650 Double pumper vs 750 vacuum secondary

Rick, I have a 302, still I did change from a 750 dual pumper (4150) to a 650 vaccum sec (4160). The fumes of unburnt fuel is practically gone, my plugs used to foul (dark coulour). Now the cars is a little quieter and almost doesn't smell. The main drawback will be the passing (WOT) will be somewaht weaker than before.

Denis

If the 750 vacuum secondary in question is a list 3310, don't use it. They are a big head ache.

-G

No carb chosen at this time. Doin the research. May even lean toward a 670 avenger if you think it will flow enough. I have read many of your posts about clevelands needing larger cfm carbs, I am runnining a 70' or 71' iron dual plane intake. would the 770 avenger be too large?

No.

A 770 carburetor is not too large. The most important consideration is calibration. You want to use a carburetor that is calibrated well for your motor's state of tune.

However, the four holes in the iron oem intake are small, sized for a 600 cfm carburetor, and will need machining to allow clearance for the larger butterflies of the larger carburetor. But then the material between the heat passage surrounding the holes for the primary butterflies and the primary holes themselves becomes very thin. I altered a few iron manifolds in years past, and to do it properly I brazed the heat passages, had the carb pad milled flat and then had the holes enlarged. A lot of work to invest in an iron intake manifold.

If the motor is reasonably stock, one route to increase the carburetor size on an M code motor is to acquire the intake manifold from a '71 or '72 Q code motor and a rebuilt 4300D Autolite carb.

If you wanna use a Holley carb installation of an aftermarket intake manifold may be easier than having an iron manifold modified. The Blue Thunder manifold is a good choice, but the Edelbrock Performer manifold will work OK too and they are relatively inexpensive to acquire on eBay. The new Edelbrock RPM Air Gap manifold is another choice in a dual plane intake manifold.

-G

600-650 cfm is enough for that motor, unless you constantly ride above 5500 rpm. The formula for carb size is on this page, look in the paragraph: Size
TuningMadeEasy

I recommend the Summit carb. I have it on both my Pantera and my Longchamp. Best carbs I've ever had, super throttle response. And no fumes.

Your Post: 750 vacuum/ 3310 Holley is a big headache. Would appreciate if you could explain further. I thught it's was a good choise with a somewhat more radical cam, Edelbrock performer and headers, or are there other issues with that carburator?

The 3310 has been a poor choice when used "out of the box" since the 1960s. I'm sure a good Holley tuner can set one up to work, but as they come out of the box ... no way. Not with a 351C anyway. They will be too rich in the lower rpm range, throttle response will not be crisp, power will be down, drivability is poor and you'll normally find a stumble or hesitation somewhere in the power band too. The 3310 boosters are a poor choice, the power valve restrictions too big, other orifices & passages are likely the wrong size too, and since its a model 4160 it has a secondary metering plate which isn't tune-able.

I recommend a new Holley from the HP series, a tuner modified Holley, or one of the many Holleys Ford installed in the Boss 302, 428 Cobra Jet, 429 Cobra Jet (they were 700 to 780 cfm, too many part numbers to list).

As an example, the Boss 351 installed in the Australian Ford XY Falcon GT-HO Phase III was equipped with the same 780 Holley carburetor as a 1970 Boss 302, Ford #D0ZF-9510-Z. That is a 780 that works.

-G

Check this fellow out;
http://www.chucknuytten.com/
might be able to help! Mark

quote:

Originally posted by SICK CAT:
Check this fellow out;
http://www.chucknuytten.com/
might be able to help! Mark

I have a Chuck Nuytten carb on my car. I got tired of screwing with my 650DP and couldn't get it to run properly on my engine, which is far from stock. I sent Chuck a 5-page questionnaire filled out with all the specs of the engine.

He returned a carb that works like a charm.

I went to him after a recommendation from Chuck Engles, who dyno-tested a CN carb. Putting the actual car on a dyno with a qualified shop and swapping jets around based on A/F mixtures and dyno pulls, he was able to improve the CN carb by a whopping 1hp and 2ftp/tq (or 2hp and 1 ftp, I don't remember and it doesn't really matter).

Anyway, it impressed me that anyone could dial in a carb that closely without installing it and testing it.

You lose your choke, as he mills it off, and will completely rebuild and blueprint your carb even if it is brand new (as it was in my case). But I'm happy with the result

In carb swaps, it pays to go to a real expert- if you can afford the cost. A box-stock race carb will always be rich- the mfgr figures you won't blow up an engine going rich so his warranty costs drop. And with a street carb. you have no way of telling if it matches your cam, intake & exhaust, or is jetted for your area. My home in N. NV is at 4750 ft of altitude; L.A is essentially at zero. Denver is at 10,000 ft. So where should they jet a box-stock carb (many of which must meet emissions specs)?
The real fix is to go find a tuner that is intimate with the needs of a 351-C, and pay him. The result will be more power, a closer-to-optimum mixture for your area & driving style, with a host of little internal tweaks inside to do this, not just a jet swap. We all make noises about "mileage means nothing; power is all"- but it DOES. Its annoying to be on a run with your friends and you are the first one to start looking for a gas staion....
A tuner carb will add 50-100% of the cost to a mail-order carb and it will be worth it- and this is from someone who has remachined carbs: moved jets, bored out and recontoured venturis and replaced throttle plates with larger ones. The months you'll spend fooling with jets, secondary springs, metering rods, etc. with a cheaper box-stock carb could be spent driving your Pantera with pleasure.
FWIW, I'm very pleased with my $750 tuner-Holley double-pumper 700, extensively reworked by an expert. Power went up while mileage ALSO went up 2mpg, over a 600 vac-sec, a 650 double-pump and a 750 vac-sec. These last three are for sale cheap to anyone who wishes to prove this wrong.

I have heard many positive comments about the Holley HP carburetor series since their introduction. The whole reason Holley developed that line of carburetors was to compete with the carburetor tuners, and with Barry Grant. The HP carbs offer a viable choice to both.

The Holley list #0-82750 is a 750 CFM Four Barrel HP Carburetor, it is a Model 4150 with secondary metering blocks and center hung fuel bowls; it has Vacuum Secondaries; a "street" fuel/air calibration; Contoured Main Body; No Choke.

-G