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Re: Why would you have to MOD your CIS ?

In message <006601bf02c6$c7666560$01181ba1@olsy.dk> thyrsted2@olsy.dk (Kenn Thyrsted) writes:

> Seemes to me that you don't have to mod the CIS for running higher boost..

> If that's true, - then why do you have to mod the CIS if you're increasing
> volume, eg by using a 2.5l crank etc..

Because it seems (certainly from my experiments) that the mechanical air
mass sensor used in Hitachi-controlled I5 engines maxes out at 4500rpm
and full boost.  At this point, the system is running open-loop and
significant extra enrichment is provided by the ECU's management of the
fuel frequency valve.  Its inputs are rpm, inlet air temperature and
boost.  Because the air mass sensor plate is maxed, the system can't see
any volume change produced by porting, boring out or a different cam.

 Phil Payne
 UK Audi quattro Owners Club
 Phone: 0385 302803   Fax: 0870 0883933