800 CFM Quadrajet Identification And Other information:

Taken from the Q&A page at  http://www.classicalpontiac.com

This information is for reference only, current as of 3/17/2000

Visit my site at:   Fred's Pontiac information

Email comments or suggestions concerning these help files to: fteufert1@worldnet.att.net

Topic: 6338

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- 800 cfm Q-Jet - Louie 2/8/99 11:22

Is the Q-jet from a 80 firebird formula 400 cid a 800 cfm or 750 cfm. Just saw one in the wrecking yard? Your help is appreciated. Lou

Responses

- Karl 2/8/99 11:44

800 Q-jets for a poncho have two holes is the back two flaps. 600-750's don't.

- Rocky Rotella rotella31@hotmail.com 2/8/99 15:06

The only 800cfm carbs were on the 71 455 HO and the 73-74 SD455. I believe the 77-79 T/A 6.6 400's had a 750 cfm carb

padgett Bio 2/8/99 15:14

An '80 Formula 400 would be a unique find, Pontiac did not put a 400 in anything after '79.

Witchdoctor Bio 2/8/99 19:07

Louie: Shine a light down the primary venturi. If it has a double booster ring, and the venturi throat is smooth all of the way around, it is a 750 body. If it has a single boster and a smooth venturi throat, it is a very rare `71 800. If it has a double booster, but a shallow venturi ring with a bump at about 45 degrees toward the outer sides, it is an 800 body. The so called Ram Air slots in the air valves are common to many 750s. The physical opening of the air valves was limited to less than 90 degrees, but modification is as simple as clipping off or filing down the tang that contacts the underside of the air horn. WD.

Steve Chin Bio 2/8/99 19:59

Louie, WD has the straight poop on the 800 CFM Q-jets. I had a '70 750 CFM carburetor that had the slots in the secondary air valves.

jo jo Bio 2/9/99 8:07

Karl if you find a 600 quad ,I'll buy it from ya.

- Louie 2/9/99 8:31

Thanks for the info. I'm, checking it out.

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Topic: 6586

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- 750 or 800 Q-Jet? - Ray Weaver rweaver@frommelectric.com 2/20/99 17:22

Thanks for answering my Q-Jet help request. I could use a little more advice. I recently finished rebuilding my Q-Jet, and on a recommendation from Doug Roe's book, I purchased a nylon fuel filter from Mercury Marine (filters same as brass unit but flows much better, costs $.84). Problem is that my Q-jet has the smaller inlet that won't accept the filter-- seems only the factory brass one will fit. I do have an 800 CFM body with the larger inlet that easily accepts the nylon filter. Would it be beneficial to replace the 750 body with the 800 body? Or, in other words, is the factory brass filter and 750 carb totally adequate for my combo? Combo is 462, 6x-4 heads gasket matched and bowls blended. '72 intake. Summit 2801 cam 214/224 (forget exact lift but somewhere around .465) 4-tube headers, 2.5 inch exhaust, 4 speed, 3:31 posi. Car is '70 LeMans Sport Convertible. Also, what would be a good starting point as far as primary metering rods and jets? The carb now has #74 jets and #43 rods.

Responses

TempesT68 Bio 2/20/99 18:51

i had put a 800 buick body on a 750 chebbie base to get the right vaccum line and throttle linkage, i noteced a bit more power out of my 350, im sure you'll notice it with that 462

Witchdoctor Bio 2/20/99 20:42

Ray: I'm at a loss about the nylon filter not fitting. I have one on my original 750 Q-J on my `73 455 wagon. As for jetting Q-Js, remember that on the primary side, the jet opening controls full throttle mixture, as except for a very few rods, the diameter of the tip is the same at .026" or so. The upper part of the rod, which is indicated by the stamped number, controls light throttle operation. On the secondary side, unless the carb has been converted to screw in jets, the opening is the same, the number .126" sticks in my mind, and full throttle jetting is controled by the tip diameter of the secondary rods, and the hanger, which controls at what point the tip is pulled into the opening with regard to air valve opening. For most of the bad street/strip combos, a primary jet of up to .078" seems to work well, while on the secondary side, the smallest tips available may still be too lean, and have to be turned down. WD.

jo jo Bio 2/20/99 21:38

I don't like the long transfer slot the cevy base plates have. .040 clearance comes up pretty fast witha 455.Why don't you buy a clear glass in line filter? By the way Ray i just bought that same summit cam ,hows it run? Iv'e never had to go any more than 73 jet with 42 rod I have the a.p.t adj all the way in.Sec orfice is 136 and iv;e never had to go any less than .050 on the power tip.The trick is to get the transitioning to the power tip correct in reference to the airvalves.Ive got 10 different rods that i use.

joe s Bio 2/20/99 23:14

Olds Q-jets have a longer inlet housing that screws onto the body, so you can use a longer filter (1"long) That might let you use the nylon filter without as much trouble. Joe

Topic: 7380

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- 800 cfm Quadrojet vs Holley - den guy Bio 3/25/99 19:14

Hello everyone, Was wondering what personal opinions you would have on the following: The Ram Air 4 or 455 HO round port ported aluminum intake and 800 cfm quadrojet vs any edelbrock intake w/ holley carb. The application being a 455 bird balanced ,Ram air 4 type cam specw, 9.5:1 comp ported heads etc..???

Responses

- Joe Inskeep jinskeep@yahoo.com 3/25/99 19:48

Den Guy, I know that if you have a Q-Jet you automatically become invisible to most self-respecting non B-O-P guys...kind of like if they see ram air manifolds vs. tube headers. Those type things also make them look REALLY bad if they lose to you in a race ("Hey man, that car still had it's stock carb and exhaust manifolds!") AND serve the dual purpose of giving you excuses if you run up against somebody you can't beat for some reason ("Well, my car's still stock, you see...") Heh, heh, heh...

- DMR 3/25/99 20:31

If I'm going to drive it on the street, Q-jet, drag race it with very limited street use, Holley.

- jv 3/26/99 12:49

DMR, Then how do you account for the success Jim Hand has on the strip? I guess he knows something magical?

- DMR 3/26/99 17:22

Jim does know the Q-jet very well, and his car's performance shows it, but I can do more with my Holley, than my Q-jet, so I use the H carb. There are those who can work majic with the Q-jet, I admire them, I don't have it worked out for the strip, yet, but it would seem Jim, and others, do. If you have the plan to make the Q-jet work, then by all means, use the Q-jet all the time.

- Brian Baker bkbaker@att.com 3/26/99 19:44

The Q-Jet is not as mysterious as everyone makes it out to be. It responds to the same basic mods you would perform on a Holley. For a street/strip application, I would take a modified Q-Jet over an "out of the box" Holley any day. The Q-jet's advantages over the Holley are better throttle response (due to the smaller primaries), and better fuel economy (provided you keep your foot out of it). Plus as Joe sez, you get the "sleeper" factor thrown in because most folks on the street won't give it a second look (especially if your also running RA/HO type exhaust manifolds). I've got $230 invested in my Q-Jet (including what I paid at a swap meet) and with it's Jones stage-11 prep, it'll outperform ANY "out of the box" Holley in my application. When's the last time you saw a 750 Holley for $230 that did exactly what you needed without further modification?

- DMR 3/26/99 23:10

My Holleys aren't "out of the box", and I use the dedicated spread bore 800 cfm Holley double pumper for my performance carbs, not the square bore d/p like the 4780. The Holley is good for me at the strip, and the Q-jet works good on the street, and I know that tuning the Q-jet is easy, but I'm more familiar with the Holley design. My street Q-jets work very well.

Topic: 7778

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- 800cfm q-jets - pace455 ajs@millnet.net 4/11/99 0:44

Hi everybody . Does anyone know what they installed 800 cfm Q-jets in ? I'm always out junking and would like to find one. thanks

Responses

- 4/11/99 8:18

I look for early to mid 70's BIG GM motors.

- 69GTO's 4/11/99 10:11

Pace: I'm not sure of the cars, but most of the yards around here have a few shelves full of carbs. The 4M series is what you want. Just measure the primaries, 1-7/32" is an 800cfm. (1-3/32" is a 750cfm) Good luck

donny Bio 4/11/99 10:46

800s came out in 75 and later in Ponchos

den guy Bio 4/11/99 13:57

I am positive that the 800cfm were in the Ram Air 4s,71-72 455HO's and the SD-455. I always thought that was it. The rest were 750cfm's.

Johnathan Bio 4/11/99 14:22

I have a 800cfm Qjet, I thought about putting it onto my 400

Steve Chin Bio 4/12/99 18:37

The Ram Air IV got a 750 CFM Quadrajet. The 455-HOs got small primary 800 CFM Q-jets (second booster rings not present), and the SD 455 got a big primary 800 CFM Q-jet. A lot of the late '70s emissions Q-jets were also 800 CFM. Telltale signs are the bulges in the primary bores (visible through the air horn by opening up the choke valve).

jo jo Bio 4/12/99 19:32

hey steve: which ring was missing on the pri side?just wondering

Witchdoctor Bio 4/13/99 11:52

Outer booster ring was eliminated. If one is patient and careful, outer rings can be removed from the std. 800 castings. It is a means to eliminate nozzle drip on bad cam, big inch engines, plus improving the primary/secondary flow ratio of the Q-Jet. WD.

Topic: 10243

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- 800cfm qjet with a 350? - marker Bio 7/30/99 10:09

Has anyone heard of a 800cfm qjet that came stock on a 350? A friend told me that they did make them.

Responses

robz Bio 7/30/99 10:37

Really? What year?

goatwrench Bio 7/30/99 21:40

Don't know if this pertains to Pontiacs, but our old 76 Buick 350 came stock with an 800 CFM Quadrajet. Probably so that the (heavy) car could pass smog specs on the dyno without having to dip into the dirty secondary side.

- Bruce B. 8/1/99 1:01

I recently built one up for a customer. It was a 1977 pontiac unit and had several unique touches that were definately performance oriented. I researched the number because I got curious. I will try and locate my notes and post more details in a day or so.

Topic: 10328

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- 750-800 cfm q-jet vs Holley - den guy Bio 8/3/99 5:55

Hello, What has been your expirience between these two carbs. Was switching away from the q-jet worth the hassle. I am running the 800cfm q-jet 1971 model and it has been reliable so far but am wondering if a switch wouldn't increase the power some if installed on a nicely built motor.

Responses

- nxpage 8/3/99 8:40

If you switch to a Holley only get a double pumper, the others are just crap. I personaly prefer Edelbrock carbs. Are you running a stock intake manifold?

- Nick 8/3/99 12:42

My opinion is to keep the Q-jet since it has worked for you, but look into doing some tuning on it to see if you are at the optimim settings and all adjustments are within spec. I differ with nxpage in that I have had good results with the 4460 Holley (vacuum secondaries, but will readily admit that it took some tuning to get there. I found that in general, Q-jets seem to go longer than Holleys before needing adjustment. My 79 T/A has the Q-jet, but I have a Holley on my 57 "non-Pontiac". Satisfied with both.

Steve Chin Bio 8/3/99 18:18

Mark, I think that you'll be happy keeping your 800 CFM HO Quadrajet. As Nick said, verify the jetting and other tuning settings for best performance, and there should be little (if any) difference in its performance vs. a Holley (since the thing is there to meter air and pre-mix a metered amount of fuel into that air).

den guy Bio 8/3/99 22:34

Since I posted this Ive ordered the Roe's q-jet book. Hope it helps me zero it in. More later!!!

- Nick 8/4/99 6:57

One other thing - there is a lot of Q-jet tuning info, parts numbers, etc etc in the Archives that can help you.

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Topic: 10472

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- 800cfm q-qjet ID - Rocky Rotella jrotella@home.com 8/8/99 20:16

I am stumped. I just picked up, what I think is, a 800cfm Q-jet at the junkyard. It is a #17058266 and came off a 78 T/A 6.6 Trans Am. I get it home and take it apart and notice the booster rings and the "bulges" that are commonly associated with 800cfm carbs. I wanted to compare it to my 76 T/A 455 #17056263 carb on the shelf. Upon disassembly, I see that this 76 carb has the same bulges. So I tried to measure, and they seem to measure the same. So the questions I am trying to get answered are: 1)what other differences are noticeable on the 800cfm carbs? 2)why does the 76 have the same "bulges" and size primaries. This situation makes me wonder if the #17058266 is not a 800cfm or if the #17056263 is. Either way, I got it for $25, surely I can re-sell it for that.

Responses

- Rocky Rotella 8/8/99 20:51

OK, upon further investigation, the 76 17056263 is a 76 400 4 speed Firebird carb. Also the 1705x263 in corresponding years is the 800cfm carb for the 400 4 speed W72 motors. So from what I can deduce, The 76 400 4 speed Firebird used 800cfm carbs too. What do you guys think, does this sound like a resonable deduction?

Kenny T Bio 8/8/99 21:12

I have a 76 Firebird 400 auto engine in my 68 Bird at the moment and it has an 800 cfm carb. My 75 455 has a 750 cfm. 1976 was a crossover year for many things and one of them was carb size.

Steve Chin Bio 8/8/99 22:56

Kenny T hit the nail squarely on the head. 1976 is the first year for wide-availability of the 800 CFM Quadrajets on Cadillac, Pontiac and Oldsmobile engines. It seems that the Buicks and C#@vies had less availability of the big primary carburetors. My best guess on this would be that the Olds, Pontiac, and Cadillacs were primarily more or less larger engines and that the Buicks and C#@vies were on average smaller, so the divisions with the larger average in engine size got more of the bigger carburetors. Of course, I could be full of hot air on this theory...

- Rocky Rotella 8/9/99 15:40

OK. I just checked and the NOS carb on my 76 T/A is a 7045264. It is a 75 A,B,G body carb. It also has the bulges, therefore I assume it is a 800cfm also. Well, I guess I have another for the shelf. Thanks to those who answered and if anyone can add, please do

goatwrench Bio 8/9/99 22:34

My 76 Buick 350 had an 800 from the factory.

OldsGuy Bio 8/10/99 12:06

compare the venturies on the primaries with a know 750 cfm or 800 cfm. this is the only difference in the two. i don't know the exact measurements off the top of my head, but will be able to tell with the carbs next to each other.

Witchdoctor Bio 8/10/99 20:17

The id. of the outer venturi ring is 1-3/32" for the 750 CFM. primary, and 1-7/32" id. for the "normal" 800 CFM. unit. There was an oddball, I believe only in 1971, that had the smaller 1-3/32" id. venturi, but WITHOUT

Witchdoctor Bio 8/10/99 20:17

The id. of the outer venturi ring is 1-3/32" for the 750 CFM. primary, and 1-7/32" id. for the "normal" 800 CFM. unit. There was an oddball, I believe only in 1971, that had the smaller 1-3/32" id. venturi, but WITHOUT

Witchdoctor Bio 8/10/99 20:33

Mouse have hair trigger. to continue, WITHOUT the outer booster ring, that was also rated at 800 CFM. The secondaries, given 90 degree throttle plate and air valve opening will all flow approximately 550 CFM., which leaves the 1-3/32" primary flowing around 200 CFM., and the larger 1-7/32" unit flowing about 250 CFM. The great difference between primary and secondary flow, along with the lack of a positive secondary accelerator pump, is the cause of the transition stumble if the air valve opens too quickly. Air moves fast, but it takes a bit for the fuel to catch up. One might wonder what would be the effect of removing the outer booster ring from the large 1-7/32" id. primary. On paper, with choke removal, you should have a Q-J that could flow around 870 CFM., if you really needed it. What it does accomplish is to make a Q-J that is less sensitive to nozzle drip with a high duration cam, and with the enlargement of the accelerator pump to accept the larger 2G pump cup, a really bad bracket racing carburetor that moves smoothly into a loose convertor range, and pull like gang busters on the top end. Not too good around town, however. It drinks gas like mad, but given the proper cam timing, has almost as much intake howl as a Tri-Power. WD.

- Rocky Rotella jrotella@home.com 8/11/99 10:49

Thanks WD. Now for calibration. I need some 75-up 43K and 44K rods. Can anyone help me out? If you have any available, please contact me. Thanks

Witchdoctor Bio 8/12/99 11:45

Jetting the Q-J for a specific application is pretty much a trial and error proposition. The power tip of all but a very, very few primary rods are the same, so full throttle primary jetting is governed by jet size. The tapered part of the primary rod works with the power valve spring to trim light throttle cruise mixture for most efficient operation. Stock, the secondary jet disc is fixed, with the secondary rod power tip dictating full throttle mixture, but again the angle of the air valve, and the hanger height will vary the actual mixture. The Doug Roe Rochester carburetor book is the best guide for tuning the Q-J that I have seen. WD.

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