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My usual recommendation usually includes a dual plane intake manifold, which you already have. The manifold’s plenum divider should not be cut down. The goal is to broaden the time between pulses in the intake system thus improving mid-range power over a wide range of engine speed. There is quite a bit of horsepower to be gained by blocking the manifold’s exhaust heat passage, but this is not recommended for folks living in colder climates.

Select a carburetor having annular booster venturis, having vacuum secondaries, having an electric choke, and calibrated for "street performance". Or better yet, calibrated for your particular application by a carburetor tuner business.

In terms of size, some owners opt for a 600 to 650 cfm carburetor. Carburetors of that size will fit on an unmodified 1970/1971 iron intake manifold (D0AE-L casting number). The 351C 4V engine of 1970/1971 was equipped with a 630 cfm Autolite carburetor (model 4300A). The “smaller” carburetor is probably the best choice for a single plane Edelbrock Torker intake manifold as well. I mention this because the Torker has been a surprisingly common choice for an intake manifold. Check out these 600/650 cfm carburetors:

600 cfm, vacuum secondary, low budget: Summit Racing #M08600VS
650 cfm, vacuum secondary, better budget: Demon Carburetors #1282020VE
650 cfm, mechanical secondary: Quick Fuel Technologies #SS-650-AN

However, in terms of selecting a carburetor for a dual plane manifold with a full height plenum divider a smaller carburetor offers no better low rpm performance than a properly calibrated carburetor of larger capacity. If the engine is equipped with a dual plane manifold (full height plenum divider) its performance at higher rpm will be impacted by a 600/650 cfm carburetor. Therefore if you want the Cleveland to perform as it is capable of performing, over a wide power band encompassing idle to 7000 rpm, and to produce maximum power at 6000 rpm, then opt for a 750 cfm version. The 351 Cobra Jet engine (Q code) was equipped with a 750 cfm Motorcraft carburetor (model 4300D).

A 750cfm carburetor has 1-11/16" throttle blades and 1-3/8" venturi throats. Carburetor jetting should be approximately #68 to #70 primary jets, and approximately #80 secondary jets. There are very few choices if you limit the selection to those having annular booster venturis, an "electric choke mechanism", and "vacuum secondaries". Check out these vacuum secondary 750 cfm carburetors:

750 cfm, low budget: Summit Racing #M08750VS
750 cfm, better budget: Demon Carburetors #1402020VE

If your preference is a mechanical secondary (aka double pumper) carburetor, check out these 750 cfm versions:

Quick Fuel Technologies #SS-750-AN
Holley #9379
Demon Carburetors #1402020

The Holley and Demon mechanical secondary carburetors do not come with electric chokes, but an electric choke can be added to either of them.
Last edited by George P
Are vacuum secondary carbs typically not equipped with a secondary accelerator pump, in if not, why not?

Just thinking out loud here, but a vacuum Secondary carb would have to open the secondary when LOW vacuum is achieved (like the power valve).... right?

So the engine vacuum is actually holding the secondaries closed.... do they flop open when the engine is not running?

Hmmmm....

I am just curious.

I know this is a little off topic, but it can be related to your post above to help someone understand the advantage/disadvantage of mechanical vs. vacuum secondaries....
Last edited by rocky
Vacuum secondaries are closed when the primary throttle blades close by a link from the primary throttle shafts to the secondary throttle shaft.

Vacuum secondaries open not from manifold vacuum but rather the vacuum created in the primary venturies as the air speed through them increases, thus the higher the primary airflow the more the secondaries open.

Vacuum secondaries have no accel pump as they open slowly and in a controlled fashion that does not lower manifold vacuum as they open, this negates the need for fuel enrichment from a acceleration pump as a stable manifold vacuum will prevent fuel from dropping out of suspension.
Re 750 vac-sec Holleys: the old rule of thumb was, a #3350 (750) just bolted on in place of a vac-sec 600 would gain you about 20 bhp and lose you about 3 mpg while softening the throttle response. Re-jetting would gain back some but not all the mileage lost and a little of the response you lost going bigger. In an autocross, you'd set a better time with the 600.

Re having a carb-tuner work on a bigger carb prior to trying it: the tuner I use in N Reno makes 19 separate changes to the carb out-of-the-box, not just jet changes. That's why the cost of the carb doubles.
If I ever saw and engine that could use a dual Holley 4v set up it is the Cleveland.

The engine loves a 600 cfm on the bottom end and it can use the huge breathing with a progressive kick in that dual 600 vacuum seconday carbs provide.

I have that set up on my 68 GT350 with it's stock looking 302 but with it's 347 innards.

The thing screams and gives 600 Holley mileage at around 18.

The only way you could do this now is with a Wieand tunnel ram and 1" open spacers under each carb, like what Marlin Jack has done, since there is no dual 4 manifold ever made for production. Only a few for Ford internal experimentation.

You will get some of the throttle progression with it, but not all of it and you will loose the fuel mileage benefit of running on just one Holley 600 (list 1850) carb.

A 650 vacuum secondary Holley is probably the best compromise although I hate to tell you to experiment but a 600 double pumper Holley surely is very responsive on this engine.
quote:
Originally posted by Cuvee:
What about a older Holley 735? I believe they came on 1968-1969 Big block Fords. I had one on my Car for years with no problems. Maybe George or Bosswrench could comment more about this Carb.?


It will work but that has become a very expensive and valuable carb because of what it goes on.

A generic 3310 is really the same carb without the numbers, but as Bosswrech has said, it tends to be "sluggish" on this engine.

I also think he is right, that a carb that will crispen the car for something like autocross will make the car more responsive on the street.

That's really an 1850 variant, 600 cfm vacuum secondary.

This isn't something new at all since if you look at the original factory "spread bore" design with the small primaries and huge secondaries, that was already something that needed fixing.
Buying an unrestored old Holley will put you solidly into a long, miserable rebuild project, full of throttle shafts that wore the carb body egg-shaped and leak vacuum, shrivelled gaskets that leak fuel & air, bad acceleration pumps and blown power valves. Sure, they're all fixable but nice weather is for driving, not thrashing in the garage. Years ago, I took off an average running 600 Holley & set it on a shelf. 5 yrs later, I put it on another Pantera to debug a problem. Started the car and the old Holley immediately burst into flames.... Good luck.
Curt

Any of the "post 1967" Holley carburetors, designed for single four barrel applications, and sold over the counter by Ford were better than the Holley carbs available from Holley, out-of-the-box from a hot rod parts dealership. Any of them, and the 735 from the 428 CJ was only one of them. In fact, there were a bunch of carbs designed for the 428 CJ, not just one. But the 429 Boss, 302 Boss, and 429 SCJ also had carbs that were good on the street. They were all the same carb, the air flow ratings varied depending upon the type of boosters. Some boosters restricted air flow more than others. They were 4150s with vacuum secondaries, not 4160s. I do not like 4160 Holley carburetors and NEVER recommend them.

Of course your 735 carb performs better than an over-the-counter 3310! The 3310 is always the carb the 735 is being compared to. That's a "no contest" situation. There's no surprise there. The original 4150 version of the 3310 installed on the 396 Mark IV Chevy big block is the only version that has ever been worth a damn. All subsequent aftermarket version of the 3310 were 4160 models, and are known for the headaches they create. The aftermarket 3310 carburetors were conceived as a rip-off of the public based on the reputation of the original version ... they weren't close to the original version in terms of features, value, or calibration. Holley had no business using the 3310 number for the aftermarket versions.

The better performance of the Ford carburetors was due to how the low speed circuits were calibrated, and the amount of intake manifold vacuum they were designed to work with. Those "factory street carbs" had to meet emissions regulations. I normally purchased 1970 or 1971 429 SCJ carbs over the counter from Ford. They worked great and passed California emission testing. Whereas the Holley carbs available from hot rod parts dealers were jetted rich like pigs and had lousy low rpm performance.

However, the carbs I've recommended on the first page are better in many ways than those old 1968 - 1971 Ford carbs. If it weren't so, I wouldn't recommend them. Pay close attention to the "annular booster" part. Nobody seems to get it, it goes over everyone's head. It makes a tremendous difference. PLUS ... as my dear friend Jack alluded ... they are available new.
Last edited by George P
No agrguments to what George is saying at all. We all have had different experiences with these carbs and have had different applications with them.

In my experience I can't even see how any of them could have gotten through California emissions tail pipe testing.
We had that here in NYS for a while and it even got worse having to drive the car through a road course (on the emmissions dyno machine) so it wasn't even just idle cleanliness.
It had to be clean on HEAVY acceleration and you couldn't put enough fuel through it to keep up on the course to do it and if you couldn't keep up with the course, it would fail you.

I can't think of any of those 60s carbs that were clean enough to get through NYS testing here in the '70s even when they were box stock. Not one.

New York was using California numbers.

The only "Holley" clean enough for that would be the '85 Mustang GT, 4180. It will idle right around 14.6-14.7, has annular boosters but is so "clean" at idle that if you have coated steel tube headers will burn the coating right off of them.


One of the issues with the Pantera IN PARTICULAR as far as emissions, it fell under the under 5,000 units a year sold loophole as an "import".
That illiminated it from being REQUIRED to have an air pump for the exhaust system BUT it still was required to pass emissions. With those numbers it was required to be under I found that impossible to do WITHOUT an air pump.

As a matter of fact there were some cases where Ford bought back the car because it couldn't get through the emissions test clean enough to pass, but I digress.



Of the '60s carbs, the one that I can think of that was closest to a bolt on "stock" application that MIGHT have worked AS IS on a Pantera specifically would have been the '70 Boss 302 carb.
The '70 version had 78 secondaries instead of 82's on the '69 version which would probably be better with the Q stock camshaft and 5700 or so rpm limitations?

Difficult to say precisely because depending on the heads and the headers that you have on the Pantera, that factor changes enough.

That's probably a $3,000 carb now if you can find one. Why bother?

None of the Ford BB 428cj carbs are particularly well suited just to bolt on a stock Q and you have to consider the stock transmission gearing in a Pantera as well.

They are just OK, but nothing spectacular at all. Again, very expensive carbs now.



A Boss 302 Mustang with it's 2.32 first gear, 3.90 rear gears and solid lifter cam has enough differences to change calibration requirements of the carb in a hydraulic cammed, 2.20 first gear Pantera BUT similar car weight and head port configurations to the P car.

The Shelby 715 carb is another one could consider but you must realize that most of these original application carbs were intended initially for much larger cubic inch engines.

The Shelby carb was originally for the 427 medium riser single 4v application that was "re-calibrated" to put on a 289.

It, like the Boss 302 carb, were WAY to big to be great street carbs and were installed in order to qualify it as "original application rules" for the small number of those cars that would eventually be used in factory class racing.

As street carbs, they figuratively and literally sucked.

It isn't just changing the fuel jetting on them either, it is changing the idle a/f ratio by changing the "air jets" in the carbs which were never intended to be modified after they were built. That is one of the big features tuner carbs can now use. Those can be EASILY changed.



I agree on the annular boosters too. You want them. They make the carb so much more responsive and I wouldn't use anything but them, now on a Holley.



Agreed on the Holley "aftermarket 3310" as well. It is not the same carb as the original GM application BUT all of these "original application" carbs aren't worth the bother and expense now of seeking one out to use.

I knew the 3310 as the original Z28 Camaro carb.



A current "tuner" carb is a much better way to go and will save you a lot of wasted time in a "calibration" process, but it all depends on how involved you want to get into with this.

I think the only thing really to choose now is the size to go with and ultimately that comes down to what you have done to the stock Pantera engine and how you intend to use it, i.e., 600, 650, 700, 750 cfm carbs.


I can also personally verify that a Holley R-4779, 750cfm "double pumper", mechanical choke, mechanical secondaries flat out "RUNS" on a 351c the equivalent of a Boss 351 BUT, and it's a big BUT, the idle is so heavy it will smart your eyes. It's just A LITTLE BIT of a problem? Razzer


If you just want to impress people looking at the engine, buy George's SHELBY Dominator intake manifold and run the 750cfm Dominator on it.

It will run well enough.

You MIGHT just need to do JUST a LITTLE "tuning" of it though...maybe...but it WILL get you where you're going but even so, you will be pretty happy with just staring at it and not even needing to go anywhere?

It's really fast just looking at it.

Just a thought?
Last edited by panteradoug
No 351C manufactured from August 1969 through mid 1974 was ever equipped by Ford with a "smog pump" (Ford's actual name for the pump was a thermactor air pump). Not in Mustangs, Cougars, Torinos, Montegos or Rancheros. It was not "omitted" from the Pantera. The Cleveland's siblings, the 351M and 400, got pumps in 1975 when catalytic converters were installed in the exhaust system. The exhaust ports in the 2V Cleveland cylinder heads were modified to allow air injection at the exhaust ports beginning that year.

Back to the topic of replacement carburetors.
quote:
Originally posted by George P:
No 351C manufactured from August 1969 through mid 1974 was ever equipped by Ford with a "smog pump" (Ford's actual name for the pump was a thermactor air pump). Not in Mustangs, Cougars, Torinos, Montegos or Rancheros. It was not "omitted" from the Pantera. The Cleveland's siblings, the 351M and 400, got pumps in 1975 when catalytic converters were installed in the exhaust system. The exhaust ports in the 2V Cleveland cylinder heads were modified to allow air injection at the exhaust ports beginning that year.

Back to the topic of replacement carburetors.


The limit was 800 ppm. The engine without a pump would do as I recall around 880. I had a pair of iron manifolds with a brass port at the front of each that would hook to I think a 3/4" id hose, and I'd add a generic Ford air pump to the a/c pulley. It would bring it down to 775 or so, just enough to get it through.

It only had to run on the machine that way.

The carb had to get switched out to for a Holley 1848 which was easy to do.

The vacuum advance needed to get plugged and the advance set down to 5 or 6 degrees.

Wonderful days.

NY emissions were VERY tough then. That engine was not clean enough stock to get it through. Late '70s up to around 85.

My 302 was tough to clean up too. It needed air plus the cats.
quote:
Originally posted by George P:
Back to Topic


Sorry big guy. I just thought that the carb that you select could be significant on a street registered/driven car that still must pass emissions testing?

I do not know the current state of the California situation. If there is no more tailpipe sniffing done there it would be no longer be an issue and my comments on that can be safely disregarded (and totally consistent with my past post history anyway?)...but!

New York is strictly a safety inspection now until you get to the OBD-II EEC cars. Then the data must be downloaded into the state computer. Basically you just can't have a "check engine light" on.
Panterapatt, I installed the Summit 750 on my 80 F-250 with a 351W, some cam. I had bought that carb with the intention of trying it on this Pantera (hot 351W) but ended up going another route. I had to increase the jets a fair amount on the 750. The design is such that while that's easy enough, you would have to tweak the float levels each time you remove the top to change the jets. I still need to increase the secondaries a bit, but it's very close now. Some had said it's basically a plug-and-play carb, just not exactly my experience for whatever reason. I am also not a carb expert, but tuning it was a good learning experience for me. Those come with a DVD that helps.

I have also used the Edelbrock 600 on my first Pantera running a basically stock 71 4V closed chamber 351C. It ran very well (on an Edelbrock Performer 4V dual plane intake). Of course, you don't see the power of that build in street driving, but that's not the carb.

I have a Quickfuel 750an on a Performer like yours. I got it because of the an boosters but it's fairly rich even after tuning on a chassis dyno. I think someone on the forum recommend changing  jet sizes somewhere, which I need to do.

Have you thought about the Holley 700 modified by Larry Stock at Pantera Parts Connection? Its listed as having many Pantera specific changes. If I were to do it again I think I would've given it a try.

They discuss it about part way down the tech tips page.

http://www.panteraparts.com/techTips.php

panterapatt posted:

Thanks. What issues did you face with it

Two minor issues:

- Installed longer studs in intake manifold because of the thick base gasket that came with the carburetor. Without the thick gasket, the carburetor primary accelerator pump assembly hits the intake.  I also like the insulating properties of the gasket.

- Since carburetor now sat up higher (not much higher but higher nonetheless), I used a dropped air cleaner base so that everything sits below the engine grill as desired. That took a little work to make happen--I bought an air cleaner from Summit to get the dropped base (1 inch drop), but the way the base is constructed hit the carb secondary fuel line inlet.  A 1/2" air cleaner spacer raised the base enough to clear the carb, and, combined with my old air filter and cover, the whole operation sits below the engine grill. I actually ended up gaining a little clearance after all that.

Engine Grillx

Hope this helps with your decision-making process which ever way you decide to go.

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  • Engine Grillx

PPATT, after all the posts on this subject, I'll ask The Question: What kind of Pantera driving do you do, mostly? Hot-street, cruising around town, shows, autocross, some/a lot of open track, or ??? The carb you need to replace that leaky 45-yr-old 600 vac-sec will vary for each of the above choices. If you are a do-it-yerselfer, Pantera owner Michael Haas wrote a 91-pg self-help Holley tuning guide ("Tuning Made Easy") in 2012 that is easy to follow and gives good results. I recommend it; at the end, you WILL understand carburetors better. You will also smell of high-test for a week. If you are not a DIY guy, buy a tuner-carb of a size that agrees with how you drive, and phone (NOT e-mail) the seller for his invaluable advice before you order from him.

Option 3: why buy another carb -unless you want to keep a traditional (but not stock) look?  A Holley Sniper EFI is in fact a complicated DIY conversion (with on-line guidance), and while you will likely not increase power, your mileage AND driveability will increase. EFI prices are coming down to rival that of tuner-carbs, too. I also suggest you NOT buy used- either a tuner carb or any EFI conversion. The builder's advice is invaluable and it is included in the price. People who invariably buy cheap/used off E-Bay, then spend hours on the phone with a good-hearted expert (for no cash to support his l'il business) while trying to straighten out their low-buck 'solution', rubs me the wrong way. Good luck, whichever path you take.

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