Air flow vs compression

[Racer18]

Without getting too crazy, and all other things being the same, which gives you more power/torque? And which is more bang for the buck? For example- if a customer had an extra $1,000 to spend, and you could only pick one or the other, which one, and why?
Finishing my first year of owning a dyno, and some things we thought were sure to help, didn't, and a few that seemed like no big deal really helped. Had 2 nearly identical engines and the one with lower compression made more power, but the other wins more

[PackardV8]

The eternal flathead question; been debated since the Model T days.

[brechlrl]

The simple answer is there is no simple answer.. IMHO it depends on what you are starting out with, and where you want to go. If you have an 8.0 to 1 351M Ford then adding a couple points of compression, spending your 1k on a set of pistons and rings might be the best route.. If you have a modest to high compression motor that runs out of breath at 4000 rpm then work on airflow. Spend the 1K on Cam, intake, heads. Solving these problems is why the pro engine builders that hang out here get the big bucks.

[novadude]

Had 2 nearly identical engines and the one with lower compression made more power, but the other wins more

Is this because the higher compression engine has a flatter torque curve and more average power over the rpm range seen in a race? I’d imagine a lower CR engine making more power would have less grunt in the lower rpm range.

[Geoff2]

Agree, no simple answer, though a CR increase could be expected to increase HP everywhere through the power range, whereas increased airflow if it is increased by enlarging port volume might lose HP in the lower ranges & only gain at higher rpms.

If CR is increased with dome pistons, it might hurt HP because of valve shrouding &/or inhibiting flame propagation.

Also, HP increase with CR increase is not linear. Going from 8:1 to 10:1 CR should yield a higher percentage increase in HP than going from 12:1 to 14:1, all else being equal.

[BOOT]

Well 1 point of comp is 3-4% ish hp and I think 1 cfm is 2 potential hp think I read somewhere(someone will correct me if wrong on either), so technically if you knew the diff you could estimate the HP for either.

[mag2555]

As posted there's by far no simple answer, but if you atleast have the minimum compression needed for your Cam choice then it's time to start playing around with advancing and retarding the Cam which will give you a clue as to what to do with your overall flow systems Intake to Exh ratio.
Sorry for the run on sentence!

[plovett]

In general, the answer is airflow. Airflow is king.

JMO,

paulie

[mag2555]

If your down on compression and your relying on air flow then it had better be at the velocity limit that the Cams power range can handle!!

[steve316]

10 to 1 street engine is not down on comp. where a race only engine would be. Like posted before no quick answer. street or race ?