69LS1 (& anyone else) Rochester 2G, 2GC, 2GV questions [Archive] - Chevelle Tech

: 69LS1 (& anyone else) Rochester 2G, 2GC, 2GV questions

Jun 12th, 04, 9:30 AM
Where do you measure to determine if it has a 1 1/4" or 1 1/2" flange? I measured one and couldn't find anything close to either of those dimensions.

For a small block 3x2 setup, wouldn't the 1 1/2" flange carbs be the ones to use?

Jun 12th, 04, 2:47 PM

Good question ! I really dont know. I know I provided that info two or three times here ... but I think I always refered to the source from where I got the info... HP Books Rochester Carbs.I simply took it straight out of the book.

The real place to see the air capacity would be the throttle bore and venturi diameter.I have only one Roch 2bbl sitting here.My 69 EC origionally came with a 250HP 350 2bbl engine and I still have the carb.I looked at it and couldnt find anything that came close to those measurements either.But was able to measure the throttle bore and venturi size ( 1 11/16 bore with 1 1/4 in venturi = 381 CFM according the the HP Book. ).... The only thing I could measure that came to 1 1/2 inches was the C/L of the air cleaner stud to the outside of the air cleaner flange... That measurement IS 1 1/2in on my carb.
Could the smaller 1 7/16 in bore 1 3/32 venturi carbs have 1 1/4 in as this measurement ? I have no clue at all.

Several years ago Edelbrock decided to get into the act and sourced a supply of Rochester 2bbls when they offered a 3X2 package on the ancient (circa 1955) C-357-B intake with 3 Roch carbs and a linkage set up.But they discontinued it several years ago and the carb info in no longer provided in the current catalogs.... The intake manifold is still available tho.

I may be totally wrong as I'm racking my brain ( whats left of it ) trying to remember what carbs they used but I'm pretty sure they were one of the larger ones with the 1 11/16th throttle bores as these were by far the more common carbs.I'll check at work and see if I can dig up an old catalog and see what they had to say... if I can find one that old.

Below is what the HP Books Rochester Carbs said as far as the 2bls go.

Model 2G.
1 1/4 flange, 1 7/16" throtlle bore,1 3/32" Venturi = 278 CFM @ 3.00 in mercury.

Model 2G.

1 1/2 in flange , 1 11/16" throttle bores.
1 3/16 " venturi = 252 CFM @ 3.00 in mercury.
1 1/4 " venturi = 381 CFM @ 3.00 in mercury.
1 5/16 " venturi = 423 CFM @ 3.00 in mercury.
1 3/8 " venturi = 435 CFM @ 3.00 in mercury.

This is the only source I have really seen on these numbers.

Jun 12th, 04, 3:48 PM
Thanks Al.

I didn't remember reading that and just went through my copy of Doug Roe's Rochester carb book - all I could find on the 2G carbs was five paragraphs (about 1/4 page), an exploded view, and a few mods in the end of the book.

Looked again and found it - a chart on Rochester carb flow ratings. Still unclear on this flange business.

My son's 66 came with a 7024112 which checks out as a carb for a 64 283/AT/AC.

Don't know if this'll be of interest, but it may:


It shows which 60-65 Chevy engines had which carb by type and number.

Thanks again.

Jun 12th, 04, 4:59 PM

I did a search and came up with a photo that may be intresting.It's a Pontiac 3X2 set up.Appearently the late 50's through 1965 Pontiac used the smaller carb as the center carb and larger carbs as end carbs.These pics show the bare manifold with no carbs and fully set up carbs.... Looking at them they are clearly different.... Both in air cleaner flange and carb/manifold flange.


Jun 12th, 04, 9:45 PM
Thanks again Al. Looks like a good article - great photos. I was surprised to see that the center carb is the smallest since they're not all that large to begin with.

dyno jonn
Jun 12th, 04, 9:56 PM
Not exactly sure what you're trying to do, but the first Chevy to use the large 2bbl was the 69 327 in a full size car. The 69 Camaro - Nova - Chevelle 2bbl 327 used the smaller carb as did the 307. Most all Pontiacs and Olds from 57 on used the larger carbs. Aftermarket manifold makers made tripower manifolds in both sizes, but for Chevy small blocks, the smaller carb manifold is by far the most common.
Jon N.

Jun 13th, 04, 9:43 PM
Thanks John, that'll come in handy as far as getting an idea on carb sizes and where they are/were. I'm thinking about a low-buck tri-power deal and was trying to avoid buying stuff that won't work. I guess it'd be 1/2 smart to get the intake first, and then find carbs that fit it.

Jun 13th, 04, 10:15 PM

I've looked into this a couple of times, everytime I look at the three old carb's I have laying in my car.

I think they would need new butterfly shafts that are long enough so that you can clamp modern linkage on them so they work right.

Please check into an intake first, then a way to gather up three same sized carb's whether they are little or big and so they match your intake.

Only the center carb. has to have everything working on it. The other ones can have their idle jets turned off, plus they don't need chokes, but do have their accelerator pumps working..

Then the linkage thing!!

It used to be you could go out to a bone y-- er, eh, Recycling Center and take them off old car in mulitiples for like $5.00/each, but that day is long gone b/c '87 was pretty much the last year carb's were ran on cars.......... I do figure that you may still find them on old P/U's thou if you can find a bunch of them somewhere out of the way??


Jun 13th, 04, 11:16 PM
I've seen the carb your looking for on 55-73 chevrolets, they were the only two barrel used from 55-67 from what I understand, and found on smaller displacement v-8's till 73. I have three here but thay are in sad shape with frozen throttle blades etc. I have also been looking for some good cores, I have a 3X2 intake for a 4-71 blower that I'm piecing together for a future street rod project. I'm sure I'll stumble across some eventually but parts are definately getting harder to find these days. I did a 3X2 setup for my friends 32 Ford a few years back, kept the center carb stock, plugged the idle circuits on the front and rear carbs, and also plugged all the breather holes in the sides with small slugs of lead. The tripower works great and it's been 3 years now, no troubles.

wes migletz
Jun 14th, 04, 1:18 PM
FWIW, I was just reading a January 1956 Hot Rod magazine. They had an article about hopping up a 1955 265. The first mod was a 3 X 2 Edelbrock intake. It was worth 18 horsepower over the stock 2 bbl intake. Anyways, the article was pretty cool. They ultimately ended-up with 229 H.P.

Jun 14th, 04, 1:42 PM

I am reasonably sure I have a Rochester you could use - if you're interested, email me. Probably from late 70's though.