In a message dated 98-12-10 19:28:20 EST, GuyotLeonF@aol.com writes:
<<
Rich,
According to the Competition Preparation Manual, the S-4 cam has the
following specs:
SPECIFICATIONS FOR S-4 CAMSHAFT V-579
Inlet opens 42 deg BTDC
Inlet closes 71 deg ABDC
Exhaust opens 71 deg BBDC
Exhaust closes 42 deg ATDC
Duration 290 deg
Lift at Valve .410"
Checking clearance at camshaft .013"
Operating clearance at valve hot .020"
Hope this helps,
Hugh Barber
San Jose, CA
'73 TR6
****************************
That is curious because:
My reference material shows:
S4 Camshaft (data from Ted Schumacher)
Lift .410"
Duration 293 degrees
Power Range 4200-6500 RPM
nb. marginal for street
S4 Camshaft (37 67 73 31). (data from Gareth Thomas Tuning book-out of print)
Lift .465"
Duration 290 degrees
Power Range 3500-6500 RPM
BHP/L (in 2498cc engine) 185 BHP
Valve Clearances: Inlet 12 thou' & Exhaust 13 thou'
Curiously as you can see, the figures for the S4 vary ?
I do not know which ones are the true figures, but AFAIK, I have a BL ST USA
'S4' Camshaft in my Vitesse, and therefore would like to know the correct
figures!!!
(My Camshaft was made as one of a set of 10 ordered from Messrs Holbay back
in
1985/6.) >>
Hello,
Very interesting! I asked about the specs on this cam because I just bought a
TVR with the TR6 engine, and the seller told me he had installed the S4 cam.
I wanted to know the specs so I would have some idea about what to expect of
the engine once I got it running.
To me, .410" lift at valve doesn't seem like much. Easy enough to check, once
you take the valve cover off, though. On my car, I have way too many things
to do before I will get a chance to do that. I certainly hope that I won't
have to remove the valve cover any time soon!! Cam timing and duration is not
as easy to check, and I hope it's a long time before I get a chance to do
that! Off the top of my head, the only thing that comes to mind that might
explain the different numbers, is that duration and timing can be measured
differently. Some measure it as soon as the valve opens, some measure it at
.020" lift, and others measure it at .050" lift (at cam).
I don't know what's going on here. Timing and duration numbers are close
enough for me, but the lift is another matter. If anyone has more info,
please let us know!!
Thanks.
Rich Rock
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