715 cfm Holley Carb

The carb on my car is dated 4B5. The guy I got the engineering sheet from made me promise I would not distribute it. I will check with him.

 

What yoke are you talking about? The race cars all used vacuum secondary’s. Double pumper carbs are better, but Holley didn't introduce them until the mid to late 1970's. I don't know if anyone modified the carbs for mechanical secondary’s as this opens up another can of worms. Most drivers were particularly sensitive to carb modifications. The relationship between the guy who worked on the carb and the driver was very important.

There was a special engineered carb for the 427 GT-40 that had the secondary’s cammed to open with the primaries and brass bushings in the throttle shafts. The accelerator pump nozzle was located right in the center and squired into all four barrels. This carb didn't have an air horn and was never a production item, no TV views or parts listing. A lot of the design features were later incorporated into the List 4224 drag racing carbs.

 

I think most of the racers removed the choke assembly, rules permitting. (Can't get away with this in NHRA Stock and Super Stock classes). My car spins right to 7000 with no problems. (non-stock camshaft and LOTS of head work)

 

Bo was right the R model used the larger 780 cfm carb like the 427 single four carb. The R model cam was referred to as the Le Mans solid lifter cam in the Ford literature.It was the next hotter solid lifter cam available from the factory hipo solid cam.I have seen the R model carbs with and without the manual choke.

 

Hi Jerry,
I wouldn't mess with the newly bought 715 Holley.
Test it first and make sure that you get it sync'ed
correctly for your engine.
Texas Swede

 

I am in agreement with BO. First off only a tiny fraction of 1% is even going to know it is supposed to have a 780cfm on a R model and 2 you couldn't tell that it wasn't unless you looked at the butterflys and or the numbers on the metering blocks which like the butterfly's are very harded to see. Of coarse the list number on the air horn is a give away but I don't think it's a issue.Your engine will probably run better if useing the smaller(715 is still over carburated for most 289's) carb.

 

Personal Experiences – For What They Are Worth
I have used the List-3259 and List-3259-1 carburetors of a variety of 1964-67 Shelby HP289 cars with great success from box stock engine to seriously modified engine. Set up properly you can cruise along at low rpm or roar to 8,500 rpm.
On SFM5S142 with an aggressive camshaft and highly worked O.E. cylinder heads the car was still accelerating at 8,500 rpm red line with a 3.50 rear gear (Calculated ground speed 163 mph with the particular tires in use. 8,500 rpm was my red line for valve train mass reasons.).
On a 1967 GT350 whose engine was stock O.E.M. specifications the engine ran just as smooth as any passenger car under any conditions.
I did a lot of testing on a couple of cars (SFM5S142 and CSX2310) over a few year period including open track events at the Hallet road course in Oklahoma. My major observations include:
1) All the popular performance improvement tips published in magazines, tricks and gadgets to make them mechanical secondaries for one example, made the cars slower. In fact doing anything that defeated or changed the Holley designed self regulating vacuum secondaries was counterproductive with some exceptions, see below.

2) In my area at my altitude (about 590 feet above sea level) the stock power valve, jetting, vacuum secondary opening rate, and float levels worked the best all around with some exceptions, see below.

3) Worn accelerator pump levers, worn accelerator pump cams, and or leaking accelerator pump check valves caused many of the problems people often complained about. If the accelerator pump circuit doesn’t work properly they must be corrected.
Exceptions
1) Vacuum secondary opening rate.
a. On a GT350 with engine modifications, gearing, and tire size to support it can be made a little faster.
b. On a Cobra can be made a little faster.

2) Float Levels – Using the float levels for a GT350 on a Cobra will lead to all kinds of engine running problems including; hard to start cold, hard to start to near impossible to start hot, sooty black rich stumble on hard cornering, engine stall on hard braking, fuel dripping to running out of booster venturi after the engine is stopped (may run and dribble out throttle shafts – especially if parked at any kind of angle to the horizon), and poor running on uphill or downhill grades. I labored over this a lot with CSX2310 until I noticed that the angle at which the engine sits in a Cobra is much different than what an engine in a GT350 sits. I made a scaled sketch of the carburetor internals and figured out what the difference in angle to the horizon is between the two chassis types. I used trigonometry to determine a base line set of float settings for my Cobra and went from there. I ended up with a great running car under all conditions from slow city traffic to flat out on a hilly bumpy road course. I left the carburetor alone and used it under all conditions without the smallest tweak between 1985 and 2007. Earlier this year the accelerator pump diaphragm started leaking so I did a gaskets only over haul and put it back on. I think they work just fine once you figure out float levels.