Motronic pistons

[alfacybersite <acs@domain.elided>]

In V8 #601 Kevin Trent asks the following questions: "...I too will be
rebuilding at least
one 2L this summer, and I am strongly considering the 10.0 Motronic
piston
& liners.   My concern and questions to the Digest are these:  Will the
compression jump from 9.0 to 10.0 CR create a need to use the top octane

gas?  Will I notice a significant increase in predetonation? The Spica
injection already runs more lean than Webers, and will this accentuate
any
predetonation problems?   My Sperry head has been milled and is no
longer
stock height and I use an 11mm cam - any valve clearance issues?"

**********

[When it rains, it pours (yes Mr. Morton I'll sell you the slogan for a
million dollars). When I started this email Kevin was a little perturbed
about the lack of information on the above subject but felt (rightly so)
there was more than enough info regarding Porsches, SUV's, and tattoos.
After windshield guy just left, opened up #602 to find virtually
everything you ever wanted to know about Motronic pistons, etc.
However...].

I've talked about this engine before, but the 2L I (along with the
machinist) built for a client's '73 Spider utilized most of the items
you are intending to install.

I personally Always run 91 / 92 octane in any Alfa engine. It has been
suggested that Chevron Techtectroline (sp?) is a Good Thing for the
Spica pump's pistons.

As Tom Sahines comments, the amount the head has been milled will have a
lot to do with pinging and whether valves 'might' hit the pistons.

Backing up a moment, I have been assured by others the Motronic's,
because of their later design are more sophisticated, and are every bit
as 'hot' as the 10:4 to 1. It's nice to have Tom verify this. I will
admit I hold Jon Norman's opinions in high regard also and if he feels
the 10:4 to 1's are best, dunno. My feeling though is there is
considerably less likelihood of the 10:0 to 1's hitting, so why not use
them unless you're looking for that very last  HP and don't mind
fiddling with octane boosters.

Being perhaps a bit lazy, I used the rings which came with the pistons /
liners. I'm somewhat inclined to think the liners are no doubt honed to
make the standard issue rings break in quickly and properlywhich they,
in fact, did. It's possible they might need replacing at 60 to 70k, but
assume this will still take a number of years for them to 'wear out'. I
put several hundred miles on the engine before turning it over to the
client and the engine broke in amazingly quickly. There is no need to
remove pistons from liners if not changing rings. Keep liners / pistons
pretty dry with only a hint of oil when installing pistons to rods.

The rear main and rod bearing surfaces on this crank were scored, so had
all surfaces taken to .10 under and rehardened. From the crank back to
the flywheel, all was balanced. The rods were indexed (Alfa rod's big /
small ends are not all that consistent).

A rebuilt Spica unit was installed along with Centerline's 11.3 mm
camshafts. Had meant to install their 11.0 cams, but they were out. I
worried needlessly there might be valve to piston clearance problems and
fairly serious pinging.

Unlike Tom Sahines, I sort of go for broke when checking valve to piston
clearance. I semi snug down the head using the 'final' head gasket. I
then bend / slide in a length of solder under each of #1's exhaust valve
then turn the engine over 'by hand', check thickness of solder between
'dents, then do the same for the inlet valves. In this case, it took a
fairly thick piece of solder before there were dents in it. Looked like
a safe enough gap to me and buttoned all up.

Smooth, smooth engine, idled like a champ, had a nice amount of oomph,
no pinging, didn't overheat, and to the best of my knowledge, doesn't
use excessive amounts of oil.

If you have the patience and cash to do a complete job, I feel this is a
great combination with which to add oomph and still have a very
tractable street machine.

Need I add...a definite win win situation?

Biba
Irwindale, CA USA

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