I have always wondered why the Buick factory installed a 800 CFM carburetor on the 1971 Stage 1 (why not the 1970 model) when it has lower compression and HP. Anybody know why?
Larry, I did some research and you are right-on, Buick made the first 800 cfm Qjet in 1971, Pontiac came out with their's in 1973.
I'm pretty sure Pontiac had a 800 CFM in 71 on their 455 HO cars, but I thought it was a one year only application..
Well, when you do research using the internet, you never know what information you'll get and just how accurate it is. From the article I read: Two basic sizes of Quadrajet were produced over the years; 750 and 800 CFM versions. The 800 CFM unit (identified by a slightly larger primary venturi) was relatively rare, found only on 1971-73 Buicks and 1973 Pontiacs. What gets me is, the Olds 455, there is no mention that Olds ever got an 800 cfm carburetor. That seems strange to me. However, all the GM divisions could do what they wanted. Here is the link to this article if anybody is interested. - Rochester Quadrajet: The Rodney Dangerfield of Carburetors (motorstate.com)
Realize the time to engineer, test and produce the 800 CFM carburetor began before the crapshow that was the "newer emission standards" by the Clean Air Act passed in 1970 by Congress. So, even though the engines were "detuned", using various methods, the 800 CFM carbs likely were already being produced, and scrapping them made little sense and would be lost investment in the already ordered and production, with little to no benefit in the move to new pollution standards. It's simple economics and business practices. Use the widgets you've bought, if the impact of doing so, is less than the process to change nets you more on the bottom line and has more positive than negative effect on operations.
Ironically Pontiac had an 830 cfm Qjet in 1970 that was legal to use on a 70 Stage 1 stocker, but using a 71 Buick 800 cfm on the same 70 Stage 1 was illegal.
Yep! That makes perfect sense, just like GM using up carbureted 305s in Chevies long after the debut of the Tune Port injection system. They had all these engines, carbs, mechanical fuel pumps, air cleaners and non FI fuel tanks (and a lot of ‘leftover’ chassis that they could either reengineer for injection, or just built out with carbs), and the cheapest thing was send the ‘performance’ stuff out the door with FI but send the Montes, Caminos, Caprices and trucks out with carbs. Patrick
I agree, Buick was probably working on the 800 cfm carb back in 1968, knowing they were going to build the 455. The big surprise is Pontiac had an 830 cfm in 1970. Wonder why I didn't find that in my research. Maybe because I put in 800 cfm. If they had an 830 cfm in 1970, in 1973 they must have been doing a detune process, coming out with the 800 cfm.
I think we're wading into speculation and dis-information here. This excerpt is from a technical paper written by engineer Lars Grimsrud for the Corvette club. it answers all the questions here: "All pre-1971 Q-Jets are 750 cfm. In 1971, Pontiac introduced an 800-cfm carb for use on the 455 H.O. Ram Air engines. This was a unique design, used only in 1971, and only by Pontiac. It can be identified by looking at the venturi booster venturies: A “normal” Q-Jet has a booster ring (also known as the “Intermediate Ring”) that surrounds the center discharge tube and venturi. The 800 cfm 1971 Pontiac has no Intermediate Ring: Only the center discharge venturi sticks out into the main venturi: it looks like “it’s missing something” in the venturi. Buick also had an 800-cfm Q-Jet in 1971, used on their 455s from 1971 through 1974. Buick took a different approach: Instead of eliminating the Intermediate Ring, Buick enlarged the outer bore size of the primary venturi, making the outside walls almost straight with no real “venturi shape.” The problem with doing this is that there are internal passages in one area of the venturi wall, so to make the walls larger and straight, Buick had to put a “bulge” in each of the outside walls. This makes it very easy to tell that you’re looking at an 800-cfm carb: Just look for the bulge. If looking at the carb from the front (fuel inlet towards you), the bulge in the driver’s side primary venturi is in the 2-o’clock position. The one on the passenger side is in the 10-o’clock position. In 1973 and 1974, Pontiac used this Buick design 800 cfm carb on their 455 Super Duty engines. These are the only 800 cfm divorced choke carbs built. In 1975, the passenger car Q-Jets changed to the M4M design. All Pontiac M4M carbs are 800 cfm. Buick/Olds/Cadillac also made common use of the 800 cfm design. It is very rare to see a Chevy 800 carb – it was seldom used."
Great article. Have to wonder why Chevy never used their 800 carb on their 454. Very strange. Thank you for posting this information. VET
And I might be part of the dis-information here too. A couple of months ago, we brought my X to our local track for a chassis re-cert. Our area cert guy died and they had to import one from Ohio, and he is the shorter guy (Pete something I think) . The taller guy is getting trained and will soon be our new local guy. Anyway, when Ohio saw the Buick, verbal diarrhea ensued and we had a heck of a time getting out of there. He allegedly is the NHRA Pontiac and Buick stocker and super stocker guru, and he want on to tell me all about Jason Line's and Lenny William's Buicks and having inspected them, etc. The subject of Quadrajets came up, and he allegedly told Jason that he could legally use a 70 Pontiac carb w/ the intermediate booster ring removed from the factory because the inspection of the QJ carb only requires the throttle bore diameter and outer venturi be measured, aka the 750 casting w/ non-altered throttle plates/bores. Perhaps he meant '71? He said carb numbers don't factor into the inspection, so any make QJ can (apparently) be used. He also said Jason couldn't bring himself to use a Pontiac carb even though he is allegedly leaving 27 cfm on the table. The inspector also informed Lenny that he was using an ultra-rare Pontiac RA 800 QJ, to which Lenny allegedly didn't know. I am not a QJ flow ratings expert, nor an NHRA stocker or super stocker rules guy by any means. A lot has been written about the flow of Qjets here by Cliff and on Cliff's forums. If anyone knows, it would be Cliff. But w/o doing my own track testing on a 600+ HP engine, not a 400 or 500 deal, I am very suspect of claims that modifying Qjets by removing the intermediate booster rings has no decrease in ET's after proper calibrations, or any other means of increasing air flow to a Qjet. I think a Qjet has it's limitations as far as performance goes the more the demand for air flow goes up, and I will disagree with others as to where that point is. Yes, some stockers are in the 9's running a Qjet. That certainly does not mean that that particular combo won't benefit significantly from a Dominator or even a 1000HP or 950 QFT. I know on my 600HP high 10-second convertible, switching from a 72 "800" Qjet to a 950 QFT resulted in a VERY noticeable seat-of-the-pant difference!!
IIRC caddy 472 & 500 motors used a 800plus... I can't remember the true CFM's all I remember it was more than the 800's
Swapping carbs on the dyno, i only lost 9 hp at peak ( but a good bit of torque) going from a Holley Ultra HP 950 (the 0-80805 legit 950 cfm with 1.6" venturis) to a stage 2 prepped 800 Qjet.
good input from all.. I always am thinking in terms of a stocker, but I think that we can all agree that there's a point where a Q-Jet is not longer the optimal choice. It'll work, support 9's, still impress people but leave some ET/MPH on the table. True CFM will differ depending on who is measuring and how, but yeah a 75+ Caddy 500 will have a 800 CFM by Rochesters designation. I myself have a couple 78-79 Buick LeSabre 350 carbs that absolutely rip on whatever I throw them on. The later M4M is a terrific design that's got wide ranging performance potential.
I amazed, like I said in a previous post. Installing big cfm carb on a sb Buick and it likes it just blows me away. Can't do that to a sb Chevy. I had a Chevy 327, 365hp Vette engine (1964 model). Put all kinds of power adders and the best carb it would run on was the new in 1971, a Holley 650 spreadbore double pumper. Put larger carbs (750) and it wouldn't run. It had the Vette solid lifter 30/30 cam, also had the Offey 1969 CamAm low profile intake manifold w/ single 4 barrel. Ran fantastic with the 650, slap on a 750 and it was a bog machine. I wish I knew why you can put a 750 or 800 cfm Buick carb and the Buick small block runs great.
Funny you should mention that 75 500 Caddy. A few years ago, I had a 76 Eldorado in the shop for a full mechanical "resto" for a Rt 66 trip. It had a 500" engine, only 30k miles, and part of that was a carb rebuild. On my road test loop is a very steep hill. Every time I would take the hill with that Caddy, I had 1 foot out the door thinking it wasn't going to make it lol, and the anemic 500" engine and 800 cfm Qjet were a sign of the times.
