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NeonLX

Another 1970s powertrain oddity

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Another sleepless night and I'm paging through a car brochure, this time the full-line prestige 1974 Buick brochure. In the case of the LeSabre and Century models, a 455 CID V8 option was available, interestingly enough with a 2V carburetor (the 4V version was also available, of course). And dual exhausts were available on this 2V option (single exhaust was apparently standard). AFAIK, this was the only year that the Buick 455 came with a 2V carb.

Another interesting twist is that the ratings for the 2V version show higher peak torque (at a lower RPM) than any of the 4V versions. Fascinating.

I'll try to scan the good stuff and post it here (if anyone's interested, that is).

I love this sorta thing. :)

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Electronic traction control on a 1974 Buick????? :o

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Friend of mine had a '71 Olds Custom Cruiser that had a 2V carb for its 455 to inhale through.

I also remember seeing a '71 Bonneville with a 455 & 2V carb, think it was an uncle's.

Seems like Buick avoided doing this on their big engine until 1974 for some reason.

Oh yeah, another buddy had a '69 Caprice with a 396 2V. I loved the hide-away headlights on that tan over chocolate car.

Sheesh, thought of another one: the car I took my driver's test in was a '71 Mercury Marquis Brougham with a high compression 429 w/2V carb.

Edited by NeonLX

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But everything else being equal, CFM is based on CI & max RPM. 455 sucks 55CI more than a 400. 400 seems to be the 'reasonable' limit for 2bbls, but obviously GM thought otherwise. The OEMs were against the wall RE MPG, slapping a 2bbl on is a lot quicker than ramping production up of the various 350s.

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But everything else being equal, CFM is based on CI & max RPM. 455 sucks 55CI more than a 400. 400 seems to be the 'reasonable' limit for 2bbls, but obviously GM thought otherwise. The OEMs were against the wall RE MPG, slapping a 2bbl on is a lot quicker than ramping production up of the various 350s.

They had quadrajets back then. Why not just use those and make the secondaries more reluctant to open? Under light throttle, they operate as a small 2bbl anyway.

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^ Exactly, and you're quite right on the Q-jets. Still, and not knowing exactly how MPG was tested then, perhaps eliminating the 'extra' 2 bbls allowed better MPG. I've heard the 2bbls flow better than the QJs running on just the primaries... but it's still 'wrong' in my book. ;)

But why anyone would choose to deny themselves the wonderous rush of the QJ secondaries, I could not possibly understand :

Quad-Jet.jpg

  • Upvote 1

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Perhaps the main advantage of 2-BBL offerings was the reduced manufacturing cost. The smaller Q-Jet primaries contribute to improved fuel atomization and are capable of superior economy. A 2-BBL would have higher initial throttle gain because of the larger bores, but such responsiveness is short-lived as the 'advantage' is lost once more throttle is applied, and this setup makes it more difficult to modulate power delivery on take-off. Some packages (e.g. Oldsmobile's 'Turnpike Cruiser' option comes to mind) took advantage of this enhanced initial responsiveness by matching it to a numerically lower final drive; the latter would have been the main contributor to improved fuel mileage, while the 2-BBL would preserve (light) throttle drive-ability in general use.

Edited by KevinW

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Yes, thanks for that, KevinW.

This would help explain the higher peak torque rating at a lower RPM for the 2V-equipped Buick 455s (but so would nutty rating methodology, eh? :)).

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