Q-jets design changes through the years..

[Toronado]

What year of Rochester Q-jet is the best model?
They have been around for a long time, and are
well known for there performance. But they have gone
through design changes from there first model.
Did they reach a peak in design and performance,
and if so which ones are the best Q-jets?

[omaha]

that is a hard one to answer. I guess it comes down to personal opinions. Some swear by the early 70's chevy truck carbs. I like the '77-'78 Oldsmobile or Pontiac carbs.  I guess there are some years/versions  to stay away from. Like the 1975-early 1976 with the weird APT. Also the very early ones are really not that good. (66-68?) [cant remember exactly] {float design/needle and seat}.  So the question should be, which ones are the best ones to "stay away from".   Hey, when you can pick them up at a swap meet for as little as $15,   who's complaining.  Get Cliff's book and make 'em work for what you got.  Where else you gonna get an 800 cfm carb for $15.  I think they are fantastic carbs and most of them have lots of potential. Obviously the "electronic" versions have somewhat limited potential. [but still can be used even without the electronic controls].   Pick one based on linkage, fuel inlet location, pull-off style and the various year design limitations. [eg. needle/seat/float, APT style, and electronics].
       The performance ones {eg; 455 GS Buick etc.} can be matched by the low performance ones with some minor changes.    So, have fun!!!

[Toronado]

Great info, omaha.
So why are the Q-jets 1975 and earlier ones
not as good as the 1977-1978? The reason
Im asking is because my Q-jet is made in 1970.
I know the leaking well plugs on before 1969.
I just never have heard some one explain
the design differences, are the idle passages
different or what? I will replace mine with one from 77-78
if its a better performer for my 455cid. Or is it possible
to mod the earlier ones to be comparable to the BEST ones?

[Cliff Ruggles]

Oldsmobile continued with the early float design till 1974.  The Cadillac units also used it till 74.  Marine carburetors were the only units that used that design thru all years of production, and to this day I'm not exactly sure why?

Our book covers this topic thoroughly.  Basically, any of the later carburetors will be equal in potential, and superior to early units in several areas.

Even the electronic carburetors make great HP carburetors, we can always leave the M/C solenoid out of them and run them straight off the jets for high performance work.....Cliff