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2 or 4 barrel carb? #63751 03/14/11 02:27 PM
Joined: Oct 2007 Posts: 43 MO K kyull67 OP Active BB Member
OP kyull67 Active BB Member K Joined: Oct 2007 Posts: 43 MO	I'm almost done with my turbo setup, just need a carb and a few other items. I'm looking at either the holley 2 barrel 500cfm or edelbrock 4 barrel 500cfm. What would be the better choice for the street on a 250c.i. and 6 psi blow through? I have a clifford intake and custom exhaust manifold. Thanks. http://www.67-72chevytrucks.com/vboard/showthread.php?t=257202

Re: 2 or 4 barrel carb? kyull67 #63752 03/14/11 02:46 PM
Joined: Apr 2004 Posts: 3,556 Likes: 35 Dysart, Iowa tlowe #1716 1000 Post Club
tlowe #1716 1000 Post Club Joined: Apr 2004 Posts: 3,556 Likes: 35 Dysart, Iowa	The 2 bbl Holley will work good with low boost and will start being a cork over 325hp. A 4bbl 500 will be better, not sure about the Edelbrocks for a blow thru setup. Don't know what mods need to be done to them to work. A small Holley double pumper with mech secondaries in the 500 range would be great, they do not make one. You can get a 600 though. Inliner Member 1716 65 Chevelle Wagon and 41 Hudson Pickup Information and parts www.12bolt.com

Re: 2 or 4 barrel carb? tlowe #1716 #63753 03/14/11 03:15 PM
Joined: Oct 2007 Posts: 43 MO K kyull67 OP Active BB Member
OP kyull67 Active BB Member K Joined: Oct 2007 Posts: 43 MO	I think 600cfm may be too much for my lower rpm street motor. If I can find good instructions on modifying the edelbrock for blow through then go with 4 barrels? My power goal is right at 325 hp. Thanks for the help http://www.67-72chevytrucks.com/vboard/showthread.php?t=257202

Re: 2 or 4 barrel carb? kyull67 #63754 03/14/11 03:38 PM
Joined: Oct 2007 Posts: 43 MO K kyull67 OP Active BB Member
OP kyull67 Active BB Member K Joined: Oct 2007 Posts: 43 MO	All of my research so far is steering me towards Holley for blow through set ups. http://www.67-72chevytrucks.com/vboard/showthread.php?t=257202

Re: 2 or 4 barrel carb? kyull67 #63756 03/14/11 04:14 PM
Joined: Apr 2004 Posts: 3,556 Likes: 35 Dysart, Iowa tlowe #1716 1000 Post Club
tlowe #1716 1000 Post Club Joined: Apr 2004 Posts: 3,556 Likes: 35 Dysart, Iowa	It too bad Holley does not make a 450-500 CFM double pumper. It would be a great fit. Have thought about modifying a 450 to do it. Tom Inliner Member 1716 65 Chevelle Wagon and 41 Hudson Pickup Information and parts www.12bolt.com

Re: 2 or 4 barrel carb? tlowe #1716 #63757 03/14/11 06:01 PM
Joined: Oct 2007 Posts: 43 MO K kyull67 OP Active BB Member
OP kyull67 Active BB Member K Joined: Oct 2007 Posts: 43 MO	A 450 Holley? I'll check into it. Apparently the holleys design makes it the absolute best for blow through other than C&S type. The 390cfm is probably much too small for boost? http://www.67-72chevytrucks.com/vboard/showthread.php?t=257202

Re: 2 or 4 barrel carb? kyull67 #63760 03/14/11 06:45 PM
Joined: Jul 2000 Posts: 4,585 Likes: 19 Palatka FL. USA Twisted6 1000 Post Club
Twisted6 1000 Post Club Joined: Jul 2000 Posts: 4,585 Likes: 19 Palatka FL. USA	You can get the 450 as a mech. Or vaccum secondarys.You can also change the back half from a mertering plate to a metering block by useing the meter block off a 390 this is what had told me a few yrs back. And if you change over to center hung float bowls you can then have a dual feed instead of the rod the feeds from one bowl to the other. Larry/Twisted6 [oooooo] Adding CFM adds boost God doesn't like ugly.

Re: 2 or 4 barrel carb? Twisted6 #63763 03/14/11 07:54 PM
Joined: Jan 2005 Posts: 2,123 Likes: 3 Hempstead, Long Island, NY P panic 1000 Post Club
panic 1000 Post Club P Joined: Jan 2005 Posts: 2,123 Likes: 3 Hempstead, Long Island, NY	If it's blow-through, it can be any size that works with the engine N/A - the extra flow comes from the increased density. Roughly RPM × displacement ÷ 3456. If it's draw-through, it has to be large enough to supply the higher power level. RPM × displacement ÷ 3456, then × by the pressure ratio. Assuming 14.7 as ambient: 5 psi = (14.7 + 5) ÷ 14.7 = 1.34 10 psi = (14.7 + 10) ÷ 14.7 = 1.68 15 psi = (14.7 + 15) ÷ 14.7 = 2.02

Re: 2 or 4 barrel carb? panic #63767 03/14/11 09:08 PM
Joined: Sep 2004 Posts: 5,839 Likes: 1 Ca M Mean buzzen half dozen A.K.A. Hank 1000 Post Club
Mean buzzen half dozen A.K.A. Hank 1000 Post Club M Joined: Sep 2004 Posts: 5,839 Likes: 1 Ca	http://www.theturboforums.com/smf/index.php?topic=136075.0 http://www.theturboforums.com/smf/index.php?topic=22107.0 MBHD 12 port SDS EFI

Re: 2 or 4 barrel carb? panic #63774 03/15/11 02:07 PM
Joined: Oct 2007 Posts: 43 MO K kyull67 OP Active BB Member
OP kyull67 Active BB Member K Joined: Oct 2007 Posts: 43 MO	Originally Posted By: panic If it's blow-through, it can be any size that works with the engine N/A - the extra flow comes from the increased density. Roughly RPM × displacement ÷ 3456. If it's draw-through, it has to be large enough to supply the higher power level. RPM × displacement ÷ 3456, then × by the pressure ratio. Assuming 14.7 as ambient: 5 psi = (14.7 + 5) ÷ 14.7 = 1.34 10 psi = (14.7 + 10) ÷ 14.7 = 1.68 15 psi = (14.7 + 15) ÷ 14.7 = 2.02 OK. It's a blow through setup. (4000rpm)(254c.i.)/3456 = 293.98 CFM?? So I think I'll just run the Holley 390cfm four barrel. I've used on on this motor naturally aspirated and it worked great. Thanks again for all of the help! I'll post my progress in a few weeks. http://www.67-72chevytrucks.com/vboard/showthread.php?t=257202

Re: 2 or 4 barrel carb? kyull67 #63793 03/16/11 12:54 PM
Joined: Oct 2007 Posts: 43 MO K kyull67 OP Active BB Member
OP kyull67 Active BB Member K Joined: Oct 2007 Posts: 43 MO	OK guys, Just talked to Randy from the Carb Shop aka customcarbs.com I'm going to supply them with an old used mechanical secondary holley 390cfm and they will send it back tested and ready to run under boost! So, I'm in the market for a mechanical secondary Holley 390cfm if anyone has one laying around. http://www.67-72chevytrucks.com/vboard/showthread.php?t=257202

Re: 2 or 4 barrel carb? kyull67 #63794 03/16/11 12:58 PM
Joined: Jul 2007 Posts: 376 Bremerton, WA 56er Contributor
56er Contributor Joined: Jul 2007 Posts: 376 Bremerton, WA	You don't need a bigger carb to blow through than you would put on the motor naturally aspirated. Sometimes a smaller one actually works better. If you have the 390, I would definitely use it, as the price is right. I'm an edelbrock guy, and they can be used, but the lack of solid floats become a liability after a certain point. "The first rule of overkill: You can never have too much overkill." "Overkill is underrated."

Re: 2 or 4 barrel carb? 56er #63795 03/16/11 01:10 PM
Joined: Feb 2010 Posts: 136 nashville tn B Boucher Contributor
Boucher Contributor B Joined: Feb 2010 Posts: 136 nashville tn	I am using a Holley 2300 350 cfm 2 bbl. It works really good and easy to mod.

Re: 2 or 4 barrel carb? Boucher #63809 03/17/11 01:51 PM
Joined: Oct 2007 Posts: 43 MO K kyull67 OP Active BB Member
OP kyull67 Active BB Member K Joined: Oct 2007 Posts: 43 MO	Thanks for the info guys! http://www.67-72chevytrucks.com/vboard/showthread.php?t=257202

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