Air Filter Upgrade

The 4″ air filters supplied with the carbs are way too small for what the carbs need to flow at full throttle, so I have been looking at what is available for Rochester 2G’s.  There are replicas of the original Chev & Pontiac air cleaners for about US$750, and there are a reasonable number of different types of hot rod air cleaners.  The problem is most of them are for show and not go.  Most of them have a small filter area which means they will struggle to flow enough CFM, and the filter quality is questionable as most of them come from China.  Even K&N filters filter less than a quality OEM paper filter element.

In the end I bought three 4 1/2″ x 7″ filters from O’Brien Truckers.  I ordered the filters with concealed set screws to hold the tops on, however it seems that they don’t read english very well at O’Briens and sent filters with centre bolt retention.  When I contacted Dennis O’Brien he admitted that he assumed I wanted the centre bolt and proceeded to tell me all the reasons why I needed the centre bolt.

Why he would send the wrong thing half way around the world has me beat.

This is what I wanted
This is what I wanted
This is what he sent
This is what he sent

After unsuccessfully trying to negotiate a better outcome with Dennis (unless I want to spend even more money) I decided to just go with what I have.  That doesn’t mean that I am not pi$$ed off.  O’Brien truckers?….Never again.

IMG_3523  IMG_3524

The quality of the castings is OK, but they are definitely not designed for airflow of any kind with the right angle corner in the base.  Fluid dynamics and the way air will turn the corner means that the flow in the throat will be measurably less than it should be.


I decided to do some flow work on the top corner to see if I can open it up and get some flow.  I proceeded to go to work with my Dremel and a carbide burr.  90 minutes later I had a result which was much better.  The burr kept on clogging up which slowed things down.  I remember from when I was a youg tradesman that kerosene was the correct coolant for aluminium, so I tried dipping the burr in kerosene – no different.  I then tried spraying it with silicone spray – this made a considerable difference and the burr clogged much slower and was much easier to clear.

IMG_3527  IMG_3530


I paid particular attention to the transition around the centre strap.  I am not convinced that this is required as the centre bolt through the top cover should hold everything on.  I may even remove the centre straps in the future as I expect they will affect flow significantly.

IMG_3533  IMG_3534


Hopefully I get a chance to do some more work on the filters next weekend.

They came with a 1 7/8″ filter element as based on the dimensions on the O’Briens website I couldn’t fit the taller filter under the hood.  When the filters arrived, the horns that connect to the carb are taller than required.  The centre carb requires clearance for the choke housing which means the horn is only 1/2″ longer than needed however the end carbs don’t have a choke so I can cut them lower.


To do something a little bit different I might use a 1 7/8″ filter in the centre assembly and the taller 2 1/2″ filters on the ends.  This would also allow maximum flow through the end carbs when they are open 9i.e. when you want to go faster!).  I found some coloured filters at Allstate Carburetor and Fuel Injection which could look really cool, and the other option I am looking at is a Uni Filter (the best option for filtration).

The filters that came with the air filters look like crap.  I can see lot of light through them which means that they won’t be doing much filtering.


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s