[Bman05Ltd]

Hi folks,
I’ve done some research recently on the stock PT Cruiser intake and wanted to share my information for the good of the order. My PT is an ’05 Limited, naturally aspirated with a 5-speed manual tranny.

First, I carefully measured the dimensions of the stock components. I found the following:
Throttle body:
tapers to 2.1” ID just in front of plate; 2.36” OD (60 mm), 2.52” w/ lip

Flexible Hose: 2.36” ID (60 mm) on both ends

Airbox:
Outlet on Lid: 2.075” ID, 2.350” OD
“Helmholtz” Air Horn: 1.820” ID inlet end, 2.075” ID exit end
Inlet Elbow (“black silencer”): Exit end (in air box) 2.30” OD, 2.11” ID
Inlet end of elbow: narrows to 1.98” OD, 1.82” ID
Hole in airbox: 2.54” OD

Second, I have the fortune of working for a company with a Superflow flow bench and I bench flowed the intake and its components. I removed everything forward of the throttle body. First I flowed the entire assembly, then each component, as described below. I also flowed a 2.5” OD straight tube (12” long) with a simple 45 degree flare on the end to get a baseline example. In previous testing I have found that adding a simple flare can add ~25% more cfm flow at the same resistance (inches of H2O). I am assuming that the maximum theoretical cfm used by the engine is 270 (2.4L @ 6ooo rpm with 1.05% volumetric efficiency), so I made all measurements at 270 cfm flow. I found the following:

12” 2.5” OD pipe with flare: 3.5” H2O
Full stock assembly w/ K&N Panel Filter: 23.3” H2O
Remove black elbow from box and put on mildly flared 2.5” OD 90 degree bend: 22.4” H2O
Same set-up with brand new Mopar paper filter: 22.5” H2O
Stock set-up with stainless elbow, no filter: 17.0” H2O
Stock set-up with bottom of box removed: 8.4” H2O
Same as last, with Helmholtz silencer removed: 14.7” H2O
Lid removed, flexible hose only: 7.2” H2O

My conclusions:
The black elbow on the outside of the box (entry snorkel) does indeed restrict maximum intake. The while air horn inside the lid, even though it narrows down to 1.82”, has such an efficient flare that it beats the “blunt” edge of the side of the air box lid hands down (even without polishing the evident parting line inside the horn). It should be noted that as I was testing, not only did removing the air horn increase the resistance to flow, it was also MUCH louder. Perhaps it is different on turbo cars, but I don’t see where removing this will actually help low or high speed air flow on any N/A car. Also, it seems that a clean K&N panel filter shows almost exactly the same resistance to flow as a clean paper Mopar filter.

My original plan was to modify the stock air box to allow for a higher volume of cooler outside air (per “diy,” Airaid, Volant, etc.). I’ve since decided to put everything ahead of the throttle body on the shelf and start over. I’ll post pictures and results after I’ve finished development.

I hope this is helpful!
Bman