What Holley CFM's For Mild 383?

[3yearcuda]

A friend of mine is building a 74 Dart Swinger with a 1969 383, Edelbrock performer, headers, 727, 8 1/4 (323's). Engine is stock but hopes for a mid radical cam, 30 over, maybe aluminum heads down the road.
He wants a Holley but is unsure of how big. Some have told him 750, some say 670 street avenger. What would you folks suggest for this stock 383 with lots of potential down the road. Thanks for your help.

 

[EL5DEMON340]

750 Dp

 

[69Dartconvt69]

I would go with a 750 single feed like the factory, no need for a DP at this point. If he upgrades later he will need a different carb, for example, you can't stuff an 850 Dominator on it now, in hopes of growing into it.

Think of an engine as an air compressor, the carb has to match the amount of air it can suck in and exhaust out. When an engine has more compression, and bigger valves it can use more CFM's from a carb. There is more to it when it comes to jets and such but that should give you the basic idea.

JB

 

[JoeDust451]

750 holley 3310, no need for a DPer on such a mild set-up.

 

[3yearcuda]

The 670 Street Avenger is what he has in mind. With improvements soon such as 30 over, cam, mild headwork, wouldnt a double pumper of some kind keep him from having to buy another carb soon?

 

[1968FormulaS340]

Holley 750 vacuum secondary would work now and later.

 

[C130 Chief]

A double pumper will make no more power, nor will it flow more air. It will use more fuel and may not be as smooth on the street (although a well trained right foot helps).

I'd put a 780 AVS or 750 vac secondary Holley on it myself.

Against the outside chance they might know something about carbs, why not call Holley and ask them?

 

[daredevil]

Borrowed this from the best carb guy i know,Damon at Fugly Racing.com. 4) Get the proper carb for your vehicle- undersized carbs, while great for response will be dead at the top end, run richer as a rule (excess velocity causes main circuits to come in wrong) and usually get worse mileage. Oversize carbs (especially vacuum / air secondary type) will have an untunable low end bog, lazy acceleration and nearly impossible idle problems. Somewhere in between is what we are looking for. A simple equation to get you close : ((Max rpm X CID) / 3456 )X V1. V1 is a variable representing the efficiency of your engine . Use .85 for a normal street engine, 1.00 for a fairly stout street engine ( we're talking close to strip car here) 1.2 for a highly modified strip only vehicle. (Yes< I know these are not the same numbers as some books show, but they work for these carbs) BE HONEST (you don't have to tell anybody) -along those lines do not use 7600 for the rpm on your hydraulic cam 8.5:1 street engine.

EXAMPLE: 440, hydraulic street , 5800 max rpm. ((5800 X 440)/3456) X .85 or ((2552000)/ 3456) X .85 or 738 X .85=627 or a 625

440, 620 lift mechanical, 6800 rpm max ((6800X440)/3456) X 1.00 or ((2992000)/3456) X1.00 or 865 X 1.00=865 or 800 (biggest) or 2 X 500

SEE how much difference it makes?

Typically, you can get away with 1 size bigger / smaller eg a 750 will probably be fine on you stock 440 ...but you say " CG said his likes a dominator"....does that mean it truly works in an optimum manner?? If you have a high stall converter, 4 speed , don't care about mileage/ drivability.... by all means put the biggest thing you can find on it....

 

[EL5DEMON340]

I've got to give myself a pat on the back, i've used DP carbs on everything for the last 25 years, even a 600 dp on a stock Cordoba 400cid that hauled a**. Just have to know how to tune squirter size and pump shot, not that hard.

 

[crackedback]

That VE computation is great, UNTIL, you actually go to a track and what should be the right size doesn't work as well as a larger carb.

If a stockish 340 runs better with a 750 vac sec Holley, then a mild 383 should eat that up as well.

I'd put a 750 Vacuum Secondary carb on it. Good mix of drivability and power with the right spring kit.