This is the entire K&N Flow Control air cleaner assembly complete with a 14x4-inch K&N filter. This combination made 575 for peak power that was 8 hp over the baseline, but also improved the torque throughout the entire curve.
Engine Specs
- GM Performance Parts 454 H.O. short-block
- 10:1 compression ratio
- JE custom standard bore forged pistons
- Crane mechanical flat-tappet cam, 252/262 degrees duration at 0.050, 0.554/0.554-inch lift, 110-degree lobe separation angle, Crane 1.7:1 Gold Race roller rockers
- World Products iron Grumpy Jenkins Merlin heads, 2.300/1.88-inch valves, ARP head bolts, Crane dual valvesprings
- World Products Merlin 4150 style single-plane manifold
- Holley R4779-6 750-cfm mechanical secondary carb
- Hooker 13/4-inch headers, 3-inch exhaust with Flowmaster mufflers
- MSD billet distributor, MSD-7A CD ignition, MSD plug wires
| Parts List |
| All parts listed are K&N products | |
| Component | PN |
| 14x3-inch air filter | E-1650 |
| 14x4-inch air filter | E-3750 |
| 14x3-inch air filter assm., 7/8-inch drop | 60-1430 |
| 14x4-inch air filter assm., 7/8-inch drop | 60-1440 |
| 14x4-inch Flow Control, 390-800 cfm * | 61-4020 |
| 14x4-inch Flow Control, 830-850 cfm* | 61-4040 |
| Stub Stack | 85-0200 |
| 14-inch-diameter X-Stream Air Flow Top | 66-1401 |
| CCarbon-fiber lid, 14-inch diameter | 85-6840 |
| *With choke housing on carburetor | |
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The Flow Control system clearly worked, so we played around with various pieces until we tried a flat base, a 14x4-inch K&N filter, a Stub Stack, and topped off with a 14-inch-diameter X-Stream airflow top. This package really helped direct air into the engine, and the big Rat responded with 581 peak hp and more torque almost everywhere. The average power ended up very close to the Flow Control system in Test 3. | 
This innovative car crafter combined a 14x3-inch filter with an XStream lid and then added a plastic snorkle to the underside of the hood to pull air in from the cowl. |
For kicks, we also tried this 9-inch-diameter air filter equipped with a new paper element. We bolted this air cleaner on our Rat, and it immediately cost us 35 hp at the peak with torque losses all the way through the test! It clearly does make a difference what air cleaner you use, especially at 500 hp and above. | 
Certainly the paper filter cost airflow and became a restriction, but we've also noticed that this step (arrow) on some air cleaner bases will kill airflow especially when used with an HP or Demon style carburetor with its radiused entry design. On a 550hp 420ci small-block with carb-style throttle-body, a 1-inch-tall step like this one cost us 10 hp at the peak. |
This 351W small-block Ford could use a taller filter element to help clear the carb's choke housing. | |