There really isn't enough room for an adapter. Holley has a spread bore replacement carb.

 

76/77 did not have el. chokes.
The electronic Q-J started in 80 for Calif. & 81 Federal.

 

are the Holley Dbl.Pumper 6211-800 CFM(replacement spread bore) as good as the origional Rochester's? Also, will a 800cfm Q-Jet work on a modified 350 zz4 that came with an Edelbrock Thunder Series 800cfm? Thanks!

 

What transmission and differential ratio do you have? My 79, L-82 has a 350 auto with a 3:73 differential. Just not going to get great gas mileage with my combo. Great around town and quick acceleration, but running 3500 RPM at 70MPH. The stock q-jet runs off of the small front barrels during normal cruise. A 500 cfm carb isn't going to be any better.

 

That sounds pretty much exactly like what I've got for mine. Pretty quick off the line, but terribly high RPM's at highway speeds. I've decided that I'm putting a 700r4 into it as a next project to get a few more RPM's out of the engine.

 

The sad part about today's market for carbs for our cars is that if you want a NEW carb, and don't want to go changing other parts like your intake, you have only one choice: the Holley 4165/6210. They run about $400 and are available from Jegs, Summit Racing, and I am sure a bunch of other folks.

The rest of the advice you are getting is also good. A good quality Q-jet core re-built by someone who knows what they are doing should turn out to be as good as a new carb. The Q-jet is a little harder to tune than the mechanical secondary Holley, but I found my way through it on my old car, so I'm sure the average weekend mechanic can find their way through it (as I like to think I am average, but I might be kidding myself), especially with all the help available here.

 

Quick sizing of a carburetor:

Engine displacement: 350 cubic inches
Redline RPM: 6000 (this is a guess, you can re-do it with whatever yours is)

The first thing to realize is that each cylinder "charges" every other revolution, so you will fill your displacement Redline RPM/2 times per minute. So 350 cubic inches * 3000 charges per minute = 1,050,000 cubic inches / minute. 1 cubic foot = 12*12*12 = 1,728 cubic inches so CFM needed is:

(1,050,000 cubic inches/minute) / (1728 cubic inches/cubic foot) = 607.6 CFM

So, the Holley 650 is a good choice size-wise. The 3456 number quoted above is just 1728*2, so it is good, but understanding the why is always interesting to me. It is good to keep in mind that this is a quick and dirty method since engine vacuum will come into play if we are designing a racing engine or something, but this works plenty well for street engines.

 

I just ended up having my old Q-jet professionally rebuilt. The guy's a genius when it comes to GM's, and whatever he did to the carb worked wonders for the car. It runs like a champ and I couldn't be happier with it. Saved me a good amount of money, too, and I get to keep more of my machine original.

 

I don't know about with a standard air cleaner but on mine it's fine.

 

does anyone know what part# 800cfm QJ would be used? Were the 800's for 454's? I have a modified ZZ4 350 w/ modified TH400, 2500 stall converter, trying to figure out what part# to get. Thanks!

 

For mileage, you're not going to find a 4-bbl carb that will perform better than a Q-Jet. The primary venturies have very efficient boosters, and the 1975+ integral choke carbs have an Adjustable Part Throttle (APT) feature that allows you to precisely dial in the cruise mixture with the turn of a screw. You can easily get a Q-Jet on a 350 to produce over 20mpg hiway once properly tuned and with the timing correctly set up. You have to do significant work to any Holley to match this level of fuel efficiency. GM abandoned the "AFB" carbs in 1966 because they could not come close to matching this level of performance and efficiency.

There were no electric chokes in '76 or '77. First year for electric choke was 1980. The 1980 electric choke can be installed on any 1975-1979 integral choke Q-Jet as long as you remove the choke cover gasket. First year for the "electronic Q-Jet" on passenger cars was 1981.

Q-Jets are 750 cfm. The exceptions are the 800 cfm units that were used on Pontiac 455 Super Duty, Buick 455 Stage 1, a few Olds 442 455's, and some Caddy 472/500 engines. With the exception of the Caddy carbs, the Pontiac/Buick/Olds carbs are extremely pricey, many fetching over $1,200 for original examples due to the extremely limited production. You sure you really want/need part numbers..? I have them, but you won't find those carbs at swap meets.

Lars

 

Thanks Lars! Can the 800 cfm units(Pontiac,Caddy,etc.) be used on a modified 350? I have an Edelbrock 800 Thunder Series on it now, came that way from Edelbrock.

 

You can use any Q-Jet on virtually any engine. The Pontiac/Olds/Buick carbs have a straight-in inlet which is difficult to use on a Chevy due to the position of the thermostat housing. The Caddy carbs have a side inlet like Chevy. Beware that most people advertising "800 cfm Q-Jets" for sale don't have a clue how to identify one, and most "800 cfm" Q-Jets being sold are plain ol' 750's.

Yes, the "Thunder" Series AVS-style Edelbrocks are available as 800 cfm units. In my humble opinion, if you have an engine that's modified enough to utilize this level of cfm capacity, you're usually better off running one of the high-end Holleys (HP-series or better), Mighty Demons, or QuickFuel series carbs in that size range.

Lars

 

Hesaz

 

i thought the 76, 77 corvette 350 c.i. motors came with a 800 cfm q-jet with an electric choke?

 

lars i have reread your post. i might have been told wrong but i was just repeating what i was told by the carb. shop. is at least true that the 76, 77 corvettes came with an 800 cfm q-jet and the electric choke was added?

 

Chevy used the 800cfm least of all the GM divisions.
Cadillac even used them on it's 301cu in.
Pretty common after 1975, rare before
Primariy venturies are different 1 7/32" dia vs. 1 3/32" dia
Easy way to tell
Look down the primary venturi for a bump down about an inch
Solid "lip" then it's 750.
Single bump, 800

77's did not have electric choke.

 

thanks noonie, i'll check and see. when you say primary, you referring to the front smaller barrells right?

 

a few years ago you could get brand new quads from edlebrock, they still make a marine application. i bought one to put on big block chevy pickup, thing worked perfect right out of the box, set base idle and fast idle for choke, never touched it again for years. i contacted them recently and was told there wasnt much demand so discontinued. i wonder what the agreement is for edlebrock, exclusive manufacturer.