Question about Holley CFM

[Cornpatch MO]

I could get a REAL deal on a 4250 style Holley. Dual acc. pumps, mechanical secondarys, hand choke, changeable jets in the secondary. My friend said it was a 750 CFM--just what I want for my mild 440. I checked the numbers and found that the 650 and the 750 bottom plate - butterflys is the same on both. And that the carb is only a 650CFM. I am really dis-appointed. He said it really worked well on a 450+ Cu.in. Olds or Buick? that had been warmed up a little. He claimed that I didn't need a 750CFM. even tho the calculators say I do.
What you all think, The engine will probably not go over 5-5500RPM. but I want to get it there in a hurry!! It is about 9:5 comp. and.475 lift cam. I think about small port heads as having more velocity and am open to the idea that possibly I don't need the 750 CFM.............................MO

 

[Meep-Meep]

If it's a deal and the carb is good use it. CFM is mostly a function of venturi area and throttle bore diameter, so depending on the booster style, it probably really is hovering in the 650 range. For the street smaller is better (to a point).

 

[Photon440]

Below 5500 rpm, that carb is all you need.

 

[67 coronet]

a 650 will pull power on a street 440 to 5100 rpms by the math.it should work fine.as meep said you want a smaller carb on a street motor to increase velocity signal through the venturies.keeps a better throttle responce.

 

[Cornpatch MO]

Thanks for the input. I bought that 650CFM list 4777-4 - double pump-mechanical secondarys- rear block has replacable jets carb today. It is fairly clean, but I will put a new kit in it.

Any advice as to how to set it up for my mild 440- 9.5 comp.- dual plane hi- riser- 4 speed -355 rear gear? I am guessing 72 jets front and 78 jets rear to start with...........................MO

 

[Meep-Meep]

Since this is a 4777 I'd change the metering block to allow a leaner main jet for cruise. Those double pumpers are really race carbs and I think with a metering block change it would run a bit crisper. But to answer your question, 72 jets seem a bit big for a 650. I think those had 67 or 68's stock.

 

[1966satellite]

I think this is a formula to calculate approximate required CFM:
CFM=RPM/2 times (cubic inches + Cubic inches / (Compression ratio - 1)) / 1728

 

[coloradodave]

The 4777-4 Holley double pumper (4150 series) came stock with 67 primary jets and 73 secondary jets. It doesn't have metering plates like the vacuum secondary carbs. The stock power valve is a 6.5". Try the stock jetting and play with it if you want to maximize the performance. As Meep said, these are not the best carburetors for fuel economy.

 

[67 coronet]

I think this is a formula to calculate approximate required CFM:
CFM=RPM/2 times (cubic inches + Cubic inches / (Compression ratio - 1)) / 1728

the much easyer formula is:
cfm=cubic inch x max rpm/3456.that gives a minimum cfm requirement for a stock like street motor.as performance increases so does the cfm requirement.thats why there is no sure carb for a given motor.

 

[71Beeper]

So using the above formula and plugging the numbers we get the following.
440 x 5,500 = 2,420,000
2,420,000/3456 = 700.23148 cfm.
So the 650 carb will be perfect for the street.

 

[Cornpatch MO]

The 4777-4 Holley double pumper (4150 series) came stock with 67 primary jets and 73 secondary jets. It doesn't have metering plates like the vacuum secondary carbs. The stock power valve is a 6.5". Try the stock jetting and play with it if you want to maximize the performance. As Meep said, these are not the best carburetors for fuel economy.

Thanks all, I do appreciate all the input. Since I bought this carb un-molested for$100 I am going to start out with it. Lots of stuff to tinker with so it will be fun. I have several jets and power valves and pump cams, so I won't have much any more money in it than the cost of an O/H kit. .......................................MO