6.1 hemi head flows plenty for 426 cubes!!

[dntnvme]

There has been allot of talk lately about whether or not the 6.1 cylinder head can flow enough to support 426 cubes. I of course feel it flows enough to support 700hp easily and found this info online that supports this theory as well and thought some of you might enjoy reading it.

"There are three basic components to consider when choosing ported cylinder heads:
Airflow
Cross-sectional area or volume (size)
Velocity (airspeed, measured in ft. per second)

First, consider airflow. Most everyone knows that the more airflow an engine can get the more power it can make. Unfortunately, many look only at the flow number at .800 lift as the sign of a good head. If you’re going to run a .500 or .600 lift camshaft, that number won’t mean anything since the cam will never see that lift. The important thing here is to look at the average airflow up to the maximum lift of your camshaft. Good low-lift and mid-lift flow is very important. Good low-lift flow gets the air column moving quickly. As airflow rapidly increases at mid-lift, it picks up speed and rams air into the cylinder for maximum fill before the intake valve slams shut trapping the mixture for compression. The better the fill, the more power you make. (This emphasizes the need to match the camshaft to the flow characteristics if a given head.)

Now, the exhaust curve becomes important. Good low and mid-lift flow allows the camshaft designer to keep the valves closed as long as possible to try and burn as much of the intake charge as he can (fuel efficiency). He can delay opening the exhaust valve longer so as not to lose anymore of the intake charge than necessary. When he opens the exhaust valve, good low and mid-lift flow ensures that all of the spent charge can escape quickly. He is able to close the exhaust sooner so as not to contaminate (or lose part of) the next fresh intake charge. A general rule of thumb is to see an exhaust port that flows 70-80% of the intake with the larger percentage of comparison at the lower and mid-lift numbers.

Second, consider the cross-section, or volume. Simply put, the more volume of air, the more horsepower can be made. The engine will RPM better, giving it the potential to make more power. WARNING: Do not conclude that bigger is better. The more volume the more RPM’s the engine will need to turn in order to take advantage of it. The size of the engine and deciding what RPM range you want the engine to operate at becomes important.

A good example of this occurs when considering the new Chrysler Hemi’s. The 5.7 (345 ci) was designed with a moderate size port with good velocity characteristics. The 6.1 (370 ci), only 25 ci larger, was designed with a large port with great horsepower potential. However, as cast, it’s already pushing the volume limit for a 370 cu engine. It seems more suited for a 426 or larger engine especially if ported and valved to realize it’s great flow potential. This would, of coarse, make an even larger port requiring more RPM’s to take advantage of it.

The 5.7 head, on the other hand, was a very adequate high velocity port entry. The head begs for porting. It can yield up to 340 CFM or more at .600 lift without increasing the size of the port entry. The increased flow also raises the velocity and makes it a good choice as a match for a 345 ci, 370 ci, and 426 ci engine designed to run at a reasonable RPM levels, especially when used in a street machine (where torque and throttle response is king!). Remember, 340 CFM can produce well over 700 horsepower in race trim naturally aspirated. Add a blower?"

Info taken from "Knowltons Thunderheads".


Basically, he is stating that not only is the 6.1 good up to 426 cubes, but it seems ideal for a 426 as it sits and that a ported 5.7 is also good for use with a 426. I thought this info was great and wanted to share with you guys.