Shelby 427 Carb

[1Trkpony]

I just bought an ERA with an aluminium 427 Shelby built/dyno'd engine. It don't have all the specs but it was built for the street with 10.5:1 compression and a hydraulic cam. It was dyno'd at 498HP. It has shelby AL MR heads and dual plane intake. It came with a Holley 3310 780 CFM vaccum secondary carb but the previous owner had trouble with it and had a mechanic replace it with a Edelbrock 750 CFM performer carb.

I woud like to put the 3310 back (along with its turkey pan). I was looking at going to the proform main body to get a little better throttle response and tweak/tune it while I am at it. I am looking for anyone who has a 3310 on their 427s and what their set up is. Also if you have done the Proform main body upgrade. If you could either post your settings or PM me I would appreciate it.

Lastly would I be better off dumping the 3310 and going to a demon or other mechanical secondary carb? Seems that a mechanical carb might work better but I am not sure.

Thanks

[DAVID GAGNARD]

While I do not have a big block engine,I have a 350 hp 351-W and have tried about six carbs in the last 10 years,here is what I have found........

started out with a Holley 600 vac. sec. carb,ran good gave good gas mileage and performance,then I wanted "a little more", so I tried a 715 cfm marine carb,vac. sec.,could not tell any difference,but it was an old carb and may have needed more tuning than I did to it at the time......

Tried a Holley 750 vac. sec.,car ran o-k,performance was not as good as the 600,tested both on the drag strip same day..........gas mileage was down also.......

Then a buddy gave me a "wore out" 20 year old Holley 600 double pumper,I rebuilt it myself,put it on my car and track tested it,a lot better performance on the bottom end and better all around......been on my car ever since......

Everyone told me my gas mileage would suffer going from a vac. sec. to a double pumper,well, I drive my car to work at least once every two or three weeks (250 to 350 miles per day),lost all of 1 mpg with the double pumper,granted if I keep my right foot in it,gas mileage will definetly go down,but if I drive the same I only lose about 1 mpg and the performance difference is VERY noticable as well as track proven on my car........was also told the double pumpers are "more finicky" for city driving than a vac. sec. carb,to me, I find NO difference in city driving and prefer the double pumper,cause if I need to step on it,the throttle responce is immediate.........

I do not care for the Edelbrock carbs mainly cause I can not work on them and can now take apart and rebuild a Holley with my eyes practically closed.......

Holley's formula for carb size vs. motor is this,multiply your engines cubic inches by the max rpms your enigne turns and then divide that number by 3456,this will give the cfm your engine needs at it's max rpms assuming your engine is 100% effecient.......

427 cu in x 6000 rpms divided by 3456 = 741.31 cfm assuming you max your engine out at 6000 rpms,I would think a 750 to be the minimum and an 850 to be about right, and I would go with a double pumper..........

Just my opinion on the subject and that and 75 cents might get you a cup of coffee in downtown Marksville,La., on saturday morning...

David

[Anthony]

I think for a car with a standard transmission, with a lot of shifting gears, especially with short time intervals between shifts, as the car accelerates well, you would be better off with mechanical secondaries.

The reason why holley double pumpers got bad gas mileage is I believe because they came standard with "richer" jetting than factory carbs, and therefore would get worse gas mileage with cruising, as the richer jetting was better for performance. Rejet them lean like factory carbs, and the fuel mileage will be the same.

A vacuum secondary carb has a slight delay in the secondaries opening. You can play with different vacuum springs, to the get the weakest spring that will not cause the motor to bog, but it still will not open as fast as a double pumper. Why I say this is that between every shift, if you let up on the throttle, both the carb primaries and secondaries close, and when you step back on the gas, the secondaries are again slightly delayed in opening. With an automatic transmission, you mash the throttle in first, and never lift up on the throttle between shifts, so to me, it doesn't matter as much in this case. But, if you're like me, and lift up on the throttle with every shift, I think you would be better with a double pumper.

One final thing, as you are using a dual plane intake, likely with a divided plenum, I would at least go with a 750cfm carb, if not higher, 780-850. If you run an open plenum intake, you could probably do fine with a 700-750 cfm.

[jared1970]

Check out Jet Performance. They custom build Holley carburetors of just about any size for individual applications. I had them make one of their stage 2 750's for my 428. I've only had it running on a starter stand at this point, so I can't tell yet how it will act on the street. Seems to run great on the stand. May not be what you're looking for, but you should check it out. My stage 2 750 with vacum secondaries and electric choke cost about $500.
Go to www.jetchip.com then click on fuel systems then click on carburetors. A page will come up with all the different models they work with.

[ted]

The 3310 and 3310-1 780 cfm carbs are good carbs providing they are mechanically sound to begin with and not worn out. The later model 3310's (3310-2 and up) have a different fuel discharge nozzle design and also work well but the 780 version has just worked better on my 427's. I actually tried three different carbs on my 427 HiRiser and they were all within 3 hundreths of each other in quarter mile racing. The carbs were the 3310 780, an 850 DP, and a 1050 Dominator which required an adapter. Changing the intake to one that had the Dominator carb flange welded in place of the original ran et's in the same time range as the three aforementioned carbs on a standard Holley flanged intake.

Just food for thought.