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Discussion Starter · #1 · (Edited)
I need advise to choose the right Carb.

My built is a BBC 427 .030 over, 11:25 comp, factory rect port heads 3919840 with some porting job, factory high rise rectangular port manifold (the one with the snow flake mark), Lunati hydraulic roller cam, basic operating range 2600-6800 RPM , intake duration at 050 inch lift is 241, exhaust duration at 050 inch lift is 249, advertised duration 292 int/300 exh, intake valve lift 0.625", exhaust valve lift 0.625", lobe separation 110, muncie m20 4 speed , 3.73 rear gear.

i want to choose from the Holley mechanical pumper list and i want to know which carburetor will suit my built the best.

850 or 950?

currently i have the holley 750 mechanical pump carb but i was told that the 427 425hp came with 830 CFM from the factory so i think i should go step further than the 750 that i have.

i like the idea of having big carb like 950 that can blow tires at almost any gear but at the same time i hate the idea of having overcarb the engine. So is the 950 is the way to go or it will be way over ?

thank you.
 

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i like the idea of having big carb like 950 that can blow tires at almost any gear but at the same time i hate the idea of having overcarb the engine. So is the 950 is the way to go or it will be way over ?

thank you.
My 1970 SS454 LS6 has 3.31 gears and a 780 cfm vacuum secondary Holley...it will light the tires up at 50 MPH if I floor it.
With exhaust manifolds....

currently i have the holley 750 mechanical pump carb but i was told that the 427 425hp came with 830 CFM from the factory so i think i should go step further than the 750 that i have.
You were told wrong. The L72 427/425 HP came with a 780 cfm vacuum secondary Holley.
The L88 427 (in 1969) came with an 850 Holley double pumper.
 

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850 or 950?

currently i have the holley 750 mechanical pump carb but i was told that the 427 425hp came with 830 CFM from the factory so i think i should go step further than the 750 that i have.

i like the idea of having big carb like 950 that can blow tires at almost any gear but at the same time i hate the idea of having overcarb the engine. So is the 950 is the way to go or it will be way over ?

thank you.
Are you referring to Holley's HP Series 950? If so, that carb is not 950cfm :noway: That carb is actually a 750 main body and an 850 base plate which flows around 820-830cfm. I had one on a pretty hot 454 (around 550hp) a few years back and loved the 950HP on that combo. VERY crisp throttle response that still pulled hard to 6500 rpm. :thumbsup: :yes:

https://www.holley.com/products/fuel_systems/carburetors/hp/classic_hp/parts/0-80496-1
 

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A smaller carb will increase throttle response and give more low end.
 

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I have installed my modified 750 double pumper in place of 600cfm carbs and my ported 750 has much better throttle response.
It is not all about size as much as it is mixture distribution.

I do like big cfm though especially if you want to Rev it.
My little 350 with [email protected] .050 cam runs stronger with a 750 than a 600.
No matter how I modified the 600 it would start laying down around 5,000 rpm.

I would probably take an 850 or 750 double pumper and tweak it if I had to run a single carb on a BBC.
I really like 2 carbs though.

Here is a little reading.
Holley double pumper modifications ? Speed Talk

How to Improve Airflow in Holley Carburetors

Bill Jones Page 4

Buddy has a 750 double pumper that a guy in Norman Ok. did and it flows 890 cfm and is super responsive.
Thinned throttle shafts porting and epoxy etc etc. It feeds a 302 SBC with [email protected] .050 cam.
 

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I had my carb custom done by Prosystems , great experience , good price , spot on the Afr + went 2mph faster than the 850 mighty demon :) could not be happier . Ask for a quote on their website
 

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950 hp gets my vote. The difference between it and a worked 1050 Dominator on my 427 was .002, and it not as prone to loading up at idle and all around driveability is much improved...
 

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Discussion Starter · #10 ·
My 1970 SS454 LS6 has 3.31 gears and a 780 cfm vacuum secondary Holley...it will light the tires up at 50 MPH if I floor it.
With exhaust manifolds....



You were told wrong. The L72 427/425 HP came with a 780 cfm vacuum secondary Holley.
The L88 427 (in 1969) came with an 850 Holley double pumper.
it seems that i was told wrong. but would the 950cfm work with my combination?
 

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Discussion Starter · #11 ·
Are you referring to Holley's HP Series 950? If so, that carb is not 950cfm :noway: That carb is actually a 750 main body and an 850 base plate which flows around 820-830cfm. I had one on a pretty hot 454 (around 550hp) a few years back and loved the 950HP on that combo. VERY crisp throttle response that still pulled hard to 6500 rpm. :thumbsup: :yes:

https://www.holley.com/products/fuel_systems/carburetors/hp/classic_hp/parts/0-80496-1
yes it's Holley 4150 HP Carburetors 0-80496-1 https://www.summitracing.com/int/par...96-1/overview/.

does your 454 is similar in specs like mine (rpm range, heads airflow and and gearing)?
 

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I had a .060 over 427 in my car. 13:1 compression, shifted at 7300 and crossed at 7400. 5500 converter with a transbrake and 4.88 gears. The car weighed 3360 with me in it and went 10.30 at 130 with an 850.
 
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Discussion Starter · #13 ·
i still didn't get the answer that i am looking for.

I can afford either 850 or 950 but i like to do it correct and do it once. i am afraid to buy the 950 and have over-carb problems and at the same time i don't want left any power on the table.
 

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does your 454 is similar in specs like mine (rpm range, heads airflow and and gearing)?
454(.030" overbore)
TRW 2349 Forged pistons (10.0 cr)
Ported open chamber oval port (049 casting)
(2.19/1.88 valves, 308cfm intake, 200cfm exhaust)
Isky Solid Roller cam
248 deg @.050" intake
252 deg @.050" exhaust
.638" lift intake
.646" lift exhaust
110 deg LSA
Isky Red Zone Roller lifters
Pro Systems Holley 4150HP Pro Series carb 950 cfm
Edelbrock RPM Air-Gap manifold
Hedman headers: 2" primary/3" collectors, 3" X-Pipe & exhaust with DynoMax UltraFlo mufflers
Super T-10, 2.64 1st gear, 12 Bolt w/ 4.30 gears
 

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66 El Camino 57 Chevy pickup 2004 Tahoe
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get the 950HP, it's an 830 CFM carb, just right for your setup.

You know, right, that the Holley traditional DPs are pig rich driving around town or on the hiway. If you really want to do a DP get one of the newer models that has screw-in air bleeds so you'll at least have a chance of correcting the rich deal.

And you're smart trying to avoid the classic hot rodders mistake of buying a carb larger than needed. Better off buying one size smaller than one size bigger.
 
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