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#1 |
Senior Member
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Location: Chesapeake, Va
Posts: 1,275
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carb CFM?
what is the CFM rating on the factory Quadrajet carbs that came on out trucks,(72 C-10, 350 4 barrel)??
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Mike 72 C-10 Cheyenne off frame resto and Upgraded to 4 wheel disk, Tilt, Dakota Digital Dash / Rear slider. 421 SBC / TH350 3000RPM Stall Progression Ignition /Holley 750 DP/3:73 gear Eaton Limited Slip unit / 2 1/2 exhaust glasspacks ![]() |
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#2 |
Registered User
![]() Join Date: Oct 2011
Location: Victoria, B.C
Posts: 3,794
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Re: carb CFM?
...they could flow up over 700-750cfm...but generally delivered less, since its very hard for a 350 to use over 600cfm....unless it really revs out.
Coley
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....for some men, there is experience, skill and effort....for the others...there is visa and UPS LOL 1966 Chevy 1/2 ton (Florida- Red/white) 1972 Chevy 1/2 ton (California- Blue/white) 2005 Chevy Silverado HD2500/Duramax 2000 Dodge Ram 1500 |
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#3 |
Registered User
![]() Join Date: Jul 2013
Location: Forestburg, Texas
Posts: 659
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Re: carb CFM?
^^^^YEP^^^^
Some CBOP 455/473's were 800CFM.
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Mark Jesus is the Way! 2003 2500HD CCLB Duramax/Ali (Clifford) 2014 2SS/RS black on black Camaro (Betty) 2006 Pontiac SOLSTICE silver/black (Lula-Bell) 1970 C/10 Short Wide (Peggy) 1964 C/10 Short Step (Hambone) RIP Jimmy Hamilton Thank you for the trucks |
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#4 |
Senior Member
![]() Join Date: Mar 2012
Location: Chesapeake, Va
Posts: 1,275
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Re: carb CFM?
okay so the reason i am asking is, the crate motor I installed recommended a 600 CFM carb, I put a 600 DP on it but it seems like something is holding it back when i get on it , I was thinking upgrading to a 650 DP Holley with a four corner idle setting,
so if the manufacture suggested a 600 on a rated 385 HP small block, but the factory stock engine QJ was a 750, and if i look at other top end combos at summit they recommend a 750 CFM carb ( most of them are 375 HP and higher. Just thinking the 650 would give me a little more juice
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Mike 72 C-10 Cheyenne off frame resto and Upgraded to 4 wheel disk, Tilt, Dakota Digital Dash / Rear slider. 421 SBC / TH350 3000RPM Stall Progression Ignition /Holley 750 DP/3:73 gear Eaton Limited Slip unit / 2 1/2 exhaust glasspacks ![]() |
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#5 |
Registered User
Join Date: Aug 2009
Location: Bowser
Posts: 13,621
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Re: carb CFM?
Put a 750 vac secondary 3310 on it and be done with it.
Years ago I tried swapping my factory type 3310 on my 70 LS6 to a 650 dp and it felt doggy, put the vac sec carb back on. World of difference with the secondaries opening slower. Your 2000rpm TQ is holding you back. |
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#6 |
Senior Member
![]() Join Date: Mar 2012
Location: Chesapeake, Va
Posts: 1,275
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Re: carb CFM?
Geezer,
can you explain the Converter theory of holding me back
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Mike 72 C-10 Cheyenne off frame resto and Upgraded to 4 wheel disk, Tilt, Dakota Digital Dash / Rear slider. 421 SBC / TH350 3000RPM Stall Progression Ignition /Holley 750 DP/3:73 gear Eaton Limited Slip unit / 2 1/2 exhaust glasspacks ![]() |
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#7 | |
Registered User
Join Date: Feb 2009
Location: southeasternfoothillsofusa
Posts: 1,557
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![]() Quote:
Sam |
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#8 |
Senior Member
![]() Join Date: Mar 2012
Location: Chesapeake, Va
Posts: 1,275
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Re: carb CFM?
well the recommended stall converter for my engine was 2200 to 2500, since my cruising rpm is around 2500 on the highway, i went for a slightly smaller stall speed.
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Mike 72 C-10 Cheyenne off frame resto and Upgraded to 4 wheel disk, Tilt, Dakota Digital Dash / Rear slider. 421 SBC / TH350 3000RPM Stall Progression Ignition /Holley 750 DP/3:73 gear Eaton Limited Slip unit / 2 1/2 exhaust glasspacks ![]() |
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#9 | |
Registered User
Join Date: Aug 2009
Location: Bowser
Posts: 13,621
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Re: carb CFM?
Quote:
To turn 2500rpm you need a 32" tall tire. |
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#10 | |
Senior Member
![]() Join Date: Mar 2012
Location: Chesapeake, Va
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Re: carb CFM?
Quote:
I am running at 31 x 10.5 x 15 so my factory tach says 2500 at around 65 give or take
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Mike 72 C-10 Cheyenne off frame resto and Upgraded to 4 wheel disk, Tilt, Dakota Digital Dash / Rear slider. 421 SBC / TH350 3000RPM Stall Progression Ignition /Holley 750 DP/3:73 gear Eaton Limited Slip unit / 2 1/2 exhaust glasspacks ![]() |
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#11 |
Registered Cruiser
Join Date: May 2002
Location: Las Vegas NV
Posts: 2,230
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Re: carb CFM?
When it comes to carburetors, bigger isn't necessarily better. A 600cfm carb is more than enough.
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I intend to live forever. So far, so good. |
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#12 |
Registered User
Join Date: Jan 2013
Location: Mickleton, NJ
Posts: 1,776
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Re: carb CFM?
I have a 625 cfm Street Demon on my 355, and it freaking screams. When you go too big you gain a little at WOT, but part throttle and tip in get doggy and will bog out.
I'm running a manual trans, so I need it to run well right off the bottom for low speed take off. I had to adjust my secondaries a lot and add a larger accelerator pump nozzle, but now its running awesome. 600-650 cfm is plenty until you get up to a 383.
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Shawn 1970 Chevy C-10 SWB, 350, TKO 600 5 speed My build http://67-72chevytrucks.com/vboard/s...d.php?t=559881 |
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#13 |
Registered User
Join Date: Aug 2012
Location: Junction City, KS
Posts: 782
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Re: carb CFM?
It would have been a 750 quadrajet. I recommend running a quadrajet on it from SMI Carburetor. They do great work. Tell them the specifics of your engine, and they build it to perform to your motor. They have excellent reviews. And if you need any help while installing, you can call them up.
http://www.smicarburetor.com/product...ID2/9/sfID3/32
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Joseph Joe's 69 GMC http://67-72chevytrucks.com/vboard/s...d.php?t=543253 1969 GMC SWB-350 SBC 700R4 2013 Ram 2500 CC Laramie Longhorn Edition-6.7 PPEI EFI Live CSP5 5” ProFlo Exhaust |
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#14 |
Hittin E-Z Street on Mud Tires
![]() Join Date: Nov 2004
Location: Greenville, SC
Posts: 23,090
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Re: carb CFM?
Are you sure it's tuned properly? Both carb and timing? If so, you can try rejetting the secondaries for some more power.
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Jesse James 1967 C10 SWB Stepside: 350/700R4/3.73 1965 Ford Mustang: 289/T5-5spd/3.25 Trac-Loc 1968 Pontiac Firebird: Project Fire Chicken! 2015 Silverado Double Cab 5.3L Z71 2001 Jeep Wrangler Sport 4.0L 5spd 2020 Chevrolet Equinox Premium 2.0L Turbo 2011 Mustang V6 ~ Wife's ride ![]() American Born, Country by the Grace of God ![]() 1967 CST Shop Truck Rebuild! My 1967 C-10 Build Thread My Vintage Air A/C Install Project "On a Dime" Trying my hand at Home Renovation! 1965 Mustang Modifications! |
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#15 |
Senior Member
![]() Join Date: Mar 2012
Location: Chesapeake, Va
Posts: 1,275
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Re: carb CFM?
timing is set to specs for engine and I adjusted the A/F mix with a vac gauge, i have not changed any jets out yet , might try that, there is a speed shop in town that will tune it, change jets ect ect. in on the dyno for about 200 bucks a session.
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Mike 72 C-10 Cheyenne off frame resto and Upgraded to 4 wheel disk, Tilt, Dakota Digital Dash / Rear slider. 421 SBC / TH350 3000RPM Stall Progression Ignition /Holley 750 DP/3:73 gear Eaton Limited Slip unit / 2 1/2 exhaust glasspacks ![]() |
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#16 |
Registered User
Join Date: Jan 2013
Location: Eastern TN
Posts: 1,921
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Re: carb CFM?
Qjets flow 750 for the side entry and front entry were 800 cfm. The reason that GM got away with so much carb is that a Qjet does not act like any other carb. That secondary choke flap looking thing is an air door. It will only let as much air as the motor use get through. So theoretically you could put it on a 231 cid motor and have no issues. It just wouldn't pull much through the secondaries. The primaries of the standard GM qjet flow around 250 or 270 cfm. The exact number escapes me but the primaries are like the size of a dime which is why they run so nice down low. The 3310 Holley carbs act similiar with the stiffer secondary springs. The heavy spring doesn't even open the secondaries all the way! The spring kit comes with a neat little chart that shows this along with the approx RPM the secondaries will start to open and full secondary operation happens. Swapping springs makes a world of difference because of this.
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