[Diy_efi] RE: Diy_efi digest, Vol 1 #413 - 12 msgs

[Shannen Durphey]

Within a limited torque range, some models of Dynojet can be used with
rpm/mph based loading.  I've done a few cals using this route.

Using the dynojet to tune WOT blasts gives reasonable results.  Using it to
tune part throttle cruise conditions requires using the brake, or constant
manipulation of the throttle and roller speed.  Tricky, but it can be done.

Using a braking type dyno to tune a car for WOT can produce misleading
results.  A lightweight car with a high power to weight ratio would
typically never see the same load and duration that can be applied with a
brake type dyno.  Running up to a specific rpm and holding that rpm while
fuel and spark are tuned in will tend to heat parts more than they would be
heated in "normal" operation.  The consequences can be more fuel/ less
spark than optimal get dialed into the final tune.  Power may be down, fuel
consumption may be up, or both can occur.  The inertial loads alone provide
more than enough resistance to provide an acceptable street and competition
tune for these vehicles.  

To think that you can get a tune right "to the gnat's butt" on _any_ type
of dyno is to assume that you will be running under the same conditions
always.  No matter how an engine is tuned, someone has to check occasionaly
for signs that things aren't right.  The equipment is to get things closer,
sooner.

A wide band sensor mounted in the tailpipe can be used to provide a
successful tune, just like reading plugs can be used to provide a
successful tune.  To say that the length of the exhaust makes the sensor's
readings useless only implies that the tuner doesn't know what to do with
them.  It only takes a little practice making changes and watching results
to get a feel for how to use the results.

For many, many street cars, WB + inertial dyno + competent tuner is very
satisfactory.  The issue is finding a competent tuner.

Shannen


Adam Wade wrote:

> --- Erik Jacobs <emj14 at columbia.edu> wrote:
> 
> > An inertial dyno is, for example, a dynojet??
> 
> Yes.
> 
> > What's an example of an eddy-current dyno??
> 
> Factory Pro, Mustang, Fuchs, Superflow are all eddy
> current, with varying mass of the drum (the more
> massive the drum, the more inertial factor you have to
> "dial in".
> 
> > Well for someone who isn't fighting for tens of
> > horsepower, let alone tenths of horsepower, is
> > inertial dyno (dynojet) + wbo2 + competent tuner
> good
> > enough?? =)
> 
> *frown*  I'll have to give a qualified "that depends".
>  the only thing that an inertial dyno can really
> measure is a single load condition, beacuse you cannot
> vary the load.  It also cannot be held on a load/speed
> site for more than a small fraction of a second.
> 
> With carbs, I have found it to be a useful tool for
> picking a main jet, since usually the roller is sized
> to give a fair amount of load compared to maximum. 
> For tuning part-throttle and cruise mixtures, I have
> not found it very much help at all, and driving the
> car around and using an O2 sensor on the road would
> probably net superior results than trying on the dyno
> first and then going driving for the "final".  Again,
> YMMV, and different kinds of applications may find
> different hardware is better suited; this is only MY
> experience with motorcycle engines (50-200 bhp) on
> dynos designed for those vehicles.
>

_______________________________________________
Diy_efi mailing list
Diy_efi at diy-efi.org
http://www.diy-efi.org/mailman/listinfo/diy_efi