Knock Sensor Applications

John Faubion jfaubion at beaches.net
Sun Oct 20 18:14:42 GMT 1996


> OEMs use an advance determination method called MBT (Minimum spark
advance
> for Best Torque), unfortunately knock can sometimes set in before best
> torque is realized.
> 
> So far, things do not look very good. All of the above leads me to a
> number of conclusions (all mine):

Everyone is talking about knock sensor problems. Why not do it the way we
do in kart racing? We only have a single cylinder. With everyone so close
to each other in terms of weight and power, any loss in power will get you
passed! We use cylinder head and exhaust temperature gauges. The CHT mounts
under the spark plug and EGT is obviously mounted in the exhaust stream. We
tune the engines using low and high speed jets on the carburetors. The key
to good tuning and max. power are watching the relationship between the two
gauges. As you lean out the carburetor both CHT and EGT will rise. This
will continue until the point of incipient detenation (can't be heard). At
this point the CHT keeps rising and EGT drops. If you let this continue the
piston sticks in the bore and your out of the race. 

There are some drawbacks to this method. The EGT responds almost
instaneously while the CHT lags behind a bit. We also use aluminum heads
which would allow the CHT to respond sooner than an iron head. In addition
we also only have a single cylinder to deal with instead of 4 to 8. Still I
think this might be a better way to tune for max. power since the lamba
sensor doesn't do a great job of it at WOT. Does this help spark any new
ideas?

John Faubion



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