How to improve CFM flow in a BBD from a 78 Super Six

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I have a 78 Volare Premier with the Super Six that has a Carter BBD 8137S carb tag. Base is casting 2543 with main metering jet .086 and has metering rods 2228 .0665x.0635x.056. I have carb apart and cleaned but the venturi assembly is damaged on one side. Looks like it was tried to be removed and the brass jet is damaged on the one side. Here is the question? I have a BBD from a 318 that I got for parts and need to know if the cluster from it will work in my original. The Carter book says the my original has 220 CFM and the 318 I have is 285 CFM using 089 main jets but has 2 different rods. Can I get up to the 285 CFM on my original using the 089 mains and different rods along with the Venturi from the 318 parts carb. Thanks in advance Mike.
 

AJ/FormS

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rods and mains have nothing to do with cfm flow.
And the rated flow is just a rating.
You could theoretically install that 285 cfm carb on a lawnmower and and it will never get past what that measely lawnmower can pull. OR you could install that 285 on a 400 cubic inch engine and pull a lot more thru it than 285.
So the carb manufacturers figured out a scientific way to rate them by pulling air thru them at a standard pressure differential,and a standard temperature and measuring the cfm flow.
But not every manufacturer uses the same test method, and 2bbls are tested differently than 4bbls. And there are formulas to "reconcile" the different methods.
Finally. if your engine can only pull 220cfm on the test machine, then it will not make any more power using a 285. The common formula for estimating the amount of air your engine can ingest is;
rpm x cid/3456; where cid is cubic inch displacement. The Formula is for an engine that is able to ingest this air at 100% Volumetric Efficiency so you have to down-calculate to your Efficiency.
Ok so
(225 x4500) /3450 =293 cfm and if your 225 manages a VE of .75, then
293 x.75VE = 220cfm. Now, your engine will a different VE at every different rpm you test it at so the .75VE I chose might be the best she can do in stock trim.
Can your slanty pull more than 220cfm, well maybe, at a higher VE or at a higher rpm. Say you bumped the compression up and installed a free-flowing exhaust and a cam that works to 5200. Now your numbers could be
(225 x 5200) /3450 x .84 =285 cfm

But say you never go over 4000,
and your 225 is well used; then
225 x 4000/3450 x .65VE =175cfm

Finally, if the 285 fits on your intake, just bolt it on and see what happens. I bet it will be just fine, if a lil sluggish on the get-go.
But do not attempt to swap the guts,from one carb to another; that is a recipe for disaster.

But say you had a fresh 318;
318 x4400/3450 x .70VE= 285cfm
Can the 318 pull more than 285?
Well sure, just like yours. But just cuz the carb is rated at 285 does not mean that it cannot pull any more thru it; remember that 285 is just a rating at a certain pressure differential. Nothing changes at 286 cfm, nor 290 or even 300 .... except the pressure differential, which is measured as Vacuum inside the intake manifold.

BTW-1
as to the damage on the venturi, those brass parts you see there may have a tiny hole on the top which has to remain open and correctly sized for the circuits to work properly. But the venturi doesn't much care about anything else, as long as it ain't broke. If they are tubes sticking up, that is for to get them up out of turbulent air. You can get brass-tubes at the model-airplane store and rig something up, just make sure that when yur done, it won't ever fall into the engine,lol
 
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XfbodyX

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There is a good bit of factory lit on what will and what wont interchange in the 225 2bbl vs the 318 2bbl.

A holley 2280 in 78 on the 318, ive never seen one up close.

If this would help I could scan it.

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BudW

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The /6 Carter BBD looks similar to the BBD used on 318's - but, for the most part, that is about all. Most all of the parts are different between the /6 and 318 BBD's.
That said, I believe the rated CFM for both, are the same.

If you really want more CFM, I might suggest a larger carburetor like the one used for 360/383/400 2-bbl or something like that (which uses a wider mounting flange) - but not sure it will be that much more help in the long run. Without forced air (turbo or supercharger) and/or without major modifications, I don't think a /6 will flow that much more air the existing BBD will flow (but could be wrong).
BudW
 

Oldiron440

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Every engine I've seen on a dyno will show it's highest VE at peek torque and for a stock motor that's only 80 to 85 percent efficiency. It's only after better a better exhaust, intake and usually a cam do you need a larger carburetor.

For a slant six peek torque is in the 3000 rpm range with little hp increase after 4000 rpm.
 

XfbodyX

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This is straight from chrysler 1976, looks like the greenies were at it then as well.

But like any 78 T quad even... for performance they belong in the replacement carbs box.

Id start looking for a 2bbintake and a /6 header if I were really trying or you can still from time to time find a performance cam that does make even a smog setup run a hair better.

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Ricco Heatherly

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I have a 78 Volare Premier with the Super Six that has a Carter BBD 8137S carb tag. Base is casting 2543 with main metering jet .086 and has metering rods 2228 .0665x.0635x.056. I have carb apart and cleaned but the venturi assembly is damaged on one side. Looks like it was tried to be removed and the brass jet is damaged on the one side. Here is the question? I have a BBD from a 318 that I got for parts and need to know if the cluster from it will work in my original. The Carter book says the my original has 220 CFM and the 318 I have is 285 CFM using 089 main jets but has 2 different rods. Can I get up to the 285 CFM on my original using the 089 mains and different rods along with the Venturi from the 318 parts carb. Thanks in advance Mike.
Are you set on the BBD as the carb to use? Our bunch up in the Seattle area have had good luck with the 32/36 or 38/38 Weber setup. The 258 Jeep guys use them, due to the awful late model BBD's that their rigs used...and their adapter bolts up to the Super Six manifold. The displacement being so close, the jetting works too.
Also, Clifford Engineering has setups that us them.
Just a thought...
 
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Aspen500

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Just my experience with something similar. For the heck of it, I bolted an intake and 2 brl carb from a 360 on my '81 D150 318 and notice no difference in (seat of the pants) power. All I managed to do was use more gas. Ended up bolting the stock intake and carb back on. It was an experiment that didn't work out.

Now, with port matching the 360 intake to the 318 heads and rejetting the carb may have yielded different results however.
 
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