Carburetor replacement - 361 2 bbl.

[BrianWindsor]

Just purchased a '65 Windsor convertible, 361 - 2 bbl. Now it needs to tolerate that ethanol crap, so if I stay to a 2 bbl, Holly makes a 500 CFM and 350 CFM. I would like the engine to produce it's best torque with limited interference, any thoughts on carbs? Small CFM for higher velocity or larger CFM because it's larger. Thanks....

 

[CBODY67]

Chase a 1.69" throttle bore Rochester 2bbl, which has the same mounting pad as your Chrysler's carb. It's "Chevy linkage" might require the Edelbrock adapter, as with an aftermarket 4bbl carb. The larger throttle bores will add cfm and probably run dang near as hard as a 600cfm 4bbl does, without the intake manifold change.

ANY Holley 2bbl will have its unique base plate bolt configuration. Think "Ford 2bbl", which will require an adapter to make it work. Best to get something that will bolt directly to the intake manifold. DO check the size of the existing holes in the manifold, though. IF your throttle linkage "pulls" the throttle open, rather than "pushes" it open, so much the better.

Issues with the "air cleaner mounting hole", too.

Just some thoughts,
CBODY67

 

[BrianWindsor]

Thanks for that info. I am not building a pavement pounder here, just need to improve it and I have a 3200# Streamline trailer to pull, so looking for all the torks it can make without getting too silly. I figure I may have to fab something for the air cleaner, not a problem. I figgered the 500 cfm Holly was way too much for this application.

 

[Gerald Morris]

Thanks for that info. I am not building a pavement pounder here, just need to improve it and I have a 3200# Streamline trailer to pull, so looking for all the torks it can make without getting too silly. I figure I may have to fab something for the air cleaner, not a problem. I figgered the 500 cfm Holly was way too much for this application.

500 cfm isn't TOO much for a 361, if jetted and linked properly for it. BUT, if you want to stick with a 2-bbl setup, the advice you've seen recently probably is the very best there is on that subject. Holley once made, during the 1970s, a small 4-bbl called the "Economiser" which had a capacity around 437 cfm if I recall correctly.

You can easily find an air cleaner to accommodate whatever you use. I too like building these B-block engines for high torque, low rev curves, as I drive our family ride, a '68 Newport around town with my wife and children in it. Thus I like closed quench heads, which your 361 will have. KEEP THOSE! I opted for an Edelbrock 1405 (600 cfm, manual choke) over 2 barrels finally because I HAD one, which, with minimal service, got put back into primo condition and which I currently enjoy. I would like to get a rod and spring kit for it someday, but noted that the current springs behave very nicely, so it may be a question of just using a thicker rod, to lean out the secondaries a little.....

Best Moparring 2 U!

 

[cbarge]

Canadian built Windsor convertibles are very rare.
Not many were built and even fewer are alive after 50+ years.

 

[Sixpactogo]

I have a Holley 2bbl that came on a 69 383 Newport. Should bolt right on to your 361. Put an updated kit in it for the dog piss ethanol.

 

[CBODY67]

I have a Holley 2bbl that came on a 69 383 Newport. Should bolt right on to your 361. Put an updated kit in it for the dog piss ethanol.

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Yes, the Holley 2210-family or 2bbls. Nice carburetors, but prone to the same throttle stud wing nut over-torque issues as Stromberg WWC3 2bbls before them, unfortunately. Not the same Holley 2300-family of 2bbls that Summit and Jegs sell, with the need for an adapter plate to bolt to a normal 2bbl intake.

CBODY67

 

[CBODY67]

The noted Holley Economiser 4bbl was rated at 450cfm, with the same primary throttle bore size as a normal spreadbore 4bbl (1.38" diameter). From the earlier 1980s when everybody was trying to get better fuel economy. I put one on my father's '69 Chevy pickup 350 as he drove it so easy the QJ's power piston would stick in the "eco" position. That Eco carb is a nice piece, just not a lot of airflow for even a normal 350 Chevy V-8. Might be just right for something in the 270CID range?

 

[Big_John]

Just purchased a '65 Windsor convertible, 361 - 2 bbl. Now it needs to tolerate that ethanol crap, so if I stay to a 2 bbl, Holly makes a 500 CFM and 350 CFM. I would like the engine to produce it's best torque with limited interference, any thoughts on carbs? Small CFM for higher velocity or larger CFM because it's larger. Thanks....

One thing to keep in mind when looking at CFM ratings, 2 bbl and 4 bbl carbs are rated differently.

4bbl carbs are rated using a 1.5 in/hg pressure drop and 2bbl carbs are rated using a 3.0 in/hg pressure drop. So, to compare the two, divide the 2bbl rating by 1.414 to get an approximate 4bbl rating and multiply the 4bbl rating by 1.414 to get an approximate 2bbl rating. Example: A 500CFM 2bbl carb is roughly the equivalent of a 354CFM 4bbl. The infamous 6-pack setup with 3 2bbl carbs (350CFM center and two 500CFM outboard carbs) is 1350CFM total, but an equivalent 4bbl is 955CFM.

I'm seeing that this isn't being addressed in this thread when comparing carbs.

 

[Toolmanmike]

Just purchased a '65 Windsor convertible, 361 - 2 bbl. Now it needs to tolerate that ethanol crap, so if I stay to a 2 bbl, Holly makes a 500 CFM and 350 CFM. I would like the engine to produce it's best torque with limited interference, any thoughts on carbs? Small CFM for higher velocity or larger CFM because it's larger. Thanks....

Either carb will work. I think the 390 would be a better fit for a 361. You will need an adapter to make it work. And then there's the choke, throttle and auto trans kickdown you will need to modify to make work correctly.

 

[CBODY67]

@Big_John is accurate in his comments. "CFM" is a unit of air flow, but the vacuum drop at which the reading is taken is different. Same reason that cyl head port airflow is at a particular vacuum drop.

I first ran across the car airflow ratings in a HP Books book on Holley Carburetors, circa 1974. First time I'd see the rating criteria mentioned anywhere. I suspected the reason for the different vacuum drops was so they could use the same air flow machine to rate both carburetor types. Just a suspicion.

CBODY67

 

[CBODY67]

The old towing criteria used to be to use a rear axle gear ratio that would put the engines rated torque peak at the legal speed you'd be towing at. Might be better to go ahead and put a ~600cfm 4bbl on it, a lower gear in the back, and enjoy the towing experience.

You CAN still keep things stock looking. Hide the elec choke wire in the existing wires along the front of the cowl, then the harness that runs down the rh valve cover going to the distributor. Buy a '68 Road Runner air cleaner, to get the needed air cleaner base plate to use with the existing air cleaner atop. Paint the intake manifold engine color. Unless somebody looks closely, it'll look "all stock".

With, say, a 625cfm AVS2, you'll have the smaller diameter primary side (as the existing 2bbl), but also have enough additional airflow for those 2nd gear pulls up hills, too.

Nothing against "big 2bbls", but for your purposes, a 4bbl setup might be the best alternative.

Enjoy!
CBODY67

 

[Big_John]

@Big_John is accurate in his comments. "CFM" is a unit of air flow, but the vacuum drop at which the reading is taken is different. Same reason that cyl head port airflow is at a particular vacuum drop.

I first ran across the car airflow ratings in a HP Books book on Holley Carburetors, circa 1974. First time I'd see the rating criteria mentioned anywhere. I suspected the reason for the different vacuum drops was so they could use the same air flow machine to rate both carburetor types. Just a suspicion.

CBODY67

IIRC, Holley determined that they couldn't reliably do that much pressure drop (3.0 in/hg) with a 4bbl carb.

In other words, the 2bbl sucked more than the 4bbl.

 

[Jakter]

Just purchased a '65 Windsor convertible, 361 - 2 bbl. Now it needs to tolerate that ethanol crap, .

Put an updated kit in it for the dog piss ethanol.

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I just use ethanol compliant parts where needed, buy gas whenever needed from the closest station when needed, in a state where all we have is ethanol gas and have driven 10's of thousands of miles between any of the old vehicles I've owned and maybe had one incident that might have been because ethanol in the gas.

Much ado about nothing.

 

[Gerald Morris]

The old towing criteria used to be to use a rear axle gear ratio that would put the engines rated torque peak at the legal speed you'd be towing at. Might be better to go ahead and put a ~600cfm 4bbl on it, a lower gear in the back, and enjoy the towing experience.

You CAN still keep things stock looking. Hide the elec choke wire in the existing wires along the front of the cowl, then the harness that runs down the rh valve cover going to the distributor. Buy a '68 Road Runner air cleaner, to get the needed air cleaner base plate to use with the existing air cleaner atop. Paint the intake manifold engine color. Unless somebody looks closely, it'll look "all stock".

With, say, a 625cfm AVS2, you'll have the smaller diameter primary side (as the existing 2bbl), but also have enough additional airflow for those 2nd gear pulls up hills, too.

Nothing against "big 2bbls", but for your purposes, a 4bbl setup might be the best alternative.

Enjoy!
CBODY67

This was precisely the rationale I arrived at when committing to 4 barrel carburetors, aside from relative availability of new carburetors.

Now, so folks can stop wondering about WHY the square root of 2 needs invocation when comparing 2 and 4 barrel carbs:

P1 + 1/2ρv1² = P2 + 1/2ρv2², with other factors such as (plenum depth) altitude and temperature all being equal. The velocity of the air/fuel mixture varies quadratically, while pressure is linear. Volumetric flow is a linear function of velocity (Cubic Furlongs per Millennium) with Furlongs/Millennium as the velocity component. Thus, if P2 is twice P1, then to keep things equal, a 2 pops into the simplified Bernoulli's equation given, then get's rooted, then approximated at 1.41421356237... or, if inverted as 0.707106781187.... Please pardon my crude approximations, but my Transcendental Slide-rule is worn.