Cowl plenum air cleaner, cold air induction, etc

[Jon Mello]

I had Jim Webb check the cowl plenum duct screws in his red '67 rally sport Z-28. His screws look pretty
much the same as Paul Lasiter's although Paul's have four tiny bumps in a line across the head of the screw
and it looks as though Jim's might only have two bumps. There are no other markings on the screws.

[Jon Mello]

The diameter of an original, authentic cowl plenum air cleaner lid is 16.75".

[Jon Mello]

The cowl plenum air cleaner base is 16" across, from the outer edge of the top lip on one side to the same point on the other side.

[Jon Mello]

Here's a look at the underside of the correct lid.

[Jon Mello]

Here's a closer look at the groove that the top lip of the air cleaner base rides in. There is a very similar
looking lid that you will see at swap meets that is close to the same size (around 17" dia) that has rubber
in the groove. Don't be fooled into buying it. It won't fit on an original GM cowl plenum air cleaner base.

[motorman]

this type air cleaner was originally supplied for the Z-11 impala drag cars.

[motorman]

this type air cleaner was originally supplied for the Z-11 impala drag cars.

also was used on the 63 NASCAR impalas with the "mystery" engine at daytona

[Jon Mello]

Yes, you're right. 1963 was the first use by Chevrolet for this style of air induction. The W-series (409 style) 427 Z-11
engine used a modestly different looking cowl plenum air cleaner than the MKII "Mystery Motor" Impalas used at Daytona.

[1109RWHP]

Has anyone tested the power gain from an open element filter to a cowl induction setup? Just curious if it actually was a benefit.

[Jon Mello]

There's no doubt it's a benefit but I haven't seen published figures that show what the horsepower gain was.
There would be more benefit on a course with longer straights where a car sustained higher speeds for longer
time (Daytona and Sebring) than there would be for shorter tracks with slower speeds.

[MO]

If it didn't work better, they wouldn't still be using it in NASCAR.

[motorman]

Has anyone tested the power gain from an open element filter to a cowl induction setup? Just curious if it actually was a benefit.

you gain 1% in HP for every 10 degrees you lower the intake air temp

[motorman]

also those systems cause air turbulence around the carb air bleeds unless you use the L-88 screen on top of the carb to straighten out the air flow if you run without a air filter

[Jon Mello]

also those systems cause air turbulence around the carb air bleeds unless you use the L-88 screen on top of the carb to straighten out the air flow if you run without a air filter

That's a good tip. Thanks.

[Jon Mello]

If someone is needing a cowl plenum air cleaner for their Trans-Am Camaro or street car, there's one for sale on ebay right now with a buy-it-now of $3,000.

http://www.ebay.com/itm/1967-1968-Z28-Camaro-Trans-Am-Cowl-Plenum-Air-Cleaner-SCCA-Smokey-Yunick-/121168600120