Re: A pop quiz on some engine tests

[four.rings@MCIONE.com]

Here are the first two answers to the quiz that I received.

Phil Payne wrote:

> Both lapping and piston top cleaning increase the volume of the
> combustion chamber.  But is this enough?

And Mark Pollan wrote:

> I'll take a shot.  Non-uniform carbon deposits causing non-uniform
> albeit higher compression.

You guys ARE GOOD!
Yep, just cleaning the C deposits and sitting the valves deeper by
lapping them has somewhat increased the combustion chamber volume hence
decreasing the compression. The pitfall that I had fallen into was that
I somehow automatically presumed that the leak down test was the same
thing as the compression test only done from the "opposite" end so to
speak. Wrong! They are two different tests altogether.

She is a bit more sluggish off the line now (thanks to the lower
compression), but the 2-piece EM gave it the 2700prm spool-up point as
opposed to the 3000rpm with the 1-piece unit before.

I have also replaced the buzzing clogged fuel pump this past Sunday and
now I can clearly see that the car was starving at the high boost
levels.

BTW, once I figured out that I have decreased the compression, I
immediately increased the WG spring stiffness in order to try the car at
a higher max boost before pinging.

Ambient temperature was about 18°C.
She rather leisurely took off at a neg boost level. Once she hit 2700rpm
(atmo pressure: 0 psi on the analogue gauge/1.0 bar on the digital one -
i.e. about 0.6 bar boost), she really came to life.
>From 0 psi she jumped to 12 psi in notime at all with a nice rush of
power.
>From 12psi to 20psi she went like a friggin' freight train! Quite
entertaining.
I had to lift off immediately coz I was doing triple digits in rural NJ.
:)

-- 
Igor Kessel
'89 200TQ -- 18psi (TAP)
'98 A4TQ -- nothing to declare
Philadelphia, PA
USA