TPI Questions

[Gary Derian]

When nitrogen and oxygen (air) are combined at high temperatures nitrigen
oxides are formed.  Nitrogen oxides are an ingredient which leads to the
formation of ground level ozone.  EGR adds exhaust, an inert gas, to the
intake.  This dilutes the air/fuel mixture and lowers the combustion
temperature which reduces the formation of NOx.  Lower combustion
temperature also makes an engine less prone to detonation.  The less NOx
created in the engine, the less is emitted out the exhaust, even with 3-way
catalysts.  Most but not all engines have EGR.

In the bad old days of the 70's, engines ran with EGR and retarded spark.
This led to a great loss of economy.  Modern engine controls can advance the
spark during heavy EGR use.  The EGR permits lots of advance without
detonation.  This gets back most all of the economy.  When EGR is removed,
the part throttle advance must be cut back to "normal" levels otherwise
detonation will occur.

At full throttle, EGR is not used so spark advance and power are already at
proper levels.

Gary Derian <gderian at cybergate.net>

-----Original Message-----
From: Clare Snyder <clsnyde at ibm.net>
To: diy_efi at coulomb.eng.ohio-state.edu <diy_efi at coulomb.eng.ohio-state.edu>
Date: Tuesday, August 12, 1997 2:58 PM
Subject: Re: TPI Questions



>>
>>I was under the impression that EGR was to clean up emissions by
>>recirculating exhaust gas. I read that a performance mod was to
>>disable the EGR valve with big cams.
>>
>>gchan at compserv.senecac.on.ca
>>>
>
>Big cams blead off effective compression at low speeds, where the ping is
>usually the problem. A big cam can negate the requirement for EGR . Ping at
>full throttle is not affected by EGR as it is shut down in that mode
>
>My opinion, only, for what it is worth
>