RE: Motronic Pistons

[Tom Sahines <tsahines@domain.elided>]

The Motronic pistons work just fine. My dyno work has shown that there is
no significant power difference using the Motronic or the 10.4:1 high
compression pistons. If the head has NOT been significantly shaved (.040")
then premium pump gas will work just fine. Set the ignition timing to 36
degrees maximum to start with. If necessary you can reduce it to 34 degrees
with little power loss.

If you are building a motor one of the most important things to do is to
check the clearance between the pistons and the head / valves. The engine
must be partially assembled to do this and will have to come apart to be
modified. Any new configuration I am working with will always be checked. I
use a thin layer of clay on the top of the piston. I also have a thin used
head gasket that I assemble the motor with when performing this check.

You can usually get away using 11mm cams and Motronic pistons without
clearance problems. Milling the head more than .020" may cause some
interference with the large intake valves and the edge of the valve relief
pocket in the piston.

It is absolutely imperative to perform this clearance procedure on a 1300
and especially a 1400 rebuild. These engines are notorious for interference
problems. 
Tom Sahines ARA Tech Hot Line
Milpitas CA

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