[Richiehd]

Anyone have any idea how much CFM a Holley 650 HP flows out of the box?

[F-BIRD'88]

Nope but the 750HP flows more.

[gearheadslife]

Originally Posted by Richiehd

Anyone have any idea how much CFM a Holley 650 HP flows out of the box?

think you answered your own question

[ap72]

Originally Posted by gearheadslife

think you answered your own question

the "650" is a label, not a flow measurement, none of the holley's flow what their label is, all the basic holleys are under and the HP's are a little over.

It'd be neat to see a spreadsheet of all of the common carbs on a flow bench, I think people would be really surprised by what some of them really flow.

[gearheadslife]

Originally Posted by ap72

the "650" is a label, not a flow measurement, none of the holley's flow what their label is, all the basic holleys are under and the HP's are a little over.

It'd be neat to see a spreadsheet of all of the common carbs on a flow bench, I think people would be really surprised by what some of them really flow.

correct me if I'm wrong.. but I'd think a 650 cfm car that didn't flow that or at least -1% or 650+ would be false advertising

[vinniekq2]

My actual 650 was on a flow bench.It flowed 641 and after installing an 850 base plate it flowed 773cfm,,,now how do we know the flow bench is accurate?a different flow bench might offer different numbers.
What I cared about was improvement,or increases

[ap72]

Originally Posted by gearheadslife

correct me if I'm wrong.. but I'd think a 650 cfm car that didn't flow that or at least -1% or 650+ would be false advertising

You would be wrong as Holley doesn't promise any particular flow, its just a label. They're not the only ones that do it either- most carb companies do. From what I recall Demon carb's are actually better than their label would indicate though (I think they're the only "non race" carb that is).

[painted jester]

Originally Posted by vinniekq2

My actual 650 was on a flow bench.It flowed 641 and after installing an 850 base plate it flowed 773cfm,,,now how do we know the flow bench is accurate?a different flow bench might offer different numbers.
What I cared about was improvement,or increases

I agree! Heres a little adition vinnie

Years ago the Society of Automotive Engineers provided a standard for Airflow that's still used today. For 4-barrel carburetors that number is measured airflow at 1.5" pressure drop, or used on a flowbench is 20.4" water. For example a 750cfm carburetor should flow 750 (cubic feet per minute) at this pressure drop. A carburetor has fuel flowing through it which actually displaces some airflow (usually around 8%), so this should actually be flowed with fuel or wet flowed. Tests are not absolute but averages not including, temp, atmospheric pressure, temp, or engine efficiancy

Jester

[painted jester]

Your engine needs X amount of airflow to reach a certain power level efficiently. The formula for CFM consumed is (CFM = CID x RPM x VE ÷ 3456). Here CID = Cubic Inches; & VE = Volumetric Efficiency. This is just a rough estimate as VE number is the basic efficiency or cylinder filling of the engine. Let's take a typical small block chevy 383ci stroker engine at 6500 rpm assuming 100% VE. Plug in the numbers & you get a CFM requirement of 720. Street motors might be 90% & a good race engine might be 125% with a single carb! But put on a tunnel ram or a high rise race intake and cfm climbs drasticly because of the velocity of the ram effect aiding the engines ability to flow more air !! throwing that formula out the window

I thought this might help

Jester

[Richiehd]

OK< I got some interesting answers, kind of what I expected. My question was posted because I know a Holley 650 is advertised as flowing 650 cfm, we all agree on that. However, the HP, not the Street HP, should by theory flow more, because of modifications and polishing of the veturies. I wondered if anyone had actually seen any numbers. Im running 355, World Heads, solid lifter cam and wet exhaust on my 16 foot Jersey Skiff. We can turn 7000 no problem, and the mid range creates awesome acceleration. I was thinking of going to bigger carb but would hate to lose the midrange.

[vinniekq2]

you could use an out of the box 850

[painted jester]

I agree

Jester

[F-BIRD'88]

If you are spinning it 7000rpm you can use two 650's

(on a tunnel ram. YOU will have MORE MID range.

and more top speed too.

[ap72]

Originally Posted by Richiehd

OK< I got some interesting answers, kind of what I expected. My question was posted because I know a Holley 650 is advertised as flowing 650 cfm, we all agree on that. However, the HP, not the Street HP, should by theory flow more, because of modifications and polishing of the veturies. I wondered if anyone had actually seen any numbers. Im running 355, World Heads, solid lifter cam and wet exhaust on my 16 foot Jersey Skiff. We can turn 7000 no problem, and the mid range creates awesome acceleration. I was thinking of going to bigger carb but would hate to lose the midrange.

properly built and tuned a bigger carb will NEVER cause a loss of power in the mid range or even off idle.

That old wives tale comes from people who can't build and tune carbs.

[F-BIRD'88]

For a single 4 barrel hi performaance carb on a hi perf 350 the 750cfm holley is the best choice
99% of the time. It is every bit as responsive as a 650 if not more and aways makes more power
and torque.

If you want to actually make your boat go faster get a tunnel ram and two 650's or it.
The edelbrock street tunnel ram is a good choice. Now you will gain some MPH on the water.

This chart illustrates the power gain from a single 4bbl to a tunnel ram w 2 650's.
This 355sbc is similar to yours
http://image.hotrod.com/f/techarticl...il_chart_z.jpg

while the power test starts at 4500rpm the tunnel ram will out power any single 4 bbl manifold typically from as low as 2500-2800 rpm. You will have more mid range power.