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Lynn,
I address this to you or anyone that wants to
comment.
I'm just re-evaluating, the PP position and I'm
looking at the latest possible closing position for the PP (100 degrees
ATDC).
In the standard opening ( 12A housing set-up with
my degree wheel) I have opening at 32 degree ATDC, closing at 310 degrees with
exhaust closing at 55 degrees ATDC. This gives a moderate overlap of 23 degrees
and an Inlet opening period of 278 degrees (quite large).
With the PP (approx 2") we have an early opening of
20 degrees BBDC and 65 degrees ABDC, open for only 85 degrees- but an over lap
of 165 degrees.
This gives an additional overlap of 142 degrees and
reduced inlet opening time of 193 degrees - it's a wonder the rotary runs at all
with reduced opening time and additional over lap. One compensation however is
that the inlet is direct and bigger.
In considering a later PP, I figure the inlet
opening could be 40 degree ABDC (only restriction is the top housing bolt
hole) and closing at 100 degree
ABDC.
This would then would reduce the overlap by 55
degrees, so the overlap would be ( 165 - 55) 110 degrees, still high but not
quite as high, thus reducing exhaust contamination of the inlet ( at low RPM)
and inlet going into the exhaust (at high RPM).
The inlet timing would be the same ( 85
degrees) - but later, but not so late as to get into the compression stage,
which might cause further issues.
I remember discussing this with someone ( it might
have been Lynn) but I can't remember what the negatives are with such a late
PP.
Can someone put me straight on this
again!
I hope I got those degrees right!
George ( down under)
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