Re: [[Tech] Compression]

[Brett Van Sprewenburg <brett@netacc.net>]

>And while we're on the topic and not that it really matters, but what is the
>compression ratio of the 1.8 head on the 2L block? I got 10.8:1 from somewhere
>( a hallucination???) but not sure where I saw that number, I've heard that
>the 1.8 head increases compression. And what he said, is there a way to
>calculate it knowing cylinder compressions?
>Eternally curious, Cathy
>


The 1.8L head doesn't exactly increase compression itself as far as I
know, but the compression of the 2L 16v block / pistons and a 16v
head of nominally 'normal' deck height is 10.8:1.  The reason for
the increase over the 1.8L block is primarily due to the differences
in the pistons.  The 1.8L piston has a valve relief cut all the way
across the face of the piston, basically a slot.  The 2L piston has
a pair of smaller depressions as little round valve reliefs, obviously
there is somewhat more piston metal taking up the squish area in the
2L pistons then on the 1.8L's.  It's this little difference that makes
the compression grow that .8 points.  It really doesn't take much,
as .030ish off the deck height is worth around .5 in compression ratio.

As far as figuring the compression ratio out, there are direct ways of
doing so, but it partly involves having the head and block apart and
pipet'ing fluid into the chambers through a plexiglass cover with a
small hole in the middle...you really probably don't want to know. :)

==Brett

 \/  '84 Scirocco (ITB racer 2B) | "Hot VW's, take two home. They're small"
\/\/ '88 Scirocco 16v (Show), '92 Passat 16v (Winter+) | - brett@netacc.net

--
Email LIST problems to: scirocco-l-probs@scirocco.org.
To unsubscibe send "unsubscribe scirocco-l" in the message to majordomo@scirocco.org