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Re: Why would you have to MOD your CIS ?
In a message dated 9/19/99 6:37:48 PM Eastern Daylight Time,
<< 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.
The main problem, from what I have studied and understand, is that the
N/A CIS is calibrated for just that, N/A not turbo fuel duties. Where N/A
motors run best on the stoichiometric ratio of 14.7:1 air/fuel ratio,
combustion under forced applications requires a richer fuel mixture, one
reason being that unburnt fuel actually absorbs heat from the combustion
chamber and prevents knocking and detonation. Some have tried to run a turbo
engine from the normal CIS and had catastrophic engine failure for these same
Thus, in any turbo application, there must be 3 dimentional mapping of
fuel, spark, and boost. By enrichening the fuel mixture under boost (by
proper method, activating cold start valves is a very poor one), ensures
proper fuel requirement and cooling in the combustion chamber.