Rochester 2GV info needed

av8 · May 06, 2004, 10:55:10 PM

:?: Does anyone have performance (flow) figures on Rochester 2GV 2 bbl carburetors? Am I correct in assuming that because of the wide range of applicaitons 2GVs are available with different flowrates?

C9 · May 07, 2004, 09:52:58 AM

Quote from: "av8":?: Does anyone have performance (flow) figures on Rochester 2GV 2 bbl carburetors? Am I correct in assuming that because of the wide range of applicaitons 2GVs are available with different flowrates?

Correct on the different flow rates.
Pontiac 2 bbl Rochesters were favored by circle track racers - locally and probably elsewhere - who were limited to a single 2 bbl. (They did a clever trick by using a 4 bbl intake manifold and an upside down 2 bbl to 4 bbl adapter. HP was reputed to increase, probably due to the larger plenum area.)

I think the Rochester 2 bbls are good for 250 cfm, but don't quote me. The info is around here somewhere, but so far I haven't seen it.

The Pontiac Rochesters were also favored by those in the know when setting up a competition three 2 bbl setup or better yet the Man-A-Fre, but were difficult to find in the SF Valley due to the Saugus Speedway (Bonelli Stadium) circle track guys nabbed em up.

I'm fairly sure I have a list of numbers for the various Rochesters if that would help.

flt-blk · May 07, 2004, 12:05:59 PM

I am also interested in flow rates on the 2G. It would be interesting to
see exactly how much extra fuel dumps in when all 3 carbs open on my S2D motor.

If you have a # for Cadillac 3X2 (57-59) that would be great.

Thanks
TZ

C9 · May 07, 2004, 03:25:34 PM

Quote from: "flt-blk"I am also interested in flow rates on the 2G. It would be interesting to
see exactly how much extra fuel dumps in when all 3 carbs open on my S2D motor.

If you have a # for Cadillac 3X2 (57-59) that would be great.

Thanks
TZ

No numbers found for 1957.

1958# -
7012201
7012202
7012203
7012205

1959# -
7013033
7013034
7013035
7013037

flt-blk · May 07, 2004, 04:41:42 PM

I'll check the numbers.
Are they all 250CFM??

I need to run the CFM calculation again to see what my motor really requires.

Thanks

TZ

C9 · May 08, 2004, 08:19:19 AM

Quote from: "flt-blk"I'll check the numbers.
Are they all 250CFM??

I need to run the CFM calculation again to see what my motor really requires.

Thanks
TZ

The would have differing flow rates due to different venturi sizes.
Venturi area was how carbs were chosen in the good ol daze, but CFM is a much better way to go.

av8 · May 08, 2004, 10:10:20 AM

Thanks for the comments on the Pontiac carburetors and the numbers, Jay. I don't have a lot of confidence in being able to find an early Pontiac GV in good rebuildable condition. Instead, I'll probably buy a later (late '60s) 2GV spec'd for a SBC from Carburetors Direct ($190 including core charge).

If you haven't already guessed, I'm thinking about using the 2GV on the 8CM Mercury I'm building for my F-1. At this point I plan on using a Mercury manifold, which has the same bolt pattern as the 2GV. My criteria are good drivability, good fuel economy, and a substantial performance improvement over the stock 8BA. I think I'll find most of it in the Mercury "stroker" motor, and I'm hoping the 2GV will enhance the package overall without any fusiness. I'd previously spec'd an Offy 4-bbl manifold with a 390-cfm Holley 4160 but have since decided that, for my purposes, it may not be worth the $520 premium.

Here's the Mercury manifold, all tidied up in preparation for a coat of primer before it goes on the shelf awating engine assembly next month. The manifold is "made-to-order" for the addition of a PCV valve which will replace the road-draft tube.

40cpe · May 08, 2004, 10:33:13 AM

How about explaining the fixture in the background in that picture?
Thanks,
Gene

av8 · May 08, 2004, 09:31:22 PM

Quote from: "40cpe"How about explaining the fixture in the background in that picture?
Thanks,
Gene

It supports a crankshaft while I whittle and polish it, to lighten it, reshape the leading edges, and grind and polish away all the stress risers. I made this one just last week, to replace a simple wooden "vee-block" fixture that I'd been using. With the vee blocks, the crankshaft was supported in old main-bearing shells taped to the end journals. During carving and polishing, the crankshaft is turned a few degrees at a time, again and again, and in spite of grease and tape to protect the journals from marking, it was virtually unavoidable. This isn't a big problem on a crank that is yet to be turned and micro-polished later on, but there are times when the crank is fresh and needs no work on the journals.

The new fixture supports the crankshaft on the ends, with a counterbore bolt screwed into the nose and a counterbored aluminum plug that fits into the pilot-bearing bore in the flange end. BTW, I've been planning and meaning to build the new fixture for a couple of years and just finally got around to it because of increased demand for the work.

First, the old vee-block fixture . . .

. . . and the new one.

C9 · May 09, 2004, 08:54:20 AM

Cool tool.

I love knocking out inventive stuff like you've shown.

Just about to finish up on what I hope will be an interesting little gadget.
Machine work is done, welding today - not much - and I should know by this afternoon if it works.

I'll post the info one way or the other.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Far as carbs go, I've always thought the 2 bbl Holley that comes on 72 and other Pintos - and maybe all of them - is a great carb.
All except for the nitrocellouse float that sometimes - most times - gets 'waterlogged' w/gasoline and sinks.

Not the handsomest carb in the world, but it's a good mixer and the part I like about it is it's internally progressive.
One barrel opens halfway and then the other comes in.

A pair of these on a flathead with the right intake - big plenum? - oughta work great.
Arranging the barrels in a fore and aft mode instead of transverse may be the way to go as well.
Since they come on a 120 cid engine, a flathead with 239 - 255 cid and maybe even bigger ought to respond like nobody's business.

I don't think there'd be a lack of airflow, engines - up to a point, flow restrictions and all that - suck in pretty much what they want.
Which I guess is the long way round to saying that carbs will pull more than their CFM rating - but you knew that....

av8 · May 09, 2004, 10:41:46 AM

Quote from: "C9"Cool tool.

I love knocking out inventive stuff like you've shown.

Just about to finish up on what I hope will be an interesting little gadget.
Machine work is done, welding today - not much - and I should know by this afternoon if it works.

I'll post the info one way or the other.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

I look forward to seeing what you're up to, Jay.

I've considered running a pair of 2GVs on a flathead with progressive linkage like that used on the Chevy BWs and 2/4 Corvettes -- the one with and adjustable rod that slides in a C-shaped stirrup on the second carburetor and begins opening its throttle after the throttle in the master carburetor is halfway or more open. Sort of like a 4-bbl with mechanical secondaries.

32tom · May 09, 2004, 03:59:18 PM

Quote from: "av8"
Quote from: "C9"Cool tool.

I love knocking out inventive stuff like you've shown.

Just about to finish up on what I hope will be an interesting little gadget.
Machine work is done, welding today - not much - and I should know by this afternoon if it works.

I'll post the info one way or the other.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

I look forward to seeing what you're up to, Jay.

I've considered running a pair of 2GVs on a flathead with progressive linkage like that used on the Chevy BWs and 2/4 Corvettes -- the one with and adjustable rod that slides in a C-shaped stirrup on the second carburetor and begins opening its throttle after the throttle in the master carburetor is halfway or more open. Sort of like a 4-bbl with mechanical secondaries.

sirstude · May 10, 2004, 05:56:38 PM

I was talking to a friend of mine last week that races 305" Hydros and they used to be limited to a Rochester 2GC. He dyno'ed about 50 of them and found 13 HP difference from the low to the high. This was on a 200HP 305. Don't know if any Gm brand was better, but there was sure a difference. Still, it's only just over 10%.

I ran 3 of them in my Studebaker on a 383 small block stroker. Sure was LEAN crusing down the road. Of course I was turning 3800 at 75mph with the gears I had.

Doug

Rochie · May 11, 2004, 10:10:16 AM

av8,
pardon me if this has been mentioned but, the Pontiac 2gv had a larger bolt configuration on the base plate and won't fit on "any" manifold. As far as regular 2gv when I built my small block tri-power I scrounged through a couple of old junk yards before I found some decent rebuildable cores. Seems they're getting tough to find and the large base Pontiac carbs are even worse. The stock car boys around here used them all up.
Rochie

av8 · May 11, 2004, 01:36:57 PM

Quote from: "Rochie"av8,
pardon me if this has been mentioned but, the Pontiac 2gv had a larger bolt configuration on the base plate and won't fit on "any" manifold. As far as regular 2gv when I built my small block tri-power I scrounged through a couple of old junk yards before I found some decent rebuildable cores. Seems they're getting tough to find and the large base Pontiac carbs are even worse. The stock car boys around here used them all up.
Rochie

Thanks for the heads-up. I'd planned to specify a 2GV for a 283/307/327 1968 SBC. That should get me ahead of the smogification add-ons, and the jetting should be close to what I need for my 260-cid flathead.