Rochester 2GC info
 

Just doing a little bench racing and looking at the 350 Chevy 250/230 with the Rochester 2GC 1686/1375. I was checking to see if any other of the GM (Buick,Pontiac or Olds) cars ran the big 2 bbl. I didn't look at them all but it appeared only Chevy listed carb. measurements on the NHRA blueprint guide. Was the big 2bbl only used on the 350 Chevy? I would expect Billy Nees or Mark Yacavone, the gurus of the odd and obscure combos to chime in on this one. I have the highest respect for these guys because I love odd and obscure combos too.

Re: Rochester 2GC info
 

You can find them on Chevy 400`s as well. They are certainly getting harder to find with the 1.375 venturi. Not sure about BOP.
I agree, Billy and Mark would know.
Alan Peters too.


Mike A114
P/SA

Re: Rochester 2GC info
 

I believe that the 1969 and 1970 Chev 350 250 were the only engines to use this size carb. I queried the database for the ClassRacerInfo website and they were the only two engines that used a Rochester carb with 1.375" venturi.


There were some Oldsmobile engines from 1969 thru 1972 that used 2-Bbl carbs with 1.313" venturi.


There are no listed carb sizes for the Pontiac 2-Bbl carbs in the Tech Bulletins until 1974.

Re: Rochester 2GC info
 

Learn something everyday.
Thought the 400 used the large 2GC.
Thanks Dwight.


Mike A114
P/SA

Re: Rochester 2GC info
 

Even the 69 Impala 396/265 used the 1.25 carb, strange as that sounds.

Re: Rochester 2GC info
 

Yeah I noticed the early 400 Chevy and 396 used the smaller carb. From what I could find the 400 and 396 carb was around 12 or so CFM less than the 1969 and I think 1970 model 350's. Wonder how much the difference in CFM was worth?

Re: Rochester 2GC info
 

How many of the 1.375 venturi's do you need? I think i have a couple
in the shed. Also venturi clusters and baseplates left over from the local circle track racers who now are allowed to run holley 4412's.

Now is it true or false, nhra no longer is enforcing the carb. P/number but as long as it meet's dimensional configuration and " original visual design" it's good...... (notice i said original design ).
So with that being said and "untouched rochesters" being harder to find. Why can't the marine carb. (that meets the above specification) be used??? Easier to find (yes, even in the darn) desert and has all the good parts already installed (ok, maybe not all, but it has the "good booster cluster" and comes very darn close on the "fuel curve" needed.

Norm

Re: Rochester 2GC info
 

I was told the difference between the big
and small carb is about .5



Mike A114
P/SA

Re: Rochester 2GC info
 

You have a PM


Mike A114
P/SA

Re: Rochester 2GC info
 

I may be interested in 2 of these carbs. New dirt track rules from imca and they are quoting the 1.375 carb as being the 1 to use. Price for 2 complete shipped to 85013 if interested in selling.

QUOTE=NORMAN BARNARD;482788]How many of the 1.375 venturi's do you need? I think i have a couple
in the shed. Also venturi clusters and baseplates left over from the local circle track racers who now are allowed to run holley 4412's.

Now is it true or false, nhra no longer is enforcing the carb. P/number but as long as it meet's dimensional configuration and " original visual design" it's good...... (notice i said original design ).
So with that being said and "untouched rochesters" being harder to find. Why can't the marine carb. (that meets the above specification) be used??? Easier to find (yes, even in the darn) desert and has all the good parts already installed (ok, maybe not all, but it has the "good booster cluster" and comes very darn close on the "fuel curve" needed.

Norm[/QUOTE]

Re: Rochester 2GC info
 

Jeff, sent you a pm on some of the bigger 2bls.

Re: Rochester 2GC info
 

I to am interested in the 1.375" venturi carbs. Thanks.

Re: Rochester 2GC info
 

While researching some other carb's today i ran across the following. Carb's 7042118 and 7042838 (large 1.375 venturi's) were installed on all models of that year with the 400 motor.

Document used was the napa carburetor application and parts guide......then checked the nhra eng. Spec. Sheet and found 1.250
venturi listed..maybe typo???/ these carb's have never been machined as the parting line(s) in the venturi are still there....

Any suggestions?????

Re: Rochester 2GC info
 

Here's another one:
The 1969 full size Chevy 327 /235 used some form of the big base carb.
The 327 /210 used the small 1.09 carb .
That is the difference between the two engine options..
Yet the NHRA specs list both using the same (small ) carb and manifold.

Re: Rochester 2GC info
 

Mark & Norm -

When I was building the database for the ClassRacerInfo application, I had to physically enter about 90% of the engine data. That's why I have repeatedly asked for input for any discrepancies that are found since I know tat I make lots of mistakes. But that also means that I read every tech sheet in the book and know that NHRA office personnel have made mistakes, too. As you two have pointed out in your examples, there are "questionable" items in the specs (and the class guide, too!). I compiled an Excel spreadsheet for some of the tech specs and it is not a short list. Mostly the items are for engines that have never been raced so it's not like anybody is getting screwed on the deal. Engines that have been pounded on over the years have forced corrections (remember the 4-bbl 260 Olds?) and many times racers have worked with the tech department to get corrections done.

I wish there were an easy way to submit corrections and then some public feedback about to explain what makes acceptable documentation and what doesn't work. I know the tradition of "writing a letter to the tech department" works, but most racers don't even know it is available and that those processes are active now. The stumbling block for NHRA to manage the technical data is the cost of the time to do the tasks necessary and management decisions.

Norm, information from aftermarket sources is rarely accepted as evidence for spec accuracy. While it may be correct and the assumption is that it is pointing to factory specs, documentation from the OEM is the best source . . . most of the time.

Mark, if we have never had that conversation about the 327-235hp carburetor, I am in total agreement that the bigger carb was on that engine. I have parts books from that era that clearly shows the same intake manifold used as on the 350 250, and Rochester specs indicate that the components of the carbs listed are for the big series 2GC.

Finally, my goal for ClassRacerInfo is to be the most complete and accurate source of data for Stock & SS racers as well as representing the NHRA data. And having the data in a database where you can query for data is so cool and powerful.

I'm finished rambling.

Re: Rochester 2GC info
 

Dwight, remember a couple of Texas Jr Stock racers punching the inserts out of the boosters in 2bl Rochesters? Took me a while to find out how they made 2bls run that fast. One of one of those guys recently-ex-friend told me. I asked about it, so they showed me. Got through tech a long time that way. Only a mechanic that kind of specialized in carbs & tuning would likely have even noticed while looking at one.
A record or two was set like that. :-)

Re: Rochester 2GC info
 

Ed, I've found some Marine 2Gs that didn't have the inserts in them over the years. Especially on OMC 2.3 FFFord motors

Re: Rochester 2GC info
 

Never head about that! But it sure doesn't surprise me! LOL!


My very, very first race car was a '57 Chev 283-185 hp 150 business coupe and I found that I could use secondary boosters from certain 4GCs that didn't have the inserts and pick up a bunch. I never ran fast enough to be seriously inspected, but I doubt that it would have been caught.

Re: Rochester 2GC info
 

guy's that's an old trick from the 60's , but it reduced the booster signal . brad urban from the carburetor shop also tried it years ago but with limited success.

for our circle track customers that have to run a 2gc or a marine carb. we designed a
a cnc'd alum. insert that replaces the original restrictive insert. booster signal improved as did the total cfm.

the above may not be legal per your track rules. but some times it pay's to think outside the "box".......

Re: Rochester 2GC info
 

If I told you who it was (no longer racing) you would not be suprised at all. LOL
I will tell you at the track some time. Not ratting them out here.

As for booster signal, yes they need jetted differently. Both were stick cars.

Re: Rochester 2GC info
 

Was there anything else back then??:D

Re: Rochester 2GC info
 

Powerglides. Robert "Hutch" Hutchison was one of the first I remember making one fast in Div 4.
Personally, I broke a lot of 3 speeds in my '56 around that time. Took me a while to get my head out, and soften up the clutch.

Re: Rochester 2GC info
 

Anyone have an opinion on whether to use the power valve in these or block it off. I have a Deano carb and it is blocked off, haven't tried to 'restore' it to a power valve setup.

Re: Rochester 2GC info
 

Mike, How high are you foot braking it?

Re: Rochester 2GC info
 

Bad air 3000, good air 3500. By the way, just installed Kenny's converter today. With the old converter, 3500 was really wanting to push the brakes. Car was .04-.06 slower at 2500.

Re: Rochester 2GC info
 

Mike, you'll go nut's trying to use a pv in a roch. 2gc carb as they had so many deravations of the pvrc they used.. Plug it, retap the jetting holes and use the holley jetting, better selection and easily obtainable. Tip:, now your ready to begin playing with the fuel curve !!!!!!! (assuming you have a good wide band data logger).

Re: Rochester 2GC info
 

I don't think you need to worry about a power valve then.
As long as it drives around the pits okay...

Re: Rochester 2GC info
 

No issue in the pits. Thanks. Will know this weekend if the converter helps- it should be a little looser.

Re: Rochester 2GC info
 

We used to do that to the old 4GCs. We were told then that we could not remove & plug it. Many of us pulled the piston/spring, pushed the piston up, and put a ding in the rod with a pair of dykes so it could not extend again, and jetted up. Easy to find Rochester jets back then.

Re: Rochester 2GC info
 

Found a good source of 2GC part including jets-Mike's Carburetor Parts. Has everything for 2GC's.


http://www.carburetor-parts.com/Rochester_c_31.html

Re: Rochester 2GC info
 

Does anyone run a 2gc combo in super stock? I was looking at it as an option for both stock and super stock, I just have no clue where to start looking for info on how to make a 2gc work in either configuration.

I would be N/SA or SS/MA, in my 70 chevelle.

Hate the off season, ideas run rampant. Lol...

Re: Rochester 2GC info
 

John, there's plent of guy's on here that will share the info. With you. You didn't say what the engine spec's were!!!!

I see where your from upstate new york just east of rochester.
I'm also from upstate called batavia, about half way between
rochester and buffalo .

If i can be of help, just send me a pm......good luck.....norm

Re: Rochester 2GC info
 

I'm no expert, but I found this interesting link for 2GC info - Hot Rod Magazine article


http://www.hotrod.com/how-to/engine/...g-carburetors/

Re: Rochester 2GC info
 

I believe Mike Town runs one in SSGT.

Re: Rochester 2GC info
 

Along with Jeff Town, Tony Shaffer and myself. There are probably others out there as well.

Tim

Re: Rochester 2GC info
 

As stated in the article, the 1.250 venturi can be bored out to the 1.375 configuration, without going through the casting.
Not S/SS legal of course, but could be used as a test carb to get you started.

Re: Rochester 2GC info
 

Mark, why is it not legal to perform that process? I didn't think tech. Was looking for the part number any more, if the factory
defined carb. (roch.) meets the dimensional specifications indicated by nhra in the engine specifications for the combination
your running your good !!!!!

Good rochester cores are getting hard to find and the law of supply and demand willkeep the price too high for the sportsman. The flip side of this is maybe nhra needs to consider allowing the mercury marine carb. As a replacement as it meets the large bore rochester dimensions, doesn't require the necessary machining like the roch. To be competative along with
other things.

Just my 2-cent's for today.......norm

Re: Rochester 2GC info
 

Norm, It is illegal because it leaves machine marks and takes away the anodizing.
That being said, a grungy old core that was dipped in acid to clean it, wouldn't have any anodizing left, if you follow me.
Remember..Any machine marks or sanding scratches visible, and yer out!

I'm not familiar with the Mercury Marine carb.Made by who?
Link? Pic?

Re: Rochester 2GC info
 

Here's a couple of pictures of the marine 2G - it measures 1.375 but it has sleeves in each bore. I've never built one to try yet - one of these days.

Tim

Re: Rochester 2GC info
 

Mark....you have a pm.....