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4 Barrel Carb Selection and Tuning


55PackardGuy
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This is a carryover from (believe it or not) the PT Boat thread. The discussion about Holley carbs being chosen for the Packard PT Boat engines kind of took on a life of its own from there.

Here's part of the last post from that thread, and I hope a suitable starting point for this new thread:

Since the later Packard V8s had both Rochester and Carter carbs, I think there is room for quite a bit of discussion about carburetor choices and tuning, especially 4-barrel carbs on Packard V8 engines and perhaps on earlier Packard straight eight engines.

Maybe some kind of cross-references can be created between Packard 4-barrel manifolds and available carburetors of today, instead of the usual vague comments like, "Well I modified the manifold this way and put on a Edelbrock and an XYZ spacer and it works pretty good."

Carbs can make or break mileage and driveability, yet even jet size and tuning of stock carbs on V8 Packards (or other models), seems to have had little discussion, and practical information on retrofitting available new carbs and manifolds is hard, if not impossible, to find.

So, are there any theoretical or off-the-shelf product insights here? Or any real-world experiences that have helped keep Packards performing at their best?

Or some folks might have experience with swapping between stock Carter and Rochester 4-barrel carburetors on Packards, and seen some gains or losses in performance.

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I haven't tried every Packard manifold, and every available carburetor; but based on the demise of Packard prior to flange design changes in four barrel carbs about 1960, I would seriously doubt that any off-the-shelf new carb available today will bolt onto an original Packard 4 barrel manifold without modifications or an adapter.

There are some currently available Zenith single barrel carbs that will bolt directly onto Packard 6 manifolds and work exceptionally well.

Jon.

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Wasn't there a thread on one of the forum -here or pinfo- regarding some Edelbrock carbs being a direct bolt on -- albeit with some modifications to the linkage and choke? Not sure if those are a copy of an earlier carb but if so, perhaps that is why they would bolt on. Some posters gave them good marks as a modern replacement.

Edited by HH56 (see edit history)
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A little more time to type.

The Packard manifold up through and including 1954 was the original "square" 4-barrel bolt pattern, which is actually 3 3/4 x 3 7/8 inches. This bolt pattern has not been produced since Holley obsoleted the model 2140-G used on I.H.C. trucks through the mid-1970's.

In 1955, Packard went to the early "Carter" rectangular bolt pattern, which is 4 1/4 x 5 5/8 inches. MOST (certainly not all) Carter AFB carbs from 1957 up have this bolt pattern. A few have the wider "Holley" pattern. A few have dual Carter/Holley patterns. Thus it is conceivable that most O.E. and A/M Carter AFB's (and the later clones) would bolt to the latest Packard manifold.

However, the standard throttle bore spacing changed in 1961. The centerline of the throttle bores was widened by 1/4 inch, thus even the smallest Carter AFB's made after 1960 would have the throttle plates hitting the intake unless:

(A) an adapter were used (this could be a very thick gasket that sealed both intake and carb)

(B) machine wider bores in the intake manifold.

The Packard carbs were approximately 450 CFM, thus even if an adapter were constructed such that the throttle plates did not hit, the manifold (without modification) would be a "bottleneck" thus effecting the air velocity in the carburetor and upsetting the calibrations.

We have replaced a number of Packard carbs with the Carter 400 CFM AFB (numbers 9400s and 9410s); but even these, the smallest AFB's produced, required an adapter so the throttle plates would not hit, as they were produced from about 1970~1981. This size was discontined about 1981 due to lack of sales.

Even should the manifold be modified so one of the larger AFB's would clear, one would run into calibration difficulties with current A/M clones, as the attack angle of the auxiliary airvalve is designed for high RPM, low torque engines. We have numerous would be customers who have bought these things for their Pontiac, Olds, Caddy, Buick, Ford, Chrysler, etc., etc., etc.; that cannot eliminate the secondary bog caused by the airvalve whipping open too soon, and then call us asking us how they should modify the incorrect carb they bought elsewhere so it will work. Of course, if one simply drives the car onto a trailer, or at low speed to the local drive-in cruise-in; then the secondary bog is not an issue.

Personally (and professionally) I would highly recommend the use of the original carburetors unless one is building a retro-racing Packard.

Jon.

Edited by carbking (see edit history)
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A little more time to type.

We have numerous would be customers who have bought these things for their Pontiac, Olds, Caddy, Buick, Ford, Chrysler, etc., etc., etc.; that cannot eliminate the secondary bog caused by the airvalve whipping open too soon, and then call us asking us how they should modify the incorrect carb they bought elsewhere so it will work. Of course, if one simply drives the car onto a trailer, or at low speed to the local drive-in cruise-in; then the secondary bog is not an issue.

Personally (and professionally) I would highly recommend the use of the original carburetors unless one is building a retro-racing Packard.

Jon.

A couple of questions for the knowledgeable sir:

Did the ubiquitous small-block Chevy of early vintage use the same pre-1960 bores? And, if so, why hasn't there been a re-bop of this?

Regarding the "bog" thing. Does the AFB carb have mechanical secondaries or vacuum? If vacuum, is it possible to just put in a stronger spring on the diaphragm so the secondary opens slower? If mechanical, the driver should be able to make some adjustments in how fast he puts his foot in it.

Finally, how were the mid-fifties Ford V8 manifolds that used the Holley set up? Any crossover possibilities there?

These are all pretty naive questions, I know, but just wondering what's been done?

Could you suggest any tuning mods in the original Packard Carter and Rochester carbs, particularly for mileage and driveability? One thing I remember about the Rochesters on all 3 Packard V8s we had is that they tended to flood pretty easily in cold weather. (Of course, that's a pretty common carburetor ailment and depends a lot on the driver's knowledge.)

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Secondary actuation . . . the AFBs that were OEM for Chevy had an air valve with counterweights that were "mid-throttle bore" over the actual secondary throttle plates. If the bottom throttle plates were wide open, the mid-bore throttle plates modulated how much air went in and when. It was common for racers to file the counterweights (removing weight) for quicker openning. Remember, too, that the biggest Chevy V-8 in this timeframe was the 327 and later the 348.

Chrysler had AFBs, too, but some of the later ones had full manual secondaries with NO counterweigted "air valve" above them. My '67 Newport 383 4bbl is that way. It was the small pattern and about 500cfm. From idle, there was no bog with WOT, but after I cleaned and smoothed the venturis and throttle bores, then I got a very slight bog. It also had the small air cleaner "circle".

All things considered, unless somebody is just bent on having a 4bbl on their Packard V-8, it might be better to make an adapter plate and put a larger 2bbl on it. I'm thinking about the 1.69" throttle bore Rochester 2bbls that were on Chevy 350s in the early-to-mid 1970s. These 350 2bbls would run pretty much right along with the similar 350 QJets below about 4000rpm, from observations. Seems like some of the later 1950s Pontiacs first used that same size Rochester? Maybe even some of the Ford-spec Holley 2bbls?

Considering the "state of the art" in intake manifold, camshaft, and exhaust manifold design back then, using anything over a 500cfm carb on a stock engine is "too much", I suspect. Other than the 4bbl "kickdown feel", the larger cfm 2bbls might be easier to do on a Packard 4bbl intake and run just as well? Perhaps even a well-hidden incognito electronic TBI upgrade?

The mid-50s Ford Holleys were a completely different carb than the Ford-spec Holleys from 1958 onward (the common 4160 family).

Just some thoughts,

NTX5467

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A couple of questions for the knowledgeable sir:

Did the ubiquitous small-block Chevy of early vintage use the same pre-1960 bores? And, if so, why hasn't there been a re-bop of this?

Regarding the "bog" thing. Does the AFB carb have mechanical secondaries or vacuum? If vacuum, is it possible to just put in a stronger spring on the diaphragm so the secondary opens slower? If mechanical, the driver should be able to make some adjustments in how fast he puts his foot in it.

Finally, how were the mid-fifties Ford V8 manifolds that used the Holley set up? Any crossover possibilities there?

These are all pretty naive questions, I know, but just wondering what's been done?

Could you suggest any tuning mods in the original Packard Carter and Rochester carbs, particularly for mileage and driveability? One thing I remember about the Rochesters on all 3 Packard V8s we had is that they tended to flood pretty easily in cold weather. (Of course, that's a pretty common carburetor ailment and depends a lot on the driver's knowledge.)

Question 1 - there are plenty of A/M manifolds for SBC's.

Question 2 - other than a very few diaphragm AFB's made in the late 50's for Ford and Chrysler ala Holley, that didn't work well, Carter used weighted airvalves with an eccentric shaft. After a couple of years, Carter refused to build the diaphragm secondary carbs. You adjust the weighted airvalves by replacing them with an airvalve designed for the application in question. Some tuners hate them, but they NEVER go out of tune due to a fatigued spring, or ruptured diaphragm. Very reliable design.

I don't understand the Ford crossover question, so no answer.

As to the Rochester flooding, this is the first I have ever heard of this issue. Cold weather starting, as you mentioned, does depend a lot on driver skill. I can remember the late 1950's in northern Minnesota when my Dad used to open the hood, and put a trouble light on top of the engine, and another one up against the oil pan all night. With warm oil, he had no starting, or flooding issues.

The biggest "knock" I have previously heard on both the Carter WCFB and the Rochester 4-Jet was stalling on hard left corners. This was a design issue. A factory service bulletin was issued on both, and those who went to the selling dealer received the fix (which consisted on a sleeve inserted in a vacuum passage). When synthetic oil became available, our starting issues totally disappeared along with the need for the trouble lights, although I must admit northern Missouri does not get as cold as northern Minnesota.

As to the question on tuning mods; it is well known that most carburetor issues are really ignition related. But yes, someone who understands carburetors and their function can tune them. Case in point, our shop truck is a 1968 Ford F-100 with a 390, about as aerodynamic as a boxcar. Yet, with TWO AFB Carters that HAVE been heavily modified, the truck obtains 18 MPG at 70 MPH on E-10, and 22 MPG at 70 on genuine gasoline (or it did when one could still buy genuine gasoline at the pump in Missouri). Both the Rochesters and the Carter WCFB's are quite tunable; if one has access to the necessary machines for making the parts. You can understand the reluctance of the A/M industry in mass producing tuning parts for these carbs. We make ours in our own shop.

And we have "fixed" a lot of starting issues on restored older cars by scraping some of the restorers paint from an engine block under a bolt, and running a new ground cable.

Jon.

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Question 1 - there are plenty of A/M manifolds for SBC's.

I don't understand the Ford crossover question, so no answer.

I can remember the late 1950's in northern Minnesota when my Dad used to open the hood, and put a trouble light on top of the engine, and another one up against the oil pan all night. With warm oil, he had no starting, or flooding issues.

Jon.

My question about the Ford manifolds is cleared up some based on your answer to the first question. It's apparently easier or more profitable to engineer replacement manifolds for older SBC's to accommodate newer carburetors than making carbs to fit the old bore designs.

Obviously the lack of volume of Packard V8 production compared with SBC's, for example, precluded any manifold manufacturers designing one for Packards that would accept newer carb bore spacing. Thus, my question about "crossover" manifolds that could be scrounged off of different engines.

Intake manifolds seem to be kind of purpose built, designed for specific engine intake port size, spacing, bolt patterns, etc. with little standardization or interchangeability.

Re: Minnesota winters-- these were exactly the conditions I was talking about! Although my experience is from central Minnesota. Never used light bulb warmers on the Packards, but did use brooder lamps overnight once on the crawler tractor engine (Int'l Harvester diesel 6 that started on gas) when it snowed about 4 feet and the temp dropped below -30.

Re: "Tuning" carbs. One kit available for the Holley on my '84 302 was a lighter spring on the diaphragm, which even I could put in without much trouble. Opened faster, no bog, better acceleration.

One other "bolt-on" kind of tuning that you didn't mention was replaceable jets. These are pretty difficult "cut-and-try" work for the amateur, but some input on how you have tweaked jets under various conditions, mainly for better mileage, would be of great interest.

Was the dual 4bbl manifold on your 390 out of a Thunderbird? I know they had a very rare 3 x 2bbl in the early 60's "bullet Birds" but never heard of a dual quad 390 before. Sounds like it worked out well.

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Guy - we spent one year in Babbitt.

Give me a call sometime, and will be happy to discuss tuning techniques. 573-392-7378 (9-4 Mon-Wed central time).

The dual quad 390 manifold is an Offy A/M. I took two Carter 4759s (625 CFM comp series) bodies; and inserted the internals from a pair of Lincoln 430 carbs.

Someone is currently producing 4 barrel intakes for some of the Lincoln 12's. If there were sufficient demand, a manifold could certainly be produced for the Packard.

Carter used to offer tuning kits for the WCFB's. They were discontined in the early 1970's due to lack of sales.

Like I said, give me a call, if you wish.

Jon.

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Just one more question on the 390 dual quad manifold. Did Offenhauser actually make a dual quad manifold that FIT the 390, or did you have to modify it? And, if it was made for the 390, perhaps it was a racing modification that Ford bought from Offy for open wheel cars?

Offy made it for the Ford engine. No modification necessary.

Jon

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In the middle 1960s, there were 2x4bbl intakes for the Ford 427s, factory, which would also fit the 390s. Seems like Edelbrock also had one back then, too?

The 3x2bbl Ford FE engine intake was the standard intake manifold on the Ford 406 V-8, but also used on the limited number of BulletBirds. Seems like MOTOR TREND tested a '62 T-bird roadster with the 390 3x2bbl setup (complete with wire wheels, too!)? Not sure if the 390 and 406 carbs had the same numbers, but the Holley Variable Spec Manual should detail that. The beauty of the Ford FE engine series was that they all had the same deck height, so all of the intakes would interchange, from 332 to 428.

Just some thoughts,

NTX5467

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In the middle 1960s, there were 2x4bbl intakes for the Ford 427s, factory, which would also fit the 390s. The beauty of the Ford FE engine series was that they all had the same deck height, so all of the intakes would interchange, from 332 to 428.

Just some thoughts,

NTX5467

Now that's what I'm talkin' 'bout! Where are those interchanges between different engines by the same manufacturer, or between these and other manufacturers? This whole carb/intake thing seems to have been done in the skunkworks mostly.

Note on T-Bird V8s: the '60 (Last of the "Box Birds") was available with the Lincoln 430. I guess so you could plow the back 40 with it then shine it up, drive it on the weekends. The '58 through '60 all looked like tractors to me, yet they were far and away the better sellers compared with the '61-'63.

Never heard of the 406. Truck engine?

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This thread is mostly about single 4-bbl setups, but it would be helpful for some to know if there really were any horsepower gain with the dual quad Caribbean setup (as Packard seems to claim) or was this more "show" than "go." Also, I believe identical 352 ci engines with the Rochester claimed some hp advantage over the Carter equipped engine. Marketing?

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but it would be helpful for some to know if there really were any horsepower gain with the dual quad Caribbean setup (as Packard seems to claim) or was this more "show" than "go."
Yes, the horsepower gain is real, but few Caribbean owners then or now ever used the high-RPM horsepower.
Also, I believe identical 352 ci engines with the Rochester claimed some hp advantage over the Carter equipped engine. Marketing?
I don't recall this. Usually, whether Carter/Rochester or Autolite/Delco, like displacement and compression engines had the same horsepower ratings. Can you cite some source for the claim?

jack vines

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Yes, the horsepower gain is real, but few Caribbean owners then or now ever used the high-RPM horsepower.

I don't recall this. Usually, whether Carter/Rochester or Autolite/Delco, like displacement and compression engines had the same horsepower ratings. Can you cite some source for the claim?

jack vines

Jack,

I am going mostly by recollection, so I checked one source that might bear this out. Carnut is fairly accurate and their figures for '55 400 and the '55 Clipper Custom/Constellation, fit my recollection of the differing horsepower figures for the two. I believe that the standard carb on the Clippers was the Carter, and on the 400 was the Rochester. Other than that, cid and compression were identical, so I'm thinkin' they advertised a bit of extra HP (real or not-- manufacturers are notorious for underrating HP on identical engines in cheaper models, or even outright lying about higher HP in more expensive ones--what they call "advertised horsepower" these days)

Here are the figures I found at the Carnut site:

1955 Clipper Constellation/Custom, 245 HP @ 4600 rpm

1955 Packard 400, 260 HP @ 4600 rpm

Torque was rated identical: 355 @ 2400

15 horsepower bequeathed unto the 400 by the Packard gods? Or was there really a difference?

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WCFB:

Someone correct me if i am wrong but IIRC HOT air heated from exhaust gases is drawn (continuously) THRU the rite side INTERNAL casting wall of the WCFB by engine vacuum. It is a kind of controled CONSTANT vacuum leak to operate the automatic choke.. THis causes the carb to heat excessively to the extent of causing the ethanol to boil.

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  • 3 weeks later...
The 1955 Clipper Customs came with single exhaust and the Packard had dual exhaust systems. This, I believe is the difference in h.p. ratings between the two with the same engine. Later, I believe, dual exhaust systems were available for the Customs.

(o[]o)

This is possible, but it doesn't quite hold up to the figures that Packard printed up. They do not distinguish between dual exhaust and single exhaust in '55, for instance, but all are given the same HP rating. True, all the seniors came with dual exhaust, so maybe a generalization could be made.

However, another reason to question the figures presents itself: I do believe HP ratings in those days were Gross, rather than Net HP, and measured without accessories or exhaust systems attached.

Here are complete figures--

Packard Motor Car Information - Packard Literature and Manuals - Packard Engine Serial Number Reference

Click on the blue link: Packard Engine Serial Number Reference to get the whole lineup for 55 and 56.

Check out the 55 Custom, Constellation, vs the seniors. Both Custom and Constellation were available with dual exhaust. Where is that extra HP coming from?

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