carb sugestions for a 383 with a 6-71

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prostude
Posts: 46
Joined: Mon Apr 26, 2010 11:16 am
Location: Syracuse NY

carb sugestions for a 383 with a 6-71

#1 Post by prostude » Wed Mar 16, 2011 9:48 am

Looking for suggestions on carb cfm for a 383 1-1 drive 6-71
Was running two 450's on a 350 then went to 2 600's
Looking to run anywhere between 600 and 750 carbs
Holley dp's
Street car Old motor 10.80 @122 1.49 60' 355 6-71 stock gm heads stock rocker arms block hugger headers 1-5/8"x2.5" collector
the car ran in the 9's in the 60's with an olds motor.

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wikd69
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Re: carb sugestions for a 383 with a 6-71

#2 Post by wikd69 » Fri Mar 18, 2011 2:31 pm

prostude wrote:Looking for suggestions on carb cfm for a 383 1-1 drive 6-71
Was running two 450's on a 350 then went to 2 600's
Looking to run anywhere between 600 and 750 carbs
Holley dp's
Is this a street / strip ride ? Or strictly strip ?

If you plan to run it on the street I'd recommend looking at a set of boost referenced Holley 4150 HP's. I'm using a pair of 750 CFM 4150 HP's with the power valve vacuum port redirection (boost referencing). If you're not familiar with boost referencing (I was not) it's just a simple change to the carbs power valve vacuum signal supply - the carb bottom / base port for the PV is blocked off and the vacuum signal routed from below the blower and connected in through a passage drilled through the side of the carb body, directly into the PV chamber. This lets your blower build operate with the same idle-to-WOT transition circuits as a NA build, using vacuum states to control fuel slow as the butterflies open. Boost referenced carbs cost more than conventional carbs but for me it it was well worth the price. Having said that, if you know what you're doing, and know where to drill, you can convert a conventional carb body to allow this vacuum signal redirection. Here is a website I found with some info on modifying your carb, though it appears they are doing it via the metering block. There are additional sources on the net as well.

http://www.motorsportsvillage.com/modifycarb.html

I found the rule of thumb for power valve selection is to use PV's rated at half your vacuum at idle. I have been running at approximately 7 inches of vacuum and this translates to 3.5 PV's. Note that this in only on the primary side - my secondary power valves are plugged in the metering block.

If you're not running on the street, you can prolly live without power valves and this boost referencing feature.

Hope this was of some benefit.

Heres a shot of the carbs - note the vacuum hoses connecting in through the side of carb body...

Image

Image
1969 ProStreet Camaro RS Best 9.75@139 1.46 60'
Blown 427 BBC, TH400 w/Brake, Back-Half Ladderbar
Narrowed 12-Bolt, 4.10 Gears, Spool, Moser 33 Spline

http://www.marsh-racing.com/harrys_camaro-1.htm

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prostude
Posts: 46
Joined: Mon Apr 26, 2010 11:16 am
Location: Syracuse NY

Re: carb sugestions for a 383 with a 6-71

#3 Post by prostude » Fri Mar 18, 2011 3:07 pm

Thanks for the info that looks like a nice setup
I am very familiar with the boost referenced carbs
We are actually thinking of advertising that we can do this modification

I think I will start out with 2 650' s on this setup and tune from there
I am curious if anyone else out there is running 750's or bigger on a sbc setup
Street car Old motor 10.80 @122 1.49 60' 355 6-71 stock gm heads stock rocker arms block hugger headers 1-5/8"x2.5" collector
the car ran in the 9's in the 60's with an olds motor.

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