000 cfm but at an inflated test pressure vs a test pressure that was standardized by all of the major carb manufacturers: Holley, Carter, Rochester, Autolite many years ago.

As posted before, the fact that Smokey Yunick Dyno corrolated better on his SB Chebby engines when airflow was tested at 28" of test pressure thru the head does not mean that another dyno engine (HEMI for example) tested accurately with Bob Mullins 5" of water test pressure.

Many people just want to take a single data point and run with it, whether it is valid in all cases or not.

Have a great day and no more long posts about carb test pressure testing.

Tom V.

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  #296  
Old 03-02-2018, 12:44 PM
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Today I am going to post a little bit about an Emissions Component (Electronic Feedback Control) that was adapted to Holley Street and Performance Carburetors.

I will be revising the post (as I add either pictures or text) so please be patient with me on this specific topic.
I have noticed that I do a bunch of typing at times and then lose everything (if I click on the wrong window)
with several windows open.

So first I will post some pics and then add words later.

Here is a very good write-up on the two systems: Mile Dial and Quarter Mile Dial and the way the solenoid controls the fuel flow.
https://books.google.com/books?id=Cl...20Dial&f=false

Tom V.
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  #297  
Old 03-02-2018, 01:49 PM
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ps I wrote about this Carb System the last time on the Turbo Forums (Post #28) March 30, 2008 quite a few years ago.
https://www.theturboforums.com/threa....322567/page-2

I would have included this link in the other post but the 1 hr limit on making changes messed me up.

As was said in the article, David Vizard is a big Dyno Tester type guy and has used the Quarter Mile Dial system on his Engine Dyno Carb for many years.

Tom V.

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  #298  
Old 03-03-2018, 06:50 PM
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Great tips, My new out of the box holley 4150 HP has a backfire thru the carb. I checked timing/increased primary jets/increased squirter/checked float level. backfire remains. also turned adjustment screws out.

idles great, very responsive at moderate off idle, but hard off idle gets the backfire. not a new engine combo or anything. a healthy 455. thoughts?

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Old 03-03-2018, 08:54 PM
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1) You mentioned that you had checked the timing, what was the timing with the "Other Carb" that was on the engine previously?

2) You did not give any history on the engine or the basic facts of the engine or the Carb size, what the jetting was before you changed it, same deal for the squirter, etc..
Pretty hard to make any recommendations when there are so many grey areas in your post.

Much more info please:
List Number on the air horn of the carb is a start but we need to know if it is the right carb for the application.
Basically a generic post that says I have a problem and no other real info.

If you post that Engine/carb Info, Shaker455, myself, Darby, and several other people on the board who are good carb guys could make suggestions as well as me.

Tom V.

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Old 03-03-2018, 10:29 PM
JUDGE3 JUDGE3 is offline
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Quote:
Originally Posted by Tom Vaught View Post
1) You mentioned that you had checked the timing, what was the timing with the "Other Carb" that was on the engine previously?

2) You did not give any history on the engine or the basic facts of the engine or the Carb size, what the jetting was before you changed it, same deal for the squirter, etc..
Pretty hard to make any recommendations when there are so many grey areas in your post.

Much more info please:
List Number on the air horn of the carb is a start but we need to know if it is the right carb for the application.
Basically a generic post that says I have a problem and no other real info.

If you post that Engine/carb Info, Shaker455, myself, Darby, and several other people on the board who are good carb guys could make suggestions as well as me.

Tom V.
The carb is new out of the box 4150HP Pn # 0-80513-1, 1,000cfm, mechanical sec, down leg boosters. (previous carb was a 1050 quickfuel annular boosters and I screwed up shaker 455 tuned it and it was great shoulda kept it, but with the new engine configuration I figured best to start with another carb) see pics, Same engine, changes are: previous intake was an edelbrock victor with Wilson 1" spacer, now an edelbrock performer rpm no spacer. previously ran headers, now round port manifolds. current carb had 84 pri jets, changed to 87 (didn't have 86) squirter was a 31, had a 41 so put it on. (the quickfuel was 86/94 jetting)


Last edited by JUDGE3; 12-20-2023 at 11:04 AM.
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