Rochester Quadrajet's

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69 Cuda 440

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Rochester Carburetor's

Early Rochester 4GC Four-Barrel's

The 4GC {486 CFM} was a 'Square-Bore' Carburetor.

The 4GC {553 CFM} and {692 CFM} were also regarded as 'Square-Bore'
Carburetor's despite 1 11/16" Secondary Throttle Bore sizes.

_____________________________________________________

* 486 CFM = 1 7/16" x 1 7/16" ... {Venturi's > 1.125" x 1.250"}
* 553 CFM = 1 7/16" x 1 11/16" .. {Venturi's > 1.125" x 1.468"}
* 692 CFM = 1 9/16" x 1 11/16" .. {Venturi's > 1.125" x 1.468"}

The Rochester 4GC {486 CFM} was utilized on the Chevrolet;
* {1964/1965/1966} > 283/220 HP
* {1965} > 327/250 HP

The Rochester 4GC {692 CFM} was utilized on the Chevrolet;
* {1963/1964/1965} > 409/340 HP

The Rochester 4GC {553 CFM} was utilized on the Oldsmobile;
* {1964} > 330/310 HP

The Rochester 4GC {692 CFM} was utilized on the Oldsmobile;
* {1965} > 400/345 HP
* {1965} > 425/365 HP
 
Rochester Quadrajet's

Rochester 4MV Quadrajet Spreadbore's {1966 and later}

The 4MV Spreadbore featuring a small {1 3/8" Primary}, provided
good Fuel-Economy and Low-Emissions.

The {2 1/4" Secondary} provided good Performance with a
full-throttle for the vacuum-activated Carburetor.

While the 'basic' Carburetor was the same size for the below listed applications, different components were installed to provide for
optimal performance, which included;
* Accelerator Pump
* Jets, Rods and Hangers
* Needle and Seats
* Tubes and Vents
* Power Piston
* Fuel Inlet Fitting

Though the 4MV Spreadbore is listed with a 750 CFM Rating,
the air-flow was closer to {730 CFM's} thru the 'tapered'
Primary Bores in a Big-Block engine.

And 660 CFM in a Small-Block engine.
______________________________________________________

* 750 CFM = 1 3/8" x 2 1/4" ... {Venturi > 1.093" x Automatic Vacuum}

First found on the {1966} Chevrolet;
* 427/390 HP

Chevrolet {1967}
* 327/275 HP
* 350/295 HP
* 396/325 HP
* 427/385 HP

Chevrolet {1968}
* 327/250 HP
* 327/275 HP
* 327/300 HP
* 327/325 HP
* 327/350 HP
* 350/295 HP
* 396/325 HP
* 396/350 HP
* 427/385 HP
* 427/390 HP

Chevrolet {1969}
* 350/255 HP
* 350/300 HP
* 350/350 HP
* 396/325 HP
* 396/350 HP
* 427/335 HP
* 427/390 HP

Chevrolet {1970}
* 350/300 HP
* 350/350 HP
* 402/330 HP
* 454/345 HP
* 454/360 HP
* 454/390 HP

Chevrolet {1971}
* 350/270 HP
* 402/300 HP
* 454/365 HP

Chevrolet {1972}
* 350/200 HP
* 350/255 HP
* 402/240 HP
* 454/270 HP
 
nothingbutdarts said:
I thought the 4MV flowed more than that! Ya lern sometin new every day! LOL
Click to expand...

The 4MV {1 3/8" Primary x 2 1/4" Secondary} ~ {Venturi > 1.093" x AV}

Was rated at 750 CFM for advertising specifications.

Trenton State University

Tested the flow-rate and volumetric efficiency of the Rochester 4MV 750 Spreadbore.

Results
* High-Performance Big-Block .......... 735 to 740 CFM's
* Medium Performance Big-Block ...... 725 to 730 CFM's
* Low Performance Big-Block ............ 715 to 720 CFM's

* High-Performance Small Block ....... 665 to 670 CFM's
* Medium Performance Small Block ... 650 to 655 CFM's
* Low-Performance Small Block......... 640 to 645 CFM's
_______________________________________________________

In 1971,

Rochester did come out with another 4MV Speadbore which was
rated at 800 CFM's.

This Carburetor came thru with the same Throttle Bore sizes,
but had a larger 1.218 Primary Venturi.

It could be found on all 1971, 1972 and 1973 Buick 455's.

And also on the 1973 Pontiac SD-455.
 
69 Cuda 440 said:
The 4MV {1 3/8" Primary x 2 1/4" Secondary} ~ {Venturi > 1.093" x AV}

Was rated at 750 CFM for advertising specifications.

Trenton State University

Tested the flow-rate and volumetric efficiency of the Rochester 4MV 750 Spreadbore.

Results
* High-Performance Big-Block .......... 735 to 740 CFM's
* Medium Performance Big-Block ...... 725 to 730 CFM's
* Low Performance Big-Block ............ 715 to 720 CFM's

* High-Performance Small Block ....... 665 to 670 CFM's
* Medium Performance Small Block ... 650 to 655 CFM's
* Low-Performance Small Block......... 640 to 645 CFM's
_______________________________________________________

In 1971,

Rochester did come out with another 4MV Speadbore which was
rated at 800 CFM's.

This Carburetor came thru with the same Throttle Bore sizes,
but had a larger 1.218 Primary Venturi.

It could be found on all 1971, 1972 and 1973 Buick 455's.

And also on the 1973 Pontiac SD-455.
Click to expand...

Several of the Rochester 4MV Speadbore Carburetors were
'specially calibrated' by the Factory for performance.
 
~ Specially calibated Rochester Spreadbore's ~

1968 Chevrolet ~ 327/325 HP "L-79" {#7028229}

* Main Jet ....................... .066"
* Main Rod ...................... .036"
* Secondary Rod ............. 'BG' {.0400" Tip Diameter}
* Rod Length .................. Medium
* Mixture ........................ Rich
* Accelerator Pump .......... 82
* Needle and Seat ............ N/S-31-542 {.107" Inlet}
* Spring .......................... 7029862
* Jet Area {Cruise}........... 2.4033
* Jet Area {W.O.T.}.......... 2.8903
 
Interesting facts.

Thanks for sharing.

I have one of those 1971 buick carbs sitting on a shelf since the 80's.

Now I think it will go on ebay :)
 
YY1 said:
Interesting facts.

Thanks for sharing.

I have one of those 1971 buick carbs sitting on a shelf since the 80's.

Now I think it will go on ebay :)
Click to expand...

YY1,

It should be Part #7041243 or #7041242.

If you open up the throttle, and look down the primary bowl, there
should be 'no taper' in the bowl, just below the Booster Venturi.

Just '2' small bumps on each side of the Round bowl.

That's the 800 CFM series, with the 1.218" Primary Venturi.
 
Nick,

The 1968 Oldsmobile 350/325 HP 'Ram Rod' was specially re-calibrated.

Rochester Spreadbore {#7028255}

Main Jet ............. .074"
Primary Rod ....... .049" {'49B' Tip}
Secondary Rod ... .058" {'AT' Tip}
Mixture............... Rich

* Special Throttle-Body Assembly {#7036514}
* Fuel Inlet............ 7/8"
 
Generally Speaking

The Rochester 4MV Spreadbore {Advertised at; 750 CFM} was the same Carburetor
utilized on most of the Chevrolet > 327, 350, 396, 402, 427 and 454 Engines
from 1966 thru 1973.

The only difference was in the Main Jet, Main Rod, Secondary Rod, and Needle and Seat components.

Most of the Spreadbore's mounted on the 350 Engines had;
* Main Jets ......... .067"
* Primary Rods ... .038" or .042"

Most of the Spreadbore's on the Big-Block Engines had;
* Main Jets ......... .071"
* Primary Rods .... .044" or .046"
 
Also, not only did MoPars come with these carbs but there also a consideration should another carb not be available for use.
 
I had thought the early carbs were not called a Quadrajet. I was thinking that term was not used until they made the spreadbore.
 
chryslerfat said:
I had thought the early carbs were not called a Quadrajet. I was thinking that term was not used until they made the spreadbore.
Click to expand...

Correct Sir,

That is technically correct.

But the 4MV 'Quadrajet Speadbore' evolved from the 4GC, when it was developed
in the latter-half of 1965 with a 'true' Speadbore design.
 
How about you copy and paste a breakdown of All the Chrysler cars that actually came with a quadrajunk carb
 
The early carburetors were called "4 Jet". I have a couple in the shop that have it cast right into them.
 
Like this.
 

Attachments

  • 4 JET.jpg
    54.6 KB · Views: 332
356K miles on my Qjet with just one rebuild, it could use a freshen again, gaskets and acc. pump, choke repair, man I love that carb.
 
EL5DEMON340 said:
I know a bunch of 80's cop diplomats had them
Click to expand...

They sure did, but IMO, by the time Chrysler started using them, it was too late for any type of performance out of them. They were either smogged to death or computerized versions, both pretty much worthless for performance. Much the same as the later Thermoquads.

I think the reason Chrysler switched was because they were having problems with the Thermoquad's plastic body warping on the smog equipped cars already and they knew the under hood temperatures of the next generation smog cars was going to be higher, so they swapped to the all metal Q jet.
 
Rochester Quadrajet Spreadbore

Fun Fact #33

The first Chevrolet Engine to receive the 'rare' 800 CFM Spreadbore with the
1.218 Primary Venturi.

The '1975' ~ 400/170 HP Engine {Part #7045224}

Myth #27

The early {1970 thru 1975} Chevrolet 454 Engines were equipped with
the 'rare' 800 CFM Spreadbore.

No they were not.
 
Never seen a quadrajet on a Ford of any kind. They had the Holley and several different Motorcraft (Autolite) four barrels. The 429 and 460 used the same carburetor as the Clevelands early on which was a couple different versions of the Autolite 4300. Then, at some point, they switch to the Thermoquad on the 460. That's all I've ever seen......but that certainly doesn't mean they didn't use the quadrajet.
 
RustyRatRod said:
Never seen a quadrajet on a Ford of any kind. They had the Holley and several different Motorcraft (Autolite) four barrels. The 429 and 460 used the same carburetor as the Clevelands early on which was a couple different versions of the Autolite 4300. Then, at some point, they switch to the Thermoquad on the 460. That's all I've ever seen......but that certainly doesn't mean they didn't use the quadrajet.
Click to expand...

Scratching, my head...https://www.google.com/url?sa=t&sou...cQFjAG&usg=AFQjCNH_BokSa56C0-5Q_8qD6_MfdK2bUw
 
Interesting. Thanks Tim. No surprise since most every other auto maker at one time or another used it.
 
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