Double carb and split exhaust/ pro and cons

[GTfastbacker]

With buying the D19 Business Coupe (with a P18 engine) we got a double carburetor intake with linkage and cast split exhaust manifolds.

 

Wondering how much is the effect installing this components?

The engine is stock.

 

What carburetors are the best choice for this application?

 

Will the auto choke working with double carbs?

 

Makes it sense to do this without changing the head or milling it off?

 

Many questions…

 

Thank you

Joe

[47 1.5 ton]

I am only going to comment on this post as you haven’t had any replies. There are several in depth conversations on here recently that you can search for.

  Just want to point out that I would advise to use a pair of the exact carbs. If you have good compression numbers, opening up the exhaust will be beneficial with little input. The dual carbs might have minimal benefits but be ready for some serious tinkering to have it correct. Took me about 5 times pulling them off but I was stubborn replacing the gas tank which caused a few issues that you may not have. It is a neat set-up that I enjoy if nothing else. Advise milling the head and a light cam to up the performance a little.

  I did add the set-up to the existing motor to try out without  electronic choke carbs.

Edited August 12 by 47 1.5 ton

[Sniper]

Don't forget your carbs need to be synchronized too.  Basically, that means the airflow thru each carb is equal at idle

[47 1.5 ton]

 Sniper,  My tuning in several points above idle was the most complicated. I originally thought that setting at idle would do the trick but soon learned that balancing at higher RPM was the tough challenge and this may have been because I decided to use the factory balance tube on the manifold. Bottom line is the compression needs to be consistent and the air cleaners or I could imagine a real head ache.  I would almost bet that a 225 super six carb would work well enough and not have all the tuning required. I just wanted the nostalgia of the dual singles.

[FarmerJon]

On 8/11/2024 at 1:06 PM, GTfastbacker said:

With buying the D19 Business Coupe (with a P18 engine) we got a double carburetor intake with linkage and cast split exhaust manifolds.

 

Wondering how much is the effect installing this components?

The engine is stock.

 

What carburetors are the best choice for this application?

 

Will the auto choke working with double carbs?

 

Makes it sense to do this without changing the head or milling it off?

 

Many questions…

 

Thank you

Joe

What brand is the intake? Some are better performing than others.

I like the sound of the split exhaust on my Plymouth, even with the single carb.

[Sniper]

I have never seen carburetor synchronizing tools used at anything other than the idle setting. And we're talking about how much the throttle blade is open not so much the mixture. I'm not sure those tools would have the range to measure at wide open throttle although I suppose you could add an extended range gauge to it and accomplish it. In my case I have dual throttle body fuel injection and I hand made both air cleaners identical to one another with the widest diameter filters I can run and they're about 4 and 1/2 in tall so I shouldn't have an air flow restriction on the air filter side of it

[keithb7]

I’ve never done the dual carb set up. In theory you should get better even fuel delivery to all cylinders.  Right now, stock set up the two cylinders farthest from the single carb get less fuel in them, compared to the cylinders closest to the single carb. I suspect this is due the amount of time the intake valve is open. The intake valves all open for the same duration.  Yet the air/fuel mixture needs more time to travel to pistons 1 and 6. 
 

I am skeptical (more uneducated actually) that dual carbs will improve horsepower or torque on an otherwise stock 218.  The stock carb can be set to overfuel that stock engine. 
 

Dual carbs, I suspect will net a smoother running stock engine at idle. Especially a cold engine at first start up on a cold day. Why? Condensation droplets forming on the insides of the longer air intake manifold arms, furthest from the single carb. 

 

Perhaps dual carbs will net a little crisper throttle response.  
 

Dual carbs and dual split, balanced headers?  Now we’re talking about performance upgrades.  
 

For a stock engine, is it worth it to fiddle with dual carbs? I don’t know. 
 

 

Edited August 13 by keithb7

[47 1.5 ton]

That’s the benefits of injection— consistency! I will stand by my past experiences that no (2) carbs measure the same through a various range. I am far from an expert but my conclusion is that the performance above idle is more important so after using (2) synchronizers, I went back to base carb vacuum for tuning with air cleaners installed at multiple RPM points. Then went and verified idle with synchro tools and measurement was good. 

Edited August 13 by 47 1.5 ton

[Sniper]

4 hours ago, 47 1.5 ton said:

That’s the benefits of injection— consistency

 

And tuneability.  You can more finely adjust the AF ratio with computer controlled injection than a carb could ever hope to do.  But you do have to do the tuning, or at least get a self tuning setup but even those aren't as finely tailored as possible.

 

4 hours ago, 47 1.5 ton said:

I will stand by my past experiences that no (2) carbs measure the same through a various range.

 

No disagreement, considering they are cast and not machined, but even CNC machined units would still vary some.  Enough to matter?  maybe.

 

4 hours ago, 47 1.5 ton said:

I went back to base carb vacuum for tuning with air cleaners installed at multiple RPM points.

 

I am curious as to what you did to compensate for the flow differences?  Porting/polishing?

[moparfun]

I've had this setup for several years, Offy intake, 2 stock carbs (no choke) with fenton dual exhaust manifolds. It starts and runs better than it did with one carb, I'm very pleased with the performance and how trouble free the setup has been.

[47 1.5 ton]

 

 

“I am curious as to what you did to compensate for the flowdifferences?  Porting/polishing?  “.   
 

   The factory linkage runs from one side as apposed to being split center like the AOK set-ups. This creates a ratio as you work with the lower linkage. I was able to adjust enough to split the balance close to equal at partial throttle.  On the factory set-up w/balance tube, the dominant carb takes over and slowly equalizes back when set close.  Just kept adjusting  (lots of hours) until had good vacuum readings and rechecking idle measurements. Was not as easy as written here and not as nice as injection but does preform better than it started out with. 

Edited August 13 by 47 1.5 ton

[JBNeal]

On 8/11/2024 at 12:06 PM, GTfastbacker said:

With buying the D19 Business Coupe (with a P18 engine) we got a double carburetor intake with linkage and cast split exhaust manifolds.

 

Wondering how much is the effect installing this components?

The engine is stock.

 

What carburetors are the best choice for this application?

 

Will the auto choke working with double carbs?

 

Makes it sense to do this without changing the head or milling it off?

 

Many questions…

 

Thank you

Joe

FWIW, larger Dodge Trucks had the dual carb + spit exhaust setup from the factory, and the carb.balancing procedure was detailed in certain shop manuals...this setup had manual choke...this setup squeezed as much power as possible out of the big flatheads so they could pull loads up grades, not for drag racing...later production flatheads had a 2bbl carb with a CR approaching 9:1 without changing engine internals, so head thickness changed to boost power.

[Semmerling]

 

 

 

 

 

You have already gotten some good advice.  There is a good deal more to read here, though getting to it takes way too much work. 

 

My opinion...on your questions...

 

Wondering how much is the effect installing this components?

The engine is stock.

 

A disciplined built out of the intake and the exhaust will have significant enough results that you will not want to run without it ever again. 80% of that will be simply improving the exhaust flow and the other 20% is all intake improvements. Know this, I figure about 25% of the people that own the intakes actually end up setting them up. Like whomever you bought your truck from, they own these speed parts but do not put them on. Why? Some don't actually finish anything, others  don't stop working on upgrades until they work well, most seem to never actually start. 

 

What carburetors are the best choice for this application?
 

Just about anything other than a Chrysler B&B (designed by the son of the founder of B&B and build by Carter) they are NOT a Carter design as Carter would never design a carb like these. Though rarely talked about, they are perhaps the worst carb of the period as per a man with 50 years of being one of the leading carb experts in the country. The reason why is complicated but is a combination of spring loaded accelerator pumps, a larger #3 flange footprint that is less efficient as compared to any of the #2 carbs, and a nasty pre-load at idle, and a host of other issues. Can you make them work? Yes you can. Are these Chrysler B&Bs used as dual with Dodge? Yes, limited models and briefly, the vast were used on stationary motors in agriculture and industry. Can you get them to perform, yes but you can do better. But regardless of which you use, they must be completely rebuilt and completely identical. If they are, with maybe a thousandth drill out of the idle tubes, they will work very well. Sniper is exactly correct about adjustments past idle speed and mix. And the air cleaner thing is a complete non issue if they are identical and free flowing filters. The linkage, a proper linkage, has to be able to adjust BOTH carbs on-board throttle actuators for high rpm matching.  Regardless, the Chrysler B&B's will not deliver much fuel economy in dual set-ups. Try dual Stromberg carbs if you have access. I am currently setting up a pair of EX-22s one '34 and the other is a '34 base with a '35 lower to get the vacuum tap. I expect them to outperform the ones you see below. That will require quite a bit more work, from the flange difference, throttle actuator and linkage required, etc. etc. etc.  As mentioned, nothing is going to come close to injection and mapping, but  one has to use oxygen sensors and a whole lot more....not on these blocks for me.

 

Cast header = using an electric fuel pump. Way way too close to the stock manual pump. I wanted to use my manual pump safely so I passed on the Fenton cast copies and went with real headers. 

 

Will the auto choke working with double carbs?

 

On duals, one only needs to choke one of the carbs. I have only had a manual choke model so I can't answer the auto question. 

 

Makes it sense to do this without changing the head or milling it off?

 

Not really sure any of it makes sense. I didn't do it to make sense. You can improve the performance of your engine and you can even enjoy the process but unless you start with the cam, performance is all at the margin. Start better? Yep. Run better, yep. Accelerate up hills, yep. All that is possible without changing you heads.....but it all all helps. Exhaust?...BIG.  Dual carbs? With the right duals you might get 15% more efficiency on a Long drive in high gear. Speed Demon? Nope. My head has been milled. 

 

 

Edited August 15 by Semmerling

[Semmerling]

 

GT, we all would like to know what the duel intake and exhaust system you have are. Please do let us know. 

 

 

Edited August 17 by Semmerling

[Bob Riding]

I ran dual B&Bs for years in my P10 wagon- I also used a dual exhaust from George Asche. Only choked one carb. It ran well, but rich.

I tried balancing it with the synchronizer, and got it close but it always seemed to want to run too rich.  I ended up switching to Tom Langdon's EMPI Weber 32/36 clone, which I am very happy with. It's a 2 barrel and pairs nicely with the dual exhaust. I switched to a later model air cleaner, which Tom cut out to fit the EMPI, and I modified to accept dry filter air cleaners. 

[Sniper]

10 minutes ago, Bob Riding said:

Only choked one carb. It ran well, but rich.

 

That's because you need to rejet when you go from one carb (designed to feed the engine) to two carbs (both designed to feed the engine by themselves).

 

11 minutes ago, Bob Riding said:

I tried balancing it with the synchronizer, and got it close but it always seemed to want to run too rich.

 

Synchronizing the carbs has nothing to do with the AF ratio, just equalizing airflow through the carbs.

 

11 minutes ago, Bob Riding said:

I ended up switching to Tom Langdon's EMPI Weber 32/36 clone, which I am very happy with. It's a 2 barrel and pairs nicely with the dual exhaust.

 

Well, one carb, properly jetted, will work better than two carbs way off on the jetting.  Going back to a single B&B would have probably made the same difference.

 

Now the question really is, where do you get jets and other such tuning parts for a B&B.

[greg g]

May be off base here but when you add a carb, you effectively half the flow of air through each carb which halves the amount of fuel  that is pulled from the jets so I would think that slightly larger jets would richen the mix.  But then the argument might be that the flow from the carb through the manifold is more efficient, so slightly leaner can be used.

 

I got mine from George Ashe.  I just put them on with inch thick phenolic spacers, synced them up with one of those uniflow gauges, adjusted the idle speed and let them be, except for lowering the float levels a bit, That was in 2005.  When I put the rebuilt 56 230 engine in the intake/carbs went over as ther were on the218.

 

Any difference?   My seat of pants dyno says yes, considerably more power,ease of climbing hills, slightly improved gas mileage 19 instead of 17.  But that may be down to the 230 which had 125 hp over the 218's 97.