670 or 770cfm?

[Stacked440]

I'm convinced I want to run a Holley street avenger carb on my 440, question is...670cfm or 770cfm? I've heard 670 gives good throttle response but the 770cfm works better on the top end.  Suggestions?

[MEK-Dangerfield]

With a 440, I would suggest the 770.


  Mike

[72hemi]

Go with the 770. The 440 needs it. Or you can do like I did and install a 6 pack. I can't say enough good about a 6 pack.

[Chryco Psycho]

I would recommend an 870 in most cases unless the 440 is dead stock , even then if it was mine I would run the 870

[Oldschool]

I posted this "Oldschool" way of carb size choice a long while back, but it might be worthy to post again here.   We used to take the Cubic Inches of the engine and double that as a starting point for carb selection.  In this case, the engine is 440 CI.  Double it and you get 880.   That is an excellent starting point.  For a stock or reasonably street oriented engine, 870 CFM would work great.  IF the engine is modified for street drags or racing, then you would go even bigger.  This has always produced some strong running cars for me.  I've done this on small and big block cars and it works well......   Just my 0.02............        

[Chryco Psycho]

same in my case IW as told I was over carbed with an 850 on my 440 so I installed a 950 & the car went faster & I was again told I was over carbed with the 950 so I put a 1050 Dominator on & the car really picked up , keep in mind the tiny 6 pack works awesome on a bone stock 440 & is only 950 cfm

[moper]

I'd go the 670 route. The old methods worked great, but some carb manufacturers changed the rating system with wet flowing. HPs and Avengers are wet flowed. The 670 flows approx the same as a 3310 or 4150 series 750. The 770 flows more than a 4150 series 850cfm carb.

[heminut]

I'd go the 670 route. The old methods worked great, but some carb manufacturers changed the rating system with wet flowing. HPs and Avengers are wet flowed. The 670 flows approx the same as a 3310 or 4150 series 750. The 770 flows more than a 4150 series 850cfm carb.

But the Avenger series are also vacuum secondary carbs, which are very forgiving on size. I think I would go with the 770.

[TreeFrog]

Go with the 770. The 440 needs it. Or you can do like I did and install a 6 pack. I can't say enough good about a 6 pack.

Looking into a 440, I would like to do a 6-pack.  I hear the night-mares about tuning, and keeping them tuned, but how awesome that would be...I am waitning to see if I get the 72 Challenger, and if he keeps the 360..if he does I want to work towards a 6-pack and eventualy a shaker hood.

[72hemi]

The 6 pack carbs that I got were pretty good out of the box as far as tuning goes. I have heard that tuning them can be difficult but reading my 71 factory service manual it doesn't seem to bad.

[MEK-Dangerfield]

To further muddle this, can I ask if vacuum or mechanical secondaries are the way to go? I have a mechanical 800 cfm double-pumper on my 440. The Holley website tells me vacuum secondaries are the way to go on my car, giving it is an auto, and more than 3100 pounds. My car seems fine, but if there is a better way to go, I'm all ears. I have 10:1 compression and a big cam, 3:23 gears though.

  Mike

[Oldschool]

To further muddle this, can I ask if vacuum or mechanical secondaries are the way to go? I have a mechanical 800 cfm double-pumper on my 440. The Holley website tells me vacuum secondaries are the way to go on my car, giving it is an auto, and more than 3100 pounds. My car seems fine, but if there is a better way to go, I'm all ears. I have 10:1 compression and a big cam, 3:23 gears though.

  Mike

I like the mechanical secondary/double pumpres the best, but that's just my preference.  The DP carb will outperform the vacuum carb when it is set up and tuned to the application.  It's all about getting air/fuel into and out of your engine.  The set-up that gets the most through the engine in the shortest amount of time is the best performer, although fuel mileage suffers.  The vacuum carb only opens the secondaries as the engine will take it.  If they open too soon, the car will bog off the line until the flow velocity of the engine "catches up" with the open secondaries..  So, you would be running on the 2 front barrels and the slowly opening secondaries.  If the vacuum secondaries open too soon, there isn't enough fuel to keep the mixture rich enough to match the huge amount of air that goes through the open secondaries. Thus, the lean bog off the line.
However, the DP carbs can be tuned to overcome that bog.  By increasing the accelerator pump fuel delivery amount and the duration/timing of the fuel squirt, you can keep the mixture rich enough to burn all that huge amount of air off idle. No off idle bog, just acceleration. This in turn increases the amount of air/fuel going through the engine and increases performance.
Vacuum secondaries are great for street applications, but if you're gonna street race and make a few 1/4 mile passes, the DP is the way to go....   Just my "Old" 0.02......           

[MEK-Dangerfield]

I like the mechanical secondary/double pumpres the best, but that's just my preference.  The DP carb will outperform the vacuum carb when it is set up and tuned to the application.  It's all about getting air/fuel into and out of your engine.  The set-up that gets the most through the engine in the shortest amount of time is the best performer, although fuel mileage suffers.  The vacuum carb only opens the secondaries as the engine will take it.  If they open too soon, the car will bog off the line until the flow velocity of the engine "catches up" with the open secondaries..  So, you would be running on the 2 front barrels and the slowly opening secondaries.  If the vacuum secondaries open too soon, there isn't enough fuel to keep the mixture rich enough to match the huge amount of air that goes through the open secondaries. Thus, the lean bog off the line.
However, the DP carbs can be tuned to overcome that bog.  By increasing the accelerator pump fuel delivery amount and the duration/timing of the fuel squirt, you can keep the mixture rich enough to burn all that huge amount of air off idle. No off idle bog, just acceleration. This in turn increases the amount of air/fuel going through the engine and increases performance.
Vacuum secondaries are great for street applications, but if you're gonna street race and make a few 1/4 mile passes, the DP is the way to go....   Just my "Old" 0.02......           

Thanks OS. 

  I'm playing with my accelerator pump cams now. Just trying to get the double-pumper all tuned in. Yep, I like it, I just hate reading that I should have a vacuum secondary carb. on my car.


  Mike   

[Chryco Psycho]

I would never choose a Vacuum secondary over a mechanical .. well almost ... not on my car anyway

[Nova]

There's an old formula I use on street cars and it's
         
           engine cubes x max rpm divided by 3456

So 440cu X 6000rpm by 3456 = 764cfm