[DeTomaso] efi horse power gain

[Daniel C Jones]

> Regarding EFI versus carburation, I can see one an advantage to a
> carb being smaller LSA to get more efficiency at high RPM because
> EFI likes a larger LSA.  Since higher RPM with everything else the
> same means higher HP, an 8,000 RPM carburated engine will make more
> HP than a 7,000 RPM engine EFI engine.

I disagree with statement on a couple of points.  First, it is not
necessarily true that "EFI likes a larger LSA".  The wide lobe center
is required for EFI myth stems from attempting to use narrow LSA cams
with OEM engine computers with little or no tuning (early on the OEM
computers weren't hacked or no tuning software was available) or from
using the wrong EFI strategy.  Alpha-N, for instance, relies only on
relies only on throttle position and RPM, and can handle tight LSA and
large overlap.  Strategies which rely on hot wire mass air meters to
sense air flow don't handle large overlap cams as well.  The mass air
flow meter does not know which way the flow is going and gets fooled
by the reversion pulse air flow.  This unsteady flow over the mass air
meter which can lead to surging, particularly at idle and lower RPM.
Of course, a carb venturi also responds to reversion flow.  A friend
runs an EEC-IV mass-air based system in his drag race Mustang and the
engine has a strong surge below 3000 RPM due to the large overlap of
his cam.  Still the system works fine in his working RPM range (goes
through the traps at nearly 9000 RPM).  Sometimes you can tune out the
surge by repositioning the mass air meter relative to the intake valve
but the amount of overlap a mass air system can tolerate is finite.
Since the airflow is directly measured, mass air systems can tolerate
larger variations (in cam specs, cylinder head flow, etc.) than speed
density.

Second, narrow LSA cams do not necessarily result in higher RPM for
the same amount of total overlap.  Narrow lobe centers tend to
concentrate the power in a narrower RPM band, sometimes at the expense
of high RPM peak power.  Wider lobe centers tend to spread the power
out over a wider RPM band andmay make more peak power but may have less
area under the curve within the working RPM range.  Understand these
are very general statements and there can be exceptions to the rule.
Vizard has found each engine has an "optimal" LSA that is primarily a
function of intake valve diameter, bore, stroke and compression ratio
(for a naturally aspirated engine).  BTW, Vizard has a dyno test of
different LSA cams in a 4.6L Ford V8 in the current issue of Popular
Hot Rodding.

Dan Jones