Horsepower verse Torque

[John Dammeyer]

Hi All,

Wow!   What a response.  Thanks all for input on HP and the venturi thing.  Let
me give you some background on what prompted all this.

My clients client has delivered a twn engine Hovercraft to a customer in Italy.
Because Fuel injection wasn't completely debugged yet and delivery had to be
made my client substituted a couple of SUs scavenged from a Jaguar; one per
engine.  We shipped the fuel injection controller but used it only for ignition
and tach drive.

Now the fans used on these Hovercraft are pitched so that they load down the
engine and don't turn much faster than the torque peak of the engine; about 5200
RPM.  What's really interesting is due to, we think,  improper air flow,  one
engine top RPM is always about 400 RPM lower than the other.  They've swapped
engines from side to side and it doesn't make a difference so we've determined
loading is the cause.

Once an upgraded set of EPROMs was shipped to Italy they started getting 5900
RPM from the faster turing engine (Port side I think) and no fuel injection
engine has ever run that fast on a Hovercraft.  So needless to say,  they are
asking why?

My guess is that for some reason they've done something to load the engine
differently or else the Peak Torque happens at a higher RPM or their tachometers
are really off and they are reading the wrong RPM.  Hence the question about a
smaller venturi changing the place where maximum torque occurs.  I do know that
at full RPM the intake manifold gets really really cold from the evaporating
fuel.  It's the Fuel Injection manifold so it's nicely tuned and perhaps the
adaptor on the SU extends the intake manifold intake just enough to also cause a
torque peak shift.  We're also unclear whether they report that RPM static with
the craft tethered or while it's in motion.

We'll know in the new year because the customer has insisted on fuel injection
to meet some licensing rule so a new set of injectors and fuel pump will be
shipped over to convert the craft.  At that point,  if we don't get 5900 RPM on
the same engine then we know there is something radically different.  The
question on the HP calculation was to use check out if the HP at 5900 based on a
higher torque was still inside the design limits and what we have achieved on
the Dyno.

This has been an interesting project.  I'm now designing and building a hand
held scan tool that plugs into the CAN bus on the two ignitions so that we can
see what's happening without hauling out a PC and CAN interface.

Again,  thanks for everyone's input.  Merry Christmas.


Christmas Cheers,

John Dammeyer