Q: Firebird Q-Jet ‘Tab’ for 1967 / 1968
Does anyone have information of the bent tab used to limit the horsepower for the carburetor found on the 400 Firebird.
A: For many years, it has been widely accepted that the major difference between the 400 Firebird and GTO engine (1967-1968) has been the carburetor. Factory/Dealer specs listed the Firebird 400 at 325hp for 1967 and 330hp for 1968. The GTO was listed as 335hp for 1967 and 350hp for 1968. All 400 HO & Ram Air engines for both models were listed as 360hp for 1968 (1967 Firebird RA was listed at 335hp).
No where in the factory/dealer literature is there a mention of a different throttle bracket, tab or linkage preventing the Firebird secondaries from opening as far as the GTOs.
There have been several articles & publications over the years that have refered to such a variation on the Firebird Carb.
Hot Rod Magazine- 3/68 “…in order to produce the advertised horsepower, there is a small tab on the throttle shaft which actuates the secondaries, but only to two-thirds open at full-throttle. Somehow you don’t feel guilty at bending it rearward.”
Special Interest Autos- 10/86 “..The 400 was detuned to 335bhp by adding a small metal tab in the throttle linkage which slightly limited travel of the secondaries. Needless to say, very few of these tabs remain today where GM put them.”
Motor Trend- 12/91 “…GM only agreed to install the 400 engine if it could restrict it’s performance, which meant it placed a stop on the throttle linkage that prevented wide-open throttle. Of course, that could be removed by the owner in about 30 seconds.” (Jim Wangers)
The Fabulous Firebird- M.Lamm- 1979 “…Yet to stay within GMs horsepower ruling (1hp for every 10lbs), Pontiac not only derated the Firebird 400 V-8 to 325 bhp but also modified it so, in showroom form, it truly wouldn’t produce more than 325 bhp…. by simply changing the link between the primary and secondary barrels of the Rochester Q-Jet carb. This link was arranged with a steel tab that didn’t let the secondaries open more than 90% at full throttle.”
Firebird Decoding Guide- T. DeMauro- 1997 “A throttle linkage restrictor installed on all Firebird 400s stopped the rear two barrels of the Quadrajet from opening allthe way, thus limiting horsepower and keeping the car within the 10-lbs to 1 hp Gm corporate edict.”
So, as you can see, there was obviously something different between a GTO carb and a Firebird. Surely all of these articles were not simply created from simple rumors or suspicions but from experience. Many references were based on modifications by Royal Pontiac during prep for an article (to squeeze out more performance). No mention was ever made about the difference in the exhaust system. If anything, the HO and Ram Air Firebirds had a better exhaust system due to to Long Branch Exhaust Manifolds.
As for defining the actual component on the carb. and how it was different, there needs to be a photo comparision to better explain this. The above excerpts seem to refer to the same thing; a tab on or a part of the throttle linkage.
I am currently going through my files and pulling up detailed photos and illustrations I have pertaining to this matter. If anyone has an original ’67/’68 Firebird 400 4Bbl Carb. and wouldn’t mine taking a few close-up photos (RH & LH side), I would be glad to follow-up on this and post the final comparison photos.
A: I seriously doubt that the Rochester plant earmarked certain carbs for Firebirds and bent the tabs. How would you explain the carbs that the GTO and Firebird both share same part #? Same part # means same part. Period….
The reason for different part #s of certain models of Firebird vs GTO was that the jetting was different. Base plate assemblies which have the throttle linkages attached are the same part #s between GTO and Firebird.
A: After initially researching this through careful examination of original, unrestored cars, an extensive detailed photo collection and checking the carbs I (and friends) have, I too was convinced that both Firebirds and GTO carbs were assembled using the same Rochester components. The only possible explanation would be that the lower tab on the inner Throttle Link could have been bent to prevent full travel however, I did not find this in my research (all have been corrected ?).
Then, I received a reply from Paul Spotts who claims to have an unrestored Firebird carb with this modifed (bent) tab in place. He also says this link was a different part number and that he submitted an article to HPP that explains in detail (w/photos) this entire issue. So, I guess we’ll wait and see if it gets published. In the meantime, I’m continuing the search.
As for the shared part numbers for GTO & Firebird, I’ve noticed that over the years (following production), different Parts Catalogs start combining the usage for carbs (typical service replacement procedure).
Also on a related note, I recently came across an early ‘take-off’ 7028277 RA I carb and spent a great deal of time comparing it to a 7028267 carb I have. Other than the Rochester I.D. stamp (for specific usage), there was absolutely no other difference with regard to Rochester component numbers. Every stamped or cast number was identical on every piece. Interesting.
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Content last modified: January 15, 2014 at 8:05 pm