>Can anyone help me with understand the numbers describing the profile
>of a camshaft? As far as I remember the standard 1500 camshaft is called
>18-58-18-58 (overlap of 36 deg), while the 1300 (Spitfire Mk 3) is
called
>25-65-25-65 (overlap of 50 deg). What does the individual numbers
represent?
Peter,
Ther're normally represented as follows, in crankshaft degrees:-
A-B-C-D
A - inlet opens degrees before TDC
B - inlet closes degrees after BDC
C - exhaust opens degrees before BDC
D - exhaust closes degrees after TDC
I think your figures are a slightly different convention with the last
two digits swapped
>It seems the first and third number equals the overlap, but the overlap
be-
>tween what?
The overlap is the time the inlet and exhaust valves are open together,
hence A + D
The duration is the number of degrees each valve is open for, hence
exhaust duration is C+D +180 and inlet duration is A+B+180
Generally, a standard cam would have a duration of something like
230-270, a fast road cam would be around 280 degrees which doesn't
sacrifice much torque for more top end, and a race cam would have 300
degrees or more, and is only really useful at the top end.
>A Kent (or Moss) camshaft typically does not have this symmetri in the
numbers,
>I can't remember any figures for sure but I think the road version is
something
>like 28-56-something-else.
Normally they are symmetrical but some performance cams have a slight
advance in the recommended timing setting, and sometimes different inlet
and exhaust durations to squeeze a bit more power out .
Cheers,
Keith Bennett Keith.Bennett@bbc.co.uk
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