[DeTomaso] Cam Question

[Daniel C Jones]

> My thought is that, increasing the cubic inches by 30, and using the
> same cam, should make it more of a stump puller?

Yes.  The 30 extra cubes should increase torque by 35 ft-lbs or so and
move your HP peak down.  With that cam, you should peak under 5500 RPM,
perhaps a little lower but that depends upon the rest of the build (carb,
intake, exhaust).  In a cast iron 4V, dual plane 408C with a larger cam
(232/236 degrees, 108 LSA, 0.609"/0.621" lift) we made 440+ ft-lbs at the
lowest RPM tested (3000 RPM or so).  Ideally, you want a narrower lobe
separation than the 110 degrees of that Comp cam, particularly if you
have a good exhaust.

Are you using Scott Cook's dual plane intake manifold for the CHI 3V
heads or the CHI single plane?  The latter will be soft on torque until
around 3000 RPM due to the large plenum volume.  This can be offset to
some degree with the proper carb.  You don't want a Holley with straight
leg boosters.  You want something with down leg boosters or annular
boosters.  The ignition curve and exhaust are also improtant.

> I don't imagine the new heads will hurt anything either?

By switching from iron to aluminum at the same static compression ratio,
you'll give up a bit of effective compression due to the greater heat
transfer of aluminum (it's the ideal gas law at work: PV=gammaRT).  Not
a big effect and should be more than offset by the better head flow.

> I just hate to build the engine and regret not going with a different
> cam.  Any thoughts,  suggestions?

We will have a set of CHI 3V heads with matching single and dual plane
intakes to test on the dyno.  If you want to spring for a cam, I can
work up some specs and we can dyno test both your existing cam and the
custom cam.  Not sure if our time frame fits yours, though.  We won't
be getting to the aluminum heads until later in winter.

Dan Jones