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Author Topic:   Rochester big bore 2 barrel
dode
Dirt Forum Champ
Total posts: 613
posted February 09, 2004 10:51 AM  
What rules are you running under, and what do they allow to be done? Or does it just have to "look" like a Rochester 2bbl?

They can be made to out-perform any stock 4412, quite easily, but it requires some pretty heavy "surgery".

If it is really a "big bore" 2G, then it'll have 1 3/8" venturi and 1.687" baseplate, which, incidentally, is very similar to what the stock 4412 has.
Many carb builders offer numerous modification levels to those carbs. Ours, for example, can be made to flow upwards of 680cfm with 1.437" venturi and 1.75" butterflies....

Yes, they are very much simpler than a quadrajet, but they don't flow as much as one either...

KP

dode
Dirt Forum Champ
Total posts: 613
posted February 09, 2004 12:01 PM  
We can sell all the necessary parts if you'd like to try machining your own. Or we can do the entire task for you and save you the headaches of ruining a good core. It takes a LOT of knowledge of the internal workings and design of the Rochester 2G to make it perform as a race carb. There are literally dozens of areas that need machining and altering, as well as the proper parts in the proper places.
The key here is "bigger is not always better".
Thanks for the kind words, too! :-).

gould
Dirt Forum Champ
Total posts: 730
posted February 26, 2004 05:41 PM  
whats a stock big bore flow?

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KPLugnut
Dirt Forum Champ
Total posts: 1019
posted February 26, 2004 06:46 PM  
Rochester rated their biggest 2G carb at about 450cfm. Those that advertise them at 500cfm are over-generalizing (fudging numbers, too) as it takes visible modifications to gain 50cfm out of the blue on a 2G.
Keep in mind, also, that every flowbench (like every dyno) can be made to "say" anything the user wants the customer to hear simply for sales purposes/bragging rights.
Max cfm numbers really mean very little when taken out of context like that and what's most important is how fast a carb gets to its maximum and how consistantly and properly it meters the right amounts of fuel for the application it was built for.

Hope that helps some.

KP

racenmotorsports
Dirt Maniac

Total posts: 169
posted February 28, 2004 06:28 AM  
hey KP,

about how much does it cost to get a 2G done up?

KPLugnut
Dirt Forum Champ
Total posts: 1019
posted February 28, 2004 06:39 AM  
Racen, check your PM....

thanks,
KP

RACEINMUD
Dirt Freak

Total posts: 323
posted March 01, 2004 03:32 PM  
I have a KP Roch. and it ROCKS! Thanks KP! Race

James Ott
Dirt Maniac

Total posts: 131
posted August 04, 2005 04:53 PM  
Hi... Ou rules state 1.250" venturi any ideas? for which carb to use.

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"Winnig heals all wounds"

James Ott
Dirt Maniac

Total posts: 131
posted November 02, 2005 08:17 PM  
KP! I got about 10 different Rochester 2G carbs kicking around. They range form '69's to 74's all mostly just run of the mill stuff. Is there one you like better? I will send it your way for a rebuild. Our only rules are 1.250" (+.005) venturi and we can remove the choke and linkages. I'm looking for a dependable carb. let me know what you think.

KPLugnut
Dirt Forum Champ
Total posts: 1019
posted November 03, 2005 06:14 AM  
As long as the main body is the 1.25" venturi size, it really does not matter, since all the carbs I build are done the same once modifications are done. They are not just "rebuilt", they are completely remanufactured and internally re-machined from bare castings up.
Is the only rule they enforce or check the 1.25" venturi? Do they remove and/or dissassemble the carbs?
Let me know, or email me on the side and we can discuss in more detail.

KP
email: kineticperformance@thedirtforum.com

James Ott
Dirt Maniac

Total posts: 131
posted November 03, 2005 07:32 PM  
I don't think they tear em down. I was told the bore guage is made of wire and they do check the hole. Is it good or bad to have the accelerator pump cross feed hole and check ball? Just curious as I have both styles cross drilled and not. Can I send the carb dismantled?

KPLugnut
Dirt Forum Champ
Total posts: 1019
posted November 04, 2005 06:35 AM  
Disassembled is fine. Pump feed circuit style doesn't matter. Orifice size, pump diaphram geometry, volume and refill speed matter. Fuel signal, booster design/size/position, emulsion circuit work, bleed sizes, etc etc etc all matter as well.
And FWIW, a "wire guage" is bogus and not accurate at all, but no worries, the carb will pass tech.

KP

James Ott
Dirt Maniac

Total posts: 131
posted November 04, 2005 01:13 PM  
KP carb will be shipped postal tomorrow

James Ott
Dirt Maniac

Total posts: 131
posted November 12, 2005 09:05 AM  
KP how much flow (cfm) can be had from a 1.250 venturi 2G? curious to know!

KPLugnut
Dirt Forum Champ
Total posts: 1019
posted November 12, 2005 01:04 PM  
If the only rule is that it has to have 1.25" venturi, then about 550 or so, depending how wild you wanna get, and how far we push the limits. But the important thing is not how much cfm, it's how well it's calibrated and what kind of signal the carb generates, which determines throttle response, torque, etc. It does no good at all to have a huge CFM potential if the carb takes all day to accelerate, does it? :-)

KP

James Ott
Dirt Maniac

Total posts: 131
posted November 13, 2005 09:36 AM  
Wow. I was curious as I have been fooling around with Desktop Dyno trying to get an idea of what will help with the rules we run.

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