tmorris@convex.UUCP (09/20/85)
I have to agree that for the most part ,there is little to be gained
in the mileage/performance market by using unleaded fuel. There are , as
always , some exceptions to the rule . In this case the exceptions are
GM cars equipped with ESC.
Electronic Spark Control is used on some GM vehicles in conjunction
with the Computer Command Control System. On some pickups and vans it is
used without the computer. Many vehicle types have the computer ,but no ESC.
If you followed all that , you realize that:
(and my apologies for lack of clarity)
1. You can have ESC and no computer.. trucks
2. You can have a computer and no ESC .. most cars
3. You can have a computer and ESC .. some cars
OK , OK you say , what does ESC mean to me ? What do it do ?
Well , if you have a Turbo Monte Carlo , or a 84 or 85 vette , or a van
or pickup with an ESC distributor , you may want to try a different gasoline.
The ESC system uses a detonation sensor to monitor engine ping .This
little sucker is VERY sensitive , and relays its information to either the
ESC controller or computer , depending on the vehicle type . The ESC con-
troller (or computer ) then sends a signal to the distributor to retard the
timing by 2 degrees. The sensor listens again . If it hears (actually senses
vibration at the proper frequency) more noise ,it cuts back 2 more degrees.
The entire process works so fast that all you can lose 12 or 13 degrees of
advance and only hear one tick of the ping !
The end result is that the car pings very little or not at all on
low grade fuel , but the performance has been drastically altered. The GM
tech manuals I used to work with told us to tap the exhaust manifold with
a hammer while watching the timing with a timing light (a two man process
on some vehicles ). Sure enough , you can pull 20 degrees off the timing
in a heartbeat!
I don't remember which gasoline it was , but one of them had an
ad that featured three 1984 vettes taking off from the line . Of course
the one with *their* gasoline lead the pack , but considering how ESC
works , the gasoline that had the best octane rating would have an
advantage.
As far as mileage goes , on of the most mileage-critical tune-up
adjustments made is the timing.(We're talking factory-set carb mixtures here)
Knocking(pun intended) 12 or so degrees off per acceleration can't really
help...
HAPPY MOTORING !