Greg,
I saw a recent article on a setup which measured the cam and dumped it into
a windows program. In this program you were able to compare the effects of
different cams. Print out all the specs and get a graph like you are talking
about. Price was not mentioned but from the ad I would guess the $175 -225
range. I was not interested at the time so I didn't get all the hard facts.
I will see if I can find the manufacturer. It looked very complete and
simple.
Gene
----- Original Message -----
From: "Greg Locke" <glocke@ihug.co.nz>
To: "Alpine list" <alpines@autox.team.net>; "Hillman list"
<hillman@can-inc.com>
Sent: Friday, December 01, 2000 12:16 AM
Subject: cam timing
> Well guys I've finally done something I've been meaning to do for years. I
> have made a contraption that traces the lobe profile on a camshaft, onto
> graph paper, with the degrees rotation on the horizontal axis, and the
lift
> on the verticle. It is pretty dodgy, (i.e. not at all precision
engineering)
> but it has certainly revealed some intersting things regards our cam specs
> provided by the men at Rootes.
>
> The reason for this (some might say madness) is I have been running what
> according to the rootes spec sheet is really a full race cam in my race
car.
> The cam comes from a Hillman Hunter/Sunbeam rapier fastback of 1974 and is
> specced by rootes as 38-72 72-38, i.e. has a duration of 290 degrees. It
was
> the wildest standard cam I could find, hence my fitting it. But it
> originally comes from a single carb or dual carb, family road car. And
> indeed in my race car, the engine pulls very cleanly from 800 revs and
> really has no "coming on cam" feel to it. Something has definitely been
> amiss. I have been considering fitting an isky SB-3 cam which is specced
at
> 33-73 73-33 giving 286 degrees duration, which is a semi race cam... but
> according to the specs from rootes, my cam should actually be wilder!
>
> After reading various books I discovered the whole "cams should be
measured
> at .050" camlift scenario" whereas engine manufacturers such as rootes
give
> timings that are are from when the valve first leaves it's seat till when
it
> returns. Thus, if the clearance is set to 14 thou, and the rocker ratio is
> 1.4, this equates to only about .010" camlift. So I have been wondering
what
> the rootes cams would measure as when done "correctly", i.e. to .050"
spec.
>
> Well, now I know!.
>
> I have put a few cams I have through this test, and there is a reasonable
> amount of error, due to the basic construction technique of this device..
> but nevertheless it gives a reasonable approximation of the true picture
>
> Cam 1 Sunbeam Alpine Series 4a/ Humber sceptre mark 1
> Rootes say 19-57 61-15, duration 258 degrees, overlap = 34 degrees
>
> The first thing is that the graph shows an incredibly slow initial opening
> period, which must be the quietening ramp to ensure minimal tappet noise.
> The .010" point is part way along this ramp, and as such the valve is
> initially opened very slowly. When measured at the .050" camlift points
the
> duration is really only about 200 to 210 degrees, and the overlap between
> the exhaust and inlet valves is non existent, and may actually be negative
> by 10 degrees or so. So this is really a very mild cam. The camlift is
about
> 0.260" giving about 0.36" valvelift
>
> Cam 2 Sunbeam rapier H120, Hillman hunter GLS (twin weber std, 110hp)
> Rootes say 58-66 84-40, duration 304 degrees, overlap 98 degrees
>
> Whoa! the engine shouldn't even run below 3000 revs with a cam like this,
> and checking it out as for the previous cam, rootes radical timing specs
can
> be revised as such. Duration approx 240 degrees, but it does actually have
> some genuine overlap of about 40 degrees. It's initial quieting ramps are
> much smaller, maybe to keep the valve on the seat as long as possible to
get
> rid of heat. So this is definitely a bit more than a standard road cam,
but
> certainly not the race cam it presents itself as.
>
> As such, I have not measured my cam in the race engine, because of just
> that, it is still in the race engine, but from the pattern that has
emerged,
> I would think it probably has a true overlap of no more than 220 degrees,
> and as such the iski cam should indeed wake my engine up somewhat.
>
> If anyone has some comments on this, please let me know. I have found it a
> very interesting exercise, and am interested in any feedback, or previous
> findings by other people that relate to this.
>
> Greg
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