Carb sizes for a 406 - Chevy Nova Forum
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Old 29th-August-2007, 03:08 PM   #1
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Carb sizes for a 406

Just wondering about peoples experiences with different carb sizes on a 406 would there be a significant difference in performance between a Holley 670 Avengr and a Holley 750 dbl pumper?
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Old 29th-August-2007, 03:16 PM   #2
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I'm running a 800 Holley on my 408sbc. It was pretty good right out of the box. Changed P.V and jets was all.
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Old 29th-August-2007, 03:32 PM   #3
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Carb

I like Holley # 9381-830 cfm or #9380-850 cfm on my 406's. Annular boosters just tune better.
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Old 29th-August-2007, 03:35 PM   #4
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I run a modified Holley Pro-Series 750 4150 on my 406.
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Old 29th-August-2007, 03:39 PM   #5
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800 cfm Q-jet on mine.
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Old 29th-August-2007, 09:19 PM   #6
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Edelbrock 750 on ours.
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Old 29th-August-2007, 11:03 PM   #7
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Dale's (teddisnoke)406 runs a 770 Street Avenger; works pretty damn good--almost in the 11's with 3.08 gears.
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Old 29th-August-2007, 11:13 PM   #8
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750 demon double pump on mine. Suspect its too small though.
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Old 30th-August-2007, 12:33 AM   #9
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850 DP works for me
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Old 30th-August-2007, 12:46 AM   #10
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my brother has a 700 holley dp on his 406
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Old 30th-August-2007, 02:09 AM   #11
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Quote:
Originally Posted by Mike Goble View Post
800 cfm Q-jet on mine.
Ditto. Tryed a 650 and 750 DP and the Q-jet flat out was the best.
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Old 30th-August-2007, 12:44 PM   #12
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My 406 needed a Holley 950 HP XE built specifically for my engine combinatipn by Patrick James.
Prior I had on a Speed demon 750, no choke, but could not regulate a good fuel curve no matter how much jet we put in it.

There are a number of formula's on the internet to calculate the correct CFM based on engine size Vol Eff % etc.
A simple 2 bbl did a fantastic job pulling school busses around on factory 400's.

Carb should be rated not on cubes alone, but how wild the build is.
Here is a link to Stan Wiess site. he is an old school guy, and only one of 100's of carb sizing resources.
To answer your question if there would be a signifigant difference between a 670 Aven, and a 750 double pumper, it depends on the engine spec, and on a mild build 406, the 750 has more CFM, and tuning potential.

http://users.erols.com/srweiss/calccarb.htm
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Old 30th-August-2007, 12:54 PM   #13
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One thing to remember when using these carb calculators is that peak VE and peak rpm don't occur at the same point. You may have a 100% VE motor at 5500 rpm, but at 7000 rpm the VE is down to 90%. Which do you enter in the calculator?

Another pet peeve of mine is the nitpicking over 50cfm of carb potential, as in "should I use a 650 cfm or a 700 cfm carb"? The carb setup is as important as the size, the ability of it to get the right mix of fuel and air into the intake in a timely manner overshadows other considerations.
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Old 30th-August-2007, 01:23 PM   #14
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Mike,
I agree, Carb sizing is pretty complicated for the novice guy if they don't know even ruff numbers of thier Vol Eff %.

There is no argument the tuning of any carb is where lots of power potential is unleashed, not just the CFM size.
SteelRat I belive has more potential with the 750 Holley. I hate buying parts twice, so if I know I am going to put heads, or a cam in an engine later, I would buy the right size carb now. A 670 Aven will limit a 406 depending on its spec's faster than the 750 will.


With induction on my 406, I kept reminding myself that a 406 is 10 cubes bigger than a 396BB, and just 20 cubes short of a 426 Hemi.

A 750 works fantastic on a GM Crate 454, or even a Crate 502.
Put a cam, and heads on those, and they would suck the metal off the inside of that 750 trying to get air.
Carb sizing is relative to not just cubes, Vol Eff, but most important how hairy the build is.
As I mentioned 2bbl 400's pulled 50 passanger school buses around for years.
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Old 30th-August-2007, 01:34 PM   #15
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Quote:
Originally Posted by 68SSGrandpa View Post
Mike,
I agree, Carb sizing is pretty complicated for the novice guy if they don't know even ruff numbers of thier Vol Eff %.
Carb sizing is relative to not just cubes, Vol Eff, but most important how hairy the build is.
What is "hairy" and how does the "hairiness" of the build effect the selection of a carburetor? Do NASCAR engines make the power they do because they're "hairy" or because they have a high VE at a high rpm?
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