quadrajet size question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

BCOWANWHEELS · 09-05-2007, 01:44 PM

anybody know what CFM the stock Q-JET carb is for a 350 chevy ? and how big same carb is for a 396-402 bbc.
thanks
bob

ChevLoRay · 09-05-2007, 02:07 PM

Good question. I'm running an Edelbrock Q-Jet on my truck, which has a 350. The carb is rated 750CFM. It ran great out of the box and still does after 6 years. I think it would be more than adequate on your big block. Based on the computation, what I have is too big for the engine. But it runs great, hasn't flooded or bogged. Always starts. Keeps me braggin'. What else could a man ask for?

Blazer1970 · 09-05-2007, 05:33 PM

They are all basically the same carb, rated at 750 cfm max. Because of the design of the Q-Jet, it will only flow the air that the engine requires. Big block and small block versions of the carb will have different primary jets and metering rods, and different secondary metering rods.

*Billla* · 09-05-2007, 05:45 PM

My understanding is that the Q-Jet will flow 780 CFM unmodified. As noted, it acts like a vacuum secondary carb although it isn't in a pure sense.

Hoping to avoid the "yes it is <-> no it isn't" on the vacuum secondary comment

neonlarry · 09-05-2007, 05:56 PM

There were some Qjets, mostly on BOPC cars the were rated @ 795CFM. You can tell the difference by looking down the primaries:
http://dyeager535.topcities.com/qjetidentify.html

DieselEater · 09-05-2007, 07:24 PM

Blazer1970 is right.......BUT, almost all truck carbs after 1976 were 800CFM, and the Edelbrock carb Model 1906 I believe was an 850!! I do have Cliff Ruggles book if you need technical advice.

That's what's so cool about Q-Jets...they work from 500 cube caddies to 305 smoggers!

A.......

Scott68-93-97 · 09-05-2007, 07:37 PM

795 cfm I agree with neonlarry, but Im not sure of trucks after 76 being higher could be but Ive never heard of it

dh81k30 · 09-07-2007, 08:32 PM

Quote:

Originally Posted by DieselEater

Blazer1970 is right.......BUT, almost all truck carbs after 1976 were 800CFM, and the Edelbrock carb Model 1906 I believe was an 850!! I do have Cliff Ruggles book if you need technical advice.

That's what's so cool about Q-Jets...they work from 500 cube caddies to 305 smoggers!

A.......

Q-jets were installed on the '85 and '86 C10's with the 4.3 liter ( 262 c.i. ) before the tbi system. Seems to work quite well on my '86.

mnunn454 · 09-05-2007, 08:47 PM

Yeah. 200 CFM through the primaries and 600 CFM through the secondaries.

That's largely why they are so driveable and fuel efficient around town/cruising and yet still yield the "Big Gulp" when smashing the throttle.

Really a pretty decent design for a street carb, IMO.

jeffspower · 09-05-2007, 09:43 PM

Buick was the first to use the larger Qjet, on the 455 in 1971, and they quit using the small Qjet on all 455's from then on. I think it was due to the fact that the B-455 loves air, and you would have to "tip into" the secondaries too easily on hills/etc. It also gives you a higher cruising speed on the primarys. Chevys seem to be a hit/ miss as to which one they have.

I had a warmed- up '71 Buick 455 with 2.73 gears & a TH400, the big Qjet- it would run 115 mph without touching the secondaries

DieselEater · 09-05-2007, 09:52 PM

Click the link under my signature and watch a Q-Jet on 500 horses do its work...Straight out of JEGS!!! Yes, this same carb will work on a 305 with very minor jet changes.

Sport/Truck · 09-05-2007, 10:35 PM

Quote:

Originally Posted by jeffspower

I had a warmed- up '71 Buick 455 with 2.73 gears & a TH400, the big Qjet- it would run 115 mph without touching the secondaries

NICE!

Scott68-93-97 · 09-06-2007, 04:49 PM

Q jets are probably the best drivability and performance carbs out there hands down and you cant argue that, Ive seen people throw on a holley thinking they have a race car and get there doors blown off by a guy with a q jet I had one on my 79 malibu I had when I was 16 and we replaced the 305 with a 450hp 350 my pops rebuilt the carb and changed jets for me and that thing screemed, They work very well and can be very economical under easy driving

68C15 · 09-07-2007, 11:31 PM

keep in ind they changed more than jets and rods from one engine to another. each calibration has different air bleeds, aeration tubes, etc.
getting all these to match is like listening to a symphony compared to a simple jet/rod change being a grunge band. there are books out there which cover this in detail. "how to build horsepower, volume II" is a good starting point.

dh81k30 · 09-08-2007, 05:43 PM

Quote:

Originally Posted by 68C15

keep in ind they changed more than jets and rods from one engine to another. each calibration has different air bleeds, aeration tubes, etc.
getting all these to match is like listening to a symphony compared to a simple jet/rod change being a grunge band. there are books out there which cover this in detail. "how to build horsepower, volume II" is a good starting point.

Using emission control equipment ( EGR, vacuum delay, hot air intake, ETC. ) or not has an effect as well.

09-05-2007, 01:44 PM	#1
BCOWANWHEELS Registered User Join Date: Nov 2006 Location: KINGSPORT,TN. Posts: 3,035	quadrajet size question anybody know what CFM the stock Q-JET carb is for a 350 chevy ? and how big same carb is for a 396-402 bbc. thanks bob __________________ I BELIEVE IN JOHN 3:16

09-05-2007, 02:07 PM	#2
ChevLoRay Old Skool Club Join Date: Jun 2001 Location: Benton, AR "The Heart of Arkansas" Posts: 10,880	Re: quadrajet size question Good question. I'm running an Edelbrock Q-Jet on my truck, which has a 350. The carb is rated 750CFM. It ran great out of the box and still does after 6 years. I think it would be more than adequate on your big block. Based on the computation, what I have is too big for the engine. But it runs great, hasn't flooded or bogged. Always starts. Keeps me braggin'. What else could a man ask for? __________________ Member Nr. 2770 '96 GMC Sportside; 4.3/SLT - Daily driven....constantly needs washed. '69 C-10 SWB; 350/TH400 - in limbo The older I get, the better I was.

09-05-2007, 05:33 PM	#3
Blazer1970 Registered User Join Date: Dec 1999 Location: Old Mission, MI, USA Posts: 2,510	Re: quadrajet size question They are all basically the same carb, rated at 750 cfm max. Because of the design of the Q-Jet, it will only flow the air that the engine requires. Big block and small block versions of the carb will have different primary jets and metering rods, and different secondary metering rods. __________________ Tim

09-05-2007, 05:45 PM	#4
Billla Account Suspended Join Date: Sep 2005 Location: Monroe, WA Posts: 3,815	Re: quadrajet size question My understanding is that the Q-Jet will flow 780 CFM unmodified. As noted, it *acts* like a vacuum secondary carb although it isn't in a pure sense. Hoping to avoid the "yes it is <-> no it isn't" on the vacuum secondary comment

09-05-2007, 05:56 PM	#5
neonlarry Registered User Join Date: Feb 2002 Location: Vacaville, CA Posts: 2,746	Re: quadrajet size question There were some Qjets, mostly on BOPC cars the were rated @ 795CFM. You can tell the difference by looking down the primaries: http://dyeager535.topcities.com/qjetidentify.html __________________ 70 C/10 Light Red 350/TH350, HEI, Duals w/40 series Flows, 91 seat, LED taillights 99 Pontiac S/C GTP, SLP Ram Air hood, GMPP Konis & springs 95 Neon ACR, MP PCM, AFX UDP, 3.0 CAI

09-05-2007, 07:24 PM	#6
DieselEater Registered User Join Date: Dec 2006 Location: Trinidad, Colorado Posts: 642	Re: quadrajet size question Blazer1970 is right.......BUT, almost all truck carbs after 1976 were 800CFM, and the Edelbrock carb Model 1906 I believe was an 850!! I do have Cliff Ruggles book if you need technical advice. That's what's so cool about Q-Jets...they work from 500 cube caddies to 305 smoggers! A....... __________________ 69' 3/4 4X4 470ci BBC 700 HP.... D60/14bolt 205/465 http://profile.myspace.com/index.cfm...ndid=127691959

09-05-2007, 07:37 PM	#7
Scott68-93-97 Registered User Join Date: Jul 2006 Location: Fair Oaks, CA Posts: 475	Re: quadrajet size question 795 cfm I agree with neonlarry, but Im not sure of trucks after 76 being higher could be but Ive never heard of it __________________ 1968 Short Fleet 350/700r4 http://67-72chevytrucks.com/vboard/s...d.php?t=249435 1997 Bagged XtdCab Vortec350/4L60e http://67-72chevytrucks.com/vboard/s...44#post2286144 1993 XtdCab Longbed 4x4 6.5Turbo/NV4500 "Daily Driver" 1985 Toyota XtdCab 4x4 22re/W-56/Dual T-cases, Doug Thorley Header, Homebrew front and rear spring packs, Tons of Mods to suspension and drivetrain, 35" boggers, coming soon ARB's and 5.29's, Possible 4.3/700r4 swap

09-05-2007, 08:47 PM	#9
mnunn454 Registered User Join Date: Dec 2006 Location: Rhode Island Posts: 602	Re: quadrajet size question Yeah. 200 CFM through the primaries and 600 CFM through the secondaries. That's largely why they are so driveable and fuel efficient around town/cruising and yet still yield the "Big Gulp" when smashing the throttle. Really a pretty decent design for a street carb, IMO. __________________ 69 C-10 SWB Fleetside 454/TH400 (For Sale) http://67-72chevytrucks.com/vboard/c...ct=1299&cat=12 70 El Camino 454 TH700 29 Model A 4-DR Sedan Deluxe

09-05-2007, 09:43 PM	#10
jeffspower Well, Whoop-dee-do! Join Date: Mar 2003 Location: Easton, Mo. pop.- me & scarcely a few others Posts: 2,302	Re: quadrajet size question Buick was the first to use the larger Qjet, on the 455 in 1971, and they quit using the small Qjet on all 455's from then on. I think it was due to the fact that the B-455 loves air, and you would have to "tip into" the secondaries too easily on hills/etc. It also gives you a higher cruising speed on the primarys. Chevys seem to be a hit/ miss as to which one they have. I had a warmed- up '71 Buick 455 with 2.73 gears & a TH400, the big Qjet- it would run 115 mph without touching the secondaries __________________ '68 GMC shortbox 4x4 350/SM465/T221- bought it in '83 SOLD '72 K20 500 Cad/TH400/NP205 SOLD '92 Chevy 2500 6.5 mech TD 4L80E crusty daily driver '72 Monte Carlo... sweet low mile toy '11 Dodge Challenger IE 392 6spd... midlife car

09-05-2007, 09:52 PM	#11
DieselEater Registered User Join Date: Dec 2006 Location: Trinidad, Colorado Posts: 642	Re: quadrajet size question Click the link under my signature and watch a Q-Jet on 500 horses do its work...Straight out of JEGS!!! Yes, this same carb will work on a 305 with very minor jet changes. __________________ 69' 3/4 4X4 470ci BBC 700 HP.... D60/14bolt 205/465 http://profile.myspace.com/index.cfm...ndid=127691959

09-06-2007, 04:49 PM	#13
Scott68-93-97 Registered User Join Date: Jul 2006 Location: Fair Oaks, CA Posts: 475	Re: quadrajet size question Q jets are probably the best drivability and performance carbs out there hands down and you cant argue that, Ive seen people throw on a holley thinking they have a race car and get there doors blown off by a guy with a q jet I had one on my 79 malibu I had when I was 16 and we replaced the 305 with a 450hp 350 my pops rebuilt the carb and changed jets for me and that thing screemed, They work very well and can be very economical under easy driving __________________ 1968 Short Fleet 350/700r4 http://67-72chevytrucks.com/vboard/s...d.php?t=249435 1997 Bagged XtdCab Vortec350/4L60e http://67-72chevytrucks.com/vboard/s...44#post2286144 1993 XtdCab Longbed 4x4 6.5Turbo/NV4500 "Daily Driver" 1985 Toyota XtdCab 4x4 22re/W-56/Dual T-cases, Doug Thorley Header, Homebrew front and rear spring packs, Tons of Mods to suspension and drivetrain, 35" boggers, coming soon ARB's and 5.29's, Possible 4.3/700r4 swap

09-07-2007, 11:31 PM	#14
68C15 blood type; Retumbo Join Date: Jan 2004 Location: next to my reloading bench Posts: 10,269	Re: quadrajet size question keep in ind they changed more than jets and rods from one engine to another. each calibration has different air bleeds, aeration tubes, etc. getting all these to match is like listening to a symphony compared to a simple jet/rod change being a grunge band. there are books out there which cover this in detail. "how to build horsepower, volume II" is a good starting point.

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