[Supras] Air cleaner choice

[Robert Pina]

There is a little known secret that APEXI makes a drop in filter.  It is a
Japan only item though, would take months to arrive.

My old setup was T4 ball bearing, with a lexus AFM 550s and a stock airbox /
K&N insert.  Very stealth and stock appearing, but capable of quite a punch.


Robert
935 Motorsports
619-670-0841


-----Original Message-----
From: supras-bounces at supras.com [mailto:supras-bounces at supras.com] On Behalf
Of berniek at technicaldevelop.com
Sent: Wednesday, November 28, 2007 9:33 PM
To: jonbhacker at yahoo.com; Supras at supras.com
Subject: Re: [Supras] Air cleaner choice

Jon:

    I never had a stock air cleaner on my '91 with the modded engine and 
never had an aftermarket air cleaner on the '90 I sold with a stock 
engine.  I do have a stock housing which I bought to try on the '91, 
however (need to open up the outlet for the Lexus AFM).  Occasionally 
there are reports which surface which indicate the stock airbox to be 
OK, probably because of air drawn from before the bulkhead.


    The '91 had an HKS filter on it from the previous owner, which 
passes dirt.  I used it initially on the new engine, with care to avoid 
following dump trucks, etc., while on the lookout for something better.  
Eventually I found an APEXI while paper filter with a 3" radiused rubber 
connection for the aftermarket adapter to the Lexus AFM.  There was a 
noticeable drop in performance, believed due to the fact that the paper 
filter is closed on the opposite end, and the way positions of 
components wind up, the closed end just about blocks the bulkhead 
opening for the stock airbox.  So as heat rejected from the radiator 
increases during WOT runs, it appeared to draw every hotter air.  I put 
the HKS filter back on temporarily and the performance returned (mixture 
is a little more constant at around 10.5:1 with it than varying from 
about 9.5 to 11.0 with the APEXI).  It is possible that tracking of the 
volumetric flow correction thermistor in the AFM is less than perfect, 
resulting in mixture change as the filter draws ever hotter air.  I do 
no have the under-engine cover on yet either.  It is actually from the 
'90 I sold and will be put on after remaining tasks (hardpipes, 
windshield washer pump replacement, finding slow engine oil leak 
apparently from the cooler hoses, etc.).



    Bench experiments some time ago with a spare stock AFM and the Lexus 
AFM were undertaken with a big shop vac pulling air through them.  The 
square wave output was very clean and stable, and varied with setting of 
a Variac which operated the vac.  But what I did find was that straight 
airflow into the AFM was very important, or else the square wave output 
would become unstable.  Any obstruction, such as two fingers placed over 
the intake made it unstable despite the honeycomb straightening vanes.  
So I like the HKS baseplate since it is nicely radiused.  Maybe an open 
stock paper element would be an answer, mounted with a large cylindrical 
spacer off the HKS baseplate, since it will still be a few inches from 
the bulkhead opening.  The stock airbox has a conical path into the 
flowmeter, not radiused.  Instead, it has raised walls around the 
discharge opening on the interior facing the backside of the element.  
Toyota should know more about entrance and exit coefficients, or so it 
would seem.


       Bernie

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