How much CFM does it take

[BallastBox]

How much air flow does it take to make 650 hp in a 350cu. in engine?

[Mike Mans]

There are a whole lot of variables that you would have to define, but here's a basic rule of thumb from a cylinder head perspective:

HP/2.25 = Peak CFM per runner on a Stock/Super Stock style engine. A decent engine in this world will make 2.25hp/cfm of head flow. Really efficient engines surpass it, and lesser refined motors may be a little lower. But this should get you in the ballpark.

So if you want enough head to support 650hp, you'll need around 285-290cfm of peak flow to get you there pretty easily. The big thing you need to figure out is at what peak RPM you want to make this 650hp

[Stan Weiss]

As stated above a number of factors come into play. What it really comes down to is how efficiently you are able to use the fuel.

Stan

[Henrys Toy]

Originally Posted by Mike Mans

There are a whole lot of variables that you would have to define, but here's a basic rule of thumb from a cylinder head perspective:

HP/2.25 = Peak CFM per runner on a Stock/Super Stock style engine. A decent engine in this world will make 2.25hp/cfm of head flow. Really efficient engines surpass it, and lesser refined motors may be a little lower. But this should get you in the ballpark.

So if you want enough head to support 650hp, you'll need around 285-290cfm of peak flow to get you there pretty easily. The big thing you need to figure out is at what peak RPM you want to make this 650hp

Is this a Super Stock engine?
If not, what are the limits or restrictions?
If no Restrictions, The valve size, valve lift, RPM, compression, Intake type, carb size all come into play as well.
A good aftermarket head (23 degree)that will flow approximately 310 to 320 CFM and a runner volume min. 190 with a single 4 bbl carb should get you into the ball park. Just my opinion, camshaft selection will have a large influence also. Less restrictions give you some leeway in getting to that 650 HP figure.

Respectfully,
Henry Kunz 1534 Stock

[BallastBox]

Thank you for your replies. Using the Edelbrock head part# 60887. Port volume is only 185. It is a super stock engine. Camshaft is .679 lift, duration @50 is 280 intake and @50 is 286 exhaust. Any chance I can get close to that figure. I realize this the cam is not radical. How much is a firing order swap worth?

[Mike Mans]

I'm no cam designer, but that cam is HUGE @ .050" in my opinion. Assuming you want a motor that will peak in the 7000 rpm range, I would call your cam guy and see what they would recommend. Do you have any idea what the heads flow now?

280/286 @ .050" is in the ballpark of what we ran in motors that peaked around 9500+ rpm years ago.

[Mike Pearson]

Originally Posted by BallastBox

Thank you for your replies. Using the Edelbrock head part# 60887. Port volume is only 185. It is a super stock engine. Camshaft is .679 lift, duration @50 is 280 intake and @50 is 286 exhaust. Any chance I can get close to that figure. I realize this the cam is not radical. How much is a firing order swap worth?

Firing order swap is worth nothing.
FYI. I dont think you are legal with that head volume on your combo

[BallastBox]

That cam is HUGE, now that's funny. It is a virgin head. Do not know what the flow figures are. I would guess cfm is probably around 230 to 250 range. Cam centerline is 108 degrees, 185 port volume is what it comes with.

[Mike Pearson]

Originally Posted by BallastBox

That cam is HUGE, now that's funny. It is a virgin head. Do not know what the flow figures are. I would guess cfm is probably around 230 to 250 range. Cam centerline is 108 degrees, 185 port volume is what it comes with.

I will give you a call tomorrow to talk about the port volume.

[Henrys Toy]

Originally Posted by Mike Pearson

Firing order swap is worth nothing.
FYI. I dont think you are legal with that head volume on your combo

Mike is correct on the firing order swap, I would concentrate more on rocker ratio's. Is this a Q-Jet carb or Holley combination? If its a Q-Jet getting the correct adaptor blended in and the space between the top of the carb and hood clearance is important.
Since this sounds like a new / start up combination changing rocker ratio's with your current camshaft will help your Cam Mfg. determine a better future cam and ramp speed selection.
Now a lot of other engine details become more important in making the required Horse Power. Oil pans and pumps, Headers, Intake Manifold selection as well as Valves and Valve Job angles are all going to become key players in your search for the 650 HP number you're looking for.

Respectfully,
Henry Kunz 1534 Stock