Good question. My guess is that it’s more performance oriented. The 4781-1 Holley was also used in Chevy’s over the counter LS-7 program.
Guy's likely right. I don't think the actual performance capabilities of the Q-Jet had been realized when the Stage 2 program was in its infancy and Holley had already "cornered" the performance market by that time. Q-Jets had really only been around for a few years and Rochester was (probably) more aligned with production as opposed to performance. Keep in mind: they were supplying carbs for all of GM's brands, with some Ford mixed in as well. Lucky for us, some outliers would change that as the 70's rolled along. Speaking of which, VET: you would do that beautiful Buick some justice and find a good '70 Q-Jet core (or '71-'74) and have Rob Ross here on the board build you one based on your engine specs. He's helped out dozens of board members - both with new builds and also fixing other builders messes - and I highly doubt you'd be the least bit disappointed. In fact: the gentleman who built your engine has long been widely known as one of the top Q-Jet go to guys as well. Rob did mine a couple years ago and it's as close to fuel injection as I ever plan on getting. Subtle, "economical" cruising is great and when you hit the loud pedal, those ginormous secondaries will set you back in your seat.
The original stage 2 intake the B4B was holley pattern only The dual pattern wasn't available till mid 70s iirc
Accelerator pump capacity. Denny explains it in this article on pages 1-2. Sorry to put this up again but its the best way to answer the question.
That's the second design has the pattern for the qjet and the ability to open the rear bores...the first has neither I had one many years ago
Wayne Robert's had all of them on display in the issue of either hemming or Muscle car enthusiast cant remember....5 or 6 different designs
I would imagine....the second design may very well have been the over the counter part of the 71-72 stage 2 with the heads.. as the first design was available in early 68...it obviously was on the 69 stage 2 package
I bought a 3bl to try on my orange car but never did...after researching them most the guys agreed they were better when converted to mech secondaries
I do have three of the first designed stepped flange Holley only square bore One is NOS. And two correct 4781-1 Stage2 carbs. And two sets of untouched heads. One set with the early vertical boss. The early vertical boss is the one the very one KB used to do the testing with for Mr. manner and Buick.
Wow, you guys are quick with the answers. I appreciate that but can't answer all you guys individually, sorry. The one thing I always run into on this forum is, Buick can take much bigger cfm carburators. I have to wonder, if that so, why didn't Buick just install the 1000 cfm Thermoquatd. Didn't some Mopars use this carb? Maybe i'am wrong here. Is the 1000 cfm thermo not setup or can't be setup to be a good carb on the street and strip? I guess, I don't understand why it was developed in the first place if it's such a huge carb with 1000 cfm. There must be a good reason for it's development? Vet Thank you all for the education I'am getting.
No 1000 thermoquad was factory issued...it was aftermarket only Buick wasn't about to use a Mopar part..they had a contract with Rochester for one thing The Buick wasn't a "hot rod" wasn't intended to be...it was a borderline luxury midsize with decent fuel economy and great power for its intended operating range....with very little maintenance Sure they could have come up with adjustable valve train for use with solid cams and put Holleys on the stage 1s etc etc .but it wouldn't have been docile and attractive to their customer base....30 to 50yr old guys who had good jobs and wanted to fast with class..... Not to mention..it would have required a whole new head approach and reciprocating parts to use such parts with any real benefit
It was developed for the same reason any other aftermarket part was... guys will buy what they are told is better.....be it true or not......it's a good carb....but it's no magical unicorn either
Buick did develop experimental adjustable rocker arms out of the Stage2 program. Ollie Colteryahn Out of the KB camp ended up with them for his GSX.
I never realized the Thermoquad was an "aftermarket" carb, that is very interesting. While on the subject of carbs and i'am a dinosaur. The 64 SB Chevy engine I installed in my 56 Belair was a Corvette. Chevy used a Carter AFB 625 cfm carb. After I added some power adders, mainly an Offenhauser low profile tunnel ram intake. I had a difficult time finding a carb that would run on this run engine. I happened to be in a speed shop and noticed that Holley had just come out with a new carb. 650 cfm, double pumper with the spread bore design. I took a big chance and bought and installed it on my car. Rev'ed the car to 4 grand dumped that clutch and the car lit-up the tires all the way through first and second, wow what a ride. So, where i'am getting at the original Carter for the SB engine must have been a very good carb, seeing that engine in 1964 produced 365 HP. That was a lot of HP for a 327. Best engine ever owned. I assume all the muscles in the mud 60's had good carbs right out of the factory. The spread bore Holley not only was a hot setup for me but I got outstanding gas mileage. I assume running the highway on the small primaries? I have a friend with a 61 Ford 406 with the 3 barrel carb. Very strange setup, i'am told that came out of NASCAR, not sure if this is true. Vet
Wow, so you could only use hydraulic cams because Buick only designed non-adjustable rockers. No way to install solid lifter cams. Hum, very interesting and strange Buick would only limit themselves to hydraulic cams. Great history lesson here.
This forum is amazing, some much to learn. Never even seen an "Adjustable" pushrod. This sounds like too much could go wrong if you don't get it right. I assume Adjustable pushrods are solid rods?
