Re: pistons

[bearbvd@domain.elided (Greg Hermann)]

>Further to the the posting about getting higher compression pistons for
>a 1600 engine, with one digester suggesting Venolia as a possible
>source;  can anyone comment about the various piston manufacturers, the
>differences in dome and lip design and the resulting influence on engine
>output?
>
>My question/interest stems from an impending lower end rebuild of my 2L
>GTV engine.  While high compression is considered a great way to
>increase horsepower, today's available fuels really do limit what one
>can get away with in that respect.
>
>So, are all 10.4:1 or all 10:1 pistons created equally?  As an example I
>have heard anything from "Borgo is just great" to "Borgo's high round
>dome splits the flame front and reduces power".

The Borgo design is out of date, and simply does not perform at all as well
as a flat-top dome design.

Others like Venolia
>favor a 'flat top' dome design,

The flat top dome design is , simply stated, VASTLY superior. More
turbulence and shorter flame travel lead to less advance requirement and
less appetite for octane.

and I'm sure there are a few other
>manufacturers

JE is probably the class of the American piston mfgrs. And they will
certainly build Alfa pistons, to whatever design.

Any respectable custom piston builder will build what you ask for!

With a good flat top dome design in a 1600, I believe that 11:1 would
behave OK on today's readily available ULP fuels.

with yet other differences still (including Alfa's own 2L
>Motronic pistons).
>
>I suppose anyone going from a stock and tired 9:1 bottom

Do not lose sight of the fact that the 1600 normale and veloce used
IDENTICAL Borgo pistons (same part number). The .7 increase in cr came from
cutting the head .040" !!

The place where there is GREAT room for improvement in performance and
durability is in more accurate machining of liners (like with them
installed in a block with a torque plate installed and warm water
circulating in the water jacket--and in use of sophisticated coatings to
both reduce wear and friction and to reduce heat transfer into the pistons.
(Among other benefits are tighter allowable piston to sleeve clearances,
and still lower leakdown rates. Most Alfa motors have attrociously high
leakdown rates!!

The other problem you will get into with compression ratios above 10 on
forged pistons in an Alfa is extremely rapid wear of the top ring groove.
The right coating can help this, as can a true synthetic oil.

Close attention to the design of your ring pack is also VERY important.
Personally, I would not take a gift of Deves rings for any engine! My own
preference is for a ductile chrome top ring, Total seal second, and a
chrome plated iron, H section, oil ring with a coil spring expander.

I am also partial to hard surface conversions on the sleeves.

Regards, Greg
>
>Peter Kemos
>Santa Cruz, CA

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End of alfa-digest V7 #672
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