Intake Port CFM and Cam Spec

[skinny z]

I've made the rounds regarding a cam spec for a given combination I intend to put together. Actually a couple as it may be a 357 or a 383.
But this questions involves the heads, as they are, without any additional porting (other than a gasket match if needed). The heads will go on whatever displacement I choose. Obviously the cam spec will change.

A little background info first.
Gen 1 SBC.
RHS iron heads. 2.02/1.6. 175cc(+/-)
RPM Air Gap intake.
750 CFM VS carb
LT headers with Pipe Max spec'd open collector (no exhaust system/mufflers)
The chassis is as yet undetermined.
Converter also undetermined. Those last two will come together once this engine package is finalized. Further to that, the target is drag racing and standing mile stuff where it's WOT. Might even see some open road stuff so any cam spec can't be too intense.
Maximum TQ and HP under 6500. (More like peak HP at 6200-6300).

Flow.jpg

The question is how much of that peak port flow really worth once the intake and carb are sitting on top?
Ultimately I'll have a professionally recommended cam produced (I've talked with Jones, Bullet, Comp, etc) but in the meantime I'm noodling around with a couple of programs. One of the data entries is minimum port cfm required along with the valve sizes.
So, how does it all fit together? Do I discount the flow bench numbers?
I've read enough here to know there are differing opinions. And once I post this there'll probably be some relevant threads to read over. But in the meantime, I'm throwing this out there for discussion.

[skinny z]

And once I post this there'll probably be some relevant threads to read over.

Surprisingly, there seems very little on the subject.
Perhaps this might be better posted in the DV forum as one of the programs I'm using is Torque Master.

[CamKing]

Port flow CFM is very important.
After calculated the flow demand for the engine, I need to calculate choke flow for the minimum cross-sectional area of the port. Most people don't know this spec, and if the port design isn't very good, the effective minimum cross-sectional area can be much less them the measured cross-sectional area.
Using port flow cfm, you can calculate an "effective" minimum cross-sectional area for the port. That's what I use to calculate the lift curve required to meet the flow demands of the engine. A few decades ago, I did work with Ferrari, and they didn't use flow benches at all, but they had every measurement you could think of on the ports, so I used the measure minimum cross-sectional area.

[skinny z]

Port flow CFM is very important.
After calculated the flow demand for the engine, I need to calculate choke flow for the minimum cross-sectional area of the port. Most people don't know this spec, and if the port design isn't very good, the effective minimum cross-sectional area can be much less them the measured cross-sectional area.
Using port flow cfm, you can calculate an "effective" minimum cross-sectional area for the port. That's what I use to calculate the lift curve required to meet the flow demands of the engine. A few decades ago, I did work with Ferrari, and they didn't use flow benches at all, but they had every measurement you could think of on the ports, so I used the measure minimum cross-sectional area.

Thanks for that CamKing.
I think I see from that then, that if I were to measure the MCSA of these heads, I could determine if the port is efficient based on how the actual measurement stacks against the theoretical or effective value (as derived form the flow numbers). Seems logical and straightforward enough.
So a question that follows might be can I expect to see the flow bench numbers during engine operation provided all else (intake, carb, exhaust, etc.) is suitably thought out? Or do you discount the measured airflow because it's not likely achievable in a given circumstance such as in a relatively mild engine such as this might be at < 450 HP?
In simulation (or cam calculator software) I'm intrigued by how much the spec changes relative to the airflow requirements. It seems even 10 CFM at peak can have a mighty swing on the cam design. Or vice versa.

[PackardV8]

So a question that follows might be can I expect to see the flow bench numbers during engine operation provided all else (intake, carb, exhaust, etc.) is suitably thought out? Or do you discount the measured airflow because it's not likely achievable in a given circumstance such as in a relatively mild engine such as this might be at < 450 HP?
In simulation (or cam calculator software) I'm intrigued by how much the spec changes relative to the airflow requirements. It seems even 10 CFM at peak can have a mighty swing on the cam design. Or vice versa.

Suitably thought out is pretty vague. Take a given intake port CFM and the installed CFM could vary by 50%; think a 2x4 race tunnel ram or IR injectors versus a single 600 CFM 4-bbl on a dual plane which will fit under the hood.

Maybe, some might suggest you're starting at the wrong end of the pipe.

The chassis is as yet undetermined. . . . the target is drag racing and standing mile stuff where it's WOT. Might even see some open road stuff so any cam spec can't be too intense.

Would having a budget, building and weighing the car, choosing the events, targeting an ET/top speed, then determining how much horsepower would be required to meet those goals be a method of choosing a cam?

[skinny z]

Suitably thought out is pretty vague. Take a given intake port CFM and the installed CFM could vary by 50%; think a 2x4 race tunnel ram or IR injectors versus a single 600 CFM 4-bbl on a dual plane which will fit under the hood.

Maybe, some might suggest you're starting at the wrong end of the pipe.

Would having a budget, building and weighing the car, choosing the events, targeting an ET/top speed, then determining how much horsepower would be required to meet those goals be a method of choosing a cam?

I can appreciate all of your comments.

By way of explanation, really what I'm trying to do is build this 350 (or 383 as the case might be) around a set of cylinder heads and intake/carb from the previous iteration. I always knew that the cam that used (or any of the three actually) were never what might produce the most lbs-ft/HP at the RPM ceiling I was working with (< 6500 RPM).
I can re-build the car around those results. One the engine spec is front of me and knowing what I have in terms of power production and RPM, then the refinements in the chassis can follow easily enough. I'm saying that because the overall car was never refined and that's next.

"Suitably thought out" being somewhat vague is fair comment I suppose. Better said, it would be that I already have the two plane intake and carb and along with the heads and whatever CID, I'm looking for a cam. These parts are considered, more or less, to be a general staple in builds of this nature. That's the suitably thought out part.

If an overall goal is what is needed then lets say as stated above, that I'm looking for the most I can wring out of this collection of parts.
Case in point. There's a well known 350 SBC with small factory heads that made 447 HP. Much was made of the choice in cam as it looked to be controversial to the average hot rodder (or magazine fed masses). Interesting in that nothing was made of the power or torque curves themselves. Just the outright power number. I'll go with that.
How it fits into drag racing will/may require a new converter and rear gear for my "race" car. Maybe not. If I go for the Texas Mile (or equivalent) that same engine may have to be fitted into a different chassis combination.

Because this whole endeavor is a refinement rather than a clean sheet, the budget, weight, ET/speed have already been considered, calculated or otherwise taken into account for the best engine I can make with what I've got. Valvetrain, ignition, fueling, cooling, safety equipment were all set in place long ago.