Figuring out what Carburetor I need

[rmorman]

Hello. I'm going to replace a Holley 750 Double pumper with a vacuum secondary carb and wanted some advice on size/model.

Here is some info on the car/engine:
1. 405 HP at the crank
2. Intake Manifold is a Dual Plane (Edelbrock Performer RPM Air-Gap).
3. Heads: PRO FILER 195CC ALUMINUM HEADS 2.02/1.60
4. 10:1 Compression
5. 1979 Monte Carlo 3500 lb (est)
6. 3:70 Gears
7. 2400 RPM Stall Converter
8. Automatic Transmission (700R-4)
9. 383 Stroker
10. Redline 6600 RPM
11. Mainly street driven

Using the Carb equation: Cubic Inches x RPM x Volumetric Efficiency ÷ 3456
((383*6600)*.90)/3456 = 658.28125

I had been HEAVILY looking at the Demon carbs, but called Ron @ Holley recommended the Ultra Street Avenger. Based on that info, I nailed it down to these:


1. 650 CFM DEMON

A. 650 CFM Speed Demon Carburetor – Down Leg Booster

I. https://www.holley.com/products/fuel...arts/1282010VE​

B. 650 CFM Speed Demon Carburetor – Annular Booster

I. https://www.holley.com/products/fuel...arts/1282020VE​

2. 750 CFM DEMON

A. 750 CFM Speed Demon Carburetor – Down Leg Booster

I. https://www.holley.com/products/fuel...arts/1402010VE​

B. 750 CFM Speed Demon Carburetor – Annular Booster

i. https://www.holley.com/products/fuel...arts/1402020VE​

3. 670 CFM HOLLEY

A. 670 CFM Ultra Street Avenger Carburetor – Straight Booster

I. https://www.holley.com/products/fuel...arts/0-86670BK​

Do you need any other info?
Do you have any advice?
What booster should I use and why?

Thanks again,
Russ

 

[Bar50]

I have a like new 670 Street Avenger I got from HAFROD the other day, I would trade for a double pumper.

 

[rmorman]

I have a like new 670 Street Avenger I got from HAFROD the other day, I would trade for a double pumper.

That would be a done deal if I didn't want to Dyno one against the other this Spring!

 

[MrSony]

Quadrajet jetted with matching rods to your engine combo. Done.

 

[lilbowtie]

Sounds like you are doing your homework and your choice will fit your needs. Google the boosters and you might be persuaded by your use and driving. More than likely he has the 4150 flange intake so the Q jet isn't a choice - there are different size Q jets too.

 

[Quadrajet Power]

You posted good info on your build.
Maybe you want to consider a Quadrajet, maybe not.
Since you mostly street drive, the Quadrajet has great street driver ping manners and can certainly deliver the power when necessary when set up for your engine.
All Quadrajets are capable of at least 750 com, but will only deliver what the engine demands, so it is never too large.
The Quadrajet needs calibrated and set up for your build, just like any carb requires. That is what we do so minor adjustments are all that are needed.

Can a Quadrajet handle the power? Sure can. Our own engine dyno'd over 510 hp with Quadrajet and we have a customer with a 572 cubic inch try to run a 9 second pass with our Quadrajet in a stock appearing class. In mid to low 10's now but carb is on our bench getting some attention.

Whatever you choose, make sure you can get support and parts to dial it in, then enjoy it!

 

[Bar50]

Experience if you want it, 750 vacuum secondary carbs were designed for the 396. In doing so, the idle circuit that is made/designed into the carb (not jet-able or adjustable) is fat or rich on most small block applications. Couple that with a healthy cam that requires more air to idle...that opens the butterfly to uncover the transition slots rendering the idle circuit useless.

The 'old way' was to drill holes into the throttle blades near the transition slots, slowly enlarging until you get desired idle speed. While closing the butterflies back down to the magic 0.060 of the transition slots that will make the idle mixture screws work.

HP series or style carbs do have tunable low speed air jets. Brand new HP carbs even have an air bleed that is accessed under the breather stud.

Dual plane intakes are more sensitive to carb sizing than open or singlee plenum versions. The large plenum fools the motor by allowing it to use the plenum volume where as the dual plane only operates on 180° of the manifold. I would take a long look at what crate engines come with in the 350 and 383 variety....most are 750 cfm or so. The intake puse of the 383 is much more sensitive to changes along the intake tract than a 350. Add good flowing heads and a cam and a 750 may not be enough.

 

[gbodytoys]

Have you considered EFI?

Holley Sniper
Fitech

The price all in (considering on what fuel system you run) could be done for approx. $1500 or less.

 

[GreenRegal87]

I have close to 400Hp at the crank give or take on my .040 over 350, using a 1406 Edelbrock (600 CFM) and no starvation issues. I think anything bigger would be way too much gas.... Im also running a dual plane Edelbrock Hi Rise intake with a transdapt 1 inch spacer.

 

[565bbchevy]

So what issues are you having with the 750 DP that makes you want to change it?