The Stovebolt Site Forums The Shop Area The HiPo Shop Rochester 2G on a 292

The head has received 1.94 intake/1.60 exhaust valves, lump kit, and will get mildly ported/gasket-matched to remove the flashing and better-line-up the ports, nothing major on the porting. The exhaust will be ductile iron dual exhaust manifolds with 2.25 inch exits, the manifolds are similar to the Fentons. The exhaust pipes will be 2.25 inch dual routed into 2.25 inch or 2.5 inch single out the back. Long glass packs for the mufflers. Aussie Speed intake manifold. HEI ignition. Camshaft will have 204 degrees duration @ .050 and .439 lift. Highway cruise rpms will be 2,2** at 70 mph. The engine will only see near 4,000 rpms on extremely rare occasions, but will see 3,000 and lower all the time. My plan is to run a Rochester 2G on this modified setup. What are your thoughts on the jetting for a 2G on a modified 292? Crusader Marine ran 292 engines with Rochester 2G carburetors, and were jetted 0.056, 0.060, 0.061, 0.062. Am I setting myself up for failure, or will this setup work well? Manual transmission if that matters.

The 2G is one of the best carburetor designs GM ever came up with. Try to find a 2 BBL for a 283 V8, not the bigger bore model that was used on Pontiac, Oldsmobile, and 305 Chevy engines. I'd suggest finding an Offenhauser 4 BBL intake and adapting it to accommodate the 2G, rather than trying to use some sort of restrictive adapter plate to mate the 2 barrel to the original equipment 1 BBL intake. Didn't the Crusader have some sort of oddball intake that worked with their water-cooled exhaust?
Jerry

I failed to mention, the 2G I am gearing up to rebuild is off of a 1965 283. It has the manual choke, small base, and the throttle shaft has zero wobble in the base. It'll need a really good soaking to loosen-up the hardened deposits. I have the intake, it's an Aussie Speed intake. Nice design. It has a nice waffle pattern under the carb to help atomize the fuel/air mixture in the plenum. If I wanted to run a Holley I could mount it in any configuration I want to without an adapter. If I decide to use a quadrajet in the future, I just need an adapter plate, and can orient it in any configuration, as well. For the time being, I am having an adapter plate made for the 2G that fits the Aussie intake. He made one (photo no. 2), but the idle speed adjustment screw hit the top of the plate in the notched area, and I didn't like the slots for the plate-to-intake-mounting, so now we are communicating on a redesign to allow full functionality of the carb and no slots. Air flow won't be restricted, it'll be able to breathe. Crusader may have had a different intake, I just discovered they used the 2G on the 292, and wrote down the jet sizes.

Here are some photos of the upgrades purchased that will be going on the 292. I don't have a photo of the cam, but you guys know what those look like...lol...

My main question(s) is regarding the jetting. I have read other threads on the bolt where it was stated the 2G was a poor choice for an inline six, that it was too much carb. I can't recall if that was regarding the smaller inline sixes, though. My thinking was, this is no longer a stock 292, it will flow air through the engine much more efficiently than a stock 292 will, so maybe, just maybe the 2G could work well on it.

I went to Carb King's website. If the 2G in my possession is in fact the factory 2G that came on the truck's 283, it is a 7023010. The tag is non-existent, and it doesn't have a governor.

Anybody? Should I do less research or provide less information to get more feedback? Asking for a friend...lol... Seriously, though, on every forum I look at, someone will ask a very vague question and get reamed to provide more details, but will get a ton of information from many different members. Not just this forum, others too. I have always provided more details hoping for good information from the experts that have done this for years, and usually end up with nothing but my research.

Honest information just shared, and honestly asking for what I should do differently to get some feedback. I want to learn from you guys.

Checking the Internet:

Attached are the Delco Rochester 2G Spec Sheets for the 7023010 that you asked about.
The listing provides part numbers but no other details (jet, bore and venturi size etc.).
Sometimes more information can be found in the automobile's service or shop manual.
A 2G is most likely for a truck and not a car (2GC or 2GV).

Other websites where some have asked questions about the 2G:

https://www.inliners.org
https://www.jalopyjournal.com

I'm plagiarizing from Jon's (carbking) post here:

There is a partial chart in the book "Rochester Carburetors" by Doug Roe. If you acquire the book, and check the chart, you will note varying CFM's for different internal venturi sizes for the different size throttle bodies. There are some internal venturi sizes not listed.

If a chart showing all Rochester carburetors and their internal venturi size exists, I have yet to see one.

Remove the airhorn (top casting), remove the venturi cluster, measure the internal diameter of the main venturi, and then consult the chart in the book.


Also there is this information:

The 2G carbs came with two different flange sizes and 5 different CFM ratings.

1 1/4" flange , 1 7/16 Bore x 1 3/32 venturi = 278 CFM.

1 1/2 Flange carbs all have 1 11/16 bores :

1 3/16 venturi = 352 CFM.

1 1/4 venturi = 381 CFM.

1 5/16 venturi = 423 CFM.

1 3/8 venturi = 435 CFM.

All ratings @ 3.0 in HG.


Jon gave this CFM calculation example which happens to include the 283 2 barrel.
https://www.thecarburetorshop.com/Carburetorsizeselection.htm

Also CFM ratings:
https://www.thecarburetorshop.com/Carbshop_carbsizesandCFM.htm

Why are you not getting feedback? There could be a variety of reasons but in this case maybe very few have done what you are proposing and no one has anything to offer you. You seem to be quite knowledgeable on this subject yourself so I would suggest you forge ahead and report back on your research. I have found over my many hotrodding years folks who really know carburetor jetting keep the information to themselves. Carbking is a rare exception. You’ve got this, have fun!

Thanks buoymaker, lots of info. I was aware of the two base sizes, definitely wasn't aware of the 5 CFM ratings. Would it be safe to say my old 2G is on the smaller CFM size? The 2G I have, has the vent on top, but no provisions from I saw for the vent cover. I probably called the vent cover the wrong thing.

Martin, I am far from knowledgeable on this. I just have a collection of parts acquired over time after lots of research on what to get for my specific build. I know next to nothing about these 2G carbs. But will be baptized by fire, if you will...lol...

I would start with the jetting the carburetor had for the 283, it will be pretty darn close to what you need. The best addition to my truck I have is an air/fuel ratio gauge. It takes about five miles of driving to figure out how to jet your carburetor. https://www.speedhut.com/gauge/GL2-250/7/Standalone-Air-Fuel-Wideband-with-Analog-Out,-O2-gauge-8-5-18

Wasting my time

I'd thought of that. Curious, though, in my research I have seen many inline six engines with 4 barrel Quadrajets, Holley and Edelbrock carburetors, and they claim the engine runs better than with the Monojet. Is it safe to say that the 4 barrel is a better choice? Or can the 2G be made to work across the rpm ranges I will run this engine? Or is it too much carb at low rpms and not enough at cruise or WOT? I know a quadrajet can be calibrated for smaller engines, and the Pontiac 250 came with them. And then there is the Holley kit sold by Tom Lowe that takes a 750 CFM Holley, and turns it into a 562 CFM 3 barrel, so the engine runs on one barrel for around town and then the secondaries operate only on WOT. I can run the 2G, or I can recalibrate a quadrajet I have, I do have options. I approach things way differently than most people, I think outside the box, and had this crazy idea that this engine being way more efficient than a stock 292, the 2G may be a good choice. I am not a racer, and haven't tinkered on these engines like a lot of you have, to say I am a complete novice is an understatement. I am just happy to have some communication on the subject, school is open.

I was actually planning to go with the Offenhauser, and was online looking for prices when I saw the Aussie. The price was right, it was already here in the USA, so I snagged it. I wish it had heat under the carb like the Offy does. I do have an idea to fabricate a heat stove to warm up the underside of the carb area. Not as good as stock, or the coolant heating option for the Offy and some Clifford's, but may help.

That is a nice gauge!

Shane, it's easy to get sidetracked.
Your original question is about a 2GC and jet size.
I for one "tune-out" when the discussion goes in other directions.

Copy that. I looked at the info you provided. I went to that website yesterday but didn't see that information specifically. Very informative, and a lot for me to digest. Way over my head for sure. Seeing that Crusader Marine used 2G's on 292 engines, my 2G being the older model, it may be a good fit for my engine.

Just trying to help here. You have $$$ tied up in new engine parts.
Why waste it on an unknown carburetor in unknown condition.
Your baseline is to start from a decently running engine.
Then you can test jets, intakes and other carburetors for improvement.
If you start off wrong, you'll be like a dog chasing his tail.

I truly appreciate it, too.

With my upgrades to the head, it will flow around 240 CFM. Stock CFM is about 165. At the moment, if I go by the unknown condition, the 2G and the current Monojet on the engine are both in unknown condition. The engine is not in the truck and going to get torn down soon to check the cylinder bores, crank and rod journals before I proceed with in stalling the altered cylinder head. The first fire up will most likely be with all of the new components since they will be rebuilt or bought new. Would you recommend installing the new head with the stock exhaust and intake? I really didn't want to go that route.

Ran some numbers.

C.I. (292) x Max RPM (4,500) = 1,314,000.... 1,314,000 x 0.80 = 1,051,200.... 1,051,200 / 3,456 = 304 CFM WOT.
I used 4,500 rpms even though I will probably never rev the engine that high.

C.I. (292) x Max RPM (2,200) = 642,400.... 642,400 x 0.80 = 513,920.... 513,920 / 3,456 = 149 CFM Cruise

Now which do you have?

1 1/4" Flange , 1 7/16" Bore
or
1 1/2" Flange, 1 11/16" Bore

Flange is the c-to-c longest distance on the throttle base mounting holes.
Bore is the big hole in the bottom of the throttle base.

It's hard for me to recommend which manifolds you should use on the rebuilt head. There is plenty of personal opinions and hot rod articles on what works best for a 292. I've found that intake and exhaust manifolds on an inline 6 can take time (heating & cooling cycles with retorquing) to settle in and not leak so I like to do it once and not mess with it again. Since you already purchased the new manifolds, I would use them.

Your engine break-in needs to be uninterrupted and another reason why I recommend using a known working carburetor. You may be busy fixing leaks, tightening loose bolts, while keeping an eye on water temp and oil pressure.

Completely agree!

Anytime one is migrating a carburetor to a new application, generally best to build the carburetor completely stock! Now one has a repeatable baseline. One can then tune from this point, and always easily go back to the baseline if the tuning mods do not perform as desired (a.k.a. the "Law of Unintended Consequences").

As far as feedback is concerned, some of us still work, and do not live on the computer. Patience is a virtue!

The 2G series is an extremely versatile and reliable carburetor, and with a proper manifold is an excellent choice. It is infinitely tunable. Most folks think of jets, but Rochester created 19 different power valves to allow for different percentages of increase over the main metering jets. Years ago, we produced a spring tuning kit to adjust the timing of the power valve opening. Some of the negative comments you may have seen concern trying to run a 2 barrel carb through a single barrel manifold with a hokey 2 ->1 adapter.

The 2G would not be my personal choice, but then you probably do not have 150,000 carburetors to choose from It really should work well for you.

Jon.

It's the small base 2G. 1-7/16" Bore. Main Venturi 1-3/32". Small Venturi 1/8". If the jets haven't been swapped out, the book says they are 0.055.

In all my research I couldn't find any reviews on the Aussie Speed intake, but I am in contact with a guy, he is building my adapter plate for the 2G, and he knows people running the Aussie, and said it is a good performer, better than the Offenhauser and Clifford. I'm excited to get this thing finished so I can run it in my C20. Definitely the last thing I want to do is mess up the break-in procedure, so I will be making sure all T's are dotted and all I's are crossed, I purposely transposed those...lol... I'm goofy like that, but detail-oriented.

Duly noted. I will just rebuild it for the 283 and get jets if needed. I can't remember if the kit I got had different springs, I'll have to look. I have heard great things about the 2G and it's tunability. I admittedly was going to run the 2G on the stock manifold with a 2-to-1 adapter, but then decided not to do it that way, got the better manifold. I wish I had more choices in carburetors, but I have the Monojet which I really don't want to use for this setup; the 2G which came off the 283 of the truck I bought in 2005; and the Quadrajet I have owned and tuned for decades. Originally I was going to use the Q-Jet, but then decided to give the 2G a try.

I understand the working part, I too am working. I appreciate everyone's feedback. I am learning as we go.

I've never had the need to rebuilt or study a 2G or a 2GC so I have to "bow out" when discussion proceeds on how to rebuild one.

The attached picture is one I found on the Internet and posted it here on Stovebolt.
At the time I thought it was crazy i.e. a 1 barrel Carter YF on a V8 small block engine.
If you look at the diagnostic box and the oil pressure gauge, the engine is obviously running.
Then a kind soul informed me that it was a homemade carburetor tester. Oh expletive!
The point is, after rebuilding your carburetor, I would find a way to test that it works good enough for your engine break-in.

One more thing. I have nothing to justify my words but I, a novice, read "Aussie Speed" to mean "flat out".
An intake designed to get the maximum speed performance out of your machine.
I would do some research and have a fall back plan in case I was not happy with everyday street performance.

As far the rebuild goes, I will follow the literature and/or advice I receive. I have watched some videos on rebuilding the 2G, and it looks straightforward enough. The carb having sat for so long, I'm sure it is gunked-up good, and I have read that the modern carb soak is subpar. I found a video on using a muriatic acid solution and soda blasting after the soak. It came out really clean. I may just use the carb soak I have and let it sit for a day, then clean the passages really well. Let me ask this. Would dunking the entire carb as-is in gasoline for a few days do any good before tearing it apart and then soaking it in the carb soak?

Yesterday I did think of the very thing you mentioned in your response. Test run the rebuilt carb on the engine in my truck before doing the break-in on the 292. That, or pull the quadrajet off the engine in the truck, and install it on the 292 for the break-in. I was planning on doing the break-in on a stand, that way the 292 will be ready to go when stabbed in the truck.

I think the Aussie intake will do good on the street too. It's that waffle pattern that really does the heavy lifting to atomize the fuel/air mixture. The Aussie Speed company does produce nothing but performance parts. What I have read about them, though, they do a lot of R&D to get their products to perform well at various rpm ranges. If this is a flat-out wide open throttle only intake, then I will be out of pocket more money for an Offenhauser and a different adapter plate for the 2G.

Speaking of the rebuild, you seemed to be working up to suggesting a jet size? If so, what do you recommend? The 283 calls for 0.055, which size jets should I order when I order the crocus cloth? Smaller? Bigger? Both? Should I also get some sized for the Crusader Marine 292 setup?

I hope I am not breaking any rules by posting the link to this video. Thought I'd share the muriatic acid carb cleaner video I mentioned.

Muriatic Acid Carb Cleaner Video

Unless you have an engine dyno, making guesstimates about jet sizes is a colossal waste of time. The best process for people without access to dyno facilities is a long hill where the engine can be run for several minutes at wide open throttle, and a stopwatch. Make one change at a time, make a test run, and record the time for a particular run. Then make ONE change, such as jetting, ignition timing, alteration of the centrifugal advance curve in the disttibutor, etc. "Rinse and repeat"! Advice gotten from an interrnet chat room (including mine) is worth exactly what it costs you to read it, no matter how much the guys with double-jointed elbows pat themselves on the back!
Jerry

Shane - the best part of that link is where it is posted that muriatic acid IS NOT COMPATIBLE WITH ALL CARBURETORS.

When using chemicals, unless you are a chemist, BE CAREFUL!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Not only can an incompatibility destroy a carburetor, the fumes can destroy YOU!

Jon.

Thanks for clarifying that Jon. I only posted it for informational purposes since I had mentioned it in a previous post. Have I considered using that method? Yes. Will I? No.

that waffle pattern that really does the heavy lifting to atomize the fuel/air mixture

All that does is to collect any large fuel droplets, preventing them from washing down into the closest intake port.

Waffles are delicious, however. I never acquired a taste for chicken and waffles. Some folks are really into that.

I do soda blasting sparingly and mostly on steel and cast iron. If there are small passages, I tape them up.
I learned the hard way that soda and other blasting materials can pack tight and even high pressure compressed air may not get it out.
Then it's a real pain to clean out those tiny passages with fine gauge wire.

If the carburetor is nasty, I use a safe degreaser, brass brush and water to clean the outside before disassembly.
Then I use an ultrasonic cleaner with s solution of dishwashing liquid and hot (not boiling hot) water.
Compressed air to clean and dry. Repeat as needed.

After 50+ years most of the original finish on most carburetors has disappeared so a clean carburetor may look dull.
A dull carburetor that runs great is much better, in my opinion, than a shiny one that runs terrible.

I'd heard of the ultrasonic cleaners, but have never seen what one can do. I see HF has them for $90. I just may have to get one. The 2G rebuild video I saw mentioned cleaning the 2G with an ultrasonic cleaner.

The finish on this 2G is gone. I'm fine with that. I'm not a bling person anyhow.

And reintroduces it into the mixture when air velocity increases.

Do not judge the capability of good ultrasonic cleaners by one you can buy for $90.

Probably could get about the same results as the $90 cleaner by boiling the parts in a 3 pound coffee can!

Ours was just a shade under 5k. And the best 5k I ever spent on tools.

Jon.

Unfortunately I don't have a business, or a shop. I cannot justify spending 5k on a tool. I wish I had a shop and could buy 5k tools. So I guess I'll stick with the subpar berrymans parts/carb cleaner dip and save my cash. Thanks for the heads-up.

I adapted a big stainless steel stock pot to one of the vibrator cleaners I use for polishing brass cartridge cases for reloading. A strong solution of Trisodium Phosphate (concrete cleaner) and hot water, and several hours of shaking in the cleaning solution softens the crud in the passageways. Then a massive amount of high pressure air from a needle-tipped blow gun through every passage blows them clean.
Jerry

Without pictures, it never happened.
We need to see it!

Learned a lesson with our ultrasonic cleaner and the vapor de-greaser. When some metals are COMPLETELY clean they will bond together just by touching. Now drop them into a home made ATF/Acetone mix to prevent cohesion (bonding). I bought both tools from the salvage dock of a big micro chip maker for a dollar a pound but passed on a 16" Hardinge lathe so of course my steal on the cleaners is forgotten but still crying over the lathe.