Maybe I'm phrasing it wrong, but if this has been addressed previously I'm not finding it thru the search function.I want to use large base Rochester 2bbls on a 3x2 2g small base-bored platform. I find numerous adapters on the internet (Vintage, Summit, etc.) to go from 3 to 4 bolt, but none to accomplish this combination. Anyone know if this adapter exists, or if this has been done (I'm sure it has)?
holley makes them, spectre makes them, mr. gasket makes them...several others. gimme a min and i'll get you part numbers.
holley #17-43 will need modification spectre #not in the new catalog mr. gasket #1937 same as holley both of those fit large and small rochester patterns and with a little bit of ingenuity you have yourself an adapter. there may be some specific ones out there but these are what i've used in the past. frank's idea isn't bad either
That would work to get them mounted, but its not just a bolt pattern thing. The throat openings on the larger Rochesters are about 1-5/8", while the smaller 2g's are shy of 1-1/2". I thought adapters usually taper between these differences to smooth out the flow. The larger Rochesters are basically what you find on the '50's Poncho tri-powers, while the smaller 2-gs are what you find on J2's and the like. I'm interested in using the large Rochesters (because I have them) on a 3x2 sbc setup on an older Vette.
<LI class=lip>Small Base Rochester Carbs to Large 4-bolt Rochester - Adapt. Plates - 1 CNC Cut Aluminum - allows using small carbs on large carb intakes - with studs, nuts, screws & gaskets $240.00 set of 3 http://www.hotrodcarbs.com/parts_list.php
Thanks, that sounds like what I'm looking for, if I use them upside down. And the hotrodcarbs site looks like a good resource. Thanks again and thanks skajaqueda and Frank, I've got something to go on when I hit the phone Monday morning.
Offenhauser has 3x2 intake for sbc that'll allow using large base Rochesters. It would look better than adapters...
Thanks, that was one of the questions I was going to ask when I got on the phone in the morning. You're right, that would be the best way to go. I have an Offy catalog around "some place," hopefully I can get a part number if they show the difference.
i thought that the 50's front feed 2g's were still the smaller base smaller cfm carbs and that the larger base front feed higher cfm 2g's didm't come out until the 350's ?. because if you use the large base higher cfm carbs (3x2 is close to a 1000 cfm's) you need one heck of a motor.
You may be right. Offenhauser says this manifold/carbs combination is equal to five 97's, which is much for a small block. But it'll be on a built and cammed 4-bolt main 350, running thru headers, flowmasters and no cats. So I'm hoping with the progressive set-up and maybe some jet tweeking it won't get drowned.
Side inlet float bowls and TriPower base plates with their thicker butterflies would be a big help with fitting up and reliability. Eliminating the power valves and increasing the main jet size to compensate in the end carburetors (like the factory did) might simplfy tuning. Adapting or immitating the Pontiac manual progessive linkage used on 65-66 stick shift setups would solve a lot headachs too. Been some good posts on the Hamb about Tripower and at least one vender out there (Pontiac Tripower.com) with good info on their website.
Seemly you found your Offy catalogue? But for someone else with same thoughts; Prod.nr. for that sbc intake is 5254. Catalogue is downloadable here; http://www.exeterautosupply.com/Offenhauser Catalog.html and that intake is found on page 24. Alliance vendor for Offy parts is "dmarv" if I remember right. Large base throttle bodies are reproduced by www.VintageSpeed.com and same parts are also found from www.SpeedwayMotors.com
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