340 six barrel end carbs on my 440

[Mr Belvedere 30144]

Hey guys I was checking the numbers on my carbs yesterday. I have only had the car for 6 weeks. The carb setup was built and tuned by a man named Lance Patton of Patton race carbs in Lawrenceville Ga. I googled him and he is well known nation wide as a prostock and street tuner and carb builder. I found that the center carb is the correct 440 carb.
list # 4144-1
1290
3418550
the end carbs are, 340 carbs
list # 4790
2670
3577185
I have read that using 340 carbs corrects a fuel flow issue in the manifold of the 440 and that the smaller venturies make for a more responsive acceleration and response.
Has anyone else ever heard this or done this? The car does run and responds amazing with very responsive throttle and no hesitation. I do not know what jets or power valves etc are in them but I know if it aint broke then don't fix it.
All this sits on an Edelbrock intake with 346 heads on a 1975 cast block.

 

[sleepar]

That sounds right for street.... keeps from loading up

 

[Mr Belvedere 30144]

I have read that as well. Yet Mopar 1 site wright up on six pack setups said not do do this. Go figure.

 

[62MAX]

For what it's worth,get your inside calipers out and measure the venturis,they are the same size !

 

[Mr Belvedere 30144]

oh ok I read they are smaller on the web but i do not know myself.

 

[mac]

Bill are the kill bleeds a different size?

 

[sleepar]

I thought the difference was in the pump shot.....

 

[62MAX]

Bill are the kill bleeds a different size?

Not sure but I can measure,I have both.The main metering orifice in the secondary plate is different as is the power valve channel restriction in the center metering block.

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I thought the difference was in the pump shot.....

No difference,same pump cam and same .031 discharge nozzle,.

 

[sleepar]

The way my friend had it was he had a set that was street 340 with everything... and a set that were 440 but they must have been modified so the differences were apparent....

 

[Mr Belvedere 30144]

I had never heard of mixing them like this until I found out mine had 2 340 carbs and 1 440 carb. But when I googled it I found that this is considered a great performing setup and the carb guy who did mine does this a lot for Hipo street 440's.

 

[Meep-Meep]

I'm 99.9999% sure the 340 and 440 carbs have the same venturi area and throttle bore size. The difference is most likely in the fine tuning like high speed bleeds and possibly the emulsion circuit. I have a 340 center carb on my 440, and it runs, but jury is still out if it will stay.

 

[sleepar]

Could the only difference be in the fuel line size...

 

[62MAX]

Could the only difference be in the fuel line size...

Fuel line size is the same unless you are referring to the line from tank,everything forward of the pump is 5/16".

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I'm 99.9999% sure the 340 and 440 carbs have the same venturi area and throttle bore size. The difference is most likely in the fine tuning like high speed bleeds and possibly the emulsion circuit. I have a 340 center carb on my 440, and it runs, but jury is still out if it will stay.

You can change that to 100.0000000% :icon_mrgreen:

 

[sleepar]

70 was the only year for the 340 so that must be the only difference a stock 440 setup has 1200 cfm and the 340 1200
2 casting numbers suggest something how ever slight was ordered which is the tuneing all else being the same.

 

[Mr Belvedere 30144]

I found this on the web,

Small block outboard carbs have a tab on one of the booster venturis to correct a distribution problem in the manifold

From Mopar1:
The 340-6 bbl. systems differ from the 440-6 bbl. in carburetor distribution so that the carburetors should not be changed from one system to another. The center carburetor on the 340 has 1-1/2 inch throttle plates while the front and rear carburetors have 1-3/4 inch throttle plates."

I am not concerned about this since I have the correct 440 center carb.

From For A-bodies:
The air bleeds and venturies are different between the carbs, 340 end carbs on a 440 will react faster on initial opening, no matter what springs you have installed vs the same springs on 440 carbs due to orifice/Venturi. Also 340 outboards had fuel distribution tabs on the venturies due to manifold problems.

I have read the above statement about the faster reaction time with the 340 end carbs on several sites on the web. The bottom line is the setup I have runs great, I don't think it could be better.

 

[Meep-Meep]

The CFM rating of the carbs is not 350 + 500 + 500. Individually they are rated as such because of the difference in pressure drop of the 2 BBL vs. the 4 BBL. In 4 BBL ratings (from memory) 500 CFM = 354 CFM and 350 CFM would be something less.

I have a 340 list number center carb and it looked identical to the 440 ones I have. I have no 340 outboard carbs so can't comment on that.