Finding 14 hp in the Right Air Cleaner Assembly

One test with a K&N Stub Stack added to the top of the carburetor did see measurable gains. This creates a gentler radius into the carb that made 5 more hp at the top. Curiously, the Stub Stack cost a little torque in the midrange power levels. The air-fuel ratio was still slightly rich at hp peak.

Also interesting is that Westech's Steve Brule mentioned that on previous dyno tests with the XStream Air Flow Top that it seems to work best when combined with flat-base air cleaner assemblies. Conversely, he has seen a slight power loss when the same lid is combined with drop-base air filter assemblies. We did not test a drop-base air filter assembly to verify this point.

At the very end of our test, just for fun, we tried a small 9-inch-diameter air cleaner assembly equipped with a 2-inch-tall paper air filter element, which cost 35 hp over the best combination. This is an indication of what can occur when you do not pay attention to little details like air cleaners and filter elements when building your fast street car.

We learned that paying attention to air cleaner design and especially to how air enters the carburetor can pay huge horsepower benefits as power numbers continue to climb. The overall key appears to be ensuring sufficient space above the carburetor to allow air to enter the carb (or throttle-body) without creating turbulence that can cause power to suffer. It appears that maintaining roughly a 2- to 3-inch clearance above the top of the carburetor is a great way to offer your engine every opportunity to make power. This is not always possible with low hood levels and tight engine compartments. But the fact remains that should you choose to restrict the inlet air into your engine, then you can expect to lose power as a result of that compromise. It doesn't get any simpler than that. Another way to look at this is with a simple question. How much money would you expect to pay to make an additional 14 hp?

Test 3 involved adding K&N's Flow Control air cleaner assembly to the big Rat. This is the base for the Flow Control air cleaner and note how the entire base is designed to create a very smooth entry for airflow past the choke housing.

Air cleaner assemblies or air filters don't make power, but the right combination of airflow-enhancing filter assemblies will help your engine make all the power it is capable of producing--and keeping that horsepower-devouring devil out of your details.

Test 1 Baseline with no air cleaner, 0-4779 750-cfm Holley w/choke

Test 2 Flat base w/14x4-inch K&N filter and Flow Top

Test 3 K&N Flow Control air cleaner w/14x4-inch filter

Test 4 Flat base, 14x4-inch filter, Stub Stack, and Flow Top

Test 5 9-inch-diameter, 2-inch-tall air cleaner w/paper filter

This is the lid for the Flow Control air cleaner assembly. The plastic lid creates a slight radius to gently turn the air coming in through the filter to make that 90-degree turn into the carburetor.