TPI Questions

[Clare Snyder]

>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
>>
>
>
>
I fully understand the emmission implications. I was responding to the
"fact" that non egr equipped vehicles with big cams do not suffer as much
from detonation as stock engines when EGR is disabled. Another part of the
reason is that, at low RPM, scavenging is incomplete, and a degree of EGR is
inherent in the operation and design. Only at higher RPMs the cyls are
effectively purged and filled. This is why 12.X :1 compression ratios are
possible on some of the lumpy hot-rod engines, while being totally
impractical on mildly tuned engines.