Editing Drop base type air cleaner

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==Overview==
The drop base air cleaner came about to allow the air filter assembly to clear the Corvette hood, yet still provide enough filter element area. Several types were used throughout the years, the most drop is the base used on the L72/l78/L88/L89 Corvette BBC engine. Other bases were also dropped and were used on various SBC engines.

==Aftermarket drop base filter assemblies==
===Edelbrock===
Edelbrock sell a version of the 14" diameter L88 type drop base air cleaner assembly. It doesn't have quite the drop of the L-88 base.

[[File:Eddy drop base air cleaner.jpg‎|thumb|400px|left|Edelbrock 14” p/n 1221 drop base air cleaner assembly]] <br style="clear: both"/>

===Moroso===
The Edelbrock version of the L88 base doesn't have quite the drop of the L-88 base, either.

[[File:Moroso drop base air cleaner.jpg|thumb|400px|left|Moroso p/n 65927 drop base air cleaner assembly]] <br style="clear: both"/>

===CFD===
One of the best looking air filter bases is made by [http://www.r2cperformance.com/cfd-4150-4-barrel-air-cleaner-bases-.aspx CFD]. It allows a lot of clearance and could be every bit as good as the GM OE drop base style bases.

[[File:CFD filter base.jpg|thumb|left|450px|CFD base for 4150 Holley carb]] <br style="clear: both"/>

===HEI clearance=== 
Besides the drop for hood clearance, to some having room for an HEI distributor is important. Considerable cutting was needed on the L88 base as seen below:
[[File:L88 drop base clearance hei.jpg|frame|left|400px| L88 14" drop base HEI clearance]]


<br style="clear: both" />The difference in the amount of drop between the two bases- the L88 is lower. Also note the Moroso (below) has better HEI clearance:
[[File:Moroso drop base clearance hei.jpg|frame|left|400px|Moroso p/n 65927 14" drop base clearance HEI]]
<br style="clear: both"/>

==Filter to avoid==
Don't be tempted to gain the clearance under hood by using one of the "hair net" Edelbrock filters. The p/n 1002 "Pro-Flow" is one of the absolute worst designs to ever be foisted on the public. The filter element degrades rapidly and is too porous, it also will disintegrate if the carb pops a flame, and it does not flow good.

[[File:EDL-1002 air cleaner.jpg]]


==Filter size formulas==
#Square inches of filter required for a motor = (CID x Maximum RPM) / 20839
#CFM required for a 4 stroke motor = (CID x Maximum RPM) / 3456
#CFM required for a supercharged motor = [(Pounds of boost / 14.7) + 1]; (CID X Maximum RPM X results from #3) / 3456

===CFM formulas for filters===
*Round: Diameter x Height x 6 x 3.14 
*Flat Panel: Length x Width x 6 
*Universal Round Taper: (Base + Top) / 2 = A; take A x Length x 6 x 3.14 
*Universal Round Straight: Diameter x Length x 6 x 3.14 

===Some helpful formulas===
*To find circumference of a circle multiply diameter by 3.1416
*To find diameter of a circle multiply circumference by .31831
*Cubic centimeters / 16.39 = square inches

==Other things that can be done to gain hood clearance==
Using a bolt to hold down the air filter assembly lid will gain some clearance. Cut or find a suitable bolt that fits instead of using a stud and wing nut.

An obvious choice is to use a shorter filter element. But remember that the engine gets all its air through the filter and if it's too small, the results are a too-rich condition, poor performance and economy, as well as a shorter air filter element service life.

==Resources==
*[http://www.bobistheoilguy.com/airfilter/airtest2.htm Air filter flow tests]
*[http://www.thedirtforum.com/airfilterheight.htm Air filter height calculator]
*[http://www.knfilters.com/filter_facts.htm#SELECT Formula under “Filter Selection”]


[[Category:Engine]]
[[Category:Carburetors]]