High performance automotive air intake

A high performance air intake for an automotive engine has an oiled gauze filter of inverted conical form, including an inverted, shaped inner apex, the filter fitting within an in-line filter body that forms a part of a slender intake line. The in-line form of the filter enables the pick-up of intake air from a cool zone below the engine, with little subsequent heating of the air, resulting in enhanced breathing of the engine, with observable performance enhancement.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention is directed to an air filter, and in particular to an air 
intake filter for an automobile engine. 
2. Description of the Prior Art 
In the operation of automobile engines, particularly in the case of high 
performance engines, a great deal of attention is focussed on the 
"breathing" of the engine. 
In the case of naturally aspirated, "unblown" engines, in which a 
supercharger is absent, the effective inflow of air into the cylinders 
significantly influences the performance of the engine. For that reason 
much effort has focussed on the polishing of valve ports, the degree and 
timing of valve lift, tuning of the length of intake passages in relation 
to the location of air flow pressure nodes etc, in order to optimize air 
flow. 
To protect the engine against undue wear it is necessary to filter the 
incoming air, in order to remove abrasive particles that would polute and 
damage various portions of the engine. 
In many instances, in high performance machines, a filter box of generally 
rectangular section is provided, having a filter of large cross-sectional 
area that produces low velocity air flow, with a small presure drop across 
the filter element. This is thought to improve the breathing performance 
of the engine. 
A major disadvantage of this arrangement is that the filter box is located 
high up in the engine compartment, and consequently is heated to a 
significant degree, so as to form an effective heater of the slow moving 
air within the filter box, thereby effectively reducing the volumetric 
efficiency of the engine. An existing form of air filter has a conical 
shaped filter of accordion-pleated, air permeable filter material. The 
conical filter is aranged with the apex of the cone located upstream, so 
that air flows from the outside of the cone, inwardly through the 
divergently inclined filter wall. 
SUMMARY OF THE INVENTION 
The present invention provides an air filter for use in an automobile air 
induction system, comprising a slender filter housing having an inlet and 
an outlet in mutual, substantially aligned relation; a filter comprising 
an air permeable wall of convergent form, forming a convergent, 
progresssively diminishing flow path within the permeable wall. 
The use of a housing of substantially uniform cross section provides a 
divergent, progressively increasing flow path outside the filter wall, in 
use to receive air from within the filter, for passage to the engine. 
In one embodiment the filter air-permeable wall member comprises a 
substantially conical form, having the apex portion of the filter member 
adjacent the outlet, and the larger diameter base portion adjacent the 
inlet, in use to receive incoming air within the conical form, for passage 
thereof outwardly through the filter wall to the outlet. 
In one embodiment of the filter an air guide is located within the cone 
adjacent the apex portion, in use to deflect incoming air within the cone 
in a direction outwardly, through the wall. A commercial conical filter of 
accordion-pleated cotton construction has been effectively used as the 
filter element, with a substantially hemispherical air guide located at 
the apex. The air filter housing used may be substantially cylindrical. 
The air filter can be used in combination with an air inlet pipe connected 
to a cool location in the vicinity of the engine, e.g. within the engine 
compartment. 
In one embodiment, the air inlet comprises a drop pipe extending downwardly 
to a cool location below the engine. 
The outlet pipe from the filter to the engine throttle body connection of 
one embodiment is of a lesser diameter than the air inlet pipe.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring first to FIGS. 1 and 2, which are of the Prior Art: 
In FIG. 1, which shows a standard high performance car air intake, the 
filter housing is divided by a planar filter element of large area, 
through which the air passes, to exit by way of an air passage to the 
throttle body of the engine intake system. FIG. 2 shows a conical air 
filter fitted by way of a rubber flange to the manifold inlet pipe, 
wherein the incoming air impinges on the outside surface of the filter 
element, passes inwardly through the divergent conical filter wall, and 
exits through the base of the element to the manifold pipe. 
Turning to FIG. 3, in an embodiment in accordance with the present 
invention an air filter 10 has a substantially cylindrical housing 12 
which contains a conical filter element 14. The filter element 14 is 
accordion pleated, being of cotton gauze material, and being washable. 
In one embodiment, a filter element 14 of four and one quarter inch base 
diameter (108 mm), by five and one half inches long (140 mm), and two 
inches diameter (51 mm) at the apex, is located within a five inch 
diameter (127 mm) housing 12 of polycarbonate plastic. The filter element 
14 includes a rubber inlet sleeve connection of three inch diameter (76.2 
mm) into which an aluminum inlet pipe 18 of three inch O.D.(76.2 mm) is 
inserted. An outlet pipe 20 of silicone rubber of two and one half inches 
I.D.(64 mm) connects the outlet of housing 12 to the engine throttle body 
21. 
A flow deflector 22 secured at the apex of the element 14 has been found to 
beneficially influence air throughput. 
The deflector 22 actually used comprised substantially about 210 degrees of 
a hemisphere of sensibly one inch diameter (25.4 mm). 
In operation, with the subject air filter installed on a 1991 Honda Civic. 
S.I. with a 4-cylinder 1.6 liter engine, the time to accelerate from 20 to 
140 km per hour was 12 seconds. With the standard OEM filter, as 
illustrated in FIG. 1, the same acceleration test took 13 seconds, on the 
same course. During the testing of this vehicle, fitted with the subject 
filter, the engine gave no indication of any "flat-spots", and appeared to 
develope more power across the full performance spectrum, as compared with 
the OEM air filter. However the time trial was a definitive, quantified 
test which demonstrated a power increase resulting from use of the 
invention. 
It was observed in operation that the outlet pipe connecting the filter to 
the engine ran significantly cooler than that of the stock car 
arrangement.