Re: CAI & Octane

["Ron Buchalski" <rbuchals@xxxxxxxxxxx>]

William,

This is incorrect information.  The reprogramming that was recommended by 
JimC deals with a lean condition that can occur at a certain RPM (somewhere 
between 4000 and 5000 RPM, if I remember correctly).  It applies when using 
the Eurosport/JimC CAI.

This software upgrade does nothing to change the factory settings of the 
mass air sensor, which is a device that has fixed settings.  For a given 
amount of air, it puts out a corresponding voltage (or current), which is 
interpreted by the DME.  The software change that JimC incorporates with his 
CAI system corrects the fuel map at those specific RPMs to solve the lean 
condition.

Otherwise, putting a CAI on your car is independent from upgrading the 
engine management software.

Regarding octane, BMW recommends 91 or higher octane on most models.  Since 
the engine incorporates a knock sensor, the DME will retard spark timing if 
knock is detected.  So yes, you can operate with lower octane, at the 
expense of (possible) lower performance.  If the octane is TOO low (and 
retarded timing can't compensate) then you run the risk of engine damage.  
So, you can pay $2 less per tankful of gas now, or you can pay $$$ for an 
engine repair later.  Is it worth the gamble?

When you upgrade software (JimC, Dinan, Autothority, etc), they re-map the 
ignition curve to take full advantage of higher octane fuels, so you are 
definitely required to run higher octane fuels.

For a picture of "real world gains" (with the JimC-designed products), see:

http://www.bonnevillemotorwerks.com/dynocharts/intake/

Some curves include software and intake mods, others include just intake 
mods.

- -rb


>Date: Mon, 31 Jul 2000 07:00:12 -0400
>From: "William T. Wallace" <ssgwallace@domain.elided>
>Subject: CAI & Octane
>
>I have been told that it's useless to get a CAI without having the OBD-II 
>reprogrammed.  Because no matter what type of filter you get, if the mass 
>air sensor has not been changed from its factory settings, the cars 
>performance will remain the same.
>
>Also, using high-octane fuel without reprogramming the OBD-II.  No actual 
>performance gain, just "good for the engine."
>
>So my question, should CAI and High Octane upgrades be performed only after 
>the OBD-II has been reprogrammed?  If not are there any real world gains?

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