7041263 vs. 7041264 Rochester Quadrajets
 

Does anyone know what the physical and/or performance differences are between a 7041263 and 7041264? I already know that the 7041263 is specified for manual transmission cars while the 7041264 is for automatic transmissions…however, my ’71 GTO came from the factory with the M22 Muncie 4-speed, but it also has the 7041264 Q-Jet, so I’m curious to know if the 7041263 would offer any advantages (or disadvantages) over the 7041264 that’s currently installed in my goat.

The manual trans 400 cid motors cam with the tad hotter 067 Cam so one might surmise that those carbs might have had richer secondary metering rods, and or a different secondary metering rod hanger and a bit lighter primary power piston spring made for by lower idle vacuum.

This is just a guess on my part!

The 263 is a single ring primary booster carburetor, for 1971, the 264 is a double ring... Big difference on the dyno or track if you are chasing numbers.

Physically, the biggest difference is the 264 has a vacuum fitting in the front of the main body next to the fuel inlet, the 263 does not.

So his 71 GTO is or has been a 455HO car?

IIRC, I THINK I've read that SOME '71 4-speed 400 engine cars also came with the single booster ring carb.

Is this correct ? :confused:

Read that those were discontinued because they were not real streetable.

Anybody have any links they can post with detailed info about that single ring carb ? :confused:

https://forums.maxperformanceinc.com...d.php?t=826882

IDK... He didn't mention that

The ‘71 in my signature came with, and still has the original 1263 carb. Paul is correct, 1263 has the single booster ring.
Cliff said they were a one year run because with the bigger primaries, they had problems getting the cars to pass emissions.

Yes, the single ring did also come on some 400's.
These carb preform great once calibrated properly.
I've been running my factory single ring on my 71' T/A.
I had recalibrated it when I ported my heads and went to a Roller cam.

All 1971 400 and 455 4 bbl engines (except H.O. or RamAir) with M/T uses the one year only single booster 7041263 Quadrajet.

The man trans carb will also have the secondary POE holes below the air flap

Sent from my SM-T817V using Tapatalk

I know Stan R and the car. He's the original owner and the car has not been screwed with (mechanically) in all these years...i.e. it's as shipped from the factory wo any question.

Since the key stuff has been mentioned, I wanted to only address this:

My understanding is that the one-year single booster ring Quadrajets had low or off idle issues that prompted many original owners to bring their car to their servicing dealer to remedy;
I have understood that it wasn't uncommon for a 7041262 (455), or 7041264 (400) Quadrajet to have been swapped on in place of the original unit, and that promptly fixed the issues.

I have not seen any documentation (eg: TSB) that spelt out what dealers were supposed to do when a customer with one of these cars came in with the idle complaints.

So, although Stan may very well be the original owner, and may have asserted that the car was built that way, I would first ask him to think long and hard if it's possible that he brought it in to a dealership when it still had a warranty complaining about idle or off-idle characteristics.
It is still possible that the car was built with the wrong carburetor, but that is the exception to the norm.

As to performance, or performance potential difference;
I believe that all 1967-1970 & 1972 Pontiac Quadrajets were officially rated at 750cfm, while the 1971 455HO & s/t carbs were rated at 800cfm;
With more potential air flow there is the potential or more power.

It is worth noting that for 1971 & 1972 both gross hp & SAE net hp ratings were published;
Finding published 1972 hp ratings is a tricky thing though, I have only found them in the 1972 GM of Canada brochures.
With the same cams, pistons, and cylinder head combustion chamber designs, I believe that the slight difference in hp ratings is the revealer here;
1971 455HO: 310 net-hp
1972 455HO: 300 net-hp
1971 455/4bbl: 260 net-hp
1972 455/4bbl: 250 net-hp
1971 400/4bbl: 255 net-hp
1972 400/4bbl: 200 net-hp

*It is worth noting that the two most significant changes from 1971 to 1972 cylinder heads was:
1) the elimination of "extra" end exhaust manifold bolt holes
2) the process used for hardening the valve seat introduced for 1972

I believe that there were shenanigans going on with the published 1972-400/4bbl hp figures, as on paper, other than the carb, it was exactly the same engine as the year prior.
Maybe it was a typo, or maybe the hp number was lowered to make the Lemans 400/4bbl match the published numbers from the full sized cars... ???

Some may haggle that the 1972 455HO heads didn't flow as good on the exhaust side, but I'd counter that with most of the hp difference would likely be observed for a stone stock car on the carburetion;
Of which we appear to be seeing about a 10hp drop.

I believe that the performance difference is fairly negligible, and that a properly set up 750cfm carb could likely run just as good as, or better than a stone stock single booster ring carb - and that stock for stock ,the hp difference would be rather negligible.

But that's just my ten cent's worth...

Gents, thanks for all of your excellent input. I know a lot more now than when I first asked the question. Just to clarify, my car has the 400, and responding to unruhjonny, I never had a low or off idle issue that would have triggered a return to the dealer for warrantee work and a possible carb swap. My biggest issue was an oil leak that the dealer repaired under warrantee which promptly returned after the warrantee expired.

However, my car was built late in the 1971 production cycle…I ordered the car in March of ’71 and it was delivered on April 10th. So maybe at this point in time the factory made the decision to just install the 7041264 Q-Jet from the get-go and avoid having customers returning to fix an idle problem caused by the 7041263. This wouldn’t surprise me cuz the factory also decided to upgrade my car with the M22 Muncie close ratio 4-speed, a heavy-duty 4-core radiator, and a heavy-duty limited slip differential with 3.90 gears, none of which I had originally ordered.

I need to either rebuild my 7041264 or replace it because of a gas leak problem, and based everyone’s input it looks like the best course of action is to just rebuild what I have and avoid replacing with a 7041263 and then ending up with an idle problem. Thanks again for all of your feedback.

Some Buick and Cadillac Qjets have the secondary POE holes below the air flap edge,
NO Pontiac Qjet have the sec. POE holes below the air valve edge, 1975 and later ON the edge but not below.

Here are pics on my SR 7041263:

Cool info.
Did you find a buildsheet in your car?
(or have the PHS?)

Wonder what the buildsheet would show?
(plus what carb it might show)

:confused:

New news to me! I had never heard this before.

I never found the buildsheet, and over the years I've removed the rear seat and door panels when working on various projects, which are the likely places where one might have been stowed. I've also never obtained the PHS documentation, but this might be worth doing just to see what pops up.

I'm happy to have had a small part in helping. :D

That would not be the case;
The factory doesn't arbitrarily make the decision to change equipment which was emissions certified, just because they want to - if at some point the '264 was being swapped for the '263 this would be common, and well documented.

Since 1971 model year cars were built through to July, yours might have been later, but not a late model year car.
My Formula 400 was built June 1970 - so not quite a year before yours.

As I have understood it, the odd time that the wrong application carb was installed at the factory, it was just a line error - and quite frankly I wouldn't try to make too much more of it.

I have understood that there were procedures in place so changes were not just arbitrarily made to cars at the assembly plant.

I'd think that odds are that the dealer accidentally (either on your part or theirs) submitted your order with option code '35G' instead of '35E';
35E would have been the M20 wide ratio four speed;
35G is the close ratio four speed.

I do believe (I could be wrong here) that in the case of 1971 Formula 400's, ordering the close ratio four speed would have triggered the same required options as ordering it on a 1970 Formula 400;
Ordering the close ratio four speed would have triggered the following options: '361' ('safe-t-track rear axle'), '368' ('performance axle'; 3.73:1), '701' ('HD radiator')

Alternately, if your order was submitted with 35E, then it's also possible that your order was accidentally swapped for a similar car, and someone who ordered the M22 on their similar car, got yours instead.

I think it's super cool that you're the original owner;
I have felt that with the 1971-1974 455HO & SD455 engines that the 400 cars (especially the 71-72 cars) don't get enough appreciation.

I'd love to see how your car hold it's own against a similar 1970 Formula 400;
I'm sure it was quicker than pretty much any other 1971 or later Formula 400!

I'd love to know more about your car - just hearing from an original owner is super duper cool in my books!

Very interesting thread. Really wish you had the build sheet, which is going to be the definitive document for this case.

Just for grins, checked the following:

Pontiac power train charts for 1971 show the 263 carb for manual transmission 400's and 455's other than the H.O. which got the 267 and the Ram Air which got the 273.

Rochester Master Products book concurs with the above.

Pontiac service bulletins from 1971 through 1976 do not show any change from a 263 to a 264 for 1971.

Would GUESS this was an error at the factory.

Pontiac would have been subject to a massive fine for arbitrarily changing emission certification standards.

The cars with the single booster AND manual transmissions WOULD idle. It was the cars with auto transmissions that had idle issues with single booster carbs.

Going forward (opinion):

The 7041263 in stock calibration will deliver SLIGHTLY better (5 percent???) fuel economy around town.

If the car is showed at a points judging show, the car will lose points with the wrong carb UNLESS you can find the build sheet. Being the original owner will not help.

Jon

Can you tell us the carb numbers for a d-port 71 455 four speed application?

I thought I've seen 267 and 273 on HO455's