396/325hp - is a Holley 650 DP good enough - Chevelle Tech
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  #1  
Old Mar 30th, 10, 10:10 AM
gatkins2004 gatkins2004 is offline
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Default 396/325hp - is a Holley 650 DP good enough

Hi all,

Can you guys give me your thoughts on a 650 double pumper on a stock 396/325 engine?

I'm wondering if i need more CFM....

Thank you,
Gary
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  #2  
Old Mar 30th, 10, 10:26 AM
Jerry70 Jerry70 is offline
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Default Re: 396/325hp - is a Holley 650 DP good enough

650 would be more than enough for a stock 325 but I don't think a a DP is a very good choice for one. QuadraJet would be my first choice for a stock L-35 but if it has to be a Holley, I like a 60o or 670 vacuum secondary.
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  #3  
Old Mar 30th, 10, 10:48 AM
gatkins2004 gatkins2004 is offline
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Default Re: 396/325hp - is a Holley 650 DP good enough

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Originally Posted by Jerry70 View Post
650 would be more than enough for a stock 325 but I don't think a a DP is a very good choice for one. QuadraJet would be my first choice for a stock L-35 but if it has to be a Holley, I like a 60o or 670 vacuum secondary.
Thanks Jerry, if i want to go more with numbers what is the correct carb for a stock 1968 ss396 chevelle?

Thank you,
Gary
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Old Mar 30th, 10, 12:22 PM
barryt barryt is offline
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Default Re: 396/325hp - is a Holley 650 DP good enough

vacuum secondaries for street use
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Old Mar 30th, 10, 2:37 PM
Schurkey Schurkey is offline
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Default Re: 396/325hp - is a Holley 650 DP good enough

"HOW BIG" of a carb is extremely dependent on "HOW HIGH" you plan to spin the engine.

If this is a putt-putt car, 650 cfm is more than enough. I wouldn't use a double pumper on a putt-putt, though.

My '69 325hp 396 used a 750 cfm Q-Jet. I suspect the '68 did, too.
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Old Mar 30th, 10, 2:44 PM
Jason 67 conv Jason 67 conv is offline
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Default Re: 396/325hp - is a Holley 650 DP good enough

Quote:
Originally Posted by gatkins2004 View Post
Thanks Jerry, if i want to go more with numbers what is the correct carb for a stock 1968 ss396 chevelle?

Thank you,
Gary
I have a rochester carb from a 68 396 325hp full size car. Would be willing to sell it. The date is a mid May if you are looking for a date. It will need to be rebuilt. Pm me if interested?

Jason
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  #7  
Old Mar 30th, 10, 5:13 PM
matt's66 matt's66 is offline
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Default Re: 396/325hp - is a Holley 650 DP good enough

I have an Edelbrock 1406 600 cfm elec. choke on my stock 396 325 and it runs awesome. Plenty of carb since it runs out of gusto at around 4400 rpm anyway because of the insanely small cam.
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Old Mar 30th, 10, 6:12 PM
lg1969 lg1969 is offline
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Default Re: 396/325hp - is a Holley 650 DP good enough

I would prefer 3310 750 cfm vacuum secondary Holley. 3310 780 vacuum secondary Holley will work, too. I believe the 750 will give you sharper throttle response. The only problem is the intake manifold. You need a square bore type manifold.
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Old Mar 30th, 10, 6:58 PM
von von is offline
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Default Re: 396/325hp - is a Holley 650 DP good enough

Quote:
Originally Posted by Jason 67 conv View Post
I have a rochester carb from a 68 396 325hp full size car. Would be willing to sell it. The date is a mid May if you are looking for a date. It will need to be rebuilt. Pm me if interested?

Jason
And I can rebuild it for very reasonable cost.
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Old Mar 30th, 10, 7:32 PM
BillsCamino BillsCamino is offline
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Default Re: 396/325hp - is a Holley 650 DP good enough

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Originally Posted by von View Post
And I can rebuild it for very reasonable cost.
Von just completed the Q-jet for my '69 SS396 w/L35.
Excellent work and highly recommended!!
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  #11  
Old Mar 30th, 10, 8:25 PM
jb66ss396 jb66ss396 is offline
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Default Re: 396/325hp - is a Holley 650 DP good enough

Quote:
Originally Posted by gatkins2004 View Post
Hi all,

Can you guys give me your thoughts on a 650 double pumper on a stock 396/325 engine?

I'm wondering if i need more CFM....

Thank you,
Gary
I use a 650 Holley DP and it's run great.
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  #12  
Old Apr 1st, 10, 5:28 PM
NastySS NastySS is offline
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Default Re: 396/325hp - is a Holley 650 DP good enough

This is a good subject since I am on the downslope of putting back together my 67 SS. I have a 66 396 going back in with forged 10:1 pistons and rods, full roller top end with the comp cams mother thumper cam and bowtie alum intake. I have a 800 cfm quadrajet and am at 5,280 above sea level. Is that going to be too much carb? Here in colorado we need lots of air. Perhaps a jet recommendation for the carb would be a good idea at this point. Any ideas?
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Old Apr 1st, 10, 6:29 PM
von von is offline
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Default Re: 396/325hp - is a Holley 650 DP good enough

Quote:
Originally Posted by NastySS View Post
This is a good subject since I am on the downslope of putting back together my 67 SS. I have a 66 396 going back in with forged 10:1 pistons and rods, full roller top end with the comp cams mother thumper cam and bowtie alum intake. I have a 800 cfm quadrajet and am at 5,280 above sea level. Is that going to be too much carb? Here in colorado we need lots of air. Perhaps a jet recommendation for the carb would be a good idea at this point. Any ideas?
The beauty of the Q jet design is that it's never too much carb if set up right. A jet size couldn't be recommended without knowing the main bleed (upper and lower) sizes. Metering rod sizes enter into this too. GM varied air bleed and jet/rod combos according to desired level of emissions tune, specific engine, etc. I.E. the stock primary jet size for a '66 396 was 71. The size for a '70 396 was 78 and it was a leaner setup for emissions reasons, due to main air bleeds being much larger.
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  #14  
Old Apr 1st, 10, 7:28 PM
rocks66ss rocks66ss is offline
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Default Re: 396/325hp - is a Holley 650 DP good enough

Why don't you do the math and see what size carb you need.

http://www.holleycarbs.com.au/chooseCarb.htm

A 396 hi performance engine, spinning it up to 6000rpm calls for a 584 cfm.

So I would say a 650 will do you fine. I have 650 DP on mine, and it works just peachy.

Copied from their site about sizing.
Carburetors with mechanical secondaries must be chosen very carefully, as a carburetor that is too big will result in "bog" or "sag". On the other hand, a carburetor that is too small will give better acceleration times, but power may fall off at higher RPM. In this case, a bigger carburetor is not necessarily better. To calculate the best size carburetor for a mechanical secondary carburetor, follow these guidelines.
The first thing you need to know is the lowest RPM at which you use full-throttle. In a manual, you should drive around to look at your personal driving, and watch your tach. In an automatic, use the convertor stall speed (about 1350 RPM for a typical Chevy converter). Typically, a heavier vehicle with a higher gear ratio (lower numerical ratio) will have a lower RPM rate here. A normal value for a 300 - 400 CID engine is a 650 or 700 CFM carburetor. A lighter car might have a 700 or 750 CFM carbie. To find the exact value, click on the link below and print out the page that opens, or hold a ruler against your screen to connect your minimum full-throttle RPM with your engine size, and extend the line to the carbie size.



Rocky
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